Measurement of photoreceptor layer in glaucoma: a spectral-domain optical coherence tomography study

A parafoveal retinal cones analysis using adaptive-optics retinal camera in patients with primary open angle glaucoma

OBJECTIVES

To study the density, spacing, and regularity of retinal cone photoreceptors using an Adaptive Optics (AO) retinal camera (Rtx1TM, Imagine Eyes, Orsay, France) in patients with Primary Open Angle Glaucoma (POAG) and to compare the outcomes with those of healthy age-matched control subjects.

METHODS

The study included 43 eyes with POAG and 31 eyes of normal subjects. POAG patients were divided into three groups according to the severity of the visual field defect. The AO Rtx1TM was used to obtain images of the parafoveal cone mosaic to calculate cone values. Analysis was performed at two and four degrees of eccentricity from the fovea along the four meridians (nasal, temporal, superior, inferior).

RESULTS

In POAG eyes, the mean ± standard deviation (SD) cone density at 2° considering all meridians was significantly lower than in normal controls (23,058.6 ± 3532.0 cones/mm2, and 25,511.7 ± 3157.5 cones/mm2, respectively; p = 0.003). Cone spacing was 7.3 ± 0.5 µm in POAG and 7.0 ± 0.4 µm in normal controls (p = 0.005), and cone regularity was 90.5 ± 4.9% and 93.5 ± 1.9% in POAG and normal controls, respectively (p < 0.001). At 4° similar trends were observed. However, no significant differences were found among patients with different severity of POAG (p > 0.05).

CONCLUSIONS

Using AO Rtx1TM, significant differences in retinal photoreceptors mosaic pattern were found between POAG eyes and age-matched controls, indicating a reduction in photoreceptors in POAG. No significant differences in retinal photoreceptor values were found among the three POAG groups.

Assessment of Early Glaucomatous Optic Neuropathy in the Dog by Spectral Domain Optical Coherence Tomography (SD-OCT)

BACKGROUND

Inherited primary open-angle glaucoma (POAG) in Beagle dogs is a well-established large animal model of glaucoma and is caused by a G661R missense mutation in the ADAMTS10 gene. Using this model, the study describes early clinical disease markers for canine glaucoma.

METHODS

Spectral-domain optical coherence tomography (SD-OCT) was used to assess nine adult, ADAMTS10-mutant (median age 45.6 months, range 28.8-52.8 months; mean diurnal intraocular pressure (IOP): 29.9 +/- SEM 0.44 mmHg) and three related age-matched control Beagles (mean diurnal IOP: 18.0 +/- SEM 0.53 mmHg).

RESULTS

Of all the optic nerve head (ONH) parameters evaluated, the loss of myelin peak height in the horizontal plane was most significant (from 154 +/- SEM 38.4 μm to 9.3 +/- SEM 22.1 μm; p < 0.01). There was a strong significant negative correlation between myelin peak height and IOP (Spearman correlation: -0.78; p < 0.003). There were no significant differences in the thickness of any retinal layers evaluated.

CONCLUSIONS

SD-OCT is a useful tool to detect early glaucomatous damage to the ONH in dogs before vision loss. Loss in myelin peak height without inner retinal thinning was identified as an early clinical disease marker. This suggests that initial degenerative changes are mostly due to the loss of myelin.

Evaluation of the Diagnostic Capability of Spectralis SD-OCT 8 × 8 Posterior Pole Software with the Grid Tilted at 7 Degrees and Horizontalized in Glaucoma

Background: The goal was to evaluate the diagnostic capability of different parameters obtained with the posterior pole (PP) software in Spectralis SD-OCT with the 8 × 8 grid tilted at 7° and horizontalized in glaucomatous eyes. Methods: A total of 299 eyes were included, comprising 136 healthy eyes and 163 with primary open-angle glaucoma (POAG). The following segmentations were evaluated: complete retina, retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), GCL and inner plexiform layer (GCLIPL), ganglion cell complex (GCC), outer plexiform layer and outer nuclear layer (OPLONL), inner retinal layer (IRL), and outer retinal layer (ORL). Different patterns of macular damage were represented using heatmaps for each studied layer, where the areas under the curve (AUROC) values and a retinal thickness cutoff point were defined to discriminate POAG patients. Results: There was not any difference in the diagnostic capability for detecting glaucoma between the grid tilted at 7° and horizontalized. The macular segmentations that offer the highest diagnostic ability in glaucoma discrimination were, in the following order, RNFL (AUROC = 0.796), GCC (AUROC = 0.785), GCL (AUROC = 0.784), GCLIPL (AUROC = 0.770), IRL (AUROC = 0.755), and the complete retina (AUROC = 0.752). In contrast, ORL and OPLONL do not appear to be helpful for discriminating POAG. Conclusions: Some results of PP software may be useful for discriminating POAG.

Protective Effects of Pituitary Adenylate-Cyclase-Activating Polypeptide on Retinal Vasculature and Molecular Responses in a Rat Model of Moderate Glaucoma

Despite the high probability of glaucoma-related blindness, its cause is not fully understood and there is no efficient therapeutic strategy for neuroprotection. Vascular factors have been suggested to play an important role in glaucoma development and progression. Previously, we have proven the neuroprotective effects of pituitary adenylate-cyclase-activating polypeptide (PACAP) eye drops in an inducible, microbeads model in rats that is able to reproduce many clinically relevant features of human glaucoma. In the present study, we examined the potential protective effects of PACAP1-38 on the retinal vasculature and the molecular changes in hypoxia. Ocular hypertension was induced by injection of microbeads into the anterior chamber, while control rats received PBS. PACAP dissolved in vehicle (1 µg/drop) or vehicle treatment was started one day after the injections for four weeks three times a day. Retinal degeneration was assessed with optical coherence tomography (OCT), and vascular and molecular changes were assessed by immunofluorescence labeling. HIF1-α and VEGF-A protein levels were measured by Western blot. OCT images proved severe retinal degeneration in the glaucomatous group, while PACAP1-38 eye drops had a retinoprotective effect. Vascular parameters were deteriorated and molecular analysis suggested hypoxic conditions in glaucoma. PACAP treatment exerted a positive effect against these alterations. In summary, PACAP could prevent the severe damage to the retina and its vasculature induced by ocular hypertension in a microbeads model.

