Correlations among near-infrared and short-wavelength autofluorescence and spectral-domain optical coherence tomography in recessive Stargardt disease

Multimodal imaging including semiquantitative short-wavelength and near-infrared autofluorescence in achromatopsia

Multimodal imaging provides insights into phenotype and disease progression in inherited retinal disorders. Congenital achromatopsia (ACHM), a cone dysfunction syndrome, has been long considered a stable condition, but recent evidence suggests structural progression. With gene replacement strategies under development for ACHM, there is a critical need for imaging biomarkers to define progression patterns and follow therapy. Using semiquantitative plots, near-infrared (NIR-AF) and short-wavelength autofluorescence (SW-AF) were explored and correlated with clinical characteristics and retinal structure on optical coherence tomography (OCT). In sixteen ACHM patients with genetic confirmation (CNGA3, n = 8; CNGB3, n = 7; PDE6C, n = 1), semiquantitative plots allowed the detailed analysis of autofluorescence patterns, even in poorly fixating eyes. Twelve eyes showed perifoveal hyperautofluorescent rings on SW-AF, and 7 eyes had central hypoautofluorescent areas on NIR-AF, without association between these alterations (P = 0.57). Patients with central NIR-AF hypoautofluorescence were older (P = 0.004) and showed more advanced retinal alterations on OCT than those with normal NIR-AF (P = 0.051). NIR-AF hypoautofluorescence diameter was correlated to patient age (r = 0.63, P = 0.009), size of ellipsoid zone defect on OCT (r = 0.67, P = 0.005), but not to the size of SW-AF hyperautofluorescence (P = 0.27). These results demonstrate the interest of NIR-AF as imaging biomarker in ACHM, suggesting a relationship with age and disease progression.

Spotlight on fundus autofluorescence

Fundus autofluorescence (FAF) imaging is based on the fluorescence from ocular endogenous fluorophores located in the retinal pigment epithelium and choroid, mainly lipofuscin and melanin. It is a noninvasive technique that provides information about the spatial distribution of lipofuscin/melanin and retinal pigment epithelium health status. An overview about the fluorophores responsible for FAF imaging and the usefulness of FAF imaging in the noninvasive assessment and monitoring of retinal diseases, such as age-related macular degeneration, diabetic retinopathy, diabetic macular edema, central serous chorioretinopthy, retinitis pigmentosa and retinal dystrophies, are discussed in this review.

STARGARDT DISEASE: Beyond Flecks and Atrophy

PURPOSE

To identify changes in the outer retina in areas without atrophy or flecks of Stargardt disease (STGD) using spectral-domain optical coherence tomography.

METHODS

Twenty-three STGD patients and 26 control subjects were assessed for outer retina (from the outer border of Bruch membrane [BrM] to the inner border of the inner segment ellipsoid zone [EZ]), BrM-retinal pigment epithelium apex, the EZ thickness, and apical process interdigitation zone.

RESULTS

Patients with STGD had increased BrM-EZ thickness in areas without apparent disease versus control subjects at 1,000, 1,500, 2,000, and 2,500 μm superior and 1,500 μm, 2,000 μm, and 2,500 μm inferior to the fovea (P < 0.05 to P < 0.001), greatest difference (3.4 μm) at 2,500 μm superiorly. The BrM-retinal pigment epithelium segment showed larger fractional contribution of 0.48 to 0.51 to the overall BrM-EZ thickness compared with 0.35 to 0.42 in control subjects. The thickness of EZ and the interspace between the retinal pigment epithelium apex and EZ were smaller in the STGD patients (P < 0.05 to P < 0.001). Patients with STGD displayed an interrupted interdigitation zone in 16 (84.2%) of 19 eyes versus 6 (23.1%) of 26 eyes of the control subjects (P < 0.001). The BrM-EZ segment of the outer retina of STGD patients lacked the typical normal trilaminar pattern.

