Imaging Glaucomatous Damage Across the Temporal Raphe

Ganglion Cell Complex Analysis: Correlations with Retinal Nerve Fiber Layer on Optical Coherence Tomography

The aim of this review is to analyze the correlations between the changes in the ganglion cell complex (GCC) and the retinal nerve fiber layer (RNFL) on optical coherence tomography in different possible situations, especially in eyes with glaucoma. For glaucoma evaluation, several studies have suggested that in the early stages, GCC analysis, especially the thickness of the infero and that of the inferotemporal GCC layers, is a more sensitive examination than circumpapillary RNFL (pRNFL). In the moderate stages of glaucoma, inferior pRNFL thinning is better correlated with the disease than in advanced cases. Another strategy for glaucoma detection is to find any asymmetry of the ganglion cell-inner plexiform layers (GCIPL) between the two macular hemifields, because this finding is a valuable indicator for preperimetric glaucoma, better than the RNFL thickness or the absolute thickness parameters of GCIPL. In preperimetric and suspected glaucoma, GCC and pRNFL have better specificity and are superior to the visual field. In advanced stages, pRNFL and later, GCC reach the floor effect. Therefore, in this stage, it is more useful to evaluate the visual field for monitoring the progression of glaucoma. In conclusion, GCC and pRNFL are parameters that can be used for glaucoma diagnosis and monitoring of the progression of the disease, with each having a higher accuracy depending on the stage of the disease.

High sampling resolution optical coherence tomography reveals potential concurrent reductions in ganglion cell-inner plexiform and inner nuclear layer thickness but not in outer retinal thickness in glaucoma

PURPOSE

To analyse optical coherence tomography (OCT)-derived inner nuclear layer (INL) and outer retinal complex (ORC) measurements relative to ganglion cell-inner plexiform layer (GCIPL) measurements in glaucoma.

METHODS

Glaucoma participants (n = 271) were categorised by 10-2 visual field defect type. Differences in GCIPL, INL and ORC thickness were calculated between glaucoma and matched healthy eyes (n = 548). Hierarchical cluster algorithms were applied to generate topographic patterns of retinal thickness change, with agreement between layers assessed using Cohen's kappa (κ). Differences in GCIPL, INL and ORC thickness within and outside GCIPL regions showing the greatest reductions and Spearman's correlations between layer pairs were compared with 10-2 mean deviation (MD) and pattern standard deviation (PSD) to determine trends with glaucoma severity.

RESULTS

Glaucoma participants with inferior and superior defects presented with concordant GCIPL and INL defects demonstrating mostly fair-to-moderate agreement (κ = 0.145-0.540), which was not observed in eyes with no or ring defects (κ = -0.067-0.230). Correlations (r) with MD and PSD were moderate and weak in GCIPL and INL thickness differences, respectively (GCIPL vs. MD r = 0.479, GCIPL vs. PSD r = -0.583, INL vs. MD r = 0.259, INL vs. PSD r = -0.187, p = <0.0001-0.002), and weak in GCIPL-INL correlations (MD r = 0.175, p = 0.004 and PSD r = 0.154, p = 0.01). No consistent patterns in ORC thickness or correlations were observed.

CONCLUSIONS

In glaucoma, concordant reductions in macular INL and GCIPL thickness can be observed, but reductions in ORC thickness appear unlikely. These findings suggest that trans-synaptic retrograde degeneration may occur in glaucoma and could indicate the usefulness of INL thickness in evaluating glaucomatous damage.

Twenty-five years of clinical applications using adaptive optics ophthalmoscopy [Invited]

Twenty-five years ago, adaptive optics (AO) was combined with fundus photography, thereby initiating a new era in the field of ophthalmic imaging. Since that time, clinical applications of AO ophthalmoscopy to investigate visual system structure and function in both health and disease abound. To date, AO ophthalmoscopy has enabled visualization of most cell types in the retina, offered insight into retinal and systemic disease pathogenesis, and been integrated into clinical trials. This article reviews clinical applications of AO ophthalmoscopy and addresses remaining challenges for AO ophthalmoscopy to become fully integrated into standard ophthalmic care.

