REDUCED GANGLION CELL VOLUME ON OPTICAL COHERENCE TOMOGRAPHY IN PATIENTS WITH GEOGRAPHIC ATROPHY

Age-related macular degeneration: suitability of optogenetic therapy for geographic atrophy

Age-related macular degeneration (AMD) is a growing public health concern given the aging population and it is the leading cause of blindness in developed countries, affecting individuals over the age of 55 years. AMD affects the retinal pigment epithelium (RPE) and Bruch's membrane in the macula, leading to secondary photoreceptor degeneration and eventual loss of central vision. Late AMD is divided into two forms: neovascular AMD and geographic atrophy (GA). GA accounts for around 60% of late AMD and has been the most challenging subtype to treat. Recent advances include approval of new intravitreally administered therapeutics, pegcetacoplan (Syfovre) and avacincaptad pegol (Iveric Bio), which target complement factors C3 and C5, respectively, which slow down the rate of enlargement of the area of atrophy. However, there is currently no treatment to reverse the central vision loss associated with GA. Optogenetics may provide a strategy for rescuing visual function in GA by imparting light-sensitivity to the surviving inner retina (i.e., retinal ganglion cells or bipolar cells). It takes advantage of residual inner retinal architecture to transmit visual stimuli along the visual pathway, while a wide range of photosensitive proteins are available for consideration. Herein, we review the anatomical changes in GA, discuss the suitability of optogenetic therapeutic sensors in different target cells in pre-clinical models, and consider the advantages and disadvantages of different routes of administration of therapeutic vectors.

Alterations of the Ganglion Cell Complex in Age-Related Macular Degeneration: An Amish Eye Study Analysis

PURPOSE

To compare the ganglion cell complex (GCC) thickness in eyes with age-related macular degeneration (AMD) vs healthy controls in an elderly Amish population.

DESIGN

Prospective cross-sectional study.

METHODS

This is a post hoc analysis of the family-based prospective study of Amish subjects. Study subjects underwent imaging with the Cirrus HD-OCT (Carl Zeiss Meditec Inc) using a macular cube protocol of 512 × 128 scans (128 horizontal B-scans, each comprising 512 A-scans) over a 6 mm × 6 mm region centered on the fovea. The ganglion cell analysis algorithm calculated the GCC thickness by segmenting the outer boundaries of the retinal nerve fiber layer (RNFL) and inner plexiform layer (IPL) in all B-scans of the volume, with the region between these boundaries representing the combined thickness of the ganglion cell layer (GCL) and the IPL. A number of parameters were used to evaluate the GCC thickness: the average GCC thickness, minimum (lowest GCC thickness at a single meridian crossing the elliptical annulus), and sectoral (within each of 6 sectoral areas: superior, superotemporal, superonasal, inferior, inferonasal, and inferotemporal). The stage of AMD was graded on color fundus photographs in accordance with the Beckman Initiative for Macular Research classification system.

RESULTS

Of 1339 subjects enrolled in the Amish eye study, a total of 1294 eyes of 1294 subjects had all required imaging studies of sufficient quality and were included in the final analysis. Of these, 798 (62%) were female. Following age adjustment, the average GCC thickness was significantly (P < .001) thinner in AMD subjects (73.71 ± SD; 13.77 µm) compared to normals (77.97 ± 10.42 µm). An independent t test showed that the early AMD (75.03 ± 12.45 µm) and late AMD (61.64 ± 21.18 µm) groups (among which eyes with geographic atrophy [GA] had the lowest thickness, of 58.10 ± 20.27 µm) had a statistically significant lower GCC thickness compared to eyes without AMD. There was no significant differences in average GCC thickness between early AMD and intermediate AMD (76.36 ± 9.25 µm) eyes.

CONCLUSIONS

The GCC thickness in AMD eyes is reduced compared to normal eyes; however, the relationship is complex, with the greatest reduction in late AMD eyes (particularly eyes with GA) but no difference between early and intermediate AMD eyes.