Proteomics-Based Identification of Retinal Protein Networks Impacted by Elevated Intraocular Pressure in the Hypertonic Saline Injection Model of Experimental Glaucoma

Elevated intraocular pressure is considered a major cause of glaucomatous retinal neurodegeneration. To facilitate a better understanding of the underlying molecular processes and mechanisms, we report a study focusing on alterations of the retina proteome by induced ocular hypertension in a rat model of the disease. Glaucomatous processes were modeled through sclerosing the aqueous outflow routes of the eyes by hypertonic saline injections into an episcleral vein. Mass spectrometry-based quantitative retina proteomics using a label-free shotgun methodology identified over 200 proteins significantly affected by ocular hypertension. Various facets of glaucomatous pathophysiology were revealed through the organization of the findings into protein interaction networks and by pathway analyses. Concentrating on retinal neurodegeneration as a characteristic process of the disease, elevated intraocular pressure-induced alterations in the expression of selected proteins were verified by targeted proteomics based on nanoflow liquid chromatography coupled with nano-electrospray ionization tandem mass spectrometry using the parallel reaction monitoring method of data acquisition. Acquired raw data are shared through deposition to the ProteomeXchange Consortium (PXD042729), making a retina proteomics dataset on the selected animal model of glaucoma available for the first time.

Binocular head-mounted chromatic pupillometry can detect structural and functional loss in glaucoma

Aim

The aim of this study is to evaluate the utility of binocular chromatic pupillometry in detecting impaired pupillary light response (PLR) in patients with primary open-angle glaucoma (POAG) and to assess the feasibility of using binocular chromatic pupillometer in opportunistic POAG diagnosis in community-based or telemedicine-based services.

Methods

In this prospective, cross-sectional study, 74 patients with POAG and 23 healthy controls were enrolled. All participants underwent comprehensive ophthalmologic examinations including optical coherence tomography (OCT) and standard automated perimetry (SAP). The PLR tests included sequential tests of full-field chromatic stimuli weighted by rods, intrinsically photosensitive retinal ganglion cells (ipRGCs), and cones (Experiment 1), as well as alternating chromatic light flash-induced relative afferent pupillary defect (RAPD) test (Experiment 2). In Experiment 1, the constricting amplitude, velocity, and time to maximum constriction/dilation were calculated in three cell type-weighted responses, and the post-illumination response of ipRGC-weighted response was evaluated. In Experiment 2, infrared pupillary asymmetry (IPA) amplitude and anisocoria duration induced by intermittent blue or red light flashes were calculated.

Results

In Experiment 1, the PLR of POAG patients was significantly reduced in all conditions, reflecting the defect in photoreception through rods, cones, and ipRGCs. The variable with the highest area under the receiver operating characteristic curve (AUC) was time to max dilation under ipRGC-weighted stimulus, followed by the constriction amplitude under cone-weighted stimulus and the constriction amplitude response to ipRGC-weighted stimuli. The impaired PLR features were associated with greater visual field loss, thinner retinal nerve fiber layer (RNFL) thickness, and cupping of the optic disk. In Experiment 2, IPA and anisocoria duration induced by intermittent blue or red light flashes were significantly greater in participants with POAG than in controls. IPA and anisocoria duration had good diagnostic value, correlating with the inter-eye asymmetry of visual field loss.

Conclusion

We demonstrate that binocular chromatic pupillometry could potentially serve as an objective clinical tool for opportunistic glaucoma diagnosis in community-based or telemedicine-based services. Binocular chromatic pupillometry allows an accurate, objective, and rapid assessment of retinal structural impairment and functional loss in glaucomatous eyes of different severity levels.

Influences of Glaucoma on the Structure and Function of Synapses in the Visual System

Significance: Glaucoma is an age-related neurodegenerative disorder of the visual system associated with sensitivity to intraocular pressure (IOP). It is the leading irreversible cause of vision loss worldwide, and vision loss results from damage and dysfunction of the retinal output neurons known as retinal ganglion cells (RGCs). Recent Advances: Elevated IOP and optic nerve injury triggers pruning of RGC dendrites, altered morphology of excitatory inputs from presynaptic bipolar cells, and disrupted RGC synaptic function. Less is known about RGC outputs, although evidence to date indicates that glaucoma is associated with altered mitochondrial and synaptic structure and function in RGC-projection targets in the brain. These early functional changes likely contribute to vision loss and might be a window into early diagnosis and treatment. Critical Issues: Glaucoma affects different RGC populations to varying extents and along distinct time courses. The influence of glaucoma on RGC synaptic function as well as the mechanisms underlying these effects remain to be determined. Since RGCs are an especially energetically demanding population of neurons, altered intracellular axon transport of mitochondria and mitochondrial function might contribute to RGC synaptic dysfunction in the retina and brain as well as RGC vulnerability in glaucoma. Future Directions: The mechanisms underlying differential RGC vulnerability remain to be determined. Moreover, the timing and mechanisms of RGCs synaptic dysfunction and degeneration will provide valuable insight into the disease process in glaucoma. Future work will be able to capitalize on these findings to better design diagnostic and therapeutic approaches to detect disease and prevent vision loss. Antioxid. Redox Signal. 37, 842-861.

