Selective cone photoreceptor injury in acute macular neuroretinopathy

Optical coherence tomography angiography suggests choriocapillaris perfusion deficit as etiology of acute macular neuroretinopathy

PURPOSE

Acute macular neuroretinopathy (AMN) can cause sudden-onset and permanent scotoma in healthy young patients. Analysis of optical coherence tomography (OCT) and OCT angiography (OCTA) of AMN patients may provide insights into disease mechanism.

METHODS

We conducted a retrospective study of consecutive SARS-Cov-2-related AMN patients that presented in our clinic between Jan 1st, 2022, and April 30th, 2023, within 30 days of symptom onset. Retinal vessel area density (VAD) of AMN lesions in OCTA was quantified and compared to an adjacent tissue control (ATC). This quantification was performed for the superficial vascular plexus (SVP), the intermediate capillary plexus (ICP), the deep capillary plexus (DCP), the choriocapillaris (CC), and choroid. Furthermore, en face OCT images were analyzed.

RESULTS

Nine AMN patients were identified, 6 of these (4 female, 2 male, average age 25 years) fulfilled the inclusion criteria and were included into this study. Average time from symptom onset to OCTA was 14.3 days. No VAD differences between AMN and adjacent tissue were found in either retinal layer (SVP, ICP, DCP). In contrast, VAD in CC was reduced by 27% against the ATC (p = 0.007) and choroidal VAD was reduced by 41% (p = 0.017). Further analysis of en face OCT could show that the pathognomonic infrared hyporeflectivity in AMN is caused by photoreceptor alterations rather than changes in the inner retinal layers.

CONCLUSIONS

Our data suggests that a perfusion deficit in the choroidal layers is responsible for AMN rather than in the DCP, which is the predominant hypothesis in current literature.

HIGH-RESOLUTION IMAGING OF THE OUTER RETINA IN TYPE 2 ACUTE MACULAR NEURORETINOPATHY

PURPOSE

The purpose of this study was to investigate the outer retinal changes in a patient with type 2 acute macular neuroretinopathy (AMN).

METHODS

A 35-year-old White woman complaining of a unilateral blind spot was imaged using various retinal imaging modalities including clinical optical coherence tomography (OCT), OCT-angiography, fundus fluorescein angiography, and adaptive optics (AO).

RESULTS

Fundus examination revealed multiple paracentral reddish brown petaloid lesions in the symptomatic left eye, while the other eye was unremarkable. Clinical OCT showed areas of hyperreflectance at the outer plexiform layer/outer nuclear layer complex with a disrupted inner/outer segment junction, which are characteristic features of type 2 AMN. AO imaging further revealed either shortening or absence of cone outer segments within the AMN lesions attributing to the darker features observed in the en face images from fundus photography and scanning laser ophthalmoscopy.

CONCLUSION

The AO findings indicate that the petaloid lesions in type 2 AMN are caused by a combination of the shortening and absence of the outer segment in individual cone photoreceptors.

Case Report: Recurrent Acute Macular Neuroretinopathy-Monitoring Recovery with Multimodal Imaging

SIGNIFICANCE

Acute macular neuroretinopathy (AMN) is a rare, nonprogressive condition affecting the outer retina that can be diagnosed clinically using widely available multimodal imaging techniques. This case report presents an exceedingly rare same-eye recurrence of AMN and describes the characteristic imaging findings of this unique, not fully understood clinical entity.

PURPOSE

The following report provides a detailed account of recurrent AMN from 4 hours of symptom onset to 4 months with repeat multimodal imaging captured at different visits. This report also devotes some discussion to the current understanding of its pathophysiology, associations, management, and imaging characteristics.

CASE REPORT

A 32-year-old woman with unilateral recurrent AMN was monitored frequently with various multimodal imaging from 4 hours after onset of new scotoma to 4 months. The primary finding in the acute stage was a hyperreflective lesion of the outer nuclear and outer plexiform layers followed by disruption of underlying external limiting membrane, ellipsoid zone, and photoreceptors. This resolved into stable outer nuclear layer thinning and subtle disruption of the deeper layers after 1 week. Fundus photography revealed a red-brown petaloid lesion adjacent to the fovea, and optical coherence tomography angiography revealed subtle decreased perfusion of the choriocapillaris layer throughout follow-up.

CONCLUSIONS

Acute macular neuroretinopathy is a rare nonprogressive condition of the outer retina most often affecting otherwise healthy young female individuals and is most associated with recent flu-like illness and oral contraceptives. The underlying mechanism of AMN remains unknown, but modern imaging techniques have elucidated the disease locus to be choroidal and/or deep capillary plexus. It is important for eye care providers to recognize AMN as a clinical entity distinct from other retinal conditions that require different management.

Extracting spacing-derived estimates of rod density in healthy retinae

Quantification of the rod photoreceptor mosaic using adaptive optics scanning light ophthalmoscopy (AOSLO) remains challenging. Here we demonstrate a method for deriving estimates of rod density and rod:cone ratio based on measures of rod spacing, cone numerosity, and cone inner segment area. Twenty-two AOSLO images with complete rod visualization were used to validate this spacing-derived method for estimating density. The method was then used to estimate rod metrics in an additional 105 images without complete rod visualization. The spacing-derived rod mosaic metrics were comparable to published data from histology. This method could be leveraged to develop large normative databases of rod mosaic metrics, though limitations persist with intergrader variability in assessing cone area and numerosity.

Deep Capillary Plexus Features in Acute Macular Neuroretinopathy: Novel Insights Based on the Anatomy of Henle Fiber Layer

PURPOSE

The purpose of this study was to identify a precise location of deep capillary plexus (DCP) injury in acute macular neuroretinopathy (AMN) lesions using multimodal imaging.

METHODS

En face structural optical coherence tomography (OCT) images were manually segmented to delineate outer retinal AMN lesions involving the ellipsoid zone and interdigitation zone. AMN lesion centroid was calculated, and image distortion was applied to correct for Henle fiber layer (HFL) length and orientation. The resulting image was registered with the corresponding en face OCT angiography (OCTA) image segmented at the DCP and structural OCT volume before grading for vascular and structural features, respectively.

