Associations between abnormal rod-mediated dark adaptation and health and functioning in older adults with normal macular health

Evaluation of a mobile app for dark adaptation measurement in individuals with age-related macular degeneration

We present clinical evaluation of a mobile app for dark adaptation (DA) measurement in age-related macular degeneration (AMD) patients and in older adults (age > 50 years) without AMD or other retinal disorders (NV). The outcome measures were the area under dark adaptation curve (AUDAC) and the time for visual sensitivity to recover by 3 log units (TR). Larger AUDAC and TR values indicated worse DA response. The association of AUDAC with AMD was analyzed using linear regression, while time-to-event analysis was used for TR. 32 AMD patients (mean ± SD; age:72 ± 6.3 years, VA:0.09 ± 0.08 logMAR) and 25 NV subjects (mean ± sd; age:65 ± 8.7 years, VA:0.049 ± 0.07 logMAR) were measured with the app. Controlling for age, VA, and cataract severity, the AMD presence was significantly associated with higher AUDAC (β = 0.41, 95% CI 0.18-0.64, p = 0.001) and with slower sensitivity recovery (β = 0.32, 95% CI 0.15-0.69, p = 0.004). DA measurements with the app were highly correlated with those obtained with AdaptDx-an established clinical device (n = 18, ρ = 0.87, p < 0.001). AMD classification accuracy using the app was 72%, which was comparable to the 71% accuracy of AdaptDx. Our findings indicate that the mobile app provided reliable and clinically meaningful DA measurements that were strongly correlated with the current standard of care in AMD.

Assessment of the Classification of Age-Related Macular Degeneration Severity from the Northern Ireland Sensory Ageing Study Using a Measure of Dark Adaptation

Purpose

To assess the differences in rod-mediated dark adaptation (RMDA) between different grades of age-related macular degeneration (AMD) severity using an OCT-based criterion compared with those of AMD severity using the Beckman color fundus photography (CFP)-based classification and to assess the association between the presence of subretinal drusenoid deposits (SDDs) and RMDA at different grades of AMD severity using an OCT-based classification.

Design

Cross-sectional study.

Participants

Participants from the Northern Ireland Sensory Ageing study (Queen's University Belfast).

Methods

Complete RMDA (rod-intercept time [RIT]) data, CFP, and spectral-domain OCT images were extracted. Participants were stratified into 4 Beckman groups (omitting late-stage AMD) and 3 OCT-based groups. The presence and stage of SDDs were identified using OCT.

Main Outcome Measures

Rod-intercept time data (age-corrected).

Results

Data from 459 participants (median [interquartile range] age, 65 [59-71] years) were stratified by both the classifications. Subretinal drusenoid deposits were detected in 109 eyes. The median (interquartile range) RMDA for the Beckman classification (Beckman 0-3, with 3 being intermediate age-related macular degeneration [iAMD]) groups was 6.0 (4.5-8.7), 6.6 (4.7-10.5), 5.7 (4.4-7.4), and 13.2 (6-21.1) minutes, respectively. OCT classifications OCT0-OCT2 yielded different median (interquartile range) values: 5.8 (4.5-8.5), 8.4 (5.2-13.3), and 11.1 (5.3-20.1) minutes, respectively. After correcting for age, eyes in Beckman 3 (iAMD) had statistically significantly worse RMDA than eyes in the other Beckman groups (P ≤ 0.005 for all), with no statistically significant differences between the other Beckman groups. Similarly, after age correction, eyes in OCT2 had worse RMDA than eyes in OCT0 (P ≤ 0.001) and OCT1 (P < 0.01); however, there was no statistically significant difference between eyes in OCT0 and eyes in OCT1 (P = 0.195). The presence of SDDs was associated with worse RMDA in OCT2 (P < 0.01) but not in OCT1 (P = 0.285).

Conclusions

Eyes with a structural definition of iAMD have delayed RMDA, regardless of whether a CFP- or OCT-based criterion is used. In this study, after correcting for age, the RMDA did not differ between groups of eyes defined to have early AMD or normal aging, regardless of the classification. The presence of SDDs has some effect on RMDA at different grades of AMD severity.

Area under the dark adaptation curve as a reliable alternate measure of dark adaptation response

PURPOSE

Quantification of dark adaptation (DA) response using the conventional rod intercept time (RIT) requires very long testing time and may not be measurable in the presence of impairments due to diseases such as age-related macular degeneration (AMD). The goal of this study was to investigate the advantages of using area under the DA curve (AUDAC) as an alternative to the conventional parameters to quantify DA response.

METHODS

Data on 136 eyes (AMD: 98, normal controls: 38) from an ongoing longitudinal study on AMD were used. DA was measured using the AdaptDx 20 min protocol. AUDAC was computed from the raw DA characteristic curve at different time points, including 6.5 min and 20 min (default). The presence of AMD in the given eye was predicted using a logistic regression model within the leave-one-out cross-validation framework, with DA response as the predictor while adjusting for age and gender. The DA response variable was either the AUDAC values computed at 6.5 min (AUDAC6.5) or at 20 min (AUDAC20) cut-off, or the conventional RIT.

RESULTS

AUDAC6.5 was strongly correlated with AUDAC20 (β=86, p<0.001, R2=0.87). The accuracy of predicting the presence of AMD using AUDAC20 was 76%, compared with 79% when using RIT, the current gold standard. In addition, when limiting AUDAC calculation to 6.5 min cut-off, the predictive accuracy of AUDAC6.5 was 80%.

CONCLUSIONS

AUDAC can be a valuable measure to quantify the overall DA response and can potentially facilitate shorter testing duration while maintaining diagnostic accuracy.

Dark Adaptation and Its Role in Age-Related Macular Degeneration

Dark adaptation (DA) refers to the slow recovery of visual sensitivity in darkness following exposure to intense or prolonged illumination, which bleaches a significant amount of the rhodopsin. This natural process also offers an opportunity to understand cellular function in the outer retina and evaluate for presence of disease. How our eyes adapt to darkness can be a key indicator of retinal health, which can be altered in the presence of certain diseases, such as age-related macular degeneration (AMD). A specific focus on clinical aspects of DA measurement and its significance to furthering our understanding of AMD has revealed essential findings underlying the pathobiology of the disease. The process of dark adaptation involves phototransduction taking place mainly between the photoreceptor outer segments and the retinal pigment epithelial (RPE) layer. DA occurs over a large range of luminance and is modulated by both cone and rod photoreceptors. In the photopic ranges, rods are saturated and cone cells adapt to the high luminance levels. However, under scotopic ranges, cones are unable to respond to the dim luminance and rods modulate the responses to lower levels of light as they can respond to even a single photon. Since the cone visual cycle is also based on the Muller cells, measuring the impairment in rod-based dark adaptation is thought to be particularly relevant to diseases such as AMD, which involves both photoreceptors and RPE. Dark adaptation parameters are metrics derived from curve-fitting dark adaptation sensitivities over time and can represent specific cellular function. Parameters such as the cone-rod break (CRB) and rod intercept time (RIT) are particularly sensitive to changes in the outer retina. There is some structural and functional continuum between normal aging and the AMD pathology. Many studies have shown an increase of the rod intercept time (RIT), i.e., delays in rod-mediated DA in AMD patients with increasing disease severity determined by increased drusen grade, pigment changes and the presence of subretinal drusenoid deposits (SDD) and association with certain morphological features in the peripheral retina. Specifications of spatial testing location, repeatability of the testing, ease and availability of the testing device in clinical settings, and test duration in elderly population are also important. We provide a detailed overview in light of all these factors.

The role of dark adaptation in understanding early AMD

The main aim of the paper is to discuss current knowledge on how Age Related Macular Degeneration (AMD) affects Dark Adaptation (DA). The paper is divided into three parts. Firstly, we outline some of the molecular mechanisms that control DA. Secondly, we review the psychophysical issues and the corresponding analytical techniques. Finally, we characterise the link between slowed DA and the morphological abnormalities in early AMD. Historically, DA has been regarded as too cumbersome for widespread clinical application. Yet the technique is extremely useful; it is widely accepted that the psychophysically obtained slope of the second rod-mediated phase of the dark adaptation function is an accurate assay of photoreceptor pigment regeneration kinetics. Technological developments have prompted new ways of generating the DA curve, but analytical problems remain. A simple potential solution to these, based on the application of a novel fast mathematical algorithm, is presented. This allows the calculation of the parameters of the DA curve in real time. Improving current management of AMD will depend on identifying a satisfactory endpoint for evaluating future therapeutic strategies. This must be implemented before the onset of severe disease. Morphological changes progress too slowly to act as a satisfactory endpoint for new therapies whereas functional changes, such as those seen in DA, may have more potential in this regard. It is important to recognise, however, that the functional changes are not confined to rods and that building a mathematical model of the DA curve enables the separation of rod and cone dysfunction and allows more versatility in terms of the range of disease severity that can be monitored. Examples are presented that show how analysing the DA curve into its constituent components can improve our understanding of the morphological changes in early AMD.

Comparison of Visual Function Tests in Intermediate Age-Related Macular Degeneration

Purpose

Identifying the most sensitive functional measure in intermediate age-related macular degeneration (iAMD) could help select an appropriate test for monitoring disease progression and evaluating the efficacy of novel interventions for the early stages of AMD. The purpose of the study was to determine which commonly used visual function test is the most discriminatory when comparing individuals with iAMD to normal participants.

Methods

In this prospective observational study, iAMD cases and healthy controls underwent visual function testing (best corrected visual acuity (BCVA), low luminance visual acuity (LLVA), mesopic microperimetry, dark adaptation, and scotopic perimetry following photobleach), clinical eye examination, and multimodal retinal imaging in a single study visit. The data of each functional parameter were converted into z-score so that all the parameters had a common scale to allow a direct comparison between different functional parameters.