CONCLUSION

Subtle changes are present within the BrM-EZ segment of the outer retina of STGD patients in areas that are devoid of atrophy and flecks. These findings suggest that pathologic changes in STGD are more widespread than that seen by clinical examination.

Quantifying the Rate of Ellipsoid Zone Loss in Stargardt Disease

PURPOSE

To determine a reliable method of using the ellipsoid zone (EZ) on optical coherence tomography (OCT) to track disease progression in Stardgardt disease (STGD).

DESIGN

Retrospective reliability study.

METHODS

STGD patients with genetically confirmed ABCA4 gene mutations seen at the Wilmer Eye Institute with follow-up visits separated by at least 12 months were identified. Spectral-domain optical coherence tomography (SD-OCT) macula volume scans centered at the fovea and fundus autofluorescence (FAF) images were obtained. The area of EZ loss was calculated from the SD-OCT and the area of retinal pigment epithelium (RPE) loss from the FAF. Scans were reanalyzed by the primary grader to assess intragrader reliability, and reanalyzed by a second grader to assess intergrader reliability.

RESULTS

Sixteen STGD patients (total of 31 eyes) were followed for a mean of 2 years (range 1-4.7 years). The mean rate of EZ loss, 0.31 ± 0.31 mm²/year, was similar to the average rate of RPE loss, 0.33 ± 0.38 mm²/year. The average area of EZ loss at the initial examination, 4.18 ± 1.91 mm², was larger than the initial area of RPE loss, 2.25 ± 1.66 mm² (P < .01). The absolute difference of the area of EZ loss on test-retest for the first grader was 0.12 ± 0.10 mm², and between graders 0.21 ± 0.21 mm². The intraclass correlation (ICC) of both intragrader and intergrader reliability for EZ loss was excellent at 0.99.

CONCLUSIONS

Tracking the area of EZ loss on SD-OCT macular volume scans longitudinally is a reliable way of monitoring disease progression in STGD. This could be used as a sensitive anatomic outcome measure in clinical trials related to STGD.

Progression of Stargardt Disease as Determined by Fundus Autofluorescence in the Retrospective Progression of Stargardt Disease Study (ProgStar Report No. 9)

Importance

Sensitive outcome measures for disease progression are needed for treatment trials of Stargardt disease.

Objective

To describe the yearly progression rate of atrophic lesions in the retrospective Progression of Stargardt Disease study.

Design, Setting, and Participants

A multicenter retrospective cohort study was conducted at tertiary referral centers in the United States and Europe. A total of 251 patients aged 6 years or older at baseline, harboring disease-causing variants in ABCA4 (OMIM 601691), enrolled in the study from 9 centers between August 2, 2013, and December 12, 2014; of these patients, 215 had at least 2 gradable fundus autofluorescence images with atrophic lesion(s) present in at least 1 eye.

Exposures

Areas of definitely decreased autofluorescence (DDAF) and questionably decreased autofluorescence were quantified by a reading center. Progression rates were estimated from linear mixed models with time as the independent variable.

Main Outcomes and Measures

Yearly rate of progression using the growth of atrophic lesions measured by fundus autofluorescence.

Results

A total of 251 participants (458 study eyes) were enrolled. Images from 386 eyes of 215 participants (126 females and 89 males; mean [SD] age, 29.9 [14.7] years; mean [SD] age of onset of symptoms, 21.9 [13.3] years) showed atrophic lesions present on at least 2 visits and were graded for 2 (156 eyes), 3 (174 eyes), or 4 (57 eyes) visits. A subset of 224 eyes (123 female participants and 101 male participants; mean [SD] age, 33.0 [15.1] years) had areas of DDAF present on at least 2 visits; these eyes were included in the estimation of the progression of the area of DDAF. At the first visit, DDAF was present in 224 eyes (58.0%), with a mean (SD) lesion size of 2.2 (2.7) mm2. The total mean (SD) area of decreased autofluorescence (DDAF and questionably decreased autofluorescence) at first visit was 2.6 (2.8) mm2. Mean progression of DDAF was 0.51 mm2/y (95% CI, 0.42-0.61 mm2/y), and of total decreased fundus autofluorescence was 0.35 mm2/y (95% CI, 0.28-0.43 mm2/y). Rates of progression depended on the initial size of the lesion.