RESULTS

Thirty-nine AMN lesions from 16 eyes (11 female patients, mean age 34 ± 4 years) were analyzed. After correcting for HFL anatomy, in 62% of AMN lesions, the centroid co-localized with a capillary vortex (pattern 1); flow defects were detected in 33% of lesions (pattern 2); and in 5% of lesions no specific pattern could be identified (pattern 3). The detection of a specific pattern increased after correcting the projection of AMN lesion for HFL anatomy (28% vs. 5%, P = 0.04). Outer nuclear layer thickness was lower in the centroid area in 10 (29%) AMN lesions from 6 patients, all corresponding to lesions fitting pattern 2 (r = 0.78, P < 0.001).

CONCLUSIONS

AMN lesions might be a result of DCP impairment at the level of the capillary vortex or draining venule. In eyes with AMN, the location of outer retinal changes associated with DCP ischemia appears to be influenced by the length and orientation of HFL.

Navigating the White Dot Syndromes with Optical Coherence Tomography (OCT) and OCT Angiography (OCT-A)

INTRODUCTION

White dot syndromes are a heterogeneous group of diseases that affect different layers in the retina and choroid. Multimodal imaging is fundamental in the diagnosis, but also can be crucial in unveiling the pathogenesis of these entities.

MATERIAL AND METHODS

Literature review.

RESULTS

Optical coherence tomography (OCT) provides depth-resolved, histological grade images of the vitreous, retina, and choroid. This technology is very useful to localize the primary nature and level of pathology of the various white dot syndromes. En face OCT can provide additional information regarding the interrelationship of lesion types. Vascular involvement at the level of the retina, choriocapillaris or choroid can be assessed by en face OCT angiography (OCT-A) and is not limited by masking, leakage or staining as can occur with conventional angiography (fluorescein or indocyanine green angiography) which requires dye injection.

CONCLUSION

OCT and OCTA are fundamental in the diagnosis and follow-up of white dots syndromes.

Challenges Associated With Ellipsoid Zone Intensity Measurements Using Optical Coherence Tomography

Translational Relevance

Qualitative evaluation of the ellipsoid zone band on optical coherence tomography is a valuable clinical tool for assessing photoreceptor structure, though more quantitative metrics are emerging. Awareness of the challenges involved in interpreting quantitative metrics is important for their clinical translation.

Evaluating seasonal changes of cone photoreceptor structure in the 13-lined ground squirrel

Cone photoreceptors of the 13-lined ground squirrel (13-LGS) undergo reversible structural changes during hibernation, including cone outer segment disc degeneration and inner segment mitochondria depletion. Here, we evaluated cone structure with adaptive optics scanning light ophthalmoscopy (AOSLO) before, during, and after hibernation. Also, intra-animal comparisons of cone structure were made at distinct physiological states (pre-hibernation, torpor, interbout euthermia, and post-hibernation) with AOSLO and transmission electron microscopy. Our results indicate that the 13-LGS cone mosaic is only transiently affected by structural remodeling during hibernation. Outer segment remodeling starts during torpid states during a period of fall transition in room temperature, with more severe structural changes during bouts of torpor in cold temperature. Cones return to euthermic-like structure during brief periods of interbout euthermia and recover normal waveguiding properties as soon as 24 h post-hibernation. Cone structure is visible with split-detector AOSLO throughout hibernation, providing evidence that intact outer segments are not necessary to visualize cones with this technique. Despite the changes to cone structure during hibernation, cone density and packing remained unchanged throughout the seasonal cycle. Pairing non-invasive imaging with ultrastructural assessment may provide insight to the biological origins of cone photoreceptor signals observed with AOSLO.

Projection-Resolved OCT Angiography of Microvascular Changes in Paracentral Acute Middle Maculopathy and Acute Macular Neuroretinopathy

Purpose

To identify the microvascular changes associated with paracentral acute middle maculopathy (PAMM) and acute macular neuroretinopathy (AMN) and to improve our understanding of the relevant involvement of the three retinal capillary plexuses using projection-resolved optical coherence tomography angiography (PR-OCTA).

Methods

This was a retrospective study of 18 eyes with AMN or PAMM imaged with OCTA. We used cross-sectional PR-OCTA to localize reduced flow signal to the superficial (SCP), middle (MCP), or deep capillary plexus (DCP) or choriocapillaris that corresponded to inner retinal PAMM or outer retinal AMN lesions on OCT.

Results

Five eyes with AMN showed outer retinal disruption on OCT associated with reduced DCP flow signal. All three eyes with AMN and follow-up had recovery of DCP flow. Thirteen eyes with PAMM showed middle retinal disruption on OCT associated with reduced flow signal in both the MCP and DCP. Of these, five also had reduced flow signal in the SCP. All 10 eyes with PAMM and follow-up showed variable recovery of flow signal in one or more plexuses. PAMM reperfusion was primarily arterial in nature. Three eyes with PAMM and no evidence of MCP reperfusion experienced severe thinning of the inner nuclear layer (INL), while seven eyes with robust MCP flow signal recovery showed relative preservation of INL thickness.

Conclusions

Using PR-OCTA, we found that AMN was associated with reduced DCP flow signal, while PAMM was associated with reduced MCP and DCP flow signal and occasionally the SCP. The MCP appears to be important in sustaining INL thickness in these eyes.

DIRECTIONAL VARIABILITY OF FUNDUS REFLECTANCE IN ACUTE MACULAR NEURORETINOPATHY: EVIDENCE FOR A CONTRIBUTION OF THE STILES-CRAWFORD EFFECT

PURPOSE

To document directional reflectivity of fundus lesions in a case of acute macular neuroretinopathy.

METHODS

Case report. Clinical and imaging data from a patient with acute macular neuroretinopathy were reviewed. Imaging comprised infrared scanning laser ophthalmoscopy, optical coherence tomography and flood-illumination adaptive optics images acquired through different entry pupils in the cardinal directions (approximately 2° eccentricity).

RESULTS

The patient reported acute bilateral paracentral scotoma revealing dark, wedge-shaped macular plaques which by optical coherence tomography were associated with focal loss of the visibility of the cone outer segment tip and inner/outer segment lines. Comparing scanning laser ophthalmoscopy images taken at different entry points in the pupil showed that macular plaques varied from hyporeflectance to isoreflectance. Cone counts by flood-illumination adaptive optics within plaques and optical coherence tomography features of the cone outer segment tip showed also a strong directional variability, peaking at near-normal values. Within each modality, fusion images showed that directional variability covered most of macular plaques.