Results

Forty-eight subjects (23 normal control, 25 iAMD) participated. Although all five parameters showed a significant reduction in function in iAMD eyes compared to controls (P ≤ 0.003), the rod intercept time (RIT) detected the greatest reduction in function followed by the scotopic sensitivity, mesopic sensitivity, BCVA, and LLVA, with the absolute mean z-score of 4.5, 2.2, 1.0, 1.0, and 1.2, respectively.

Conclusions

Among the five visual function parameters commonly used, RIT is the most discriminatory functional parameter in the early stages of AMD.

Translational Relevance

The RIT could be considered for assessing visual function and evaluating efficacy of novel interventions aimed at improving retinal function in eyes with early stages of AMD.

Scotopic thresholds on dark-adapted chromatic perimetry in healthy aging and age-related macular degeneration

To evaluate the effect of aging, intra- and intersession repeatability and regional scotopic sensitivities in healthy and age-related macular degeneration (AMD) eyes. Intra- and intersession agreement and effect of age was measured in healthy individuals. The mean sensitivity (MS) and pointwise retinal sensitivities (PWS) within the central 24° with 505 nm (cyan) and 625 nm (red) stimuli were evaluated in 50 individuals (11 healthy and 39 AMD eyes). The overall intra- and intersession had excellent reliability (intraclass correlation coefficient, ICC > 0.90) and tests were highly correlated (Spearman r_s = 0.75-0.86). Eyes with subretinal drusenoid deposit (SDD) had reduced PWS centrally, particularly at inferior and nasal retinal locations compared with controls and intermediate AMD (iAMD) without SDD. There was no difference in MS or PWS at any retinal location between iAMD without SDD and healthy individuals nor between iAMD with SDD and non-foveal atrophic AMD groups. Eyes with SDD have reduced rod function compared to iAMD without SDD and healthy eyes, but similar to eyes with non-foveal atrophy. Our results highlight rod dysfunction is not directly correlated with drusen load and SDD location.

Optimising assessment of dark adaptation data using time to event analysis

In age-related macular degeneration (AMD) research, dark adaptation has been found to be a promising functional measurement. In more severe cases of AMD, dark adaptation cannot always be recorded within a maximum allowed time for the test (~ 20–30 min). These data are recorded either as censored data-points (data capped at the maximum test time) or as an estimated recovery time based on the trend observed from the data recorded within the maximum recording time. Therefore, dark adaptation data can have unusual attributes that may not be handled by standard statistical techniques. Here we show time-to-event analysis is a more powerful method for analysis of rod-intercept time data in measuring dark adaptation. For example, at 80% power (at α = 0.05) sample sizes were estimated to be 20 and 61 with uncapped (uncensored) and capped (censored) data using a standard t-test; these values improved to 12 and 38 when using the proposed time-to-event analysis. Our method can accommodate both skewed data and censored data points and offers the advantage of significantly reducing sample sizes when planning studies where this functional test is an outcome measure. The latter is important because designing trials and studies more efficiently equates to newer treatments likely being examined more efficiently.

Are Current Methods of Measuring Dark Adaptation Effective in Detecting the Onset and Progression of Age-Related Macular Degeneration? A Systematic Literature Review

INTRODUCTION

Dark adaptation (DA) has been proposed as a possible functional biomarker for age-related macular degeneration (AMD). In this systematic review we aim to evaluate current methodology used to assess DA in people with AMD, the evidence of precision in detecting the onset and progression of AMD, and the relationship between DA and other functional and structural measures.

METHODS

MEDLINE, EMBASE, CINAHL, AMED, PsycINFO, PsycARTICLES were searched for studies published between January 2006 and January 2020 that assessed DA in people with AMD. Details of eligible studies including study design, characteristics of study population and outcomes were recorded. All included studies underwent quality appraisal using approved critical appraisal tools. This systematic review follows PRISMA guidelines (PROSPERO registration number: CRD42019129486).

RESULTS

Forty-eight studies were eligible for inclusion, reporting a variety of instruments and protocols to assess different DA parameters. Twenty of these studies used the AdaptDx (MacuLogix, Hummelstown, PA, USA) instrument and assessed rod-intercept time (RIT). Most of these reported that RIT was delayed in people with AMD and this delay worsened with AMD severity. Four studies, involving 533 participants, reported estimates of diagnostic performance of AdaptDx to separate people with AMD from visually healthy controls. DA has been compared to other measures of visual function, patient-reported outcome measures (PROMs) and structural measures. Ten studies specifically considered evidence that the presence of certain structural abnormalities was associated with impaired DA in AMD.

CONCLUSIONS

This systematic review indicates overwhelming evidence of reasonable quality for an association between impaired DA and AMD. Data on the repeatability and reproducibility of DA measurement are sparse. There is evidence that structural abnormalities such as reticular drusen are associated with prolongation of DA time. Fewer studies have explored an association between DA and other measures of visual function or PROMs. We found no studies that had compared DA with performance-based measures.

Development of the Vision Impairment in Low Luminance Questionnaire

Purpose

The purpose of this study was to design and evaluate an instrument for assessing vision-related quality of life appropriate for the specific visual impairment characteristic for all stages of age-related macular degeneration (AMD), with a focus on the low luminance deficit in early/intermediate stages.

Methods

A standardized questionnaire was developed in three steps with participants with early, intermediate, and late AMD: (1) based on in-depth interviews (n = 19) and two focus group discussions (n = 5 each), content was developed followed by 2. (2) The questionnaire development using cognitive debriefing interviews (n = 3) and leading to a preliminary version of the questionnaire. (3) This version was then administered to 127 participants with early, intermediate, and late AMD. Psychometric properties, such as response category functioning (floor and ceiling effects) and targeting of item difficulty to patient ability of the pilot Vision Impairment in Low Luminance (VILL) questionnaire were evaluated using Rasch analysis.

Results

The preliminary VILL questionnaire consisted of 68 items with a 5-step response scale. Several items were removed based on floor/ceiling effects or misfit and a final pool of 37 items remained. The response scale was collapsed to four categories as one category was underutilized. The targeting of the instrument was good with minimal difference in person and item means (0.52 logits). Precision was also good with a person separation index of 3.55 and reliability of 0.93. There was evidence of multidimensionality (eigenvalue of the first contrast = 5.95) in the scale, which could be resolved by splitting the items into subscales including a reading, mobility, and emotional well-being subscale.

Conclusions

Individuals with AMD report difficulties with vision-related activities and functioning under visually challenging conditions at all stages of the disease. These aspects were considered when developing the 37-item VILL, which demonstrates promising psychometric characteristics. Further assessments of reliability and validity are warranted.

Translational Relevance

The VILL questionnaire is a new patient-reported outcome (PRO) measure developed for future use in AMD studies.

Repeatability of Scotopic Sensitivity and Dark Adaptation Using a Medmont Dark-Adapted Chromatic Perimeter in Age-related Macular Degeneration

Purpose

Functional studies of rods in age-related macular degeneration using the Medmont Dark-Adapted Chromatic Perimeter (DACP) have demonstrated impairments in scotopic sensitivities and dark adaptation (DA). We investigated the intersession repeatability of scotopic sensitivity and DA parameters including the rod intercept time recorded from the Medmont DACP.

Methods

Scotopic thresholds (14 test points) and DA using a 30% photobleach (eight test points) were measured on two separate days from participants 50 years of age or older with a range of age-related macular degeneration severity at loci superior and inferior to the fovea. Repeatability coefficients were calculated for prebleach scotopic sensitivity, and for DA parameters including rod intercept time.

Results

Twelve participants (mean age, 79.7 ± 8.1 years) repeated Medmont DACP testing within 50 days. Repeatability coefficients for prebleach scotopic sensitivity to long wavelength (red, 625 nm) and short wavelength (cyan, 505 nm) were 5.9 dB and 7.2 dB, respectively. The DA curve-derived repeatability coefficients for cone threshold was 3.9 dB, final threshold 5.3 dB, with an R value of 0.075 decades/min, rod intercept time 7.6 minutes, and RITslope 0.54 min/degree.

Conclusions

This study establishes repeatability coefficients for scotopic thresholds and multiple DA parameters obtained with the Medmont DACP in patients with age-related macular degeneration. These repeatability coefficients will serve as the basis for determining clinically meaningful change in rod function in future clinical trials.

Translational Relevance

Measures of repeatability parameters of scotopic thresholds and DA are essential to the accurate interpretation of results in future studies and trials using these measures.

Age-related change in flicker thresholds with rod- and cone-enhanced stimuli

PURPOSE

Rod and cone photoreceptor-specific tests can be time-consuming. A new non-invasive test is described. The test is based on the measurement of flicker modulation thresholds with rod- and cone-enhanced visual stimuli, which requires only minimum adaptation time. Here, we investigated how the rod-and cone-mediated flicker thresholds vary with age.

METHODS

Monocular thresholds with rod and cone-enhanced stimuli were measured in 140 healthy adults, (age range: 18-75 years), foveally (0°) and at four parafoveal locations, at an eccentricity of 5° in each of the four quadrants using five, adaptive, interleaved staircases. Temporal frequencies, stimulus sizes, background luminance and spectral composition, were adjusted appropriately to achieve approximately 1 log unit separation in sensitivity between the rod- and cone-enhanced stimuli. Spectrally calibrated, 'neutral density' filters were used to enable adequate control of display luminance for rod enhanced stimuli.