Conclusions and Relevance

In Stargardt disease with DDAF lesions, fundus autofluorescence may serve as a monitoring tool for interventional clinical trials that aim to slow disease progression. Rates of progression depended mainly on initial lesion size.

A Comparison of En Face Optical Coherence Tomography and Fundus Autofluorescence in Stargardt Disease

Purpose

To compare morphologic changes on en face images derived from wide-field swept-source optical coherence tomography (ssOCT) to hypo- and hyperautofluorescent (hypoAF, hyperAF) areas on short-wavelength autofluorescence (SW-AF), and near-infrared (NIR)-AF in recessive Stargardt disease (STGD1).

Methods

Wide-field ssOCT cube scans were obtained from 16 patients (16 eyes). Averaged B-scans and SW-AF images were obtained using Spectralis HRA+OCT. NIR-AF images were obtained from 6 eyes. The inner/outer segment (IS/OS), OS/RPE, and RPE/Bruch's membrane boundaries were segmented, and en face slab images generated. A subRPE slab image was used to measure the abnormal RPE area, and an IS/OS slab image, the IS/OS junction loss area. These were compared to hypo- and abnormal SW-AF areas, and hypoNIR-AF areas. A preRPE(OS) slab image was used to evaluate the spatial and intraretinal locations of flecks.

Results

For all eyes, RPE atrophy was visualized as a central hyperreflective area on the subRPE slab, and IS/OS junction loss as an abnormal reflective area on the IS/OS slab; the latter was significantly larger (P = 0.04). There was good agreement between the hyperreflective area on the subRPE slab image and hypoSW-AF area, and between the abnormal reflective area on the IS/OS slab and hypo-hyperSW-AF area; the hypoNIR-AF area indicated that the hyperreflective area on the subRPE slab underestimated RPE atrophy. The spatial locations of hyperreflective flecks on the en face preRPE(OS) slab image corresponded to those on the SW-AF images.

Conclusions

Wide-field en face OCT imaging has the potential to be a clinically useful tool for the management of STGD1.

Classification and characterization of acute macular neuroretinopathy with spectral domain optical coherence tomography

PURPOSE

To classify and characterize AMN lesions with SD-OCT during a follow-up as long as 5 years.

METHODS

Retrospective study of 14 patients (18 eyes) with special focus on SD-OCT. We measured thickness of inner nuclear layer (INL), outer retinal layer (ONL), and hyperreflective band at baseline and during follow-up. AMN lesions were classified as type 1 and type 2.

RESULTS

Of 14 patients (six males, eight females, mean age 29.7 years), three patients (four eyes) had type 1 and nine (12 eyes) had type 2. Two patients did not meet the criteria for AMN type 1 or 2 and were therefore classified as new subtype of AMN. In all patients, statistically significant thinning of ONL and INL was observable. Mean ONL of all patients was 90.2 ± 7.81 and 72.3 ± 15.64 μm (p < 0.05) during follow-up; mean INL was 54.4 ± 10.71 and 37.5 ± 6.18 μm (p < 0.05) in the course. In the subgroup analysis in AMN type 2, the thinning of both ONL and INL was also statistically significant (mean ONL: 87.4 ± 6.02 and 71.6 ± 12.7 μm (p < 0.05); mean INL: 48.5 ± 5.04 and 38.5 ± 5.6 μm (p < 0.05)) in the course.

CONCLUSION

SD-OCT allows for classification, characterization, and further understanding of AMN lesions. Up to now, this is one of the largest AMN case series differentiating into different subtypes and following up for up to 5 years. Furthermore, we describe a new AMN subtype characterized by initially clinically visible yellowish parafoveal lesions, subtle pigmentary changes at late stage, lack of classic dark appearance on IR reflectance, involvement of RPE/Bruch's complex, and disruption of ellipsoid zone and interdigitation zone. The patients suffered from a prolonged visual impairment and paracentral scotomata. We propose the term AMN type 3 or "paracentral acute outer maculopathy."