Multimodal analysis in symptomatic MIDD-associated retinopathy. A case report and literature review

Purpose

To present results of contemporary multimodal ophthalmic imaging in a case of maternally inherited diabetes and deafness (MIDD) and a literature review of MIDD.

Methods

A case of a 47-year-old female with diabetes mellitus, severe insulin resistance, familial lipodystrohy, deafness and increasing problems with vision is reported. A full ophthalmic examination was done, including best corrected visual acuity (BCVA, LogMAR), funduscopy, and imaging studies: optical coherence tomography (OCT), OCT angiography (OCT-A), fundus autofloresence (FAF), visual fields (HVF) 10-2 , electrophysiology (EP) and genetic testing were performed. Literature available on the topic was reviewed.

Results

BCVA was 0.06 LogMAR in the right eye and 0.1 LogMAR in the left. Funduscopy revealed atrophy (AT) and pigmentary changes but no diabetic retinopathy. HVF confirmed corresponding defects. The imaging and diagnostic tests showed the following abnormalities: FAF: hypoautofluoresence in areas of AT and mottled appearance in the macular and peripapillary area; OCT: attenuation of outer retinal layers and retinal pigment epithelium (RPE) in the AT; OCT-A: thinning of the deep capillary plexus and choriocapillaris; EP: abnormalities on full field electroretinogram (ERG), 30 Hz flicker and single cone flash response; multifocal ERG: reduced responses; genetic testing: A-to-G transition mutation at position 3243 of the mitochondrial genome, typical for MIDD. After one year OCT ganglion cell analysis showed loss of thickness.

Conclusions

Genetic testing should be considered in diabetic patients with pigmentary retinopathy. Imaging studies and diagnostic testing showed structural and functional retinal changes, confined to the macula and progressive in nature.

Photochemical Restoration of Light Sensitivity in the Degenerated Canine Retina

Photopharmacological compounds such as azobenzene-based photoswitches have been shown to control the conductivity of ionic channels in a light-dependent manner and are considered a potential strategy to restore vision in patients with end-stage photoreceptor degeneration. Here, we report the effects of DENAQ, a second-generation azobenzene-based photoswitch on retinal ganglion cells (RGC) in canine retinas using multi-electrode array (MEA) recordings (from nine degenerated and six WT retinas). DENAQ treatment conferred increased light sensitivity to RGCs in degenerated canine retinas. RGC light responses were observed in degenerated retinas following ex vivo application of 1 mM DENAQ (n = 6) or after in vivo DENAQ injection (n = 3, 150 μL, 3-10 mM) using 455 nm light at intensities as low as 0.2 mW/cm². The number of light-sensitive cells and the per cell response amplitude increased with light intensity up to the maximum tested intensity of 85 mW/cm². Application of DENAQ to degenerated retinas with partially preserved cone function caused appearance of DENAQ-driven responses both in cone-driven and previously non-responsive RGCs, and disappearance of cone-driven responses. Repeated stimulation slowed activation and accelerated recovery of the DENAQ-driven responses. The latter is likely responsible for the delayed appearance of a response to 4 Hz flicker stimulation. Limited aqueous solubility of DENAQ results in focal drug aggregates associated with ocular toxicity. While this limits the therapeutic potential of DENAQ, more potent third-generation photoswitches may be more promising, especially when delivered in a slow-release formulation that prevents drug aggregation.

Retinal Vessel Density in Age-Related Macular Degeneration Patients with Geographic Atrophy