RESULTS

The magnitude of central and parafoveal rod thresholds was significantly higher than the central and parafoveal cone thresholds, respectively (p < 0.001) in both the age groups. However, the rate of increase in central rod thresholds (y = 0.45x-12.79; linear regression equation) was not significantly steeper than the rate of increase in central (y = 0.29x-8.53) cone thresholds (p = 0.15). Centrally, cone thresholds showed a better correlation with rod central thresholds for the age > 45 years (Spearman correlation, ρ = 0.74, p < 0.001) compared to age ≤ 45 years (ρ = 0.41, p < 0.001).

CONCLUSIONS

Thresholds with rod- and cone-enhanced stimuli are largely invariant below 45 years of age and increase rapidly above this age. This age-wise normative database can be used as an effective functional-marker to assess photoreceptor sensitivities in retinal diseases.

Local Abundance of Macular Xanthophyll Pigment Is Associated with Rod- and Cone-Mediated Vision in Aging and Age-Related Macular Degeneration

Purpose

We assessed the association between the abundance of macular xanthophyll carotenoid pigment using dual-wavelength autofluorescence and multimodal vision testing including rod-mediated dark adaptation (RMDA), a measure of retinoid re-supply, in adults ≥60 years old with and without age-related macular degeneration (AMD).

Methods

AMD severity was determined using the nine-step Age-Related Eye Disease Study grading. Tests probed cones (best-corrected visual acuity, contrast sensitivity), cones and rods (low-luminance visual acuity, low-luminance deficit, mesopic light sensitivity), or rods only (scotopic light sensitivity, RMDA). Signal attenuation by macular pigment optical density (MPOD) was estimated using a ratio of blue and green autofluorescence signal to yield mean MPOD in a 1°-diameter fovea-centered disk, mean MPOD in a 2°-diameter disk centered on a perifoveal RMDA test location, and macular pigment optical volume (MPOV, or integrated MPOD) in a 4°-diameter fovea-centered disk. Age-adjusted associations between vision and imaging measures were determined.

Results

In 88 eyes of 88 subjects (age, 74.9 ± 5.8 years) with normal eyes (n = 32), early AMD (n = 23), or intermediate AMD (n = 33), foveal and perifoveal MPOD and MPOV were higher in the AMD eyes than in the normal eyes. At the RMDA test location, higher MPOD was unrelated to AMD severity but was associated with faster RMDA.

Conclusions

In older adults with and without AMD, higher macular xanthophyll concentrations are associated with better best-corrected visual acuity and RMDA. Data are consistent with a model of cone resilience and rod vulnerability in aging and AMD and can be further explored in a larger sample study.

Functionally validated imaging endpoints in the Alabama study on early age-related macular degeneration 2 (ALSTAR2): design and methods

Background

Age-related macular degeneration (AMD), a leading cause of irreversible vision impairment in the United States and globally, is a disease of the photoreceptor support system involving the retinal pigment epithelium (RPE), Bruch’s membrane, and the choriocapillaris in the setting of characteristic extracellular deposits between outer retinal cells and their blood supply. Research has clearly documented the selective vulnerability of rod photoreceptors and rod-mediated (scotopic) vision in early AMD, including delayed rod-mediated dark adaptation (RMDA) and impaired rod-mediated light and pattern sensitivity. The unifying hypothesis of the Alabama Study on Early Macular Degeneration (ALSTAR2) is that early AMD is a disease of micronutrient deficiency and vascular insufficiency, due to detectable structural changes in the retinoid re-supply route from the choriocapillaris to the photoreceptors. Functionally this is manifest as delayed rod-mediated dark adaptation and eventually as rod-mediated visual dysfunction in general.

Methods

A cohort of 480 older adults either in normal macular health or with early AMD will be enrolled and followed for 3 years to examine cross-sectional and longitudinal associations between structural and functional characteristics of AMD. Using spectral domain optical coherence tomography, the association between (1) subretinal drusenoid deposits and drusen, (2) RPE cell bodies, and (3) the choriocapillaris’ vascular density and rod- and cone-mediated vision will be examined. An accurate map and timeline of structure-function relationships in aging and early AMD gained from ALSTAR2, especially the critical transition from aging to disease, will identify major characteristics relevant to future treatments and preventative measures.

Discussion

A major barrier to developing treatments and prevention strategies for early AMD is a limited understanding of the temporal interrelationships among structural and functional characteristics while transitioning from aging to early AMD. ALSTAR2 will enable the development of functionally valid, structural biomarkers for early AMD, suitable for use in forthcoming clinical trials as endpoint/outcome measures. The comprehensive dataset will also allow hypothesis-testing for mechanisms that underlie the transition from aging to AMD, one of which is a newly developed Center-Surround model of cone resilience and rod vulnerability.

Trial registration

ClinicalTrials.gov Identifier NCT04112667, October 7, 2019.

Detecting vision loss in intermediate age-related macular degeneration: A comparison of visual function tests

The purpose of the study was to evaluate the diagnostic accuracy of visual function tests in intermediate age-related macular degeneration (iAMD). A total of 62 subjects (38 patients with iAMD and 24 controls) were included and underwent several functional assessments: Best-corrected visual acuity (BCVA), low luminance visual acuity (LLVA), visual acuity (VA) measured with the Moorfields Vanishing Optotypes Acuity Charts (MAC), contrast sensitivity with the Pelli-Robson test, reading speed using the International Reading Speed texts (IReST) and mesopic and dark-adapted microperimetry (S-MAIA, CenterVue, Padova, Italy). Groups were compared using non-parametric Wilcoxon rank sum tests and ROC analyses. Linear regression was used to control for confounding. Results showed that all visual function test performances except the IReST were significantly reduced in iAMD patients compared to controls (p < 0.05). These effects did not alter after controlling for age and sex. Best discrimination between iAMD and controls yield the combination of LLVA and contrast sensitivity as well as MAC-VA and contrast sensitivity (ROC area under the curve 0.95 and 0.93, respectively). Our results suggest that LLVA, MAC-VA, contrast sensitivity and mesopic and dark-adapted microperimetry can capture visual impairment characteristic for iAMD. Best discrimination against iAMD is achieved with a combination of two tests.

A Pilot Study Evaluating the Effects of 670 nm Photobiomodulation in Healthy Ageing and Age-Related Macular Degeneration

Limited evidence suggests that the application of 670 nm of red light alters the course of aged decline. A previous report on 18 patients showed regression of drusen and improvement in visual functions in patients with intermediate age-related macular degeneration (AMD) by 12 months. We evaluated the functional and structural effects of applying 670 nm light to 31 patients with intermediate AMD and 11 people aged 55 years or above with normal retina. The study eyes were treated daily in the morning with a 670 nm hand-held light source housed in a torch-like tube that emitted energy equivalent to 40 mW/cm² or 4.8J/ cm² for 2 min at the viewing aperture. Visual function in terms of best-corrected visual acuity, low luminance visual acuity, scotopic thresholds and rod-intercept time were compared between baseline and 1, 3, 6 and 12 months. Structural changes on optical coherence tomography OCT and colour photographs were also assessed. Five withdrew consent voluntarily due to the intensity of the study visit assessments and two developed neovascular AMD and were excluded from further treatment and the analysis. In normal ageing, there was an improvement in scotopic thresholds in the group with no AMD by 1.77dB (p = 0.03) and no other parameters showed any clinically significant change. In eyes with intermediate AMD, there was no significant improvement in any functional or structural changes at any time point up to 12 months although the compliance was good. This pilot study shows that photobiomodulation with 670 nm has no effect in patients who have already progressed to intermediate AMD.

Correlation of retinal vascular perfusion density with dark adaptation in diabetic retinopathy

PURPOSE

To evaluate the anatomic versus functional changes in diabetic retinopathy (DR) by studying the correlation of retinal vascular perfusion density and dark adaptation (DA).

METHODS

Optical coherence tomography angiography (OCTA) and DA tests were performed in diabetic patients and nondiabetic controls. DA was measured using AdaptDx dark adaptometer and the rod intercept was recorded. Macular OCTA images were acquired using the RTVue XR Avanti with AngioVue.

RESULTS

Eighty-six eyes from 57 patients with diabetes (19 with no DR, 19 with non-proliferative DR [NPDR], and 19 with proliferative DR [PDR] who had undergone photocoagulation) and 10 eyes from 10 patients without diabetes were recruited. A significant decrease in vascular density and a prolonged rod intercept were found as DR progressed (P < .01). A negative trend was found between vascular density and the rod intercept. The negative trend in the deep layer (R² = 0.28) was more substantial than that in the superficial layer (R² = 0.14). A prolonged rod intercept was associated with elevated HbA1c (R² = 0.08).

CONCLUSIONS

The vascular density of the macula could be assessed by OCTA and the functional change in the outer retina could be measured non-invasively by DA. The severity of decreasing vascular density and prolongation of DA are proportional to progression of DR. Decreased deep retinal vascular perfusion density and impaired DA response are correlated and show a negative trend according to the severity of DR.

Retinal Pathologic Features on OCT among Eyes of Older Adults Judged Healthy by Color Fundus Photography

PURPOSE

OCT has revealed many details of retinal disease that were not available with older imaging technologies. In eyes of adults older than 60 years with healthy maculas as determined by color fundus photography (CFP) and a validated grading system, we screened for pathologic features using OCT. We also tested visual function to assess potential impact of the observed pathologic features on patients.

DESIGN

Cross-sectional study.

PARTICIPANTS

Persons recruited from primary ophthalmology care clinics.

METHODS

Color fundus photographs were assessed by the 9-step Age-Related Eye Disease Study scale. OCT macular volumes of participants at step 1 on the Age-Related Eye Disease Study scale, considered healthy, were reviewed by a retina specialist masked to other participant characteristics. Participants were tested for 6 different cone- and rod-mediated visual functions.