Intraretinal Correlates of Reticular Pseudodrusen Revealed by Autofluorescence and En Face OCT

Purpose

We sought to determine whether information revealed from the reflectance, autofluorescence, and absorption properties of RPE cells situated posterior to reticular pseudodrusen (RPD) could provide insight into the origins and structure of RPD.

Methods

RPD were studied qualitatively by near-infrared fundus autofluorescence (NIR-AF), short-wavelength fundus autofluorescence (SW-AF), and infrared reflectance (IR-R) images, and the presentation was compared to horizontal and en face spectral domain optical coherence tomographic (SD-OCT) images. Images were acquired from 23 patients (39 eyes) diagnosed with RPD (mean age 80.7 ± 7.1 [SD]; 16 female; 4 Hispanics, 19 non-Hispanic whites).

Results

In SW-AF, NIR-AF, and IR-R images, fundus RPD were recognized as interlacing networks of small scale variations in IR-R and fluorescence (SW-AF, NIR-AF) intensities. Darkened foci of RPD colocalized in SW-AF and NIR-AF images, and in SD-OCT images corresponded to disturbances of the interdigitation (IZ) and ellipsoid (EZ) zones and to more pronounced hyperreflective lesions traversing photoreceptor-attributable bands in SD-OCT images. Qualitative assessment of the outer nuclear layer (ONL) revealed thinning as RPD extended radially from the outer to inner retina. In en face OCT, hyperreflective areas in the EZ band correlated topographically with hyporeflective foci at the level of the RPE.

Conclusions

The hyperreflective lesions corresponding to RPD in SD-OCT scans are likely indicative of degenerating photoreceptor cells. The darkened foci at positions of RPD in NIR-AF and en face OCT images indicate changes in the RPE monolayer with the reduced NIR-AF and en face OCT signal suggesting a reduction in melanin that could be accounted for by RPE thinning.

The Rapid-Onset Chorioretinopathy Phenotype of ABCA4 Disease

PURPOSE

To characterize patients affected by a uniquely severe, rapid-onset chorioretinopathy (ROC) phenotype of ABCA4 disease.

DESIGN

Comparative cohort study.

PARTICIPANTS

Sixteen patients were selected from a large clinically diagnosed and genetically confirmed cohort (n = 300) of patients diagnosed with ABCA4 disease.

MAIN OUTCOME MEASURES

Phenotypic characteristics were assessed on color fundus photographs, short-wavelength autofluorescence (488-nm), and near-infrared autofluorescence (NIR-AF, 787-nm) images. Subfoveal thickness measurements were obtained from enhanced-depth imaging OCT. Generalized retinal function was determined with full-field electroretinogram (ffERG) testing, and lipofuscin accumulation was assessed by quantitative autofluorescence (qAF).

RESULTS

All patients exhibited advanced disease features, including pigment migration in the macula and retinal vessel attenuation at an early age, and reported a symptomatic onset, on average, at 7.4 years (average for ABCA4 disease is 21.9 years, P < 0.0001). Deterioration of the macula was observed to begin with an intense, homogeneous signal on short-wavelength autofluorescence, which corresponds to an attenuated NIR-AF signal and progresses to a patchy, coalescing pattern of chorioretinal atrophy within the subsequent decade. Measurement of choroidal thickness revealed a more rapid thinning of choriocapillaris with age of Sattler's layer compared with the rate in most other patients with ABCA4 disease (P < 0.001). Levels of qAF in the macula before atrophy were above both the 95% confidence intervals for healthy individuals and patients with Stargardt disease (STGD1) (>1000 qAF units). Severe attenuation of cone responses and notable decreases in rod responses were detected by ffERG. Sequencing of the ABCA4 gene revealed exclusively deleterious, null mutations, including stop codons; frameshift deletions; variants in canonical splice sites, which completely abolish splicing; and known deleterious missense alleles.