CONCLUSION

The characteristic fundus abnormalities of acute macular neuroretinopathy may show a strong directional variability. Our findings suggest that the Stiles-Crawford effect may be an important factor in signs and symptoms of acute macular neuroretinopathy.

Handheld Adaptive Optics Scanning Laser Ophthalmoscope

Adaptive optics scanning laser ophthalmoscopy (AOSLO) has enabled in vivo visualization and enhanced understanding of retinal structure and function. Current generation AOSLOs have a large footprint and are mainly limited to imaging cooperative adult subjects. To extend the application of AOSLO to new patient populations, we have designed the first portable handheld AOSLO (HAOSLO) system. By incorporating a novel computational wavefront sensorless AO algorithm and custom optics, we have miniaturized our HAOSLO to weigh less than 200 grams. HAOSLO imaged the cones closest to the fovea with a handheld probe in adults and captured the first AO-enhanced image of cones in infants.

Intraobserver Repeatability and Interobserver Reproducibility of Ellipsoid Zone Measurements in Retinitis Pigmentosa

Purpose

To examine repeatability and reproducibility of ellipsoid zone (EZ) width measurements in patients with retinitis pigmentosa (RP) using a longitudinal reflectivity profile (LRP) analysis.

Methods

We examined Bioptigen optical coherence tomography (OCT) scans from 48 subjects with RP or Usher syndrome. Nominal scan lengths were 6, 7, or 10 mm, and the lateral scale of each scan was calculated using axial length measurements. LRPs were generated from OCT line scans, and the peak corresponding to EZ was manually identified using ImageJ. The locations at which the EZ peak disappeared were used to calculate EZ width. Each scan was analyzed twice by each of two observers, who were masked to their previous measurements and those of the other observer.

Results

On average, horizontal width (HW) was significantly greater than vertical width (VW), and there was high interocular symmetry for both HW and VW. We observed excellent intraobserver repeatability with intraclass correlation coefficients (ICCs) ranging from 0.996 to 0.998 for HW and VW measurements. Interobserver reproducibility was also excellent for both HW (ICC = 0.989; 95% confidence interval [CI] = 0.983–0.995) and VW (ICC = 0.991; 95% CI = 0.985–0.996), with no significant bias observed between observers.

Conclusions

EZ width can be measured using LRPs with excellent repeatability and reproducibility. Our observation of greater HW than VW is consistent with previous observations in RP, though the reason for this anisotropy remains unclear.

Translational Relevance

We describe repeatability and reproducibility of a method for measuring EZ width in patients with RP or Usher syndrome. This approach could facilitate measurement of retinal band thickness and/or intensity.

Evaluating Descriptive Metrics of the Human Cone Mosaic

PURPOSE

To evaluate how metrics used to describe the cone mosaic change in response to simulated photoreceptor undersampling (i.e., cell loss or misidentification).

METHODS

Using an adaptive optics ophthalmoscope, we acquired images of the cone mosaic from the center of fixation to 10° along the temporal, superior, inferior, and nasal meridians in 20 healthy subjects. Regions of interest (n = 1780) were extracted at regular intervals along each meridian. Cone mosaic geometry was assessed using a variety of metrics - density, density recovery profile distance (DRPD), nearest neighbor distance (NND), intercell distance (ICD), farthest neighbor distance (FND), percentage of six-sided Voronoi cells, nearest neighbor regularity (NNR), number of neighbors regularity (NoNR), and Voronoi cell area regularity (VCAR). The "performance" of each metric was evaluated by determining the level of simulated loss necessary to obtain 80% statistical power.

RESULTS

Of the metrics assessed, NND and DRPD were the least sensitive to undersampling, classifying mosaics that lost 50% of their coordinates as indistinguishable from normal. The NoNR was the most sensitive, detecting a significant deviation from normal with only a 10% cell loss.

CONCLUSIONS

The robustness of cone spacing metrics makes them unsuitable for reliably detecting small deviations from normal or for tracking small changes in the mosaic over time. In contrast, regularity metrics are more sensitive to diffuse loss and, therefore, better suited for detecting such changes, provided the fraction of misidentified cells is minimal. Combining metrics with a variety of sensitivities may provide a more complete picture of the integrity of the photoreceptor mosaic.

Assessing Photoreceptor Structure in Retinitis Pigmentosa and Usher Syndrome

Purpose

The purpose of this study was to examine cone photoreceptor structure in retinitis pigmentosa (RP) and Usher syndrome using confocal and nonconfocal split-detector adaptive optics scanning light ophthalmoscopy (AOSLO).

Methods

Nineteen subjects (11 RP, 8 Usher syndrome) underwent ophthalmic and genetic testing, spectral-domain optical coherence tomography (SD-OCT), and AOSLO imaging. Split-detector images obtained in 11 subjects (7 RP, 4 Usher syndrome) were used to assess remnant cone structure in areas of altered cone reflectivity on confocal AOSLO.

Results

Despite normal interdigitation zone and ellipsoid zone appearance on OCT, foveal and parafoveal cone densities derived from confocal AOSLO images were significantly lower in Usher syndrome compared with RP. This was due in large part to an increased prevalence of non-waveguiding cones in the Usher syndrome retina. Although significantly correlated to best-corrected visual acuity and foveal sensitivity, cone density can decrease by nearly 38% before visual acuity becomes abnormal. Aberrantly waveguiding cones were noted within the transition zone of all eyes and corresponded to intact inner segment structures. These remnant cones decreased in density and increased in diameter across the transition zone and disappeared with external limiting membrane collapse.

Conclusions

Foveal cone density can be decreased in RP and Usher syndrome before visible changes on OCT or a decline in visual function. Thus, AOSLO imaging may allow more sensitive monitoring of disease than current methods. However, confocal AOSLO is limited by dependence on cone waveguiding, whereas split-detector AOSLO offers unambiguous and quantifiable visualization of remnant cone inner segment structure. Confocal and split-detector thus offer complementary insights into retinal pathology.