MAIN OUTCOME MEASURES

Percentage of participants with disorders detected on OCT review and visual function measures.

RESULTS

In 138 of 984 eyes (14%) considered healthy by CFP, pathologic features were detectable by OCT, with 8.4% having vitreomacular interface disorders. Among the low-prevalence disorders found, 5 eyes (0.5%) showed macular telangiectasia type 2. Relative to eyes lacking detectable chorioretinal pathologic features, eyes with any pathologic features were associated with poorer low-luminance visual acuity and rod-mediated dark adaptation. In eyes with epiretinal membranes, the largest single entity identified (n = 61 [6.2%]), significantly worse visual functions were best-corrected visual acuity (P = 0.0444), low-luminance visual acuity (P = 0.0151), and light sensitivity (central 3° and 9°; P = 0.0035 and P = 0.0097, respectively).

CONCLUSIONS

Macular pathologic features with functional visual implications not identified by clinical examination or CFP are detectable with OCT. Vitreomacular interface disorders often are visually significant and treatable conditions that are visible on OCT, but are easily missed on CFP and clinical examination. Another such condition best seen on OCT is macular telangiectasia type 2, an untreatable disorder for which a clinical trial is in progress. OCT has a potential role in primary eye care clinics to screen for retinal pathologic features, especially in eyes with decreased visual acuity and otherwise normal examination results.

Investigation of the relationship between macular pigment levels and rod-mediated dark adaptation in intermediate age-related macular degeneration

BACKGROUND

It has been shown that rod-mediated dark adaptation is significantly delayed in ageing, a change which is exacerbated in age-related macular degeneration (AMD). Levels of lutein and zeaxanthin, the two main constituents of macular pigment have been found in rod outer segments, indicating that the macular pigment may have an influence on rod-mediated dark adaptation. The aim of this study was to determine if rod-mediated dark adaptation is associated with central macular pigment levels in individuals with intermediate stage AMD.

METHODS

A cross-sectional observational study included individuals with acuity better than 6/15 Snellen and intermediate stage AMD based on graded fundus photographs using an internationally accepted grading scale. Rod-mediated dark adaptation was assessed at five degrees eccentricity in the superior retina (inferior visual field) using the rod intercept time measure from the MacuLogix AdaptDx. Macular pigment optical density was measured at 0.5 degrees eccentricity using a heterochromatic flicker photometry-based method.

RESULTS

Twenty-seven individuals (mean age 76.7 years) with intermediate stage AMD and 23 age-matched normal controls (mean age 74.0 years) were recruited. Rod-mediated dark adaptation was significantly delayed in intermediate stage AMD compared with healthy controls (32.9 minutes versus 10.7 minutes, p < 0.01). There was no statistically significant correlation between the rod intercept time and the level of macular pigment in those with intermediate AMD (r = -0.04, p = 0.85).

CONCLUSION

The results did not support the hypothesis that higher macular pigment is associated with improved rod-mediated performance or that higher levels of macular pigment protect rod-mediated function in intermediate AMD.

Characterization of Rod Function Phenotypes Across a Range of Age-Related Macular Degeneration Severities and Subretinal Drusenoid Deposits

Purpose

To examine spatial changes in rod-mediated function in relationship to local structural changes across the central retina in eyes with a spectrum of age-related macular degeneration (AMD) disease severity.

Methods

Participants were categorized into five AMD severity groups based on fundus features. Scotopic thresholds were measured at 14 loci spanning ±18° along the vertical meridian from one eye of each of 42 participants (mean = 71.7 ± 9.9 years). Following a 30% bleach, dark adaptation was measured at eight loci (±12°). Rod intercept time (RIT) was defined from the time to detect a -3.1 log cd/m2 stimulus. RITslope was defined from the linear fit of RIT with decreasing retinal eccentricity. The presence of subretinal drusenoid deposits (SDD), ellipsoid (EZ) band disruption, and drusen at the test loci was evaluated using optical coherence tomography.

Results

Scotopic thresholds indicated greater rod function loss in the macula, which correlated with increasing AMD group severity. RITslope, which captures the spatial change in the rate of dark adaptation, increased with AMD severity (P < 0.0001). Three rod function phenotypes emerged: RF1, normal rod function; RF2, normal scotopic thresholds but slowed dark adaptation; and RF3, elevated scotopic thresholds with slowed dark adaptation. Dark adaptation was slowed at all loci with SDD or EZ band disruption, and at 32% of loci with no local structural changes.

Conclusions

Three rod function phenotypes were defined from combined measurement of scotopic threshold and dark adaptation. Spatial changes in dark adaptation across the macula were captured with RITslope, which may be a useful outcome measure for functional studies of AMD.

Abdominal obesity linked to a longer cone-mediated dark-adaptation recovery time in healthy eyes

Obesity has been associated with abnormal lipid metabolism and with tissue hypoxia. Human Bruch's membrane (BrM) lipid deposits have been proposed to create a diffusion barrier to metabolic exchange between the choroid and photoreceptors, delaying the regeneration of photopigments. The speed of retinal dark adaptation (DA) is dependent on the regeneration of these photopigments. While the retina is extremely sensitive to hypoxia, the inner retina, which encodes visual contrast, is more affected by hypoxia than the outer retina. This study examines the association between adiposity measures and the time course of DA measured psychophysically through contrast detection to test the functionality of both the outer and inner retina. Cone-mediated DA recovery of contrast threshold (CT) was measured following near-total photopigment bleach for 6 min in 52 healthy eyes of 52 individuals (42.6 ± 18.3 years). Stimuli were sine-wave gratings of low-spatial frequency (1 cycle-per-degree (cpd)) and low luminance (1 cd/m²) generated at the centre of a CRT monitor. CT recovery functions were fitted to an exponential decay model to determine the time constant (τ, seconds) of cone sensitivity recovery, final cone CT (CT_f) and CT elevation (CT₀). Weight, height and waist circumference (WC) were measured and body mass index (BMI) and waist-to-height ratio (WHtR) calculated. Relationships were examined through Spearman correlation and through multiple linear regression using age, optical and adiposity measures as independent variables. The repeatability of cone time constant measurements was estimated by the Bland-Altman method and reported as the coefficient of repeatability (CoR). Mean ± SD of time constant and CT_f were 57.3 ± 27.7 s and -1.78 ± 0.20 log₁₀ units respectively. Cone time constant showed positive Spearman correlation with WC (p = 0.008) and WHtR (p = 0.023) but not with BMI (p = 0.058). Only WHtR emerged as an independent predictor of time constant (p = 0.001). CT_f was not correlated with any adiposity measures. Mean cone time constant was 41 s slower in subjects (25%, n = 13) with abdominal obesity (WHtR≥0.5). Mean CT_f was not significantly different in subjects with or without abdominal obesity. CoR for cone time constant was ±16 s. In adult subjects, greater abdominal obesity (WHtR) was related to a longer contrast recovery time for cone-mediated DA (time to dark-adapt) suggesting outer retinal dysfunction. Final contrast threshold, preferentially processed by inner retinal cells, was unaffected by abdominal obesity.

Preliminary Evaluation of a Mobile Device for Dark Adaptation Measurement

Purpose

We evaluated the feasibility of a smartphone application-based dark adaptation (DA) measurement method (MOBILE-DA).

Methods

On a Samsung Galaxy S8 smartphone, MOBILE-DA presented a 1.5° flashing stimulus (wavelength = 453 nm) between −1.15 and −4.33 log candela (cd)/m² at 8° eccentricity using an adaptive staircase, and logged timing of user response (tapping on the screen) whenever the stimulus became visible (monocularly). In a dark room, the smartphone was placed ≈40 cm from the subject, and a white smartphone screen at maximum brightness (≈300 cd/m²) for 120 seconds was used for bleaching before testing. MOBILE-DA was evaluated in normally-sighted (NV) subjects (n = 15; age, 22–82 years). Additionally, a subject with myopic retinal degeneration (MRD; VA, 20/100; age, 62 years) and another with optic nerve atrophy (ONA; visual acuity [VA], 20/500; age, 40 years) were measured. Maximum test timing was capped at 20 minutes. Linear regression was performed to determine age-effect on DA parameters: rod-cone break time (t_RCB) and test-time (t_term). Use of the normalized area under the DA characteristics (AUC) as an outcome measure was explored.

Results

For NV, the repeatability coefficients for t_RCB, t_term, and AUC were ±2.1 minutes, ±5.4 minutes, and 4.4%, respectively, and aging-related delays were observed (t_RCB, R² = 0.47, P = 0.003; t_term, R² = 0.34, P = 0.013; AUC, R² = 0.41, P = 0.006). Compared to ONA and NV, DA was greatly prolonged in the MRD subject (52% larger AUC than the NV mean).

Conclusion

The age-effect was verified for MOBILE-DA measurements in NV subjects; impaired DA in a case with retinal-degeneration was observed.

Translational Relevance

This study establishes feasibility of the smartphone-based DA measurement method as a potential accessible screening tool for various vision disorders.

Visual Defects and Ageing

Many diseases are related to age, among these neurodegeneration is particularly important. Alzheimer's disease Parkinson's and Glaucoma have many common pathogenic events including oxidative damage, Mitochondrial dysfunction, endothelial alterations and changes in the visual field. These are well known in the case of glaucoma, less in the case of neurodegeneration of the brain. Many other molecular aspects are common, such as the role of endoplasmic reticulum autophagy and neuronal apoptosis while others have been neglected due to lack of space such as inflammatory cytokine or miRNA. Moreover, the loss of specific neuronal populations, the induction of similar mechanisms of cell injury and the deposition of protein aggregates in specific anatomical areas are very similar events between these diseases. Intracellular and/or extracellular accumulation of protein aggregates is a key feature of many neurodegenerative disorders. The existence of abnormal protein aggregates has been documented in the RGCs of glaucomatous patients such as the anomalous Tau protein or the β-amyloid accumulations. Intra-cell catabolic processes also appear to be common in both glaucoma and neurodegeneration. They also help us to understand how the basis between these diseases is common and how the visual aspects can be a serious problem for those who are affected.

