Visual Acuity and Fixation Characteristics in Age-Related Macular Degeneration

Restitution of potential visual acuity in low vision patients with the use of yoke prisms

PURPOSE

To determine the efficacy of prisms when used for redirection of incoming images towards the preferred reinal loci (PRLs) for restitution of potential visual acuity (PVA) in low vision cases with age-related macular degeneration (AMD).

METHODS

Retrospective comparative interventional case series review. Low vision rehabilitation (LVR) protocol used included best corrected visual acuity (BCVA), PVA, topographic PRL identification and use of prisms to produce image redirection to the presumed PRL. The primary outcome measure selected for analysis was BCVA for viewing distance targets after use of yoke prisms.

RESULTS

Image relocation with prisms in patients with AMD resulted in significantly better BCVA levels (t₃₂ = 8.57, p < 0.0001) in the better eye. Distance BCVA levels achieved were almost identical to PVA levels (t₃₂ = 0.415, p < 0.681) (y= -0.136 + 1.195x, r = 0.8333, p < 0.001).

CONCLUSIONS

Use of yoke prisms for image redirection towards a peripheral identifiable PRL may result in PVA restitution in most cases.

Biofeedback stimulation in the visually impaired: a systematic review of literature

BACKGROUND

It is estimated that approximately 1.3 billion people live with some form of distance or near visual impairment. Numerous studies have been carried out to evaluate the effects of biofeedback (BF) and establish if it could be a useful tool in vision rehabilitation for various eye diseases.

OBJECTIVE

This systematic review aimed: 1) to examine the current evidence of BF efficacy for the rehabilitation of the visually impaired and 2) to describe methodological variations used in previous BF studies to provide recommendations for vision rehabilitation interventions.

METHODS

A systematic review was conducted in the Medline, PubMed, Cochrane Library and Web of Science databases to collect documents published between January 2000 and May 2020. Of the 1,960 studies identified, 43 met the criteria for inclusion. The following information was collected from each study: sample size, control group, any eye disease, apparatus used, frequency and number of sessions of BF, main outcomes of training and whether a follow-up was conducted. The first group included studies published as scientific articles in peer-reviewed journals. The second group included abstracts of studies presented at peer-reviewed conferences. Publications were also grouped according to the eye disease treated.

RESULTS

25 articles and 18 peer-reviewed conference abstracts (PRCAs) were included in this review. BF stimulation is a commonly used technique for the treatment of visual impairment caused by macular disease. Most BF studies evaluate the effect of training on the preferred retinal locus (PRL), particularly with regard to fixation location and stability. Across these studies, participants who received BF intervention improved fixation stability and reading speed. High variability in the number of sessions and the duration of BF training was found. Most studies did not use a control group.

CONCLUSIONS

The findings of this review present evidence for biofeedback treatment in vision rehabilitation, with improved oculomotor abilities. Currently, it is not possible to formulate evidence-based recommendations for a standard training procedure due to the poor quality of existing randomised controlled trials. High-quality studies are needed to develop standard protocols for a range of eye diseases.

Randomized Controlled Trial of a Spectacle Lens for Macular Degeneration

SIGNIFICANCE

E-Scoop, a spectacle lens, provides no clinically relevant improvements on quality of life, visual acuity, and contrast sensitivity for patients with AMD. Because patients' burden is high and therapeutic options are scarce, the incentive to develop effective vision rehabilitation interventions remains.

PURPOSE

Patients with AMD experience low quality of life due to vision loss, despite angiogenesis inhibitor interventions that slow down progression for some patients. E-Scoop, which includes low-power prisms, 6% magnification, yellow tint, and antireflection coating, might aid in daily activities by improving distance viewing. Separately, these features have little proven effectiveness. E-Scoop has not been formally tested. This study aimed to determine the impact of E-Scoop on quality of life and the effect on visual acuity and contrast sensitivity.

METHODS

In this randomized controlled, open-label trial, 190 of 226 eligible patients were included. The primary outcome was quality of life measured with the 25-item National Eye Institute Visual Function Questionnaire. Secondary outcomes were visual acuity and contrast sensitivity. The follow-up for quality of life was after 6 weeks for controls and after 3 weeks of use for E-Scoop wearers. The visual measures were repeated after 6 weeks, with optimal refractive correction, with and without E-Scoop.