The thickness of the outer retina in the macula and circumpapillary area in patients with unilateral advanced glaucoma

PURPOSE

To compare outer macular and retinal thickness in the circumpapillary area in unilateral advanced glaucomatous eyes to the normal or mild glaucomatous fellow eyes.

METHODS

Seventy-eight eyes of 39 patients with unilateral advanced glaucoma (mean deviation (MD) worse than -12.00 dB based on visual field 24-2) were included in this cross-sectional study as the cases. The healthy or mild glaucomatous fellow eyes were enrolled as the control group. All eyes underwent optical coherence tomography of the macula and circumpapillary retina by Topcon DRI Triton (Topcon, Tokyo, Japan). Ganglion cell layer 2+ was considered as the inner retina. Total retinal thickness minus the thickness of the inner retina was considered as the outer retina. Comparison between groups was done by paired-sample sign test. The correlation between structural and functional parameters was evaluated by a partial correlation coefficient.

RESULTS

Seventeen (43.6%), 15 (38.5%), and 7 (17.9%) patients had pseudoexfoliation, primary angle-closure, and primary open-angle glaucoma, respectively. The mean age was 62.69 ± 12.00 years. Thirty-three (84.6%) patients were male. The outer retinal thickness in the circumpapillary area was higher in temporal, superior, and inferior quadrants (p < 0.05). The outer macula in different parafoveal and perifoveal quadrants was also thicker (p < 0.05). Average outer parafoveal thickness in the case group had a significant negative correlation with MD (r = -0.339; p = 0.035).

CONCLUSION

Advanced glaucomatous eyes had a thicker outer retina in the macula and circumpapillary area. There was a significant negative correlation between outer perifoveal thickness and MD.

Individual Macular Layer Evaluation with Spectral Domain Optical Coherence Tomography in Normal and Glaucomatous Eyes

PURPOSE

To evaluate differences in the thickness of the individual macular layers between early, moderate, and severe glaucomatous eyes and compare them with healthy controls.

PATIENTS AND METHODS

Subjects with glaucoma presenting typical optic nerve head findings, high intraocular pressure with or without visual field (VF) damage and normal controls were included. All participants underwent 24-2 perimetry and spectral-domain OCT. Patients were divided into three groups (early, moderate, and severe) based on the mean deviation of the VF and a healthy control group. The device segmented the layers automatically, and their measurements were plotted using the means of the sectors of the inner (3mm) and outer (6mm) circles of the ETDRS grid.

RESULTS

A total of 109 eyes qualified for the study: 14 in the control group and 52, 18 and 25 in the early, moderate and severe groups, respectively. Mean age was 66.13 (SD=12.38). The mean thickness of the circumpapillary retinal nerve fiber layer (RNFL), total macular thickness (TMT), macular RNFL, ganglion cell layer (GCL) and inner plexiform layer (IPL) were significantly different between the 4 groups, with progressive decrease in thickness. Significant overall difference was found for the inner nuclear layer (INL), and the severe glaucoma group presented thicker measurements than controls and early glaucoma. Outer nuclear layer (ONL) was thinner in severe glaucoma group compared with early glaucoma group.

CONCLUSION

Individual macular layer measurement using the inner and outer circles of the ETDRS grid is useful to evaluate different stages of glaucoma. The INL thickening and ONL thinning in advanced glaucoma should be explored in the future studies.

Glaucomatous Maculopathy: Thickness Differences on Inner and Outer Macular Layers between Ocular Hypertension and Early Primary Open-Angle Glaucoma Using 8 × 8 Posterior Pole Algorithm of SD-OCT

The purpose of this study was to compare the thickness of all inner and outer macular layers between ocular hypertension (OHT) and early primary open-angle glaucoma (POAG) using spectral domain optical coherence tomography (SD-OCT) 8 × 8 posterior pole algorithm (8 × 8 PPA). Fifty-seven eyes of 57 OHT individuals and fifty-seven eyes of 57 early POAG patients were included. The thickness of macular retinal nerve fiber layer (mRNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform and nuclear layer, photoreceptor layer (PRL) and retinal pigment epithelium were obtained in 64 cells for each macular layer and mean thickness of superior and inferior hemispheres was also calculated. Thinning of superior and inferior hemisphere mean thickness in mRNFL, GCL and IPL and thickening of superior and inferior hemisphere mean thickness in PRL and inferior hemisphere in INL were found in early GPAA group. Otherwise, heatmaps representing cell-to-cell comparisons showed thinning patterns in inner retinal layers (except for INL) and thickening patterns in outer retinal layers in GPAA group. We found that 8 × 8 PPA not only allows the detection of significant thinning patterns in inner retinal layers, but also thickening patterns in outer retinal layers when comparing early POAG eyes to OHT eyes.

Photoreceptor outer nuclear layer thickness changes in optic neuritis follow up

BACKGROUND

Ganglion cell inner plexiform (GCIP) layer thinning following acute optic neuritis (ON) is well-known. However, the onset of changes in the outer retinal layers needs further study. In this study, we determine longitudinal changes in retinal layer thickness in ON.

METHODS

Thirty ON patients underwent optical coherence tomography (OCT) and visual function testing at baseline, one month, and 6 months.