Longitudinal Study of Dark Adaptation as a Functional Outcome Measure for Age-Related Macular Degeneration

PURPOSE

To investigate the natural history of dark adaptation (DA) function as measured by the change in rod intercept time (RIT) over 4 years and to correlate RIT change with age-related macular degeneration (AMD) severity.

DESIGN

Longitudinal, single-center, observational study.

PARTICIPANTS

A total of 77 participants aged ≥50 years with a range of AMD severities.

METHODS

Participants each contributing a single study eye to the analysis were assigned into person-based AMD severity groups based on fundus characteristics (drusen, pigmentary changes, late AMD, and subretinal drusenoid deposits [SDDs]). The DA function was assessed in study eyes at baseline and 3, 6, 12, 18, 24, 36, and 48 months. Mean change in DA function over time was calculated using the slope of linear regression fits of longitudinal RIT data. Patient-reported responses on a Low Luminance Questionnaire (LLQ) were obtained at baseline and yearly. Nonparametric statistical testing was performed on all comparisons.

MAIN OUTCOME MEASURE

The RIT, defined as the time taken after a photobleach for visual sensitivity to recover detection of a 5×10^-3 cd/m² stimulus (a decrease of 3 log units), was monitored in study eyes over 4 years, and the mean rate of change was computed.

RESULTS

Longitudinal analysis of 65 study eyes followed on the standard testing protocol (mean age, 71±9.3 years; 49% were female) revealed that higher rates of RIT prolongation were correlated with AMD severity group assignment at baseline (P = 0.026) and with severity group assignments at year 4 (P = 0.0011). Study eyes that developed SDD during follow-up demonstrated higher rates of RIT prolongation relative to those that did not (P < 0.0001). Overall, higher rates of RIT prolongation were significantly correlated with greater 4-year decreases in LLQ scores (total mean score, P = 0.0032).

CONCLUSIONS

Longitudinal decline in DA function, which correlated with patient-reported functional deficits, was accelerated in eyes with greater AMD severity and especially in eyes with SDD both at baseline and at 4 years. The RIT prolongation as a measure of changing DA function may be a functional outcome measure in AMD clinical studies.

Determining Optimal Test Parameters for Assessing Dark Adaptation in People With Intermediate Age-Related Macular Degeneration

Purpose

The primary aim was to determine optimal test conditions for evaluating dark adaptation in intermediate age-related macular degeneration (iAMD) in order to minimize test time while maintaining diagnostic sensitivity.

Methods

People with AMD and age-similar controls were recruited (aged >55 years). Rod intercept time (RIT) was assessed after a 76%, 70%, and 65% rhodopsin bleach at 5° eccentricity and 76% and 70% bleach at 12°. Test order was randomized and a 30-minute washout period added between tests. Results were compared between control and iAMD groups and receiver operating characteristics (ROC) curves were constructed.

Results

A total of 26 participants with variable grades of macular health attended for two visits. There was a statistically significant difference in average RIT between the control and iAMD groups at 5° (median, IQR controls = 5.8 minutes, 3.8-7.5; iAMD = 20.6 minutes, 11.1-30.0; Mann-Whitney, P = 0.01) and at 12° (mean, controls: 4.54 minutes ± 2.12 SD, iAMD = 7.72 minutes ± 3.37 SD; independent samples t-test, P = 0.03) following a 76% bleach. Area under the ROC curves was 0.83 (confidence interval [CI]: 0.64-1.0) and 0.79 (CI: 0.59-0.99) for these two test conditions, respectively. Five participants (45%) in the iAMD group had RITs >20 minutes for 76% bleach at 5°, but none for any other test condition.

Conclusions

Nearly half of the participants with iAMD produced unacceptably long recovery times (>20 minutes) using a 76% bleach at 5° eccentricity. The 76% bleach at 12° provided almost equivalent separation between AMD and controls but recovery was achieved within 20 minutes.

Epigenetic control of gene regulation during development and disease: A view from the retina

Complex biological processes, such as organogenesis and homeostasis, are stringently regulated by genetic programs that are fine-tuned by epigenetic factors to establish cell fates and/or to respond to the microenvironment. Gene regulatory networks that guide cell differentiation and function are modulated and stabilized by modifications to DNA, RNA and proteins. In this review, we focus on two key epigenetic changes - DNA methylation and histone modifications - and discuss their contribution to retinal development, aging and disease, especially in the context of age-related macular degeneration (AMD) and diabetic retinopathy. We highlight less-studied roles of DNA methylation and provide the RNA expression profiles of epigenetic enzymes in human and mouse retina in comparison to other tissues. We also review computational tools and emergent technologies to profile, analyze and integrate epigenetic information. We suggest implementation of editing tools and single-cell technologies to trace and perturb the epigenome for delineating its role in transcriptional regulation. Finally, we present our thoughts on exciting avenues for exploring epigenome in retinal metabolism, disease modeling, and regeneration.

HEALTH CONDITIONS LINKED TO AGE-RELATED MACULAR DEGENERATION ASSOCIATED WITH DARK ADAPTATION

PURPOSE

To determine the association between dark adaption (DA) and different health conditions linked with age-related macular degeneration (AMD).

METHODS

Cross-sectional study, including patients with AMD and a control group. Age-related macular degeneration was graded according to the Age-Related Eye Disease Study (AREDS) classification. We obtained data on medical history, medications, and lifestyle. Dark adaption was assessed with the extended protocol (20 minutes) of AdaptDx (MacuLogix). For analyses, the right eye or the eye with more advanced AMD was selected. Multivariate linear and logistic regressions were performed, accounting for age and AMD stage.

RESULTS

Seventy-eight subjects (75.6% AMD; 24.4% controls) were included. Multivariate assessments revealed that body mass index (BMI; β = 0.30, P = 0.045), taking AREDS vitamins (β = 5.51, P < 0.001), and family history of AMD (β = 2.68, P = 0.039) were significantly associated with worse rod intercept times. Abnormal DA (rod intercept time ≥ 6.5 minutes) was significantly associated with family history of AMD (β = 1.84, P = 0.006), taking AREDS supplements (β = 1.67, P = 0.021) and alcohol intake (β = 0.07, P = 0.017).

CONCLUSION

Besides age and AMD stage, a higher body mass index, higher alcohol intake, and a family history of AMD seem to impair DA. In this cohort, the use of AREDS vitamins was also statistically linked with impaired DA, most likely because of an increased severity of disease in subjects taking them.

Repeatability of Retinal Sensitivity Measurements Using a Medmont Dark-Adapted Chromatic Perimeter in Healthy and Age-Related Macular Degeneration Cases

Purpose

To determine the intrasession and intersession test-retest repeatability of retinal sensitivity measurements using a dark-adapted chromatic perimeter (DACP).

Methods

For intrasession testing, retinal sensitivity within the central 24° for the 505-nm stimulus was measured after 20, 30, and 40 minutes of dark adaptation (DA) and for the 625-nm stimulus was measured after the first and second 505-nm tests. For intersession testing, retinal sensitivity for both stimuli was measured after 30 minutes of DA at baseline and 1 month. The point-wise sensitivity (PWS) difference and coefficient of repeatability (CoR) of each stimulus and group were determined.

Results

For intrasession testing, 10 age-related macular degeneration (AMD) and eight control subjects were recruited. The overall CoR for the 505-nm stimulus was 8.4 dB for control subjects and 9.1 dB for AMD cases, and for the 625-nm stimulus was 6.7 dB for control subjects and 9.5 dB for AMD cases. For intersession testing, seven AMD cases and 13 control subjects returned an overall CoR for the 505-nm stimulus of 8.2 dB for the control and 11.7 dB for the AMD group. For the 625-nm stimulus the CoR was 6.2 dB for the control group and 8.4 dB for the AMD group. Approximately 80% of all test points had a PWS difference of ±5 dB between the two intrasession or intersession measurements for both stimuli.

Conclusions

The CoR for the DACP is larger than that reported for scotopic perimeters; however, the majority of test points had a PWS difference of ±5 dB between tests.

Translational Relevance

The DACP offers an opportunity to measure static and dynamic rod function at multiple locations with an acceptable reproducibility level.

Rod-Mediated Dark Adaptation and Macular Pigment Optical Density in Older Adults with Normal Maculas

PURPOSE

To examine the association between macular pigment optical density (MPOD) and rod-mediated dark adaptation (RMDA) in persons ≥60 years old with normal maculas as determined by an accepted color fundus photography grading system.

METHODS

This cross-sectional analysis used baseline data from eyes in the Alabama Study on Early Age-Related Macular Degeneration. Eyes at step 1 in the AREDS 9-step grading system were considered normal. Eyes were additionally assessed by spectral domain optical coherence tomography (SD-OCT). Foveal MPOD was estimated via heterochromatic flicker photometry, and RMDA was assessed with a computerized dark adaptometer. The association between RMDA and MPOD was examined via Spearman correlation coefficients adjusted for age.

RESULTS

In 306 eyes from 306 persons (mean age 68.2 years) in normal macular health, MPOD was not associated with RMDA (age-adjusted rank correlation = 0.043, p = 0.45). After 81 eyes with incidental macular findings by SD-OCT evaluation were excluded, the association between MPOD and RMDA remained null (N = 225, age-adjusted r = 0.015, p = 0.82).