Imaging of vitreous cortex hyalocyte dynamics using non-confocal quadrant-detection adaptive optics scanning light ophthalmoscopy in human subjects

Vitreous cortex hyalocytes are resident macrophage cells that help maintain the transparency of the media, provide immunosurveillance, and respond to tissue injury and inflammation. In this study, we demonstrate the use of non-confocal quadrant-detection adaptive optics scanning light ophthalmoscopy (AOSLO) to non-invasively visualize the movement and morphological changes of the hyalocyte cell bodies and processes over 1-2 hour periods in the living human eye. The average velocity of the cells 0.52 ± 0.76 µm/min when sampled every 5 minutes and 0.23 ± 0.29 µm/min when sampled every 30 minutes, suggesting that the hyalocytes move in quick bursts. Understanding the behavior of these cells under normal physiological conditions may lead to their use as biomarkers or suitable targets for therapy in eye diseases such as diabetic retinopathy, preretinal fibrosis and glaucoma.

Cell - Vessel Mismatch in Glaucoma: Correlation of Ganglion Cell Layer Soma and Capillary Densities

Purpose

The purpose of this study was to characterize the relationship between retinal ganglion cell layer (GCL) soma density and capillary density in glaucomatous eyes.

Methods

Six glaucoma subjects with known hemifield defects and 6 age-matched controls were imaged with adaptive optics - optical coherence tomography (AO-OCT) at 6 locations: 3 degrees, 6 degrees, and 12 degrees temporal to the fovea above and below the midline. GCL soma density and capillary density were measured at each location. Coefficients of determination (pseudo R2) and slopes between GCL soma and capillary density were determined from mixed-effects regressions and were compared between glaucoma and control subjects, between more and less affected hemifield in subjects with glaucoma, and between subjects with early and moderate glaucoma, both in a local, bivariate model and then a global, multivariable model controlling for eccentricity and soma size.

Results

The global correlation between GCL soma and capillary density was stronger in control versus subjects with glaucoma (R2 = 0.59 vs. 0.22), less versus more affected hemifields (R2 = 0.55 vs. 0.01), and subjects with early versus moderate glaucoma subjects (R2 = 0.44 vs. 0.18). When controlling for eccentricity and soma size, we noted an inverse soma-capillary density local relationship in subjects with glaucoma (-388 ± 190 cells/mm2 per 1% change in capillary density, P = 0.046) and more affected hemifields (-602 ± 257 cells/mm2 per 1% change in capillary density, P = 0.03).

Conclusions

An inverted soma-capillary density local relationship in areas affected by glaucoma potentially explains weaker global correlations observed between GCL soma and capillary density, suggesting cell-vessel mismatch is associated with the disease.

Quantification of Retinal Ganglion Cell Morphology in Human Glaucomatous Eyes

Purpose

To characterize retinal ganglion cell morphological changes in patients with primary open-angle glaucoma associated with hemifield defect (HD) using adaptive optics–optical coherence tomography (AO-OCT).

Methods

Six patients with early to moderate primary open-angle glaucoma with an average age of 58 years associated with HD and six age-matched healthy controls with an average age of 61 years were included. All participants underwent in vivo retinal ganglion cell (RGC) imaging at six primary locations across the macula with AO-OCT. Ganglion cell layer (GCL) somas were manually counted, and morphological parameters of GCL soma density, size, and symmetry were calculated. RGC cellular characteristics were correlated with functional visual field measurements.

Results

GCL soma density was 12,799 ± 7747 cells/mm², 9370 ± 5572 cells/mm², and 2134 ± 1494 cells/mm² at 3°, 6°, and 12°, respectively, in glaucoma patients compared with 25,058 ± 4649 cells/mm², 15,551 ± 2301 cells/mm², and 3891 ± 1105 cells/mm² (P < 0.05 for all locations) at the corresponding retinal locations in healthy participants. Mean soma diameter was significantly larger in glaucoma patients (14.20 ± 2.30 µm) compared with the health controls (12.32 ± 1.94 µm, P < 0.05 for all locations); symmetry was 0.36 ± 0.32 and 0.86 ± 0.13 in glaucoma and control cohorts, respectively.

Conclusions

Glaucoma patients had lower GCL soma density and symmetry, greater soma size, and increased variation of GCL soma reflectance compared with age-matched control subjects. The morphological changes corresponded with HD, and the cellular level structural loss correlated with visual function loss in glaucoma. AO-based morphological parameters could be potential sensitive biomarkers for glaucoma.

Improving Personalized Structure to Function Mapping From Optic Nerve Head to Visual Field

Purpose

Maps are required to relate visual field locations to optic nerve head regions. We compare individualized structure-to-function mapping (CUSTOM-MAP) to a population-derived mapping schema (POP-MAP).