Cone Photoreceptor Structure in Patients With X-Linked Cone Dysfunction and Red-Green Color Vision Deficiency

Purpose

Mutations in the coding sequence of the L and M opsin genes are often associated with X-linked cone dysfunction (such as Bornholm Eye Disease, BED), though the exact color vision phenotype associated with these disorders is variable. We examined individuals with L/M opsin gene mutations to clarify the link between color vision deficiency and cone dysfunction.

Methods

We recruited 17 males for imaging. The thickness and integrity of the photoreceptor layers were evaluated using spectral-domain optical coherence tomography. Cone density was measured using high-resolution images of the cone mosaic obtained with adaptive optics scanning light ophthalmoscopy. The L/M opsin gene array was characterized in 16 subjects, including at least one subject from each family.

Results

There were six subjects with the LVAVA haplotype encoded by exon 3, seven with LIAVA, two with the Cys203Arg mutation encoded by exon 4, and two with a novel insertion in exon 2. Foveal cone structure and retinal thickness was disrupted to a variable degree, even among related individuals with the same L/M array.

Conclusions

Our findings provide a direct link between disruption of the cone mosaic and L/M opsin variants. We hypothesize that, in addition to large phenotypic differences between different L/M opsin variants, the ratio of expression of first versus downstream genes in the L/M array contributes to phenotypic diversity. While the L/M opsin mutations underlie the cone dysfunction in all of the subjects tested, the color vision defect can be caused either by the same mutation or a gene rearrangement at the same locus.

Photoreceptor-Based Biomarkers in AOSLO Retinal Imaging

Improved understanding of the mechanisms underlying inherited retinal degenerations has created the possibility of developing much needed treatments for these relentless, blinding diseases. However, standard clinical indicators of retinal health (such as visual acuity and visual field sensitivity) are insensitive measures of photoreceptor survival. In many retinal degenerations, significant photoreceptor loss must occur before measurable differences in visual function are observed. Thus, there is a recognized need for more sensitive outcome measures to assess therapeutic efficacy as numerous clinical trials are getting underway. Adaptive optics (AO) retinal imaging techniques correct for the monochromatic aberrations of the eye and can be used to provide nearly diffraction-limited images of the retina. Many groups routinely are using AO imaging tools to obtain in vivo images of the rod and cone photoreceptor mosaic, and it now is possible to monitor photoreceptor structure over time with single cell resolution. Highlighting recent work using AO scanning light ophthalmoscopy (AOSLO) across a range of patient populations, we review the development of photoreceptor-based metrics (e.g., density/geometry, reflectivity, and size) as candidate biomarkers. Going forward, there is a need for further development of automated tools and normative databases, with the latter facilitating the comparison of data sets across research groups and devices. Ongoing and future clinical trials for inherited retinal diseases will benefit from the improved resolution and sensitivity that multimodal AO retinal imaging affords to evaluate safety and efficacy of emerging therapies.

Dysflective cones: Visual function and cone reflectivity in long-term follow-up of acute bilateral foveolitis

Purpose

Confocal adaptive optics scanning laser ophthalmoscope (AOSLO) images provide a sensitive measure of cone structure. However, the relationship between structural findings of diminished cone reflectivity and visual function is unclear. We used fundus-referenced testing to evaluate visual function in regions of apparent cone loss identified using confocal AOSLO images.

Methods

A patient diagnosed with acute bilateral foveolitis had spectral-domain optical coherence tomography (SD-OCT) (Spectralis HRA + OCT system [Heidelberg Engineering, Vista, CA, USA]) images indicating focal loss of the inner segment-outer segment junction band with an intact, but hyper-reflective, external limiting membrane. Five years after symptom onset, visual acuity had improved from 20/80 to 20/25, but the retinal appearance remained unchanged compared to 3 months after symptoms began. We performed structural assessments using SD-OCT, directional OCT (non-standard use of a prototype on loan from Carl Zeiss Meditec) and AOSLO (custom-built system). We also administered fundus-referenced functional tests in the region of apparent cone loss, including analysis of preferred retinal locus (PRL), AOSLO acuity, and microperimetry with tracking SLO (TSLO) (prototype system). To determine AOSLO-corrected visual acuity, the scanning laser was modulated with a tumbling E consistent with 20/30 visual acuity. Visual sensitivity was assessed in and around the lesion using TSLO microperimetry. Complete eye examination, including standard measures of best-corrected visual acuity, visual field tests, color fundus photos, and fundus auto-fluorescence were also performed.

Results

Despite a lack of visible cone profiles in the foveal lesion, fundus-referenced vision testing demonstrated visual function within the lesion consistent with cone function. The PRL was within the lesion of apparent cone loss at the fovea. AOSLO visual acuity tests were abnormal, but measurable: for trials in which the stimulus remained completely within the lesion, the subject got 48% correct, compared to 78% correct when the stimulus was outside the lesion. TSLO microperimetry revealed reduced, but detectible, sensitivity thresholds within the lesion.

Conclusions and importance

Fundus-referenced visual testing proved useful to identify functional cones despite apparent photoreceptor loss identified using AOSLO and SD-OCT. While AOSLO and SD-OCT appear to be sensitive for the detection of abnormal or absent photoreceptors, changes in photoreceptors that are identified with these imaging tools do not correlate completely with visual function in every patient. Fundus-referenced vision testing is a useful tool to indicate the presence of cones that may be amenable to recovery or response to experimental therapies despite not being visible on confocal AOSLO or SD-OCT images.