RESULTS

Mean GCIPL thickness decreased at one month relative to baseline from 63.6 ± 7.5 μm to 57.3 ± 6.8 µm in 3 mm ring (P < 0.001). There were no significant changes in GCIPL thickness between one and 6 months (P = 0.42). Outer nuclear layer (ONL) thickness in the 6 mm macular area increased from 58.9 ± 5.8 µm to 63.2 ± 6.8 μm at one month (P < 0.001) and then decreased at six month (58.8 ± 5.8 µm) relative to one month, reaching the baseline thickness. While GCIPL thinning at 1 month correlated with baseline visual acuity, change in the central ONL thickness from baseline to month 1 predicted visual outcome at month 6 (r = 0.6, P = 0.001).

CONCLUSIONS

Following ON, transient changes occur in the photoreceptor nuclei layer and then revert to baseline. This finding could predict 6 month visual acuity after ON.

Clinical relevance of protruded retinal layers in minimum rim width measurement of the optic nerve head

BACKGROUND/AIMS

Optical coherence tomography (OCT) imaging of the optic nerve head minimum rim width (MRW) has recently been shown to sometimes contain components besides extended retinal nerve fibre layer (RNFL). This study was conducted to determine whether excluding these components, termed protruded retinal layers (PRLs), from MRW increases diagnostic accuracy for detecting glaucoma.

METHODS

In this cross-sectional study, we included 123 patients with glaucoma and 123 normal age-similar controls with OCT imaging of the optic nerve head (24 radial scans) and RNFL (circle scan). When present, PRLs were manually segmented, and adjusted MRW measurements were computed. We compared diagnostic accuracy of adjusted versus unadjusted MRW measurement. We also determined whether adjusted MRW correlates better with RNFL thickness compared with unadjusted MRW.

RESULTS

The median (IQR) visual field mean deviation of patients and controls was -4.4 (-10.3 to -2.1) dB and 0.0 (-0.6 to 0.8) dB, respectively. In the 5904 individual B-scans, PRLs were identified less frequently in patients (448, 7.6%) compared with controls (728, 12.3%; p<0.01) and were present most frequently in the temporal sector of both groups. Areas under the receiver operating characteristic curves and sensitivity values at 95% specificity indicated that PRL adjustment did not improve diagnostic accuracy of MRW, globally or temporally. Furthermore, adjusting MRW for PRL did not improve its correlation with RNFL thickness in either group.

CONCLUSION

While layers besides the RNFL are sometimes included in OCT measurements of MRW, subtracting these layers does not impact clinical utility.

Optineurin E50K triggers BDNF deficiency-mediated mitochondrial dysfunction in retinal photoreceptor cell line

Optineurin (OPTN) mutations are linked to glaucoma pathology and E50K mutation shows massive cell death in photoreceptor cells and retinal ganglion cells. However, little is known about E50K-mediated mitochondrial dysfunction in photoreceptor cell degeneration. We here show that overexpression of E50K expression triggered BDNF deficiency, leading to Bax activation in RGC-5 cells. BDNF deficiency induced mitochondrial dysfunction by decreasing mitochondrial maximal respiration and reducing intracellular ATP level in RGC-5 cells. However, BDNF deficiency did not alter mitochondrial dynamics. Also, BDNF deficiency resulted in LC3-mediated mitophagosome formation in RGC-5 cells. These results strongly suggest that E50K-mediated BDNF deficiency plays a critical role in compromised mitochondrial function in glaucomatous photoreceptor cell degeneration.

Improving the structure-function relationship in glaucomatous and normative eyes by incorporating photoreceptor layer thickness

The purpose of the study was to investigate whether the structure-function relationship in glaucomatous and normative eyes is improved by considering photoreceptor layer thickness. Humphrey 10-2 visual fields (VF) and optical coherence tomography were carried out in 615 eyes of 391 subjects, including 100 eyes of 53 healthy controls and 515 eyes of 338 glaucoma patients. The relationship between mean VF sensitivity and the thickness of the retinal nerve fiber layer (RNFL) and ganglion cell layer and inner plexiform layer (GCL + IPL) was analyzed using linear mixed models, by glaucoma status and degree of myopia. The structure-function relationship was also analyzed by supplementing the RNFL and GCL + IPL thickness with the thicknesses of: (i) the inner nuclear layer and outer plexiform layer (INL + OPL); (ii) the outer nuclear layer and inner segment of photoreceptor layer (ONL + ISL); (iii) the outer segment layer of photoreceptor and retinal pigment epithelium (OSL + RPE). The model included total thickness of RNFL, GCL + IPL and OSL + RPE was highly more optimal than the model that only included the total thickness of RNFL and GCL + IPL, in all subsets of eyes by glaucoma status and degree of myopia.

DRUNET: a dilated-residual U-Net deep learning network to segment optic nerve head tissues in optical coherence tomography images

Given that the neural and connective tissues of the optic nerve head (ONH) exhibit complex morphological changes with the development and progression of glaucoma, their simultaneous isolation from optical coherence tomography (OCT) images may be of great interest for the clinical diagnosis and management of this pathology. A deep learning algorithm (custom U-NET) was designed and trained to segment 6 ONH tissue layers by capturing both the local (tissue texture) and contextual information (spatial arrangement of tissues). The overall Dice coefficient (mean of all tissues) was 0.91 ± 0.05 when assessed against manual segmentations performed by an expert observer. Further, we automatically extracted six clinically relevant neural and connective tissue structural parameters from the segmented tissues. We offer here a robust segmentation framework that could also be extended to the 3D segmentation of the ONH tissues.