Methods

Maps were compared for 118 eyes with glaucomatous field loss, circumpapillary retinal nerve fiber layer (cpRNFL) thickness measured using spectral domain optical coherence tomography (OCT), and two landmarks: the optic nerve head (ONH) position relative to the fovea and the temporal raphe angle. Locations with visual field damage (total deviation < −6 dB) were mapped to 30° ONH sectors centered on the angle given by each mapping schema. The concordance between damaged function and damaged structure was determined per location for various cpRNFL damage probability levels, with the number of concordant locations divided by the total number of damaged field locations providing a concordance ratio per eye.

Results

For the strictest concordance criteria (minimum cpRNFL thickness < 1% of normal), CUSTOM-MAP had higher mean concordance ratio than POP-MAP (60.5% c.f. 57.0% paired Wilcoxon, P = 0.005), with CUSTOM-MAP having a higher ratio in 43 eyes and POP-MAP having a higher ratio in 21 eyes. For all cpRNFL probability levels <20% of normal, more locations concorded for CUSTOM-MAP than POP-MAP. Inspection of the spatial patterns of differences revealed that CUSTOM-MAP often performed better in the arcuate regions, whereas POP-MAP had benefits inferior to the macula.

Conclusions

Anatomic parameters required for individualized structure-function mapping are readily measured with OCT and can provide improved concordance for some eyes.

Translational Relevance

Personalizing structure-function mapping may improve concordance between these measures. We provide a web-based tool for creating customized maps.

Adaptive optics for high-resolution imaging

Adaptive optics (AO) is a technique that corrects for optical aberrations. It was originally proposed to correct for the blurring effect of atmospheric turbulence on images in ground-based telescopes and was instrumental in the work that resulted in the Nobel prize-winning discovery of a supermassive compact object at the centre of our galaxy. When AO is used to correct for the eye's imperfect optics, retinal changes at the cellular level can be detected, allowing us to study the operation of the visual system and to assess ocular health in the microscopic domain. By correcting for sample-induced blur in microscopy, AO has pushed the boundaries of imaging in thick tissue specimens, such as when observing neuronal processes in the brain. In this primer, we focus on the application of AO for high-resolution imaging in astronomy, vision science and microscopy. We begin with an overview of the general principles of AO and its main components, which include methods to measure the aberrations, devices for aberration correction, and how these components are linked in operation. We present results and applications from each field along with reproducibility considerations and limitations. Finally, we discuss future directions.

Geometry of the Retinal Nerve Fibers From Emmetropia Through to High Myopia at Both the Temporal Raphe and Optic Nerve

Purpose

The geometry of retinal nerve fibers may be altered with myopia, a known risk factor for glaucoma. Recent developments in high resolution imaging have enabled direct visualization of nerve fiber bundles at the temporal raphe with clinical hardware, providing evidence that this area is sensitive to glaucomatous damage. Here, we test the hypothesis that nerve fiber geometry is altered by myopia, both at the temporal raphe and surrounding the optic nerve head.

Methods

Seventy-eight healthy individuals participated, with refractive errors distributed between emmetropia and high myopia (+0 to -13 DS). Custom high-density OCT scans were used to visualize RFNL bundle trajectory at the temporal raphe. A standard clinical OCT protocol was used to assess papillary minimum rim width (MRW) and peripapillary retinal nerve fiber layer (RNFL) thickness.

Results

Measures of raphe shape-including position, orientation, and width-did not depend significantly on axial length. In 7.5% of subjects, the raphe was rotated sufficiently that inversion of structure-function mapping to visual field space is predicted in the nasal step region. Low concordance to ISNT and related rules was observed in myopia (e.g., for RNFL, 8% of high axial myopes compared with 67% of emmetropes). Greater robustness to refractive error was observed for the IT rule.

Conclusions

High density OCT scans enabled visualization of marked interindividual variation in temporal raphe geometry; however, these variations were not well predicted by degree of myopia as represented by axial length. That said, degree of myopia was associated with abnormal thickness profiles for the papillary and peripapillary nerve fiber layer.