CONCLUSION

In a large sample of normal aged eyes, RMDA, a visual function that is rate limited by retinoid availability to photoreceptors across the complex of retinal pigment epithelium, Bruch's membrane, and choriocapillaris, is not related to MPOD in the neurosensory retina.

The Alabama VIP older driver study rationale and design: examining the relationship between vision impairment and driving using naturalistic driving techniques

BACKGROUND

Older drivers aged ≥70 years old have among the highest rates of motor vehicle collisions (MVC) compared to other age groups. Driving is a highly visual task, and older adults have a high prevalence of vision impairment compared to other ages. Most studies addressing visual risk factors for MVCs by older drivers utilize vehicle accident reports as the primary outcome, an approach with several methodological limitations. Naturalistic driving research methods overcome these challenges and involve installing a high-tech, unobtrusive data acquisition system (DAS) in an older driver's own vehicle. The DAS continuously records multi-channel video of driver and roadway, sensor-based kinematics, GPS location, and presence of nearby objects in front of the vehicle, providing an objective measure of driving exposure. In this naturalistic driving study, the purpose is to examine the relationship between vision and crashes and near-crashes, lane-keeping, turning at intersections, driving performance during secondary tasks demands, and the role of front-seat passengers. An additional aim is to compare results of the on-road driving evaluation by a certified driving rehabilitation specialist to objective indicators of driving performance derived from the naturalistic data.

METHODS

Drivers ≥70 years old are recruited from ophthalmology clinics and a previous population-based study of older drivers, with the goal of recruiting persons with wide ranging visual function. Target samples size is 195 drivers. At a baseline visit, the DAS is installed in the participant's vehicle and a battery of health and functional assessments are administered to the driver including visual-sensory and visual-cognitive tests. The DAS remains installed in the vehicle for six months while the participant goes about his/her normal driving with no imposed study restrictions. After six months, the driver returns for DAS de-installation, repeat vision testing, and an on-road driving evaluation by a certified driving rehabilitation specialist (CDRS). The data streams recorded by the DAS are uploaded to the data coordinating center for analysis.

DISCUSSION

The Alabama VIP Older Driver Study is the first naturalistic older driver study specifically focused on the enrollment of drivers with vision impairment in order to study the relationship between visual dysfunction and driver safety and performance.

ASSOCIATION BETWEEN VISUAL FUNCTION AND SUBRETINAL DRUSENOID DEPOSITS IN NORMAL AND EARLY AGE-RELATED MACULAR DEGENERATION EYES

PURPOSE

To examine the association between subretinal drusenoid deposits (SDDs) identified by multimodal retinal imaging and visual function in older eyes with normal macular health or in the earliest phases of age-related macular degeneration (AMD).

METHODS

Age-related macular degeneration status for each eye was defined according to the Age-Related Eye Disease Study (AREDS) 9-step classification system (normal = Step 1, early AMD = Steps 2-4) based on color fundus photographs. Visual functions measured were best-corrected photopic visual acuity, contrast and light sensitivity, mesopic visual acuity, low-luminance deficit, and rod-mediated dark adaptation. Subretinal drusenoid deposits were identified through multimodal imaging (color fundus photographs, infrared reflectance and fundus autofluorescence images, and spectral domain optical coherence tomography).

RESULTS

The sample included 1,202 eyes (958 eyes with normal health and 244 eyes with early AMD). In normal eyes, SDDs were not associated with any visual function evaluated. In eyes with early AMD, dark adaptation was markedly delayed in eyes with SDDs versus no SDD (a 4-minute delay on average), P = 0.0213. However, this association diminished after age adjustment, P = 0.2645. Other visual functions in early AMD eyes were not associated with SDDs.

CONCLUSION

In a study specifically focused on eyes in normal macular health and in the earliest phases of AMD, early AMD eyes with SDDs have slower dark adaptation, largely attributable to the older ages of eyes with SDD; they did not exhibit deficits in other visual functions. Subretinal drusenoid deposits in older eyes in normal macular health are not associated with any visual functions evaluated.

Lutein and Zeaxanthin Isomers in Eye Health and Disease

Current evidence suggests lutein and its isomers play important roles in ocular development in utero and throughout the life span, in vision performance in young and later adulthood, and in lowering risk for the development of common age-related eye diseases in older age. These xanthophyll (oxygen-containing) carotenoids are found in a wide variety of vegetables and fruits, and they are present in especially high concentrations in leafy green vegetables. Additionally, egg yolks and human milk appear to be bioavailable sources. The prevalence of lutein, zeaxanthin, and meso-zeaxanthin in supplements is increasing. Setting optimal and safe ranges of intake requires additional research, particularly in pregnant and lactating women. Accumulating evidence about variable interindividual response to dietary intake of these carotenoids, based on genetic or metabolic influences, suggests that there may be subgroups that benefit from higher levels of intake and/or alternate strategies to improve lutein and zeaxanthin status.

Prevalence of Undiagnosed Age-Related Macular Degeneration in Primary Eye Care

Importance

Age-related macular degeneration (AMD) is the leading cause of irreversible vision impairment in older adults in the United States, yet little is known about whether AMD is appropriately diagnosed in primary eye care.

Objectives

To examine the prevalence of eyes with AMD in patients seen in primary eye care clinics who purportedly have normal macular health per their medical record and the association of AMD with patient and physician characteristics.

Design, Setting, and Participants

In this cross-sectional study of primary eye care practices in Birmingham, Alabama, 644 persons 60 years or older with normal macular health per medical record based on their most recent dilated comprehensive eye examination by a primary eye care ophthalmologist or optometrist were enrolled from May 1, 2009, through December 31, 2011. Data analysis was performed from May 1, 2016, through December 20, 2016.

Main Outcomes and Measures

Presence of AMD as defined by the Clinical Age-Related Maculopathy Staging system based on color fundus photography and a masked grader. Types of AMD-associated lesions were noted. Patient health and physician characteristics were collected.

Results

The sample consisted of 1288 eyes from 644 participants (231 [35.9%] male and 413 [64.1%] female; mean [SD] age, 69.4 [6.1] years; 611 white [94.9%]) seen by 31 primary eye care ophthalmologists or optometrists. A total of 968 eyes (75.2%) had no AMD, in agreement with their medical record; 320 (24.8%) had AMD despite no diagnosis of AMD in the medical record. Among eyes with undiagnosed AMD, 32 (10.0%) had hyperpigmentation, 43 (13.4%) had hypopigmentation, 249 (77.8%) had small drusen, 250 (78.1%) had intermediate drusen, and 96 (30.0%) had large drusen. Undiagnosed AMD was associated with older patient age (odds ratio [OR], 1.06; 95% CI, 1.04-1.09; P < .001), male sex (age-adjusted OR, 1.39; 95% CI, 1.02-1.91; P = .04), and less than a high school education (age-adjusted OR, 2.40; 95% CI, 1.03-5.62; P = .04). Prevalence of undiagnosed AMD was not different for ophthalmologists and optometrists (age adjusted OR, 0.99; 95% CI, 0.71-1.36; P = .94).

Conclusions and Relevance

Approximately 25.0% of eyes deemed to be normal based on dilated eye examination by primary eye care physicians had macular characteristics that indicated AMD revealed by fundus photography and trained raters. A total of 30.0% of eyes with undiagnosed AMD had AMD with large drusen that would have been treatable with nutritional supplements had it been diagnosed. Improved AMD detection strategies may be needed in primary eye care as more effective treatment strategies for early AMD become available in the coming years.

Decreased Visual Function Scores on a Low Luminance Questionnaire Is Associated with Impaired Dark Adaptation

PURPOSE

We investigate whether responses on a Low Luminance Questionnaire (LLQ) in patients with a range of age-related macular degeneration (AMD) severity are associated with their performance on focal dark adaptation (DA) testing and with choroidal thickness.

DESIGN

Cross-sectional, single-center, observational study.

PARTICIPANTS

A total of 113 participants older than 50 years of age with a range of AMD severity.

METHODS

Participants answered the LLQ on the same day they underwent DA testing using a focal dark adaptometer measuring rod intercept time (RIT). We performed univariable and multivariable analyses of the LLQ scores and age, RIT, AMD severity, subfoveal choroidal thickness [SFCT], phakic status, and best-corrected visual acuity.

MAIN OUTCOME MEASURES

The primary outcome of this study was the score on the 32-question LLQ. Each item in the LLQ is designated to 1 of 6 subscales describing functional problems in low luminance: driving, emotional distress, mobility, extreme lighting, peripheral vision, and general dim lighting. Scores were computed for each subscale, in addition to a weighted total mean score.

RESULTS

Responses from 113 participants (mean age, 76.2±9.3 years; 58.4% were female) and 113 study eyes were analyzed. Univariable analysis demonstrated that lower scores on all LLQ subscales were correlated with prolonged DA testing (longer RIT) and decreased choroidal thickness. All associations were statistically significant except for the association of choroidal thickness and "peripheral vision." The strongest association was the LLQ subscale of driving with RIT (r =-0.97, P < 0.001). Multivariable analysis for each of the LLQ subscale outcomes, adjusted for age, included RIT, with total LLQ score, "driving," "extreme lighting," and "mobility" also including choroidal thickness. In all multivariable analyses, RIT had a stronger association than choroidal thickness.

CONCLUSIONS

This cross-sectional analysis demonstrates associations of patient-reported functional deficits, as assessed on the LLQ, with both reduced DA and reduced choroidal thickness, in a population of older adults with varying degrees of AMD severity and good visual acuity in at least 1 eye. These analyses suggest that local functional measurements of DA testing (RIT) and choroidal thickness are associated with patient-reported functional deficits.