Protruded retinal layers within the optic nerve head neuroretinal rim

PURPOSE

To determine the frequency with which retinal tissues other than the nerve fibre layer, hereafter referred to as protruded retinal layers (PRL), are a component of optical coherence tomography (OCT) neuroretinal rim measurements.

METHODS

Ninety healthy (30 White, Black and Japanese, respectively) subjects were included in the study. A radial scan pattern (24 B-scans centred on Bruch's membrane opening [BMO]) was used. For each of the 48 minimum rim width (MRW) measurement points, we determined whether PRL were present, absent or indeterminate. When present, the proportion of PRL within the MRW was quantified.

RESULTS

Protruded retinal layers were present in 503 (11.6%), absent in 3805 (88.1%) and indeterminate in 12 (0.3%) measurement points. Overall, 69 (76.6%) subjects had ≥1 points with PRL, with White subjects having the highest frequency and Japanese the lowest (29 [97%] and 18 [60%], respectively; p < 0.01). PRL were present in one-third of points in the temporal sector, but ≤5% in other sectors. When present, the median PRL thickness was 53.0 (interquartile range [IQR]: 33.0 to 78.5) μm, representing 20.6 (IQR: 13.0 to 28.5)% of MRW. Globally, the median PRL thickness comprised 1.3 (IQR: 0.2 to 3.5)% of the MRW; however, in the temporal sector, it exceeded 30% of MRW in some subjects.

CONCLUSIONS

Protruded retinal layers are a component of MRW measurements in most normal subjects, occurring in almost 12% of all measurement points analysed. There were racial variations in the presence of PRL and a significantly higher frequency of PRL in the temporal sector.

Analysis of inner and outer retinal layers using spectral domain optical coherence tomography automated segmentation software in ocular hypertensive and glaucoma patients

Objective

To analyse the morphological features and diagnostic ability of eight macular retinal layers using a new segmentation software Heidelberg's Spectralis Optical Coherence Tomography (SD-OCT) in healthy, ocular hypertensive and primary open angle glaucoma patients.

Methods

Single-center, cross-sectional, non-interventional study. 193 eyes from 193 consecutive patients (56 controls, 63 ocular hypertensives, 32 early primary open glaucoma patients and 42 moderate-advanced primary open glaucoma patients). Those patients presenting any retinal disease were excluded. Macular segmentation of the retinal layers was automatically performed using the new segmentation Heidelberg's Spectralis OCT software providing measurements for eight retinal layers. The software provides thickness maps divided into nine subfields.

Results

Statistically significant differences in inner layers’ thickness was found between all 4 four groups. Superior and inferior sectors of macular retinal nerve fiber layer; nasal, temporal, superior and inferior sectors of ganglion cell layer and inner plexiform layer were significantly different when comparing ocular hypertensive patients and early glaucoma patients. Areas under the ROC curves for early glaucoma diagnosis were 0.781±0.052 for macular retinal nerve fiber layer outer inferior sector, 0.760±0.050 for ganglion cell layer outer temporal sector, 0.767±0.049 for the inner plexiform layer outer temporal sector and 0.807±0.048 for the combination of all three. No differences were found between groups when considering outer retinal layers.

Conclusions

The automated segmentation software from Heidelberg's Spectralis OCT provides a new diagnostic tool for the diagnosis of ocular hypertensive and glaucoma patients.

Mapping the thickness changes on retinal layers segmented by spectral-domain optical coherence tomography using the posterior pole program in glaucoma

OBJECTIVES

To evaluate changes in retinal layers of the macula (mRLs) using OCT posterior pole program (PPP) in primary open-angle glaucoma (POAG).

MATERIAL AND METHODS

The study included 128 patients with POAG and 103 healthy controls who had PPP maps (macular grid 8×8) drawn by SD-OCT. Only one eye per patient was studied. The 9 mRLs were automatically segmented by prototype software, obtaining: a macular retinal nerve fibre layer (mRNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform+nuclear layer, photoreceptor layer, retinal pigment epithelium (RPE), outer retina and RPE+outer retina. Thickness values were obtained on 64 cells of the grid for each mRL, and mean thickness of superior and inferior hemispheres were calculated. Comparisons of mean thickness of these hemispheres and thickness of each cell between groups were determined. Differences in the cell by cell comparisons were represented quantitatively by heat maps for each mRL.

RESULTS

Photoreceptors and RPE were found in POAG group when comparing thickness of hemispheres, thinning of mRNFL, GCL, IPL, and thickening of INL. Heat maps showed symmetrical thinning patters between superior and inferior hemispheres in inner retinal layers (except for INL) and asymmetrical thickening patters in outer retinal layers in GPAA group.

CONCLUSIONS

There are thickness changes in all mRLs in POAG, when studied by PPP. Thinning of inner layers (except for INL), and thickening of outer layers in POAG show different symmetry patterns in relation to horizontal meridian.

Retinal single-layer analysis with optical coherence tomography shows inner retinal layer thinning in Huntington's disease as a potential biomarker

PURPOSE

There have been ongoing clinical trials of therapeutic agents in Huntington's disease (HD) which requires development of reliable biomarkers of disease progression. There have been studies in the literature with conflicting results on the involvement of retina in HD, and up to date there is not a study evaluating the single retinal layers in HD. We aimed to evaluate the specific retinal changes in HD and their usability as potential disease progression markers.

METHODS

This cross-sectional study used spectral-domain optical coherence tomography with automatic segmentation to measure peripapillary retinal nerve fiber layer (pRNFL) thickness and the thickness and volume of retinal layers in foveal scans of 15 patients with HD and 15 age- and sex-matched controls. Genetic testing results, disease duration, HD disease burden scores and Unified HD Rating Scales motor scores were acquired for the patients.