Adaptive Optics Reveals Photoreceptor Abnormalities in Diabetic Macular Ischemia

Diabetic macular ischemia (DMI) is a phenotype of diabetic retinopathy (DR) associated with chronic hypoxia of retinal tissue. The goal of this prospective observational study was to report evidence of photoreceptor abnormalities using adaptive optics scanning laser ophthalmoscopy (AOSLO) in eyes with DR in the setting of deep capillary plexus (DCP) non-perfusion. Eleven eyes from 11 patients (6 women, age 31-68), diagnosed with DR without macular edema, underwent optical coherence tomography angiography (OCTA) and AOSLO imaging. One patient without OCTA imaging underwent fluorescein angiography to characterize the enlargement of the foveal avascular zone. The parameters studied included photoreceptor heterogeneity packing index (HPi) on AOSLO, as well as DCP non-perfusion and vessel density on OCTA. Using AOSLO, OCTA and spectral domain (SD)-OCT, we observed that photoreceptor abnormalities on AOSLO and SD-OCT were found in eyes with non-perfusion of the DCP on OCTA. All eight eyes with DCP non-flow on OCTA showed photoreceptor abnormalities on AOSLO. Six of the eight eyes also had outer retinal abnormalities on SD-OCT. Three eyes with DR and robust capillary perfusion of the DCP had normal photoreceptors on SD-OCT and AOSLO. Compared to eyes with DR without DCP non-flow, the eight eyes with DCP non-flow had significantly lower HPi (P = 0.013) and parafoveal DCP vessel density (P = 0.016). We found a significant correlation between cone HPi and parafoveal DCP vessel density (r = 0.681, P = 0.030). Using a novel approach with AOSLO and OCTA, this study shows an association between capillary non-perfusion of the DCP and abnormalities in the photoreceptor layer in eyes with DR. This observation is important in confirming the significant contribution of the DCP to oxygen requirements of photoreceptors in DMI, while highlighting the ability of AOSLO to detect subtle photoreceptor changes not always visible on SD-OCT.

Acute Macular Neuroretinopathy Following Non-Ocular Trauma: A Hypothesis Regarding Pathophysiologic Mechanism

BACKGROUND AND OBJECTIVE

To describe the imaging characteristics and clinical course of acute macular neuroretinopathy (AMN) following non-ocular trauma, and to hypothesize a pathophysiologic mechanism for this syndrome.

PATIENTS AND METHODS

The records of five patients who developed symptoms and findings suggestive of AMN following trauma to the face or chest were retrospectively reviewed. Optical coherence tomography (OCT), infrared reflectance, fundus autofluorescence, fluorescein and indocyanine green angiography, and multifocal electroretinography were evaluated.

RESULTS

Visual symptoms started immediately or very soon after non-ocular trauma, and scotomas persisted at last follow-up (2 weeks to 10 years after trauma). OCT imaging performed within days of the trauma demonstrated focal areas of hyper-reflectivity in the outer plexiform and outer nuclear layers with eventual thinning of the outer nuclear layer, as well as variable loss of the ellipsoid and interdigitation zones.

CONCLUSION

Acute ischemic injury caused by trauma-induced hypotension and/or catecholamine release and involving the deep retinal capillary plexus is the pathogenic mechanism that most plausibly explains trauma-associated AMN.

Variation in rod and cone density from the fovea to the mid-periphery in healthy human retinas using adaptive optics scanning laser ophthalmoscopy

PurposeTo characterize the rod and cone photoreceptor mosaic at retinal locations spanning the central 60° in vivo using adaptive optics scanning laser ophthalmoscopy (AO-SLO) in healthy human eyes.MethodsAO-SLO images (0.7 × 0.9°) were acquired at 680 nm from 14 locations from 30° nasal retina (NR) to 30° temporal retina (TR) in 5 subjects. Registered averaged images were used to measure rod and cone density and spacing within 60 × 60 μm regions of interest. Voronoi analysis was performed to examine packing geometry at all locations.ResultsAverage peak cone density near the fovea was 164 000±24 000 cones/mm(2) and decreased to 6700±1500 and 5400±700 cones/mm(2) at 30° NR and 30° TR, respectively. Cone-to-cone spacing increased from 2.7±0.2 μm at the fovea to 14.6±1.4 μm at 30° NR and 16.3±0.7 μm at 30° TR. Rod density peaked at 25° NR (124 000±20 000 rods/mm(2)) and 20° TR (120 000±12 000 rods/mm(2)) and decreased at higher eccentricities. Center-to-center rod spacing was lowest nasally at 25° (2.1±0.1 μm). Temporally, rod spacing was lowest at 20° (2.2±0.1 μm) before increasing to 2.3±0.1 μm at 30° TR.ConclusionsBoth rod and cone densities showed good agreement with histology and prior AO-SLO studies. The results demonstrate the ability to image at higher retinal eccentricities than reported previously. This has clinical importance in diseases that initially affect the peripheral retina such as retinitis pigmentosa.

Quantification of retinal layer thickness changes in acute macular neuroretinopathy

Purpose

To quantitatively evaluate retinal layer thickness changes in acute macular neuroretinopathy (AMN).

Methods

AMN areas were identified using near-infrared reflectance (NIR) images. Intraretinal layer segmentation using Heidelberg software was performed. The inbuilt ETDRS -grid was moved onto the AMN lesion and the mean retinal layer thicknesses of the central grid were recorded and compared with the corresponding area of the fellow eye at initial presentation and during follow-up.

Results

Eleven patients were included (mean age 26±6 years). AMN lesions at baseline had a significantly thinner outer nuclear layer (ONL) (51±21 µm vs 73±17 µm, p=0.002). The other layers, including inner nuclear layer (37±8 µm vs 38±6 µm, p=0.9) and outer plexiform layer (OPL) (45±19 µm vs 33±16 µm, p=0.1) did not show significant differences between the study eyes and fellow eyes. Adjacent to NIR image lesions, areas of OPL thickening were identified (study eye: 50±14 µm vs fellow eye: 39±16 µm, p=0.005) with corresponding thinning of ONL (study eye: 52±16 µm vs fellow eye: 69±16 µm, p=0.002).

Conclusions

AMN presents with characteristic quantitative retinal changes and the extent of the lesion may be more extensive than initially presumed from NIR image lesions.

The fundus photo has met its match: optical coherence tomography and adaptive optics ophthalmoscopy are here to stay

PURPOSE

Over the past 25 years, optical coherence tomography (OCT) and adaptive optics (AO) ophthalmoscopy have revolutionised our ability to non-invasively observe the living retina. The purpose of this review is to highlight the techniques and human clinical applications of recent advances in OCT and adaptive optics scanning laser/light ophthalmoscopy (AOSLO) ophthalmic imaging.