We compared the retinal vessel density and inner retinal thickness in patients who had one eye with geographic atrophy (GA) and a fellow eye with intermediate age-related macular degeneration (iAMD). The vessel density from the superficial vascular complex (SVC) and deep vascular complex (DVC) through optical coherence tomography angiography and the thickness of the nerve fiber layer, ganglion cell-inner plexiform layer (GCIPL), inner nuclear layer (INL), outer nuclear layer (ONL) on a structural optical coherence tomography thickness map were measured in 28 eyes of 14 GA patients with iAMD in the fellow eye. GA eyes had significantly lower vessel density in the SVC (26.2 ± 3.9% vs. 28.3 ± 4.4%; p = 0.015) and DVC (24.2 ± 2.6% vs. 26.8 ± 1.9%; p = 0.003) than fellow eyes (iAMD). GCIPL and ONL were significantly thinner in GA eyes than in the fellow eyes (p = 0.032 and 0.024 in the foveal areas, p = 0.029 and 0.065 in the parafovea areas, respectively). Twenty-four eyes of 12 patients were followed up for 2 years and seven of the fellow eyes (58.3%) developed GA during the follow-up period and showed reduced vessel density in the SVC (26.4 ± 3.0% vs. 23.8 ± 2.9%; p = 0.087) and DVC (25.8 ± 2.2% vs. 22.4 ± 4.4%; p = 0.047) compared to baseline. Vessel density and GCIPL thickness map measurements are potential GA markers in non-neovascular AMD.

Automated foveal location detection on spectral-domain optical coherence tomography in geographic atrophy patients

PURPOSE

To develop a fully automated algorithm for accurate detection of fovea location in atrophic age-related macular degeneration (AMD), based on spectral-domain optical coherence tomography (SD-OCT) scans.

METHODS

Image processing was conducted on a cohort of patients affected by geographic atrophy (GA). SD-OCT images (cube volume) from 55 eyes (51 patients) were extracted and processed with a layer segmentation algorithm to segment Ganglion Cell Layer (GCL) and Inner Plexiform Layer (IPL). Their en face thickness projection was convolved with a 2D Gaussian filter to find the global maximum, which corresponded to the detected fovea. The detection accuracy was evaluated by computing the distance between manual annotation and predicted location.

RESULTS

The mean total location error was 0.101±0.145mm; the mean error in horizontal and vertical en face axes was 0.064±0.140mm and 0.063±0.060mm, respectively. The mean error for foveal and extrafoveal retinal pigment epithelium and outer retinal atrophy (RORA) was 0.096±0.070mm and 0.107±0.212mm, respectively. Our method obtained a significantly smaller error than the fovea localization algorithm inbuilt in the OCT device (0.313±0.283mm, p <.001) or a method based on the thinnest central retinal thickness (0.843±1.221, p <.001). Significant outliers are depicted with the reliability score of the method.

CONCLUSION

Despite retinal anatomical alterations related to GA, the presented algorithm was able to detect the foveal location on SD-OCT cubes with high reliability. Such an algorithm could be useful for studying structural-functional correlations in atrophic AMD and could have further applications in different retinal pathologies.

Longitudinal changes in the ganglion cell-inner plexiform layer thickness of age-related macular degeneration

PURPOSE

To determine longitudinal changes of the ganglion cell-inner plexiform layer (GC-IPL) thickness in patients with non-exudative age-related macular degeneration (AMD) without other ophthalmic disease.

METHODS

Thirty-three eyes of 33 patients with early and intermediate non-exudative AMD (non-exudative AMD group) and 33 normal control eyes were followed for 2 years, and GC-IPL thickness was measured by spectral domain optical coherence tomography at 1-year intervals. The mean rate of GC-IPL reduction was estimated using a linear mixed model and compared between two groups.

RESULTS

The mean age of patients in the non-exudative AMD group and control groups were 68.82 ± 6.81 years and 67.73 ± 5.87 years, respectively (p = 0.488). The mean GC-IPL thickness at the first visit was 76.61 ± 16.33 μm in the non-exudative AMD and 81.76 ± 3.69 μm in control group (p = 0.387), and these values significantly decreased over time, with an average reduction rate of average GC-IPL -0.86 μm/year in the non-exudative AMD group and -0.32 μm/year in the control group. The difference between two groups was statistically significant (p < 0.001), and there was also a significant interaction between group and duration in linear mixed models in mean GC-IPL thickness (p = 0.001).

CONCLUSIONS

The reduction rate of the GC-IPL thickness was greater in non-exudative AMD eyes, even at relatively early stages of the disease. Physicians should maintain awareness of the presence of non-exudative AMD in various cases of ophthalmic diseases where GC-IPL thickness evaluation is necessary.