RESULTS

Temporal pRNFL, macular RNFL (mRNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer and outer plexiform layer thicknesses and IPL, retinal pigment epithelium and outer macular volume were found lower in HD compared to controls, while outer nuclear layer and outer retinal layer thickness were increased (p < 0.05). We found significant correlations between inner retinal layer thicknesses, most significantly with mRNFL and GCL and disease progression markers.

CONCLUSION

The outcomes of this study points out that retinal layers, most significantly mRNFL and GCL, are strongly correlated with the disease progression in HD and could serve as useful biomarkers for disease progression.

Reduction on OFF-responses of Electroretinogram in Monkeys with Long-term High Intraocular Pressure

Background:

There are ON- and OFF-pathways in the normal vertebrate retina. Short- and long-flash electroretinogram (ERG) are suitable methods to observe the function of ON- and OFF-pathways in vivo, respectively. It is clear that high intraocular pressure (IOP) might cause dysfunction of cone-dominated photopic negative response (PhNR) in monkeys with high IOP in ON-pathway. However, whether cone-dominated OFF-responses are also affected is less known. The aim of this study was to observe photopic OFF-responses of ERG in monkeys with high IOP.

Methods:

Nine monkeys were involved in the experiment from January 2006 to December 2016. High IOP was induced in the right eye by laser coagulation of the mid-trabecular meshwork in five monkeys. Six years after the laser coagulation, both short- and long-flash of the photopic ERG were recorded. Stimulus light was red flashes superimposed on a blue background. Four normal monkeys were examined under the same ERG protocols as controls. Paired t-test was used to compare the difference of each ERG parameter between the lasered eye and the fellow eye. Analysis of variance (ANOVA) with Tukey adjustment was adopted to calculate the differences among the lasered eye, the fellow eye, and the eyes of normal monkeys.

Results:

The mean amplitude of a-wave (11.73 ± 2.05) and PhNR (8.67 ± 2.44) in lasered eyes was significantly lower than that of a-wave (21.47 ± 3.15) and PhNR (22.05 ± 3.42) in fellow eyes (P = 0.03 and P = 0.01, respectively) in response to short flash. The mean amplitude of d-wave (1.60 ± 0.59) and i-wave (3.13 ± 0.64) was significantly reduced in the lasered eyes than that of d-wave (4.01 ± 0.56) and i-wave (8.79 ± 1.75) in the fellow eyes (P = 0.02 and P = 0.02, respectively) in response to long flash.

Conclusions:

Reduced OFF-responses are recorded in monkeys with high IOP when dysfunction of photoreceptor is involved. The reduced OFF-responses to long-flash stimulus show evidence of anomalous retinal circuitry in glaucomatous retinopathy.

Intra- and interobserver reproducibility of Bruch's membrane opening minimum rim width measurements with spectral domain optical coherence tomography

PURPOSE

To investigate the reproducibility of Bruch's membrane opening minimum rim width (BMO-MRW) and retinal nerve fibre layer thickness (RNFLT) measurements using spectral domain optical coherence tomography (SD-OCT). Additionally, to investigate the reproducibility of BMO area measurements and fovea to BMO centre (FoBMO) angle.

METHODS

Participants were healthy subjects (n = 30) and patients with glaucoma (n = 26). One eye of each participant was scanned to obtain optic nerve head (24 radial B-scans) and peripapillary (one circular B-scan) images by three independent examiners. Additionally, one examiner imaged each participant three times on the same day. Intra- and interobserver reproducibilities were estimated by within-subject standard deviation (SW) and coefficient of variation (COV). Spearman's rank correlation coefficient was used to test the correlation between the magnitude of the parameter and its standard deviation.

RESULTS

The global BMO-MRW COVs (%) in healthy/glaucoma subjects were 0.87/1.34 and 1.28/3.13 for intra- and interobserver analyses, respectively, and the corresponding global RNFLT figures were 1.50/2.10 and 2.04/2.87. Global mean BMO-MRW and RNFLT showed no correlation with their respective standard deviations. The reproducibilities of BMO area and FoBMO angle were excellent and similar between the groups.

CONCLUSION

The reproducibilities of BMO-MRW, BMO area measurements and FoBMO angle were excellent in both healthy subjects and patients with glaucoma. Bruch's membrane opening minimum rim width (BMO-MRW) reproducibility is comparable to that of RNFLT measurements.

The association between photoreceptor layer thickness measured by optical coherence tomography and visual sensitivity in glaucomatous eyes

PURPOSE

To assess the thickness of the photoreceptor layer in the macular region in glaucomatous eyes.

METHOD

Humphrey 10-2 visual field (VF) testing was carried out and mean threshold (mTH) was calculated in 118 eyes from 118 patients with open angle glaucoma. Macular optical coherence tomography (OCT) measurements (RS 3000, Nidek Co.ltd., Aichi, Japan) were also carried out in all eyes. Thickness measurements were recorded in the outer segment and retinal pigment epithelium (OS+RPE), the nerve fiber layer (NFL), the ganglion cell layer and inner plexiform layer (GCL+IPL), the inner nuclear layer and outer plexiform layer (INL+OPL) and the outer nuclear layer and inner segment (ONL+IS). The relationship between mTH and the thickness of these five different layers was investigated. Additionally, the influence of OS+RPE on mTH was investigated using partial correlation eliminating the effect of other variables of NFL, GCL+IPL, INL+OPL, ONL+IS, age, gender and axial length.