The Horizontal Raphe of the Human Retina and its Watershed Zones

The horizontal raphe (HR) as a demarcation line dividing the retina and choroid into separate vascular hemispheres is well established, but its development has never been discussed in the context of new findings of the last decades. Although factors for axon guidance are established (e.g., slit-robo pathway, ephrin-protein-receptor pathway) they do not explain HR formation. Early morphological organization, too, fails to establish a HR. The development of the HR is most likely induced by the long posterior ciliary arteries which form a horizontal line prior to retinal organization. The maintenance might then be supported by several biochemical factors. The circulation separate superior and inferior vascular hemispheres communicates across the HR only through their anastomosing capillary beds resulting in watershed zones on either side of the HR. Visual field changes along the HR could clearly be demonstrated in vascular occlusive diseases affecting the optic nerve head, the retina or the choroid. The watershed zone of the HR is ideally protective for central visual acuity in vascular occlusive diseases but can lead to distinct pathological features.

Within-subject variability in human retinal nerve fiber bundle width

With the growing availability of high-resolution imaging there has been increased interest in developing new metrics for integrity of the retinal nerve fiber layer. In particular, it has been suggested that measurement of width of retinal nerve fiber bundles (RNFBs) may be useful in glaucoma, due to low between-subject variability in mean RNFB width. However, there have also been reports of substantial within-subject variability in the width of individual RNFBs. To assess within-subject variability as a potential source of selection bias in measurements of RNFB width, we used an adaptive optics scanning laser ophthalmoscope (AOSLO) to measure widths of individual RNFBs in one eye each of 11 young adults in good ocular health. In a pilot study we analyzed a large AOSLO image of RNFL in one participant then, based on those findings, in the main study we used AOSLO to image a smaller region in 10 additional healthy young adults. The pilot study of one eye found RNFB widths ranging from 10 μm to 44 μm. This suggested that biological variability was too high for measuring small changes arising from disease processes. This was confirmed in measurements of 10 eyes in the main study, RNFB widths ranged from 9 μm to 55 μm and every eye had large within-subject variability (exceeding 19 μm in all eyes) in RNFB width for nearby bundles. The within-subject variability in RNFB width, as well as variation in the width of single RNFBs over relatively short distances (<300 um) depending on the precise location of measurement, suggests that bundle width measurements would be highly susceptible to selection bias and therefore of limited clinical use.

Novel Technique for Quantifying Retinal Nerve Fiber Bundle Abnormality in the Temporal Raphe

SIGNIFICANCE

Glaucomatous nasal visual field abnormalities correspond to damage in the temporal raphe-where individual nerve bundles can be visualized. The ability to quantify structural abnormality in the raphe, with a clinically applicable protocol, sets the stage for investigating the raphe as a potential site for assessing early glaucoma.

PURPOSE

To develop a clinically applicable imaging and analysis technique for identifying retinal nerve fiber bundle abnormalities in the temporal raphe.

METHODS

Spectralis optical coherence tomography scans customized for the temporal raphe were gathered from 30 younger controls, 30 older controls, and 29 patients with glaucoma. An analysis technique was developed based on the reflectance of the nerve fiber bundles. The technique was first developed in the younger controls, and then applied to the older controls to generate normative data for quantifying nerve fiber bundle reflectance abnormalities in the patients with glaucoma. Matrix perimetric data were gathered in the patients with glaucoma to evaluate the reflectance technique's findings. Reflectance abnormality in the patients was defined when the fraction of enface area showing reflectance abnormality was greater than the 95th percentile estimated from controls. Spearman's rho was used to quantify the relation between the total deviation at the perimetric testing locations and the fraction of corresponding enface area showing reflectance abnormality.

RESULTS

Twenty-five of the 29 patients had reflectance abnormalities. Eight of these had mild to no perimetric mean deviation abnormality. Similar results were found when perimetric total deviations were compared to reflectance abnormalities in the corresponding enface locations. Spearman's rho comparing the total deviations to reflectance abnormalities found rs(174) = -0.72, P < .001.

CONCLUSIONS

The technique typically identified reflectance abnormality when perimetric abnormality was present. It also identified reflectance abnormalities even when perimetric abnormality was mild or absent. The findings support the potential of raphe imaging in detecting early glaucomatous damage.

Discordance of Disc-Fovea Raphe Angles Determined by Optical Coherence Tomography and MP-3 Microperimetry in Eyes With a Glaucomatous Hemifield Defect

Purpose

The purpose of this study was to evaluate the concordance of a temporal raphe architecture estimated using optical coherence tomography (OCT) and MP-3 microperimetry.