Quantitative deep vascular complex analysis of different AMD stages on optical coherence tomography angiography

Aims:

To investigate alterations in deep retinal vascular complex (DVC) in patients with non-neovascular intermediate AMD (iAMD), treatment-naïve quiescent macular neovascularization (qMNV), exudative AMD (eAMD) by means of OCT angiography (OCTA).

Methods:

Patients with iAMD, qMNV, eAMD and healthy controls presenting in the Department of Ophthalmology of the Centre Hospitalier Intercommunal de Créteil between January 2016 and January 2018, were retrospectively included. 3 × 3-mm OCTA (AngioVue RTVue XR Avanti) perfusion density (PD) of DVC was computed in all groups at baseline and follow up (12.0 ± 1.1 months).

Results:

A total of 46 eyes of 45 patients were enrolled: 11/46 iAMD, 10/46 qMNV, 13/46 eAMD, 12/46 control eyes. PD showed a significant decrease during follow-up in qMNV ( p = 0.0059) and iAMD ( p = 0.0076) eyes. PD in eAMD and healthy controls didn’t show significant changes.

Conclusion:

PD decreases at the level of DVC in eyes with qMNV and iAMD, while in eAMD eyes, PD is stable throughout follow up, suggesting that repeated anti-vascular endothelial growth factor (VEGF) injections do not impact on the DVC PD.

Characteristics of the inner retinal layer in the fellow eyes of patients with unilateral exudative age-related macular degeneration

OBJECTIVE

To investigate the thicknesses of the ganglion cell-inner plexiform layer (GC-IPL) and retinal nerve fiber layer (RNFL) of the fellow eyes of patients with unilateral exudative age-related macular degeneration (AMD).

METHODS

A total of 107 patients with unilateral exudative AMD [34 of typical choroidal neovascularization (tCNV), Group A; 73 of polypoidal choroidal vasculopathy (PCV), Group B] and 73 normal control eyes (Group C) were included. Drusen and subretinal drusenoid deposits were assessed in all participants using fundus photography, autofluorescence, and optical coherence tomography (OCT). The GC-IPL and RNFL thicknesses were measured using Cirrus HD-OCT and compared among groups. Linear regression analyses were used to evaluate the factors associated with GC-IPL thicknesses.

RESULTS

The average GC-IPL thicknesses of Groups A, B, and C were 77.09 ± 3.87, 80.10 ± 6.61, and 80.88 ± 6.50 μm, respectively (p = 0.022). Sectoral GC-IPLs and central macular thicknesses (CMTs) were significantly different among groups (all, p <0.05), whereas none of the RNFL parameters differed significantly (all, p >0.05). Multivariate linear regression analyses revealed that age (p <0.001), CMT (p <0.001), and tCNV (p = 0.013) were significantly associated with average GC-IPL thickness, and the rate of reduction of GC-IPL thickness with increasing age in the fellow eyes of tCNV patients was higher than those in the PCV and control groups.

CONCLUSIONS

Unilateral tCNV patients exhibited statistically significant reduction of the GC-IPL thickness in the fellow eyes, compared to values of the fellow eyes of unilateral PCV patients or control patients. RNFL values trended to be lower but did not reach statistical significance.

Optical Coherence Tomography-Angiography in Geographic Atrophy

Geographic atrophy (GA) represents the non-exudative late stage of age-related macular degeneration and constitutes a leading cause of legal blindness in the developed world. It is characterized by areas of loss of outer retinal layers including photoreceptors, degeneration of the retinal pigment epithelium, and rarefication of the choriocapillaris. As all three layers are functionally connected, the precise temporal sequence and relative contribution of these layers towards the development and progression of GA is unclear. The advent of optical coherence tomography angiography (OCT-A) has allowed for three-dimensional visualization of retinal blood flow. Using OCT-A, recent studies have demonstrated that choriocapillaris flow alterations are particularly associated with the development of GA, exceed atrophy boundaries spatially, and are a prognostic factor for future GA progression. Furthermore, OCT-A may be helpful to differentiate GA from mimicking diseases. Evidence for a potential protective effect of specific forms of choroidal neovascularization in the context of GA has been reported. This article aims to give a comprehensive review of the current literature concerning the application of OCT-A in GA, and summarizes the opportunities and limitations with regard to pathophysiologic considerations, differential diagnosis, study design, and patient assessment.