RECENT FINDINGS

Optical coherence tomography retinal and optic nerve head (ONH) imaging technology allows high resolution in the axial direction resulting in cross-sectional visualisation of retinal and ONH lamination. Complementary AO ophthalmoscopy gives high resolution in the transverse direction resulting in en face visualisation of retinal cell mosaics. Innovative detection schemes applied to OCT and AOSLO technologies (such as spectral domain OCT, OCT angiography, confocal and non-confocal AOSLO, fluorescence, and AO-OCT) have enabled high contrast between retinal and ONH structures in three dimensions and have allowed in vivo retinal imaging to approach that of histological quality. In addition, both OCT and AOSLO have shown the capability to detect retinal reflectance changes in response to visual stimuli, paving the way for future studies to investigate objective biomarkers of visual function at the cellular level. Increasingly, these imaging techniques are being applied to clinical studies of the normal and diseased visual system.

SUMMARY

Optical coherence tomography and AOSLO technologies are capable of elucidating the structure and function of the retina and ONH noninvasively with unprecedented resolution and contrast. The techniques have proven their worth in both basic science and clinical applications and each will continue to be utilised in future studies for many years to come.

[Adaptive optics for ophthalmology]

Adaptive optics is a technology enhancing the visual performance of an optical system by correcting its optical aberrations. Adaptive optics have already enabled several breakthroughs in the field of visual sciences, such as improvement of visual acuity in normal and diseased eyes beyond physiologic limits, and the correction of presbyopia. Adaptive optics technology also provides high-resolution, in vivo imaging of the retina that may eventually help to detect the onset of retinal conditions at an early stage and provide better assessment of treatment efficacy.

Parafoveal cone abnormalities and recovery on adaptive optics in posterior uveitis

Purpose

To determine if adaptive optics (AO) flood illumination imaging can detect subclinical changes in 4 cases of posterior uveitis affecting the outer retina.

Observations

In all 4 cases, the affected eye showed altered areas in the photoreceptor mosaic on AO that corresponded to changes on other imaging modalities. Abnormalities not apparent on other imaging modalities were also noted. In one case of multifocal choroiditis with acute outer retinal atrophy, AO revealed decreased visualization of photoreceptors in the unaffected eye that was not noted on spectral domain-optical coherence tomography. In the patient with multiple evanescent white dot syndrome, focal photoreceptor abnormalities were more apparent on AO compared to other imaging modalities, and these areas normalized on AO during follow-up. Five weeks after initiation of high dose prednisone and azathioprine in a patient with serpiginous choroidopathy, AO images showed recovery in apparent parafoveal cone density.

Conclusions and importance

AO detects subclinical changes in the photoreceptor layer in posterior uveitis that can recover over time. AO may be useful in following outer retinal inflammatory conditions.

Assessment of Different Sampling Methods for Measuring and Representing Macular Cone Density Using Flood-Illuminated Adaptive Optics

PURPOSE

To describe a standardized flood-illuminated adaptive optics (AO) imaging protocol suitable for the clinical setting and to assess sampling methods for measuring cone density.

METHODS

Cone density was calculated following three measurement protocols: 50 × 50-μm sampling window values every 0.5° along the horizontal and vertical meridians (fixed-interval method), the mean density of expanding 0.5°-wide arcuate areas in the nasal, temporal, superior, and inferior quadrants (arcuate mean method), and the peak cone density of a 50 × 50-μm sampling window within expanding arcuate areas near the meridian (peak density method). Repeated imaging was performed in nine subjects to determine intersession repeatability of cone density.

RESULTS

Cone density montages could be created for 67 of the 74 subjects. Image quality was determined to be adequate for automated cone counting for 35 (52%) of the 67 subjects. We found that cone density varied with different sampling methods and regions tested. In the nasal and temporal quadrants, peak density most closely resembled histological data, whereas the arcuate mean and fixed-interval methods tended to underestimate the density compared with histological data. However, in the inferior and superior quadrants, arcuate mean and fixed-interval methods most closely matched histological data, whereas the peak density method overestimated cone density compared with histological data. Intersession repeatability testing showed that repeatability was greatest when sampling by arcuate mean and lowest when sampling by fixed interval.

CONCLUSIONS

We show that different methods of sampling can significantly affect cone density measurements. Therefore, care must be taken when interpreting cone density results, even in a normal population.

Assessment of parafoveal cone density in patients taking hydroxychloroquine in the absence of clinically documented retinal toxicity

PURPOSE

To measure cone density in patients taking hydroxychloroquine (HCQ), with no clinical evidence of maculopathy.

METHODS

Patients visiting for HCQ macular toxicity screening in the Besançon University Hospital Ophthalmology Department (France) were studied. They underwent routine examination including spectral-domain optical coherence tomography, fundus autofluorescence and multifocal electroretinogram to detect HCQ-induced retinal toxicity. Cone metrics (density, spacing and percentage of cones with six neighbours) were obtained using an adaptive optics camera (RTX1, Imagine Eyes, Orsay, France). The region of interest corresponded to a 0.3° × 0.3° square placed nasally and temporally at 2° of eccentricity from the fovea.

RESULTS

Forty eyes of 23 patients were studied. The majority of the patients (21/23) were female. They were aged from 25 to 60 years (mean age ± SD: 40.1 years ± 10). The cumulative dose for HCQ ranged from 24 to 2160 g (777 ± 558 g). None of them displayed HCQ toxicity on screening tests. Bivariate analysis showed moderate cone loss with escalating doses of HCQ (linear regression, r² = 0.23, p = 0.018). Cone spacing also increased with increasing cumulative dose (r² = 0.17, p = 0.008). Cone packing remained unchanged (p > 0.05). Multivariate analysis showed that age and cumulative dose were additive and independent factors of cone dropout.

CONCLUSIONS

In this pilot study, we observed moderate cone loss as HCQ cumulative doses increased. The early detection of parafoveal cone metric changes may represent the earliest sign of HCQ macular toxicity during screening.

Functional and high-resolution retinal imaging monitoring photoreceptor damage in acute macular neuroretinopathy

BACKGROUND

To report functional and high-resolution retinal imaging abnormalities, including adaptive optics (AO) throughout the course of acute macular neuroretinopathy (AMNR).

METHODS

Two female patients (four eyes) with a diagnosis of AMNR were observed at the Clinical Investigation Center, CHNO des Quinze-Vingts, Paris, France. The patients underwent detailed ophthalmic examination including best-corrected visual acuity, slit-lamp examination, kinetic and static perimetry, full-field and multifocal electroretinogram, infrared reflectance, autofluorescence imaging and spectral-domain optical coherence tomography (SD-OCT) and AO fundus imaging at presentation and during follow-up.