Methods

We enrolled 25 eyes with either an upper or lower glaucomatous hemifield defect, as detected on the Humphrey visual field 30-2 test. A structural temporal raphe was extrapolated from visible end points of retinal nerve fiber bundles present in a perimetrically normal hemiretina on an en face Spectralis OCT image. A functional temporal raphe was drawn as a line from the fovea to the border of at least a 10-dB difference in sensitivity, at vertically adjacent test points, with at least three consecutive pairs among 25 test points placed at 8° to 18° from the fovea (2° intervals) on the MP-3. An angle determined by the optic disc center, the fovea, and the temporal raphe line (the DFR angle) was calculated. Correlations and agreement of the OCT- and MP-3-derived DFR angles and factors affecting discordance of the two estimates were evaluated.

Results

Despite no significant demographic differences, the functional DFR angle (mean ± SD, 171.8° ± 3.5°) was significantly larger than that of the structural DFR angle (166.5° ± 3.2°) in 14 eyes with upper hemifield defects and vice versa in 11 eyes with lower hemifield defects (163.4° ± 3.0° vs. 170.5° ± 3.2°). The mean deviation was significantly associated with the functional and structural DFR angle difference in eyes with only upper hemifield defects.

Conclusions

The structural temporal raphe was more deviated to the perimetrically normal hemiretina side than to the functional temporal raphe, thereby suggesting that a structural change may precede a functional loss.

Adaptive optics imaging of the human retina

Adaptive Optics (AO) retinal imaging has provided revolutionary tools to scientists and clinicians for studying retinal structure and function in the living eye. From animal models to clinical patients, AO imaging is changing the way scientists are approaching the study of the retina. By providing cellular and subcellular details without the need for histology, it is now possible to perform large scale studies as well as to understand how an individual retina changes over time. Because AO retinal imaging is non-invasive and when performed with near-IR wavelengths both safe and easily tolerated by patients, it holds promise for being incorporated into clinical trials providing cell specific approaches to monitoring diseases and therapeutic interventions. AO is being used to enhance the ability of OCT, fluorescence imaging, and reflectance imaging. By incorporating imaging that is sensitive to differences in the scattering properties of retinal tissue, it is especially sensitive to disease, which can drastically impact retinal tissue properties. This review examines human AO retinal imaging with a concentration on the use of the Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO). It first covers the background and the overall approaches to human AO retinal imaging, and the technology involved, and then concentrates on using AO retinal imaging to study the structure and function of the retina.

Vision science and adaptive optics, the state of the field

Adaptive optics is a relatively new field, yet it is spreading rapidly and allows new questions to be asked about how the visual system is organized. The editors of this feature issue have posed a series of question to scientists involved in using adaptive optics in vision science. The questions are focused on three main areas. In the first we investigate the use of adaptive optics for psychophysical measurements of visual system function and for improving the optics of the eye. In the second, we look at the applications and impact of adaptive optics on retinal imaging and its promise for basic and applied research. In the third, we explore how adaptive optics is being used to improve our understanding of the neurophysiology of the visual system.

Improving our understanding, and detection, of glaucomatous damage: An approach based upon optical coherence tomography (OCT)

Although ophthalmologists are becoming increasingly reliant upon optical coherence tomography (OCT), clinicians who care for glaucoma patients are not taking full advantage of the potential of this powerful technology. First, we ask, how would one describe the nature of glaucomatous damage if only OCT scans were available? In particular, a schematic model of glaucomatous damage is developed in section 2, and the nature of glaucomatous damage seen on OCT scans described in the context of this model in section 3. In particular, we illustrate that local thinning of the circumpapillary retinal nerve fiber layer (cpRNFL) around the optic disc can vary in location, depth, and/or width, as well as homogeneity of damage. Second, we seek to better understand the relationship between the thinning of the cpRNFL and the various patterns of sensitivity loss seen on visual fields obtained with standard automated perimetry. In sections 4 and 5, we illustrate why one should expect a wide range of visual field patterns, and iilustrate why they should not be placed into discrete categories. Finally, section 6 describes how the clinician can take better advantage of the information in OCT scans. The approach is summarized in a single-page report, which can be generated from a single wide-field scan. The superiority of this approach, as opposed to the typical reliance on summary metrics, is described.