Macula Ganglion Cell Thickness Changes Display Location-Specific Variation Patterns in Intermediate Age-Related Macular Degeneration

Purpose

The purpose of this study was to examine changes in the ganglion cell layer (GCL) of individuals with intermediate age-related macular degeneration (AMD) using grid-wise analysis for macular optical coherence tomography (OCT) volume scans. We also aim to validate the use of age-correction functions for GCL thickness in diseased eyes.

Methods

OCT macular cube scans covering 30° × 25° were acquired using Spectralis spectral-domain OCT for 87 eyes with intermediate AMD, 77 age-matched normal eyes, and 254 non-age-matched normal eyes. The thickness of the ganglion cell layer (GCL) was defined after segmentation at 60 locations across an 8 × 8 grid centered on the fovea, where each grid location covered 0.74 mm² (approximately 3° × 3°) within the macula. Each GCL location of normal eyes (n = 77) were assigned to a specific iso-ganglion cell density cluster in the macula, based on patterns of age-related GCL thickness loss. Analyses were then performed comparing AMD GCL grid-wise data against corresponding spatial clusters, and significant AMD GCL thickness changes were denoted as values outside the 95% distribution limits.

Results

Analysis of GCL thickness changes revealed significant differences between spatial clusters, with thinning toward the fovea, and thickening toward the peripheral macula. The direction of GCL thickness changes in AMD were associated more so with thickening than thinning in all analyses. Results were corroborated by the application of GCL thickness age-correction functions.

Conclusions

GCL thickness changed significantly and nonuniformly within the macula of intermediate AMD eyes. Further characterization of these changes is critical to improve diagnoses and monitoring of GCL-altering pathologies.

Detection of Reduced Retinal Vessel Density in Eyes with Geographic Atrophy Secondary to Age-Related Macular Degeneration Using Projection-Resolved Optical Coherence Tomography Angiography

PURPOSE

To compare retinal vessel density in eyes with geographic atrophy (GA) secondary to age-related macular degeneration (AMD) to age-matched healthy eyes by using projection-resolved optical coherence tomography angiography (PR-OCTA).

DESIGN

Prospective cross-sectional study.

METHODS

Study participants underwent macular 3- × 3-mm OCTA scans with spectral domain OCTA. Reflectance-compensated retinal vessel densities were calculated on projection-resolved superficial vascular complex (SVC), intermediate capillary plexus (ICP), and deep capillary plexus (DCP). Quantitative analysis using normalized deviation compared the retinal vessel density in GA regions, 500-μm GA rim regions, and non-GA regions to similar macular locations in control eyes.

RESULTS

Ten eyes with GA and 10 control eyes were studied. Eyes with GA had significantly lower vessel density in the SVC (54.8 ± 2.4% vs. 60.8 ± 3.1%; P < 0.001), ICP (34.0 ± 1.5% vs. 37.3 ± 1.7%; P = 0.003) and DCP (24.4 ± 2.3% vs. 28.0 ± 2.3%; P < 0.001) than control eyes. Retinal vessel density within the GA region decreased significantly in SVC, ICP, and DCP. Retinal vessel density in the GA rim region decreased in SVC and ICP but not in DCP. The non-GA region did not significantly deviate from normal controls. Eyes with GA had significantly reduced photoreceptor layer thickness; but similar nerve fiber layer, ganglion cell complex, inner nuclear layer, and outer plexiform layer thickness.

CONCLUSIONS

Eyes with GA have reduced retinal vessel density in SVC, ICP, and DCP compared to those in controls. Loss is greatest within regions of GA. Vessel density may be more sensitive than retinal layer thickness measurement in the detection of inner retinal change in eyes with GA.