RESULTS

Both cases showed concomitant loss of integrity of the outer retinal structures on SD-OCT, and marked abnormalities on AO imaging with disruption of the visibility of the cone mosaic. In the first case, photoreceptor damage was seen to progress during several weeks before healing. In both cases, there were persistent morphological abnormalities of photoreceptors 1 year after onset.

CONCLUSION

This study further highlights the value of AO fundus imaging to facilitate detection, mapping, and monitoring of damage to the cone outer segments during AMNR. In particular, residual damage to the cone mosaic can be precisely documented.

Normal Perceptual Sensitivity Arising From Weakly Reflective Cone Photoreceptors

PURPOSE

To determine the light sensitivity of poorly reflective cones observed in retinas of normal subjects, and to establish a relationship between cone reflectivity and perceptual threshold.

METHODS

Five subjects (four male, one female) with normal vision were imaged longitudinally (7-26 imaging sessions, representing 82-896 days) using adaptive optics scanning laser ophthalmoscopy (AOSLO) to monitor cone reflectance. Ten cones with unusually low reflectivity, as well as 10 normally reflective cones serving as controls, were targeted for perceptual testing. Cone-sized stimuli were delivered to the targeted cones and luminance increment thresholds were quantified. Thresholds were measured three to five times per session for each cone in the 10 pairs, all located 2.2 to 3.3° from the center of gaze.

RESULTS

Compared with other cones in the same retinal area, three of 10 monitored dark cones were persistently poorly reflective, while seven occasionally manifested normal reflectance. Tested psychophysically, all 10 dark cones had thresholds comparable with those from normally reflecting cones measured concurrently (P = 0.49). The variation observed in dark cone thresholds also matched the wide variation seen in a large population (n = 56 cone pairs, six subjects) of normal cones; in the latter, no correlation was found between cone reflectivity and threshold (P = 0.0502).

CONCLUSIONS

Low cone reflectance cannot be used as a reliable indicator of cone sensitivity to light in normal retinas. To improve assessment of early retinal pathology, other diagnostic criteria should be employed along with imaging and cone-based microperimetry.

Adaptive optics imaging of cone mosaic abnormalities in acute macular neuroretinopathy

BACKGROUND AND OBJECTIVE

To assess the cone photoreceptor mosaic in acute macular neuroretinopathy (AMN) using adaptive optics (AO) imaging.

PATIENTS AND METHODS

Four patients with AMN were evaluated retrospectively by near-infrared reflectance (IR) confocal scanning laser ophthalmoscopy (SLO), spectral-domain optical coherence tomography (SD-OCT), and a flood-illuminated retinal AO camera. Microperimetry was performed in one patient.

RESULTS

The cone photoreceptor density was decreased at the level of the AMN lesions. The cone mosaic disruption appeared heterogeneous and more widespread than the lesion detected in the IR-SLO and SD-OCT images. The areas of cone loss correlated with SD-OCT and microperimetry. After resolution of the AMN lesion on IR-SLO, there was incomplete recovery of the cone photoreceptor mosaic.

CONCLUSION

Cone photoreceptor damage and reconstitution were documented in vivo at the cellular level in AMN using AO imaging. AO imaging appeared more sensitive than combined IR-SLO and SD-OCT to detect and follow photoreceptor damage in patients with AMN.

Outer retinal structure after closed-globe blunt ocular trauma

PURPOSE

To evaluate outer retinal structural abnormalities in patients with visual deficits after closed-globe blunt ocular trauma.

METHODS

Nine subjects with visual complaints after closed-globe blunt ocular trauma were examined between 1 month after trauma and 6 years after trauma. Spectral domain optical coherence tomography was used to assess the outer retinal architecture, whereas adaptive optics scanning light ophthalmoscopy was used to analyze the photoreceptor mosaic integrity.

RESULTS

Visual deficits ranged from central scotomas to decreased visual acuity. Spectral domain optical coherence tomography defects included focal foveal photoreceptor lesions, variable attenuation of the interdigitation zone, and mottling of the outer segment band, with one subject having normal outer retinal structure. Adaptive optics scanning light ophthalmoscopy revealed disruption of the photoreceptor mosaic in all subjects, variably manifesting as foveal focal discontinuities, perifoveal hyporeflective cones, and paracentral regions of selective cone loss.

CONCLUSION

We observe persistent outer retinal disruption in subjects with visual complaints after closed-globe blunt ocular trauma, albeit to a variable degree. Adaptive optics scanning light ophthalmoscopy imaging allows the assessment of photoreceptor structure at a level of detail not resolvable using spectral domain optical coherence tomography or other current clinical imaging tools. Multimodal imaging seems to be useful in revealing the cause of visual complaints in patients after closed-globe blunt ocular trauma. Future studies are needed to better understand how photoreceptor structure changes longitudinally in response to various traumas.

Assessing photoreceptor structure after macular hole closure

PURPOSE

To describe photoreceptor structure and recovery after macular hole (MH) closure with pars plana vitrectomy (PPV) using adaptive optics scanning light ophthalmoscopy and spectral domain optical coherence tomography.

METHODS

A pilot imaging study of four eyes from four subjects undergoing PPV for MH was conducted. Imaging with spectral domain optical coherence tomography and adaptive optics scanning light ophthalmoscopy was performed at varying time points after PPV.

RESULTS

Despite successful MH closure, disruption of the foveal inner segment ellipsoid zone was seen in all patients when imaged at a mean of 117 days after PPV. Disruption of the photoreceptor mosaic was seen using adaptive optics scanning light ophthalmoscopy at locations corresponding to regions of ellipsoid zone disruption on spectral domain optical coherence tomography. Cone density immediately surrounding these disruptions was normal, except for one patient. In 2 patients who were imaged serially up to 516 days after PPV, recovery of cone cells within regions of mosaic disruption could be detected over time.

CONCLUSION

Photoreceptor disruption exists even after apparent MH closure. Remodeling of the foveal cone mosaic continues for many months after surgery, perhaps accounting for the delayed postoperative improvements of visual acuity in some patients. Spectral domain optical coherence tomography and adaptive optics scanning light ophthalmoscopy are useful tools for monitoring photoreceptor recovery after surgical closure of MH.