Automatic identification of the temporal retinal nerve fiber raphe from macular cube data

We evaluated several approaches for automatic location of the temporal nerve fiber raphe from standard macular cubes acquired on a Heidelberg Spectralis OCT. Macular cubes with B-scan separation of 96-122 µm were acquired from 15 healthy participants, and "high density" cubes with scan separation of 11 µm were acquired from the same eyes. These latter scans were assigned to experienced graders for subjective location of the raphe, providing the ground truth by which to compare methods operating on the lower density data. A variety of OCT scan parameters and image processing strategies were trialed. Vertically oriented scans, purposeful misalignment of the pupil to avoid reflective artifacts, and the use of intensity as opposed to thickness of the nerve fiber layer were all critical to minimize error. The best performing approach "cFan" involved projection of a fan of lines from each of several locations across the foveal pit; in each fan the line of least average intensity was identified. The centroid of the crossing points of these lines provided the raphe orientation with an average error of 1.5° (max = 4.1°) relative to the human graders. The disc-fovea-raphe angle was 172.4 ± 2.3° (range = 168.5-176.2°), which agrees well with other published estimates.

Individual differences in the shape of the nasal visual field

Between-subject differences in the shape of the nasal visual field were assessed for 103 volunteers 21-85years of age and free of visual disorder. Perimetry was conducted with a stimulus for which contrast sensitivity is minimally affected by peripheral defocus and decreased retinal illumination. One eye each was tested for 103 volunteers free of eye disease in a multi-center prospective longitudinal study. A peripheral deviation index was computed as the difference in log contrast sensitivity at outer (25-29° nasal) and inner (8° from fixation) locations. Values for this index ranged from 0.01 (outer sensitivity slightly greater than inner sensitivity) to -0.7 log unit (outer sensitivity much lower than inner sensitivity). Mean sensitivity for the inner locations was independent of the deviation index (R²<1%), while mean sensitivity for the outer locations was not (R²=38%, p<0.0005). Age was only modestly related to the index, with a decline by 0.017 log unit per decade (R²=10%). Test-retest data for 21 volunteers who completed 7-10 visits yielded standard deviations for the index from 0.04 to 0.17 log unit, with a mean of 0.09 log unit. Between-subject differences in peripheral deviation persisted over two years of longitudinal testing. Peripheral deviation indices were correlated with indices for three other perimetric stimuli used in a subset of 24 volunteers (R² from 20% to 49%). Between-subject variability in shape of the visual field raises concerns about current clinical visual field indices, and further studies are needed to develop improved indices.

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.

Retinal ganglion cell neuronal damage in diabetes and diabetic retinopathy

BACKGROUND

To examine the association of diabetes and diabetic retinopathy (DR) with retinal ganglion cell (RGC) loss.

DESIGN

Observational case-control study.

PARTICIPANTS

Type 2 diabetes cases and age-gender matched controls without diabetes.

METHODS

Spectral-domain optical coherence tomography (OCT) parameters of RGCs were calculated after automated segmentation of macular scans. DR severity was graded on fundus photographs using the modified Airlie House Classification system. Generalized estimating equation was used to compare OCT parameters between cases and controls, adjusted for covariates.

MAIN OUTCOME MEASURES

Average ganglion cell-inner plexiform layer (GC-IPL) and average retinal nerve fibre layer (RNFL) thicknesses.

RESULTS

We analyzed 227 cases and 227 controls. The mean age (years) of cases was 58.3 and controls was 58.1 (P = 0.13). Among cases, 101 had none, 25 had mild and 101 had moderate or severe DR. Compared with controls, GC-IPL and RNFL were thinner in all cases [mean difference (95% confidence interval [CI]): GC-IPL -4.49 µm (-2.92; -6.06), RNFL -0.93 µm (-0.09; -1.85)], including cases with no DR [mean difference (95% CI), GC-IPL -4.37 µm (-2.72; -6.02), RNFL -1.06 µm (-0.10; -2.02)]. Cases with any DR had thinner GC-IPL than controls [mean difference (95% CI): GC-IPL -4.81 µm (-2.12; -7.50)]. Among cases, subjects with moderate or severe DR had thinner GC-IPL than subjects with no DR [mean difference (95% CI): GC-IPL -2.07 µm (-0.08; -4.07)].

CONCLUSIONS

RGC loss is present in subjects with diabetes and no DR, and is progressive in moderate or severe DR. RGC neuronal damage in diabetes and DR can be clinically detected using OCT.