CONCLUSIONS

The ROC phenotype is a unique classification of ABCA4 disease, which is caused by deleterious null biallelic ABCA4 mutations and is characterized by the rapid deterioration of retinal pigment epithelium and photoreceptor layers in the macula and significant choroidal thinning within the first 2 decades of life.

Towards Treatment of Stargardt Disease: Workshop Organized and Sponsored by the Foundation Fighting Blindness

Accumulation of fluorescent metabolic byproducts of the visual (retinoid) cycle is associated with photoreceptor and retinal pigment epithelial cell death in both Stargardt disease and atrophic (nonneovascular) age-related macular degeneration (AMD). As a consequence of this observation, small molecular inhibitors of enzymes in the visual cycle were recently tested in clinical trials as a strategy to protect the retina and retinal pigment epithelium in patients with atrophic AMD.

To address the clinical translational needs for therapies aimed at both diseases, a workshop organized by the Foundation Fighting Blindness was hosted by the Department of Pharmacology at Case Western Reserve University on February 17, 2017, at the Tinkham Veale University Center, Cleveland, OH, USA. Invited speakers highlighted recent advances in the understanding of the pathophysiology of Stargardt disease, in terms of its clinical characterization and the development of endpoints for clinical trials, and discussed the comparability of therapeutic strategies between atrophic age-related macular degeneration (AMD) and Stargardt disease. Investigators speculated that reducing the concentrations of visual cycle precursor substances and/or their byproducts may provide valid therapeutic options for the treatment of Stargardt disease. Here we review the workshop's presentations in the context of published literature to help shape the aims of ongoing research endeavors and aid the development of therapies for Stargardt disease.

Fundus Autofluorescence Patterns of Submacular Fluid Resolution Following Repair of Macula-Involving Rhegmatogenous Retinal Detachments

BACKGROUND AND OBJECTIVE

Submacular fluid (SMF) can persist for months to years following rhegmatogenous retinal detachment (RD) repair. The authors' objective was to describe fundus autofluorescence (FAF) and optical coherence tomography (OCT) findings associated with the absorption of persistent submacular fluid (SMF) following RD repair.

PATIENTS AND METHODS

Retrospective review of clinical data and FAF and OCT imaging from sequential postoperative visits in a cohort of patients with persistent SMF following RD repair.

RESULTS

In 11 of 13 eyes with persistent SMF, patches of decreased FAF signal corresponded to SMF on OCT. In eight eyes, there was a hypo- to hyperautofluorescence transition at the time of SMF resolution. These areas of increased FAF signal correlated with inner segment/outer segment (IS/OS) junction loss on OCT.

CONCLUSION

FAF imaging can be informative when following SMF after RD repair; a hypo- to hyper-FAF signal transition correlates with SMF resolution and photoreceptor loss. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:1020-1029.].

FUNDUS AUTOFLUORESCENCE IN RUBELLA RETINOPATHY: Correlation With Photoreceptor Structure and Function

PURPOSE

To illustrate altered fundus autofluorescence in rubella retinopathy and to investigate their relationships with photoreceptor structure and function using multimodal imaging.

METHODS

The authors report four cases of rubella retinopathy aged 8, 33, 42, and 50 years. All patients had dilated clinical fundus examination; wide-field color photography; blue, green, and near-infrared autofluorescence imaging and spectral domain optical coherence tomography. Two patients also underwent microperimetry and adaptive optics imaging. En face optical coherence tomography, cone mosaic, and microperimetry were coregistered with autofluorescence images. The authors explored the structure-function correlation.

RESULTS

All four patients had a "salt-and-pepper" appearance on dilated fundus examination and wide-field color photography. There were variable-sized patches of hypoautofluorescence on both blue and near-infrared excitation in all four patients. Wave-guiding cones were visible and retinal sensitivity was intact over these regions. There was no correlation between hypoautofluorescence and regions of attenuated ellipsoid and interdigitation zones. Hyperautofluorescent lesions were also noted and some of these were pseudo-vitelliform lesions.