Peripapillary Pachychoroid in Nonarteritic Anterior Ischemic Optic Neuropathy

Purpose

This study examined the peripapillary choroidal thickness (PCT) in nonarteritic ischemic optic neuropathy (NAION) in comparison to contralateral eyes and normal eyes.

Methods

We used enhanced depth imaging spectral-domain optical coherence tomography to image the optic nerve head of 20 NAION, 10 contralateral eyes, and 102 normal eyes. Following compensation, the scans were manually delineated to identify relevant surfaces including Bruch's membrane opening (BMO), Bruch's membrane, and anterior sclera. The PCT was defined as the measurement between Bruch's membrane and the anterior sclera and was measured at increasing distance from BMO. Models adjusted for age, BMO area, and axial length were used to compare the mean PCT between NAION and normal eyes, and contralateral eyes and normal eyes. Paired t-tests were used to compare the PCT between NAION and contralateral eyes.

Results

The mean PCT was thicker in NAION and contralateral eyes when compared with normal eyes at all distances from BMO (P < 0.001). The PCT was not significantly thicker in contralateral eyes when compared with affected NAION eyes. Choroidal thickness was thinnest in the inferior quadrant in all eyes regardless of the group.

Conclusions

Increased peripapillary choroidal thickness was noted in both NAION and contralateral eyes. The thicker choroid may be an associated feature or a result of the disorder. Although further longitudinal study is required to determine causation, these findings may suggest that a thickened peripapillary choroid may be a component of the disk-at-risk clinical phenotype.

Visual Function in Older Eyes in Normal Macular Health: Association with Incident Early Age-Related Macular Degeneration 3 Years Later

Purpose

In older eyes in normal macular health, we examined associations between impaired photopic acuity, mesopic acuity, spatial contrast sensitivity, light sensitivity, and the presence of low luminance deficit (difference between photopic and mesopic acuity) at baseline and incident AMD 3 years later. Associations were compared with an association between delayed rod-mediated dark adaptation and incident AMD, previously reported for this cohort.

Methods

Enrollees were 60 years or older. Eyes at step 1 in the AREDS nine-step classification system based on masked grading of color fundus photographs were included. Photopic and mesopic acuity, contrast sensitivity, and light sensitivity, and the presence of low luminance deficit, were measured at baseline. Demographic, lifestyle, general health, and blood markers were assessed at baseline as potential confounders. Three years later fundus grading was repeated to determine AMD presence.

Results

For the analysis, 827 eyes of 467 persons were eligible. Impaired mesopic acuity at baseline was associated with incident AMD, age-adjusted rate ratio (RR) 1.57 (95% confidence interval [CI] 1.04–2.35), whereas impaired photopic acuity, contrast sensitivity and macular light sensitivity, and the presence of a low luminance deficit were not. The mesopic acuity association was slightly weaker than the association between abnormal dark adaptation and incident AMD (RR 1.85, 95% CI 1.07–3.20).

Conclusions

Impaired mesopic acuity in eyes in normal macular health is a risk factor for incident early AMD 3 years later, however, photopic acuity, contrast sensitivity, and light sensitivity, and the presence of a low luminance deficit are not risk factors.

Vision-targeted health related quality of life in older adults: patient-reported visibility problems in low luminance activities are more likely to decline than daytime activities

Background

Commonly used vision-targeted health-related quality of life questionnaires almost exclusively focus items on vision under daytime conditions. Older adults even when in good eye health frequently report experiencing vision problems at night and under low environmental light levels, and psychophysical studies also document these visibility problems. Here we compare the progression of self-reported low luminance visibility problems and self-reported visibility problems under daytime conditions in older adults.

Methods

Trained interviewers administered two questionnaires to older adults in normal eye health: the National Eye Institute Visual Function Questionnaire – 25 (NEI VFQ-25) where items are almost entirely focused on difficulties in daytime activities, and the Low Luminance Questionnaire (LLQ) where items are focused on difficulties seeing at night and under low luminance conditions. The following visual functions were also measured: visual acuity, low luminance visual acuity, low luminance deficit, contrast sensitivity, light sensitivity in the macula, and rod-mediated dark adaptation. The protocol was repeated 3 years later.

Results

Scores on the NEI VFQ-25 composite and its subscales were unchanged between baseline and 3-year follow-up, whereas scores on the LLQ composite and 5 of 6 subscales significantly decreased (corresponding to less functionality) at the 3-year follow-up. Participants were more likely to display a ≥ 5 point decrease on the LLQ composite than on the NEI VFQ-25 over 3 years. Visual functional tests were largely unrelated to changes in NEI VFQ-25 and LLQ scores from baseline to follow-up.

Conclusions

Older adults’ vision-targeted quality of life as measured by questionnaire is more likely to exhibit a practically significant decrease over 3 years using a questionnaire that focused on low luminance activities (LLQ) than one focused on daytime activities (NEI VFQ-25). That the results of visual functional testing did not correspond to older adults’ decline in self-reported problems in low luminance activities emphasizes the importance of questionnaires in understanding visual difficulties from the patients’ own perspective.

The Association Between Subretinal Drusenoid Deposits in Older Adults in Normal Macular Health and Incident Age-Related Macular Degeneration

Purpose

Subretinal drusenoid deposits (SDD) have been associated with the progression to late age-related macular degeneration (AMD). To determine whether SDD in eyes in normal macular health increases risk for early AMD, this study examined the association between presence of SDD at baseline in a cohort of older adults in normal macular health and incident AMD 3 years later.

Methods

Subjects enrolled in the Alabama Study on Early Age-Related Macular Degeneration (ALSTAR) were assessed for the presence of SDD using color fundus photos, infrared reflectance and fundus autofluorescence images, and spectral-domain optical coherence tomography volumes. The study sample included 799 eyes from 455 participants in normal macular health per grading of color fundus photographs using the 9-step Age-Related Eye Disease Study (AREDS) classification system. Age-related macular degeneration was defined as eyes having an AREDS grade ≥2 at the 3-year follow-up.

Results

Twenty-five percent of participants had SDD in one or both eyes at baseline. At follow-up visit, 11.9% of eyes in the sample developed AMD. Compared to eyes without SDD, those with SDD were 2.24 (95% confidence interval [CI] 1.36–3.70) times more likely to have AMD at follow-up. After adjusting for age, C-reactive protein quartile, and family history of AMD, the association persisted.

Conclusions

Results suggest that SDD in older eyes with normal macular health as defined by the AREDS scale is a risk factor for the development of early AMD. Older adults in seemingly normal macular health yet having SDD may warrant closer clinical monitoring for the possible onset of early AMD.

The Effects of Diabetic Retinopathy and Pan-Retinal Photocoagulation on Photoreceptor Cell Function as Assessed by Dark Adaptometry

Purpose

The pathophysiology of vision loss in persons with diabetic retinopathy (DR) is complex and incompletely defined. We hypothesized that retinal pigment epithelium (RPE) and rod and cone photoreceptor dysfunction, as measured by dark adaptometry, would increase with severity of DR, and that pan-retinal photocoagulation (PRP) would exacerbate this dysfunction.

Methods

Dark adaptation (DA) was measured in subjects with diabetes mellitus and healthy controls. Dark adaptation was measured at 5° superior to the fovea following a flash bleach, and the data were analyzed to yield cone and rod sensitivity curves. Retinal layer thicknesses were quantified using spectral-domain optical coherence tomography (OCT).

Results

The sample consisted of 23 controls and 73 diabetic subjects. Subjects with moderate nonproliferative diabetic retinopathy (NPDR) exhibited significant impairment of rod recovery rate compared with control subjects (P = 0.04). Cone sensitivity was impaired in subjects with proliferative diabetic retinopathy (PDR) (type 1 diabetes mellitus [T1DM]: P = 0.0047; type 2 diabetes mellitus [T2DM]: P < 0.001). Subjects with untreated PDR compared with subjects treated with PRP exhibited similar rod recovery rates and cone sensitivities. Thinner RPE as assessed by OCT was associated with slower rod recovery and lower cone sensitivity, and thinner photoreceptor inner segment/outer segment layer was associated with lower cone sensitivity.

Conclusions

The results suggest that RPE and photoreceptor cell dysfunction, as assessed by cone sensitivity level and rod- and RPE-mediated dark adaptation, progresses with worsening DR, and rod recovery dysfunction occurs earlier than cone dysfunction. Function was preserved following PRP. The findings suggest multiple defects in retinoid function and provide potential points to improve visual function in persons with PDR.

Prevalence of Subretinal Drusenoid Deposits in Older Persons with and without Age-Related Macular Degeneration, by Multimodal Imaging

PURPOSE

To assess the prevalence of subretinal drusenoid deposits (SDD) in older adults with healthy maculas and early and intermediate age-related macular degeneration (AMD) using multimodal imaging.

DESIGN

Cross-sectional study.

PARTICIPANTS

A total of 651 subjects aged ≥60 years enrolled in the Alabama Study of Early Age-Related Macular Degeneration from primary care ophthalmology clinics.

METHODS

Subjects were imaged using spectral domain optical coherence tomography (SD OCT) of the macula and optic nerve head (ONH), infrared reflectance, fundus autofluorescence, and color fundus photographs (CFP). Eyes were assessed for AMD presence and severity using the Age-Related Eye Disease Study (AREDS) 9-step scale. Criteria for SDD presence were identification on ≥1 en face modality plus SD OCT or on ≥2 en face modalities if absent on SD OCT. Subretinal drusenoid deposits were considered present at the person level if present in 1 or both eyes.

MAIN OUTCOME MEASURES

Prevalence of SDD in participants with and without AMD.