RESULTS

Randomization resulted in 99 E-Scoop and 86 control group patients for intention-to-treat analysis. No differential change was found between the E-Scoop and control groups on the 25-item National Eye Institute Visual Function Questionnaire using Rasch analysis (Cohen d = -0.07, P = .53). Statistically significant but small effects were found in favor of E-Scoop on binocular visual acuity (mean difference, 0.05 logMAR [2.5 letters, P < .001]) and contrast sensitivity (mean difference, 0.10 logCS [2 letters, P < .001]).

CONCLUSIONS

No effect of E-Scoop on quality of life was found. E-Scoop showed effects that were statistically significant, although not clinically meaningful and within typical variability, on visual measures.

Orientation of the preferred retinal locus (PRL) is maintained following changes in simulated scotoma size

Although macular lesions often enlarge, we know little about what happens when the preferred retinal locus (PRL) is enveloped by the lesion. We present a prospective study of subjects with normal vision who were trained to develop a PRL using simulated scotomas with a gaze-contingent visual display. We hypothesized that, when subjects had developed a robust PRL and the scotoma size was increased, the PRL would move to remain outside the scotoma and in a direction that maintained the orientation (theta) of the PRL relative to the fovea.

Nine subjects with normal vision were trained to develop a PRL and were then exposed to scotoma sizes that ranged from 4° to 24° in diameter. Subjects tracked a stimulus using saccades or smooth pursuits. Fixation stability was measured by calculating the bivariate contour ellipse area (BCEA). To measure the reassignment of the oculomotor reference (OMR) to the PRL, we analyzed the spread (BCEA) of saccade first landing points.

All subjects developed a robust PRL that did not vary more than 0.8° on average between blocks of trials of a scotoma size, and they maintained the orientation of the PRL as the simulated scotoma size varied (±9° median standard deviation in theta, defined as orientation angle). Fixation stability and OMR to the PRL worsened (larger BCEA) with increasing scotoma size. This, and related studies, could guide development of a PRL training method to help people with central vision loss.

Low Vision and Plasticity: Implications for Rehabilitation

Low vision is any type of visual impairment that affects activities of daily living. In the context of low vision, we define plasticity as changes in brain or perceptual behavior that follow the onset of visual impairment and that are not directly due to the underlying pathology. An important goal of low-vision research is to determine how plasticity affects visual performance of everyday activities. In this review, we consider the levels of the visual system at which plasticity occurs, the impact of age and visual experience on plasticity, and whether plastic changes are spontaneous or require explicit training. We also discuss how plasticity may affect low-vision rehabilitation. Developments in retinal imaging, noninvasive brain imaging, and eye tracking have supplemented traditional clinical and psychophysical methods for assessing how the visual system adapts to visual impairment. Findings from contemporary research are providing tools to guide people with low vision in adopting appropriate rehabilitation strategies.

Performance of a computerised visual acuity measurement device in subjects with age-related macular degeneration: comparison with gold standard ETDRS chart measurements

PURPOSE

The aim of the study was to compare the performance of two different COMPlog computerised, single letter scoring, visual acuity (VA) measurements against gold standard Early Treatment Diabetic Retinopathy Study (ETDRS) chart measurements in patients with age-related macular degeneration (AMD). One computerised algorithm presented five and the other presented three letters per line; both computerised algorithms utilised half, rather than the full-letter width spacing standard on ETDRS charts that might induce crowding, fixation problems, increased test-retest variability (TRV), and bias.

METHODS

Fifty patients with AMD (mean age 83 years) underwent timed test and retest VA measurements using ETDRS charts and COMPlog five (C5) and three (C3) letters per line computerised VA measurement algorithms. All tests utilised single-letter scoring methodology. Bland and Altman methods were employed. Performance was measured in terms of bias, TRV, and test time.

RESULTS

The C5 and C3 scores showed no bias compared with the ETDRS chart measurements. C5 measurements had equal TRV to the ETDRS chart (±0.13 logMAR) with similar median test times (105 and 96 s, respectively). C3 measurements were slightly more variable (TRV ±0.17 logMAR), but 30 s quicker than ETDRS chart measurements.

CONCLUSIONS

The closer letter spacing employed in COMPlog testing algorithms appears to have no adverse effect on VA measurements compared with the gold standard ETDRS chart in patients with AMD. The three letter per line testing algorithm facilitates faster testing but with a two letter increase in TRV.