CONCLUSION

Patchy hypoautofluorescence on near-infrared excitation can be a feature of rubella retinopathy. This may be due to abnormal melanin production or loss of melanin within retinal pigment epithelium cells harboring persistent rubella virus infection. Preservation of the ellipsoid zone, wave-guiding cones, and retinal sensitivity within hypoautofluorescent lesions suggest that these retinal pigment epithelium changes have only mild impact on photoreceptor cell function.

Intersession test-retest variability of conventional and novel parameters using the MP-1 microperimeter

Purpose

To investigate the intersession test–retest variability (TRV) of topography- and threshold-based parameters derived from the Nidek MP-1.

Design

Prospective observational study.

Methods

Sixteen participants with and without central scotoma underwent microperimetry in one eye over three sessions at 1-month intervals in a single institution. We calculated 95% coefficient of repeatability (CR) for the number of normal-suspect (NS) loci, relative scotoma (RS) and dense scotoma (DS), median macular sensitivity (MS), mean sensitivity of responding loci (RLS), perilesional loci (PLS), and extralesional loci (ELS). Topographical agreement score of mapping NS and DS loci (TAS_NS and TAS_DS) were also calculated for each patient.

Results

Mean (range) age was 50 (21–86) years. The CR (95% confidence intervals) for NS, RS, and DS were 9.9 (6.5–13.3), 9.5 (6.2–12.7), and 3.0 (1.1–4.1) respectively. CR (95% CIs) for median MS, mean RLS, PLS, and ELS were 3.4 (2.3–4.5), 1.6 (1.1–2.2), 1.8 (0.9–2.6), and 2.8 (1.5–4.0) dB. We found significant change in thresholds between Test 1, and Tests 2 and 3 (both P=0.03), but not between Tests 2 and 3 (P=0.8). Medians (range) TAS_NS and TAS_DS were 74% (39%–100%) and 77% (0%–97%), respectively, between Tests 2 and 3.

Conclusion

We recommend the use of four DS loci (upper limit of CR) as the limit of TRV for assessing change. There was large interindividual variability in NS or DS mapping agreement. We recommend discarding the first microperimetry test and caution the use of a change in spatial distribution to determine disease progression.

Predicting Progression of ABCA4-Associated Retinal Degenerations Based on Longitudinal Measurements of the Leading Disease Front

PURPOSE

To evaluate the progression of the earliest stage of disease in ABCA4-associated retinal degenerations (RDs).

METHODS

Near-infrared excited reduced-illuminance autofluorescence imaging was acquired across the retina up to 80 degrees eccentricity in 44 patients with two ABCA4 alleles. The eccentricity of the leading disease front (LDF) corresponding to the earliest stage of disease was measured along the four meridians. A mathematical model describing the expansion of the LDF was developed based on 6 years of longitudinal follow-up.

RESULTS

The extent of LDF along the superior, inferior, and temporal meridians showed a wide spectrum from 3.5 to 70 degrees. In patients with longitudinal data, the average centrifugal expansion rate was 2 degrees per year. The nasal extent of LDF between the fovea and ONH ranged from 4.3 to 16.5 degrees and expanded at 0.35 degrees per year. The extent of LDF beyond ONH ranged from 19 to 75 degrees and expanded on average at 2 degrees per year. A mathematical model fit well to the longitudinal data describing the expansion of the LDF.

CONCLUSIONS

The eccentricity of the LDF in ABCA4-RD shows a continuum from parafovea to far periphery along all four meridians consistent with a wide spectrum of severity observed clinically. The model of progression may provide a quantitative prediction of the LDF expansion based on the age and eccentricity of the LDF at a baseline visit, and thus contribute significantly to the enrollment of candidates appropriate for clinical trials planning specific interventions, efficacy outcomes, and durations.