RESULTS

The thickness of the OS+RPE layer was significantly decreased with the decrease of mTH (coefficient = 0.63 p <0.001). Partial correlation analysis suggested OS+RPE thickness is significantly (coefficient = 0.31, p <0.001) related to mTH, independent from NFL, GCL+IPL, INL+OPL, ONL+IS, age, gender and axial length.

CONCLUSIONS

The thickness of the RPE+OS layer appears to be related to visual sensitivity in glaucoma.

Gene Expression Profiling of the Optic Nerve Head of Patients with Primary Open-Angle Glaucoma

Background. The pressure-induced axonal injury of the vulnerable ONH has led many researchers to view glaucoma from the perspective of the genetic basis of the angle of the ONH. However, genetic studies on POAG from this perspective are limited. Methods. Microarray dataset GSE45570 of the ONH of healthy individuals and POAG patients were downloaded from the Gene Expression Omnibus. After screening for the DEGs using the limma package, enrichment analysis was performed using DAVID. The DEG interaction network was constructed using cancer spider at BioProfiling.de. Thereafter, DEG-related TFs were predicted using TRANSFAC, and TF-DEG regulatory networks were visualized using Cytoscape. Results. Thirty-one DEGs were identified including 11 upregulated and 20 downregulated DEGs. Thereafter, gene ontology terms of nucleosome assembly, sensory perception and cognition, and pathway of signaling by GPCR were found to be enriched among the DEGs. Furthermore, DEG interaction and TF-DEG networks were constructed. NEUROD1 was present in both the DEG network and the TF-DEG network as the node with the highest degree and was predicted as a marker gene in the ONH of patients with POAG. Conclusion. NEUROD1 may contribute greatly to the ONH of patients with POAG and was found to be involved in eye development and diseases.

Ultra-high resolution profiles of macular intra-retinal layer thicknesses and associations with visual field defects in primary open angle glaucoma

The structural characteristics of the outer retinal layers in primary open angle glaucoma (POAG) are still controversial, and these changes, along with those in the inner retinal layers, could have clinical and/or pathophysiological significance. A custom-built ultra-high resolution optical coherence tomography (UHR-OCT) combined with an automated segmentation algorithm can image and measure the eight intra-retinal layers. The purpose of this study is to determine the thickness characteristics of the macular intra-retinal layers, especially the outer layers, in POAG patients. Thirty-four POAG patients (56 eyes) and 33 normal subjects (63 eyes) were enrolled. Thickness profiles of the eight intra-retinal layers along a 6-mm length centred on the fovea at the horizontal and vertical meridians were obtained and the regional thicknesses were compared between two groups. The associations between the thicknesses of each intra-retinal layer and the macular visual field (VF) sensitivity were then analysed. POAG affected not only the inner retinal layers but also the photoreceptor layers and retinal pigment epithelium of the outer retina. However, the VF loss was correlated mainly with the damage of the inner retinal layers. UHR-OCT with automated algorithm is a useful tool in detecting microstructural changes of macula with respect to the progression of glaucoma.

Cone Integrity in Glaucoma: An Adaptive-Optics Scanning Laser Ophthalmoscopy Study

PURPOSE

To investigate photoreceptor changes in eyes with glaucoma.

DESIGN

Cross-sectional study.

METHODS

The study included 35 eyes of 35 patients with primary open-angle glaucoma who had suffered parafoveal visual field loss at least 3 years previously, as well as 21 eyes of 21 normal subjects. Eyes with an axial length ≥26.0 mm were excluded. All subjects underwent a full ophthalmologic examination, including spectral-domain optical coherence tomography (SDOCT) and prototype adaptive-optics scanning laser ophthalmoscopy (AO-SLO) imaging.

RESULTS

As determined using AO-SLO, eyes with glaucoma did not differ significantly from normal eyes in terms of either cone density (26 468 ± 3392 cones/m² vs 26 147 ± 2700 cones/m², respectively; P = .77; measured 0.5 mm from the foveal center) or cone spatial organization (ratio of hexagonal Voronoi domain: 43.7% ± 4.4% vs 44.3% ± 4.9%; P = .76; measured 0.5 mm from the foveal center). Furthermore, SDOCT showed that the 2 groups did not differ significantly in terms of the photoreceptor-related layer thickness, and that the photoreceptor ellipsoid zone band was continuous in all normal and glaucoma eyes. In glaucoma eyes with vertically asymmetric severity, the more affected side did not significantly differ from the less affected side in terms of cone density, cone spatial organization, or photoreceptor-related layer thickness. In 8 eyes (22.9%) with glaucoma, dark, partition-like areas surrounded the cones on the AO-SLO.

CONCLUSIONS

Both AO-SLO and SDOCT showed cone integrity in eyes with glaucoma, even in areas with visual field and nerve fiber loss. In AO-SLO, microcystic lesions in the inner nuclear layer may influence images of the cone mosaic.

CORRELATION OF OPTICAL COHERENCE TOMOGRAPHY AND MACULAR PIGMENT OPTICAL DENSITY MEASUREMENTS IN TYPE 2 IDIOPATHIC MACULAR TELANGIECTASIA

PURPOSE

Macular telangiectasia is associated with neurodegenerative changes including focal outer retinal atrophy and a loss of macular pigment (MP). We aimed to investigate whether an association between spectral domain optical coherence tomography neurodegenerative signs and MP abnormalities can be detected.