RESULTS

Overall prevalence of SDD was 32% (197/611), with 62% (122/197) affected in both eyes. Persons with SDD were older than those without SDD (70.6 vs. 68.7 years, P = 0.0002). Prevalence of SDD was 23% in subjects without AMD and 52% in subjects with AMD (P < 0.0001). Among those with early and intermediate AMD, SDD prevalence was 49% and 79%, respectively. After age adjustment, those with SDD were 3.4 times more likely to have AMD than those without SDD (95% confidence interval, 2.3-4.9). By using CFP only for SDD detection per the AREDS protocol, prevalence of SDD was 2% (12/610). Of persons with SDD detected by SD OCT and confirmed by at least 1 en face modality, 47% (89/190) were detected exclusively on the ONH SD OCT volume.

CONCLUSIONS

Subretinal drusenoid deposits are present in approximately one quarter of older adults with healthy maculae and in more than half of persons with early to intermediate AMD, even by stringent criteria. The prevalence of SDD is strongly associated with AMD presence and severity and increases with age, and its retinal topography including peripapillary involvement resembles that of rod photoreceptors. Consensus on SDD detection methods is recommended to advance our knowledge of this lesion and its clinical and biologic significance.

Recent advances in the dark adaptation investigations

Dark adaptation is a highly sensitive neural function and may be the first symptom of many status including the physiologic and pathologic entity, suggesting that it could be instrumental for diagnose. However, shortcomings such as the lack of standardized parameters, the long duration of examination, and subjective randomness would substantially impede the use of dark adaptation in clinical work. In this review we summarize the recent research about the dark adaptation, including two visual cycles-canonical and cone-specific visual cycle, affecting factors and the methods for measuring dark adaptation. In the opinions of authors, intensive investigations are needed to be done for the widely use of this significant visual function in clinic.

Delayed Rod-Mediated Dark Adaptation Is a Functional Biomarker for Incident Early Age-Related Macular Degeneration

PURPOSE

To examine whether slowed rod-mediated dark adaptation (DA) in adults with normal macular health at baseline is associated with the incidence of age-related macular degeneration (AMD) 3 years later.

DESIGN

Prospective cohort.

PARTICIPANTS

Adults aged ≥60 years were recruited from primary care ophthalmology clinics. Both eyes were required to be step 1 (normal) on the Age-Related Eye Disease Study 9-step AMD classification system based on color fundus photographs graded by experienced and masked evaluators.

METHODS

Rod-mediated DA was assessed at baseline in 1 eye after a photobleach using a computerized dark adaptometer with targets centered at 5° on the inferior vertical meridian. Speed of DA was characterized by the rod-intercept value, with abnormal DA defined as rod-intercept ≥12.3 minutes. Demographic characteristics, best-corrected visual acuity, and smoking status were also assessed. Log-binomial regression was used to calculate unadjusted and adjusted risk ratios (RRs) and associated 95% confidence intervals (CIs) for the association between baseline DA and incident AMD.

MAIN OUTCOME MEASURES

Presence of AMD at the 3-year follow-up visit for the eye tested for DA at baseline.

RESULTS

Both baseline and follow-up visits were completed by 325 persons (mean age, 67.8 years). At baseline, 263 participants had normal DA with mean rod-intercept of 9.1 (standard deviation [SD], 1.5), and 62 participants had abnormal DA with mean rod-intercept of 15.1 (SD, 4.0). After adjustment for age and smoking, those with abnormal DA in the tested eye at baseline were approximately 2 times more likely to have AMD in that eye (RR, 1.92; 95% CI, 1.03-3.62) by the time of the follow-up visit, compared with those who had normal DA at baseline.

CONCLUSIONS

Delayed rod-mediated DA in older adults with normal macular health is associated with incident early AMD 3 years later, and thus is a functional biomarker for early disease. The biological relevance of this test is high, because it assesses translocation of vitamin A derivatives across the retinal pigment epithelium and Bruch's membrane, 2 tissues with prominent age- and AMD-related pathology.

The protective role of tacrine and donepezil in the retina of acetylcholinesterase knockout mice

AIM

To determine the effect of different concentrations of the acetylcholinesterase (AChE) inhibitors tacrine and donepezil on retinal protection in AChE(+/-) mice (AChE knockout mice) of various ages.

METHODS

Cultured ARPE-19 cells were treated with hydrogen peroxide (H2O2) at concentrations of 0, 250, 500, 1000 and 2000 µmol/L and protein levels were measured using Western blot. Intraperitoneal injections of tacrine and donepezil (0.1 mg/mL, 0.2 mg/mL and 0.4 mg/mL) were respectively given to AChE(+/-) mice aged 2mo and 4mo and wild-type S129 mice for 7d; phosphate buffered saline (PBS) was administered to the control group. The mice were sacrificed after 30d by in vitro cardiac perfusion and retinal samples were taken. AChE-deficient mice were identified by polymerase chain reaction (PCR) analysis using specific genotyping protocols obtained from the Jackson Laboratory website. H&E staining, immunofluorescence and Western blot were performed to observe AChE protein expression changes in the retinal pigment epithelial (RPE) cell layer.

RESULTS

Different concentrations of H2O2 induced AChE expression during RPE cell apoptosis. AChE(+/-) mice retina were thinner than those in wild-type mice (P<0.05); the retinal structure was still intact at 2mo but became thinner with increasing age (P<0.05); furthermore, AChE(+/-) mice developed more slowly than wild-type mice (P<0.05). Increased concentrations of tacrine and donepezil did not significantly improve the protection of the retina function and morphology (P>0.05).

CONCLUSION

In vivo, tacrine and donepezil can inhibit the expression of AChE; the decrease of AChE expression in the retina is beneficial for the development of the retina.

Serum levels of lipid metabolites in age-related macular degeneration

Age-related macular degeneration (AMD) is a neurodegenerative disease that causes adult-onset blindness. There are 2 forms of this progressive disease: wet and dry. Currently there is no cure for AMD, but several treatment options have started to emerge making early detection critical for therapeutic success. Analysis of the eyes of Abca4(-/-)Rdh8(-/-) mice that display light-induced retinal degeneration indicates that 11-cis-retinal and docosahexaenoic acid (DHA) levels were significantly decreased as compared with the eyes of control dark-adapted C57BL/6J mice. In addition, exposure to intense light correlated with higher levels of prostaglandin G2 in the eyes of Abca4(-/-)Rdh8(-/-) mice. Intense light exposure also lowered DHA levels in the eyes of wild-type C57BL/6J mice without discernible retinal degeneration. Analysis of human serum from patients with AMD recapitulated these dysregulated DHA levels and revealed dysregulation of arachidonic acid (AA) levels as well (∼32% increase in patients with AMD compared with average levels in healthy individuals). From these observations, we then built a statistical model that included levels of DHA and AA from human serum. This model had a 74% probability of correctly identifying patients with AMD from controls. Addition of a genetic analysis for one of the most prevalent amino acid substitutions in the age-related maculopathy susceptibility 2 gene linked to AMD, Ala(69)→Ser, did not improve the statistical model. Thus, we have characterized a reliable method with the potential to detect AMD without a genetic component, paving the way for a larger-scale clinical evaluation. Our studies on mouse models along with the analysis of human serum suggest that our small molecule-based model may serve as an effective tool to estimate the risk of developing AMD.

RefMoB, a Reflectivity Feature Model-Based Automated Method for Measuring Four Outer Retinal Hyperreflective Bands in Optical Coherence Tomography

PURPOSE

To validate a model-driven method (RefMoB) of automatically describing the four outer retinal hyperreflective bands revealed by spectral-domain optical coherence tomography (SDOCT), for comparison with histology of normal macula; to report thickness and position of bands, particularly band 2 (ellipsoid zone [EZ], commonly called IS/OS).

METHODS

Foveal and superior perifoveal scans of seven SDOCT volumes of five individuals aged 28 to 69 years with healthy maculas were used (seven eyes for validation, five eyes for measurement). RefMoB determines band thickness and position by a multistage procedure that models reflectivities as a summation of Gaussians. Band thickness and positions were compared with those obtained by manual evaluators for the same scans, and compared with an independent published histological dataset.

RESULTS

Agreement among manual evaluators was moderate. Relative to manual evaluation, RefMoB reported reduced thickness and vertical shifts in band positions in a band-specific manner for both simulated and empirical data. In foveal and perifoveal scans, band 1 was thick relative to the anatomical external limiting membrane, band 2 aligned with the outer one-third of the anatomical IS ellipsoid, and band 3 (IZ, interdigitation of retinal pigment epithelium and photoreceptors) was cleanly delineated.

CONCLUSIONS

RefMoB is suitable for automatic description of the location and thickness of the four outer retinal hyperreflective bands. Initial results suggest that band 2 aligns with the outer ellipsoid, thus supporting its recent designation as EZ. Automated and objective delineation of band 3 will help investigations of structural biomarkers of dark-adaptation changes in aging.

Functional optical coherence tomography enables in vivo physiological assessment of retinal rod and cone photoreceptors

Transient intrinsic optical signal (IOS) changes have been observed in retinal photoreceptors, suggesting a unique biomarker for eye disease detection. However, clinical deployment of IOS imaging is challenging due to unclear IOS sources and limited signal-to-noise ratios (SNRs). Here, by developing high spatiotemporal resolution optical coherence tomography (OCT) and applying an adaptive algorithm for IOS processing, we were able to record robust IOSs from single-pass measurements. Transient IOSs, which might reflect an early stage of light phototransduction, are consistently observed in the photoreceptor outer segment almost immediately (<4 ms) after retinal stimulation. Comparative studies of dark- and light-adapted retinas have demonstrated the feasibility of functional OCT mapping of rod and cone photoreceptors, promising a new method for early disease detection and improved treatment of diseases such as age-related macular degeneration (AMD) and other eye diseases that can cause photoreceptor damage.