Persistent remodeling and neurodegeneration in late-stage retinal degeneration

Retinal remodeling is a progressive series of negative plasticity revisions that arise from retinal degeneration, and are seen in retinitis pigmentosa, age-related macular degeneration and other forms of retinal disease. These processes occur regardless of the precipitating event leading to degeneration. Retinal remodeling then culminates in a late-stage neurodegeneration that is indistinguishable from progressive central nervous system (CNS) proteinopathies. Following long-term deafferentation from photoreceptor cell death in humans, and long-lived animal models of retinal degeneration, most retinal neurons reprogram, then die. Glial cells reprogram into multiple anomalous metabolic phenotypes. At the same time, survivor neurons display degenerative inclusions that appear identical to progressive CNS neurodegenerative disease, and contain aberrant α-synuclein (α-syn) and phosphorylated α-syn. In addition, ultrastructural analysis indicates a novel potential mechanism for misfolded protein transfer that may explain how proteinopathies spread. While neurodegeneration poses a barrier to prospective retinal interventions that target primary photoreceptor loss, understanding the progression and time-course of retinal remodeling will be essential for the establishment of windows of therapeutic intervention and appropriate tuning and design of interventions. Finally, the development of protein aggregates and widespread neurodegeneration in numerous retinal degenerative diseases positions the retina as a ideal platform for the study of proteinopathies, and mechanisms of neurodegeneration that drive devastating CNS diseases.

Retinal Ganglion Cell Death as a Late Remodeling Effect of Photoreceptor Degeneration

Inherited or acquired photoreceptor degenerations, one of the leading causes of irreversible blindness in the world, are a group of retinal disorders that initially affect rods and cones, situated in the outer retina. For many years it was assumed that these diseases did not spread to the inner retina. However, it is now known that photoreceptor loss leads to an unavoidable chain of events that cause neurovascular changes in the retina including migration of retinal pigment epithelium cells, formation of “subretinal vascular complexes”, vessel displacement, retinal ganglion cell (RGC) axonal strangulation by retinal vessels, axonal transport alteration and, ultimately, RGC death. These events are common to all photoreceptor degenerations regardless of the initial trigger and thus threaten the outcome of photoreceptor substitution as a therapeutic approach, because with a degenerating inner retina, the photoreceptor signal will not reach the brain. In conclusion, therapies should be applied early in the course of photoreceptor degeneration, before the remodeling process reaches the inner retina.

Inner retinal thickening in newly diagnosed choroidal neovascularization

PURPOSE

Automated segmentation of retinal layers by spectral-domain optical coherence tomography (SD-OCT) is usually erroneous in the presence of retinal diseases. The purpose of this study is to report the changes in ganglion cell complex (GCC) comprising retina nerve fiber layer (RNFL), ganglion cell layer (GCL), and inner plexiform layer (IPL) in neovascular age-related macular degeneration (AMD) patients by manually correcting the automated segmentation errors.

METHODS

Thirty eyes of 30 patients with new-onset choroidal neovascularization secondary to neovascular AMD and 30 eyes of 30 healthy subjects were included. The inner retinal thicknesses were measured using early treatment diabetic retinopathy circle in the central 1 mm (fovea) and surrounding 3 mm diameter (parafovea) after checking the accuracy of automated segmentation lines. Manual segmentation was done to ensure the accurate segmentation, when needed.

RESULTS

Neovascular AMD patients had thicker mean RNFL, GCL, IPL, and GCC thicknesses within the fovea compared to healthy eyes (p = 0.04, p = 0.001, p = 0.032, and p = 0.005, respectively). In the parafoveal area, among the thickness-related measurements, the only significant difference was a thicker mean RNFL (p = 0.002).

CONCLUSION

Diffuse thickening of inner retinal layers in neovascular AMD may overestimate actual GCC thickness within fovea. This pseudo-increase in GCC thickness and inner retinal layers in general likely does not reflect more cells or tissue, but rather diffuse edema which leads to a falsely increased reading of layer thickness. Such false readings may also make the assessment of other conditions that lead to reduced inner retinal layer thickness such as glaucoma, optic nerve disease, or retinovascular occlusions more difficult.