Flecks in Recessive Stargardt Disease: Short-Wavelength Autofluorescence, Near-Infrared Autofluorescence, and Optical Coherence Tomography

PURPOSE

We evaluated the incongruous observation whereby flecks in recessive Stargardt disease (STGD1) can exhibit increased short-wavelength autofluorescence (SW-AF) that originates from retinal pigment epithelium (RPE) lipofuscin, while near-infrared AF (NIR-AF), emitted primarily from RPE melanin, is usually reduced or absent at fleck positions.

METHODS

Flecks in SW- and NIR-AF images and spectral-domain optical coherence tomography (SD-OCT) scans were studied in 19 STGD1 patients carrying disease-causing ABCA4 mutations. Fleck spatial distribution and progression were recorded in serial AF images.

RESULTS

Flecks observed in SW-AF images typically colocalized with darkened foci in NIR-AF images; the NIR-AF profiles were larger. The decreased NIR-AF signal from flecks preceded apparent changes in SW-AF. Spatiotemporal changes in fleck distribution usually progressed centrifugally, but in one case centripetal expansion was observed. Flecks in SW-AF images corresponded to hyperreflective deposits that progressively traversed photoreceptor-attributable bands in SD-OCT images. Outer nuclear layer (ONL) thickness negatively correlated with expansion of flecks from outer to inner retina.

CONCLUSIONS

In the healthy retina, RPE lipofuscin fluorophores form in photoreceptor cells but are transferred to RPE; thus the SW-AF signal from photoreceptor cells is negligible. In STGD1, NIR-AF imaging reveals that flecks are predominantly hypofluorescent and larger and that NIR-AF darkening occurs prior to heightened SW-AF signal. These observations indicate that RPE cells associated with flecks in STGD1 are considerably changed or lost. Spectral-domain OCT findings are indicative of ongoing photoreceptor cell degeneration. The bright SW-AF signal of flecks likely originates from augmented lipofuscin formation in degenerating photoreceptor cells impaired by the failure of RPE.

Autofluorescence imaging with near-infrared excitation:normalization by reflectance to reduce signal from choroidal fluorophores

PURPOSE

We previously developed reduced-illuminance autofluorescence imaging (RAFI) methods involving near-infrared (NIR) excitation to image melanin-based fluorophores and short-wavelength (SW) excitation to image lipofuscin-based flurophores. Here, we propose to normalize NIR-RAFI in order to increase the relative contribution of retinal pigment epithelium (RPE) fluorophores.

METHODS

Retinal imaging was performed with a standard protocol holding system parameters invariant in healthy subjects and in patients. Normalized NIR-RAFI was derived by dividing NIR-RAFI signal by NIR reflectance point-by-point after image registration.

RESULTS

Regions of RPE atrophy in Stargardt disease, AMD, retinitis pigmentosa, choroideremia, and Leber congenital amaurosis as defined by low signal on SW-RAFI could correspond to a wide range of signal on NIR-RAFI depending on the contribution from the choroidal component. Retinal pigment epithelium atrophy tended to always correspond to high signal on NIR reflectance. Normalizing NIR-RAFI reduced the choroidal component of the signal in regions of atrophy. Quantitative evaluation of RPE atrophy area showed no significant differences between SW-RAFI and normalized NIR-RAFI.

CONCLUSIONS

Imaging of RPE atrophy using lipofuscin-based AF imaging has become the gold standard. However, this technique involves bright SW lights that are uncomfortable and may accelerate the rate of disease progression in vulnerable retinas. The NIR-RAFI method developed here is a melanin-based alternative that is not absorbed by opsins and bisretinoid moieties, and is comfortable to view. Further development of this method may result in a nonmydriatic and comfortable imaging method to quantify RPE atrophy extent and its expansion rate.

Near-infrared autofluorescence: its relationship to short-wavelength autofluorescence and optical coherence tomography in recessive stargardt disease

PURPOSE

We compared hypoautofluorescent (hypoAF) areas detected with near-infrared (NIR-AF) and short-wavelength autofluorescence (SW-AF) in patients with recessive Stargardt disease (STGD1) to retinal structure using spectral domain optical coherence tomography (SD-OCT).