Decreased fixation stability of the preferred retinal location in juvenile macular degeneration

Macular degeneration is the main cause for diminished visual acuity in the elderly. The juvenile form of macular degeneration has equally detrimental consequences on foveal vision. To compensate for loss of foveal vision most patients with macular degeneration adopt an eccentric preferred retinal location that takes over tasks normally performed by the healthy fovea. It is unclear however, whether the preferred retinal locus also develops properties typical for foveal vision. Here, we investigated whether the fixation characteristics of the preferred retinal locus resemble those of the healthy fovea. For this purpose, we used the fixation-offset paradigm and tracked eye-position using a high spatial and temporal resolution infrared eye-tracker. The fixation-offset paradigm measures release from fixation under different fixation conditions and has been shown useful to distinguish between foveal and non-foveal fixation. We measured eye-movements in nine healthy age-matched controls and five patients with juvenile macular degeneration. In addition, we performed a simulation with the same task in a group of five healthy controls. Our results show that the preferred retinal locus does not adopt a foveal type of fixation but instead drifts further away from its original fixation and has overall increased fixation instability. Furthermore, the fixation instability is most pronounced in low frequency eye-movements representing a slow drift from fixation. We argue that the increased fixation instability cannot be attributed to fixation under an unnatural angle. Instead, diminished visual acuity in the periphery causes reduced oculomotor control and results in increased fixation instability.

The physics and psychophysics of microperimetry

PURPOSE

To assess the influences of stimulus parameters (physics) on measures of visual field sensitivity (psychophysics).

METHODS

Subjects' thresholds were measured on three different clinically available perimeters: the Humphrey Field Analyzer (HFA), the Nidek MP1 (MP1), and the Opko OCT/SLO (OSLO). On all machines, visual field testing was done with a 10-2 spatial distribution of test points, using Goldmann Size III and Size I stimuli, with a presentation time of 200 ms, and using a 4-2 threshold algorithm.

RESULTS

All the MP1 and OSLO data fell below the values for the corresponding points on the HFA. For the Goldmann Size III target, the HFA median threshold was 33 dB, whereas the MP1 median threshold was 19 dB and the OLSO, 18 dB. Using the increment intensity values at each dB level for each microperimeter, the data were converted to equivalent HFA dB. Using this conversion, the smallest increment displayed in the MP1 (1.27 cd/m) was equivalent to 34 HFA dB, and the brightest increment displayed by the MP1 was 14 HFA dB (127 cd/m). The smallest increment displayed in the OSLO (1.56 cd/m) was equivalent to 33.1 HFA dB, and the brightest increment displayed by the OSLO was 13.6 HFA dB (137 cd/m). There was good correspondence among these results when compared using equivalent increment threshold units. However, discrepancies in our findings made us acutely aware of the importance of evaluating the consequences of design choices made by the manufacturers.

CONCLUSIONS

The findings underscore the need for users to check their assumptions about what the equipment is doing and to always evaluate the psychophysical consequences of the stimuli that are used by a particular instrument.

Eccentric gaze direction in patients with central field loss

PURPOSE

This study describes the binocular eccentric gaze direction (EGD) of 434 patients with binocular central field loss and presents a comparison with other studies on eccentric gaze behavior.

METHODS

We reviewed the records of 434 patients with bilateral central scotomas. Eligible patients had not received eccentric viewing training and demonstrated a spontaneously developed eccentric gaze behavior. Data were collected on monocular and binocular EGD, visual acuity, and underlying ocular pathology. Findings concerning the EGD were compared with other studies that evaluated gaze behavior in patients with central field loss.

RESULTS

In the group of 434 patients, age-related macular disease was the most frequent pathology (77%). The majority of these patients demonstrated a binocular EGD (bEGD) to the right (50%). In 25% of the patients, a superior bEGD was found. Less often, a bEGD to the left (14%) and to inferior (11%) were encountered. Review of the literature indicates that the majority of patients developed a monocular EGD in the superior direction.

CONCLUSIONS

This is a study on bEGD behavior in a large population of patients with bilateral central scotomas. The bEGD was guided by the gaze of the better-seeing eye. The preference for a bEGD to the right differs from findings of previous studies. Review of the literature suggests that not only the ocular pathology but also the method of investigation is most likely to influence the observed EGD. Most studies evaluated the location of the preferred retinal locus using a monocular technique; this may not reflect an individual's actual binocular behavior as it relates to activities of daily living.