Genotype-dependent variability in residual cone structure in achromatopsia: toward developing metrics for assessing cone health

PURPOSE

Gene therapy trials for inherited photoreceptor disorders are planned. Anatomical metrics to select the best candidates and outcomes are needed. Adaptive optics (AO) imaging enables visualization of photoreceptor structure, although analytical tools are lacking. Here we present criteria to assess residual photoreceptor integrity in achromatopsia (ACHM).

METHODS

Two AOSLOs, at the Medical College of Wisconsin and Moorfields Eye Hospital, were used to image the photoreceptor mosaic of 11 subjects with ACHM and 7 age-matched controls. Images were obtained, processed, and montaged using previously described methods. Cone density and reflectivity were quantified to assess residual cone photoreceptor structure.

RESULTS

All subjects with ACHM had reduced numbers of cone photoreceptors, albeit to a variable degree. In addition, the relative cone reflectivity varied greatly. Interestingly, subjects with GNAT2-associated ACHM had the greatest number of residual cones and the reflectivity of those cones was significantly greater than that of the cones in the subjects with CNGA3/CNGB3-associated ACHM.

CONCLUSIONS

We present cone reflectivity as a metric that can be used to characterize cone structure in ACHM. This method may be applicable to subjects with other cone disorders. In ACHM, we hypothesize that cone numerosity (and/or density) combined with cone reflectivity could be used to gauge the therapeutic potential. As gene replacement would not be expected to add cones, reflectivity could be a more powerful AO-metric for monitoring the cellular response to treatment and could provide a more immediate indicator of efficacy than behavioral measures, which may take longer to change.

Microscopic inner retinal hyper-reflective phenotypes in retinal and neurologic disease

PURPOSE

We surveyed inner retinal microscopic features in retinal and neurologic disease using a reflectance confocal adaptive optics scanning light ophthalmoscope (AOSLO).

METHODS

Inner retinal images from 101 subjects affected by one of 38 retinal or neurologic conditions and 11 subjects with no known eye disease were examined for the presence of hyper-reflective features other than vasculature, retinal nerve fiber layer, and foveal pit reflex. The hyper-reflective features in the AOSLO images were grouped based on size, location, and subjective texture. Clinical imaging, including optical coherence tomography (OCT), scanning laser ophthalmoscopy, and fundus photography was analyzed for comparison.

RESULTS

Seven categories of hyper-reflective inner retinal structures were identified, namely punctate reflectivity, nummular (disc-shaped) reflectivity, granular membrane, waxy membrane, vessel-associated membrane, microcysts, and striate reflectivity. Punctate and nummular reflectivity also was found commonly in normal volunteers, but the features in the remaining five categories were found only in subjects with retinal or neurologic disease. Some of the features were found to change substantially between follow up imaging months apart.

CONCLUSIONS

Confocal reflectance AOSLO imaging revealed a diverse spectrum of normal and pathologic hyper-reflective inner and epiretinal features, some of which were previously unreported. Notably, these features were not disease-specific, suggesting that they might correspond to common mechanisms of degeneration or repair in pathologic states. Although prospective studies with larger and better characterized populations, along with imaging of more extensive retinal areas are needed, the hyper-reflective structures reported here could be used as disease biomarkers, provided their specificity is studied further.

Adaptive optics retinal imaging--clinical opportunities and challenges

The array of therapeutic options available to clinicians for treating retinal disease is expanding. With these advances comes the need for better understanding of the etiology of these diseases on a cellular level as well as improved non-invasive tools for identifying the best candidates for given therapies and monitoring the efficacy of those therapies. While spectral domain optical coherence tomography offers a widely available tool for clinicians to assay the living retina, it suffers from poor lateral resolution due to the eye's monochromatic aberrations. Ophthalmic adaptive optics (AO) is a technique to compensate for the eye's aberrations and provide nearly diffraction-limited resolution. The result is the ability to visualize the living retina with cellular resolution. While AO is unquestionably a powerful research tool, many clinicians remain undecided on the clinical potential of AO imaging - putting many at a crossroads with respect to adoption of this technology. This review will briefly summarize the current state of AO retinal imaging, discuss current as well as future clinical applications of AO retinal imaging, and finally provide some discussion of research needs to facilitate more widespread clinical use.

Automatic detection of modal spacing (Yellott's ring) in adaptive optics scanning light ophthalmoscope images

Purpose An impediment for the clinical utilisation of ophthalmic adaptive optics imaging systems is the automated assessment of photoreceptor mosaic integrity. Here we propose a fully automated algorithm for estimating photoreceptor density based on the radius of Yellott's ring.

Methods The discrete Fourier transform (DFT) was used to obtain the power spectrum for a series of images of the human photoreceptor mosaic. Cell spacing is estimated by least-square fitting an annular pattern with a Gaussian cross section to the power spectrum; the radius of the resulting annulus provides an estimate of the modal spacing of the photoreceptors in the retinal image. The intrasession repeatability of the cone density estimates from the algorithm was evaluated, and the accuracy of the algorithm was validated against direct count estimates from a previous study. Accuracy in the presence of multiple cell types and disruptions in the mosaic was examined using images from four patients with retinal pathology and perifoveal images from two subjects with normal vision.

Results Intrasession repeatability of the power spectrum method was comparable to a fully automated direct counting algorithm, but worse than that for the manually adjusted direct count values. In images of the normal parafoveal cone mosaic, we find good agreement between the power-spectrum derived density and that from the direct counting algorithm. In diseased eyes, the power spectrum method is insensitive to photoreceptor loss, with cone density estimates overestimating the density determined with direct counting. The automated power spectrum method also produced unreliable estimates of rod and cone density in perifoveal images of the photoreceptor mosaic, though manual correction of the initial algorithm output results in density estimates in better agreement with direct count values.

Conclusions We developed and validated an automated algorithm based on the power spectrum for extracting estimates of cone spacing, from which estimates of density can be derived. This approach may be used to estimate cone density in images where not every single cone is visible, though caution is needed, as this robustness becomes a weakness when dealing with images from patients with some retinal diseases. This study represents an important first step in carefully assessing the relative utility of metrics for analysing the photoreceptor mosaic, and similar analyses of other metrics/algorithms are needed.