METHODS

The SD-OCT volume scans, and SW-AF and NIR-AF images were obtained from 15 eyes of 15 patients with STGD1 and registered to each other. Thickness maps of the total retina, receptor-plus layer (R+, from distal border of the RPE to outer plexiform/inner nuclear layer boundary), and outer segment-plus layer (OS+, from distal border of the RPE to ellipsoid zone [EZ] band) were created from SD-OCT scans. These were compared qualitatively and quantitatively to the hypoAF areas in SW-AF and NIR-AF images.

RESULTS

All eyes showed a hypoAF area in the central macula and loss of the EZ band in SD-OCT scans. The hypoAF area was larger in NIR than SW-AF images and it exceeded the area of EZ band loss for 12 eyes. The thickness maps showed progressive thinning towards the central macula, with the OS+ layer showing the most extensive and severe thinning. The central hypoAF areas on NIR corresponded to the OS+ thinned areas, while the hypoAF areas on SW-AF corresponded to the R+ thinned areas.

CONCLUSIONS

Since the larger hypoAF area on NIR-AF exceeded the region of EZ band loss, and corresponded to the OS+ thinned area, RPE cell loss occurred before photoreceptor cell loss. The NIR-AF imaging may be an effective tool for following progression and predicting loss of photoreceptors in STGD1.

Fundus Autofluorescence and RPE Lipofuscin in Age-Related Macular Degeneration

Genes that increase susceptibility to age-related macular degeneration (AMD) have been identified; however, since many individuals carrying these risk alleles do not develop disease, other contributors are involved. One additional factor, long implicated in the pathogenesis of AMD, is the lipofuscin of retinal pigment epithelium (RPE). The fluorophores that constitute RPE lipofuscin also serve as a source of autofluorescence (AF) that can be imaged by confocal laser ophthalmoscopy. The AF originating from lipofuscin is excited by the delivery of short wavelength (SW) light. A second autofluorescence is emitted from the melanin of RPE (and choroid) upon near-infrared (NIR-AF) excitation. SW-AF imaging is currently used in the clinical management of retinal disorders and the advantages of NIR-AF are increasingly recognized. Here we visit the damaging properties of RPE lipofuscin that could be significant when expressed on a background of genetic susceptibility. To advance interpretations of disease-related patterns of fundus AF in AMD, we also consider the photochemical and spectrophotometric features of the lipofuscin compounds responsible for generating the fluorescence emission.

Rescue of the Stargardt phenotype in Abca4 knockout mice through inhibition of vitamin A dimerization

Stargardt disease, an ATP-binding cassette, subfamily A, member 4 (ABCA4)-related retinopathy, is a genetic condition characterized by the accelerated accumulation of lipofuscin in the retinal pigment epithelium, degeneration of the neuroretina, and loss of vision. No approved treatment exists. Here, using a murine model of Stargardt disease, we show that the propensity of vitamin A to dimerize is responsible for triggering the formation of the majority of lipofuscin and transcriptional dysregulation of genes associated with inflammation. Data further demonstrate that replacing vitamin A with vitamin A deuterated at the carbon 20 position (C20-D3-vitamin A) impedes the dimerization rate of vitamin A--by approximately fivefold for the vitamin A dimer A2E--and subsequent lipofuscinogenesis and normalizes the aberrant transcription of complement genes without impairing retinal function. Phenotypic rescue by C20-D3-vitamin A was also observed noninvasively by quantitative autofluorescence, an imaging technique used clinically, in as little as 3 months after the initiation of treatment, whereas upon interruption of treatment, the age-related increase in autofluorescence resumed. Data suggest that C20-D3-vitamin A is a clinically amiable tool to inhibit vitamin A dimerization, which can be used to determine whether slowing the dimerization of vitamin A can prevent vision loss caused by Stargardt disease and other retinopathies associated with the accumulation of lipofuscin in the retina.