Plasticity of fixation in patients with central vision loss

The aim of this study was to explore the plasticity of fixation in patients with central vision loss. Most of these patients use preferred retinal loci (PRLs) in the healthy eccentric part of the retina to fixate, but fixation stability and retinal location are not always optimal for best visual performance. This study examined whether fixation stability and a new PRL location can be trained and whether these changes in ocular motor control transfer into better reading performance. Six patients with age-related macular degeneration participated in the study. Fixation stability measurements, microperimetry, and auditory biofeedback training were performed with the MP-1 microperimeter. The auditory biofeedback was used during five 1-h long training sessions to improve fixation and relocate the PRL. Fixation location and stability were recorded while viewing four different targets: a cross, a letter, a word, and a nine-cycle radial grating. Visual acuity was assessed with the Early Treatment Diabetic Retinopathy Study (ETDRS) chart and reading performance with the MNRead test. The results showed that all patients developed a new PRL in an optimal location for reading, and they were able to use it consistently while viewing different targets. Fixation stability improved 53% after training. Learning transferred to the old PRL even though fixation stability at this location was not trained. All these improvements in ocular motor control translated into better reading performance: reading speed improved 38% and reading acuity and critical print size gained two lines. We conclude that the ability of the ocular motor system to fixate is flexible in patients with central vision loss: a new PRL can be trained, fixation stability can be improved, and learning transfers to an untrained location. These gains in ocular motor control result in better visual performance. This property can be successfully used to optimize the residual vision of patients with central vision loss.

Functional deficits in early stage age-related maculopathy

BACKGROUND

It is of interest to examine paracentral functional deficits in early age-related maculopathy (ARM), as histopathological studies indicate that this is where the earliest changes occur. The purpose of this study is to detect the sensory functional deficits at chosen retinal areas around the fovea and at the fovea itself in patients with early age-related maculopathy and to determine the type of functional losses that are more pronounced in early ARM.

METHODS

Ten participants with early ARM and 10 age-matched controls took part. Crowded and uncrowded visual acuity and static and transient contrast sensitivity were measured in the same selected eye of each participant at eight predetermined retinal locations plus the fovea in patients with early ARM and controls. All measurements were made using computer-generated targets.

RESULTS

A significant difference between the controls and subjects with ARM was found in low spatial frequency static contrast sensitivity (p = 0.05) but not for transient contrast sensitivity (p = 0.586). Visual acuity (uncrowded VA and crowded VA) showed a borderline difference (p = 0.072 and p = 0.084, respectively). Compared to controls, there was no evidence of increased contour interaction effects in early ARM (p = 0.595).

CONCLUSION

The subjects with very early ARM showed significant loss of low spatial frequency static contrast sensitivity before the loss of high contrast VA, indicating that static contrast sensitivity may be one of the earliest functional losses in early ARM and this loss was found to extend across the central 10 degrees of the retina.

Is there tachyphylaxis to intravitreal anti-vascular endothelial growth factor pharmacotherapy in age-related macular degeneration?

PURPOSE

To determine whether repetitive injections of intravitreal bevacizumab and/or triamcinolone acetate in patients with exudative age-related macular degeneration (AMD) results in a decrease in biological response.

DESIGN

Retrospective comparative case series.

PARTICIPANTS

Forty-three eyes of 43 patients with exudative AMD.

METHODS

Pre- and postinjection optical coherence tomography (OCT) sections of 43 patients with AMD were analyzed to determine the change in the biologic response after each subsequent injection of intravitreal bevacizumab (2.5 mg/100 microL), preservative-free triamcinolone acetonide (pfTA) (4.0 mg/100 microL), or a combination of bevacizumab (1.25 mg/50 microL) and pfTA (2.0 mg/50 microL). The retinal thickness of each OCT sector was determined and expressed as volume. Standardized volumetric change index (SVCI) was determined to identify a statistically significant change. Pre- and postinjection (6 weeks) SVCI differences were plotted as a function of time to determine the biological response after each intravitreal treatment.

MAIN OUTCOME MEASURES

Change in SVCI after intravitreal injections and the number of injections required to decrease the biological response by 50% (INJ(50)).

RESULTS

There was no difference in the age, gender, and preinjection thickness of the retina in each of the 3 groups. The SVCI after intravitreal bevacizumab injections decreased, indicating a possible tachyphylactic response to bevacizumab. This decrease in biological response was partially alleviated with the addition of pfTA. Combination of pfTA and bevacizumab increased the INJ(50) from 2.9 with bevacizumab alone to 5.1 injections. A biphasic biologic response was observed with pfTA characterized by a rapid increase in efficacy with the second injection, peaking at the third injection and gradually decreasing afterward.

CONCLUSIONS

Repeated intravitreal injections of bevacizumab in exudative AMD seemed to be associated with decreased bioefficacy. However, combined pharmacotherapy with triamcinolone acetate lessened this effect. Thus, multitargeted pharmacotherapy in exudative AMD may have a therapeutic benefit.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.