METHODS

Forty-seven eyes of 27 macular telangiectasia Type 2 patients (mean age 66.7 years, range 50-82 years, 12 male) were investigated. An MP pattern was recorded using a dual-wavelength autofluorescence method and classified according to severity (I-III). Outer plexiform, inner nuclear, and photoreceptor layer thickness values were measured in Spectralis spectral domain optical coherence tomography scans. Thickness values were compared with those of a control group of 14 healthy age-matched eyes.

RESULTS

Macular pigment redistribution was found to be Class I in 11 eyes, Class II in 28 eyes, and Class III in 8 eyes. More advanced stages of MP loss were associated with a greater, statistically significant thinning of the outer plexiform and inner nuclear layer complex and photoreceptor layers (P ≤ 0.001). Lower absolute levels of MP were also associated with a thinning of the photoreceptor layer. Thinning was restricted to within the parafovea, more severe at temporal eccentricities.

CONCLUSION

Our findings support the hypothesis that in macular telangiectasia Type 2 cellular degenerative processes leading to a thinning of these layers also result in reduction and redistribution of MP.

Microcystic Inner Nuclear Layer Changes and Retinal Nerve Fiber Layer Defects in Eyes with Glaucoma

Objective

To examine microcystic inner nuclear layer (INL) changes in glaucomatous eyes and to determine associated factors.

Design

Retrospective, cross-sectional, observational study.

Methods

Two hundred seventeen eyes of 133 patients with primary open angle glaucoma (POAG), 41 eyes of 32 patients with preperimetric glaucoma and 181 normal eyes of 117 subjects were ultimately included. Microcystic INL lesions were examined with infrared fundus images and with 19 vertical spectral domain optical coherence tomography (SD-OCT) images in the macular area.

Results

Microcystic INL changes were observed in 6.0% of eyes with POAG, but none of the normal eyes or eyes with preperimetric glaucoma showed microcystic INL changes. The proportion of eyes with advanced glaucoma was significantly larger (P = 0.013) in eyes with microcystic lesions than without. The visual field mean deviation (MD) slope was also significantly worse (P = 0.027) in eyes with microcystic lesions. No significant differences were observed in age, sex, refraction, axial length, intraocular pressure, or MD value between eyes with and without microcystic INL lesions. In several cases, microcystic INL lesions occurred along with glaucomatous visual field progression. The retinal nerve fiber layer (RNFL) thickness (P = 0.013) and ganglion cell layer (GCL) + inner plexiform layer thickness (P = 0.023) were significantly lower in areas with microcystic lesions than without. The INL was also significantly thicker (P = 0.002) in areas with microcystic lesions.

Conclusions

Microcystic INL lesions in glaucomatous eyes are closely associated with RNFL and GCL thinning and correlated with worse MD slope. These INL lesions may indicate focal and progressive damage in glaucoma.

Regional choroidal blood flow and multifocal electroretinography in experimental glaucoma in rhesus macaques

PURPOSE

To test a hypothesis of regional variation in the effect of experimental glaucoma on choroidal blood flow (ChBF) and retinal function.

METHODS

Five rhesus macaques underwent laser trabecular destruction (LTD) to induce elevated intraocular pressure (IOP). Intraocular pressures were elevated for 56 to 57 weeks. Multifocal electroretinographic (mfERG) and multifocal visual evoked cortical potential (mfVEP) testing were performed at regular intervals before and during the period of IOP elevation. At euthanasia, the IOP was manometrically controlled at 35 (experimentally glaucomatous eye) and 15 (fellow control eye) mm Hg. Fluorescent microspheres were injected into the left ventricle. Regional ChBF was determined.

RESULTS

All of the experimentally glaucomatous eyes exhibited supranormal first-order kernel (K1) root mean square (RMS) early portions of the mfERG waveforms and decreased amplitudes of the late waveforms. The supranormality was somewhat greater in the central macula. Second-order kernel, first slice (K2.1) RMS mfVEP response was inversely correlated (R(2) = 0.97) with axonal loss. Total ChBF was reduced in the experimentally glaucomatous eyes. The mean blood flow was 893 ± 123 and 481 ± 37 μL/min in the control and glaucomatous eyes, respectively. The ChBF showed regional variability with the greatest proportional decrement most often found in the central macula.

CONCLUSIONS

This is the first demonstration of globally reduced ChBF in chronic experimental glaucoma in the nonhuman primate. Both the alteration of mfERG waveform components associated with outer retinal function and the reduction in ChBF were greatest in the macula, suggesting that there may be a spatial colocalization between ChBF and some outer retinal effects in glaucoma.

Optical coherence tomography: future trends for imaging in glaucoma

Optical coherence tomography captures a major role in clinical assessment in eye care. Innovative hardware and software improvements in the technology would further enhance its usefulness. In this review, we present several promising initiatives currently in development or early phase of assessment that we expect to have a future impact on optical coherence tomography.

Critical pathogenic events underlying progression of neurodegeneration in glaucoma

Glaucoma is a common optic neuropathy with a complex etiology often linked to sensitivity to intraocular pressure. Though the precise mechanisms that mediate or transduce this sensitivity are not clear, the axon of the retinal ganglion cell appears to be vulnerable to disease-relevant stressors early in progression. One reason may be because the axon is generally thin for both its unmyelinated and myelinated segment and much longer than the thicker unmyelinated axons of other excitatory retinal neurons. This difference may predispose the axon to metabolic and oxidative injury, especially at distal sites where pre-synaptic terminals form connections in the brain. This idea is consistent with observations of early loss of anterograde transport at central targets and other signs of distal axonopathy that accompany physiological indicators of progression. Outright degeneration of the optic projection ensues after a critical period and, at least in animal models, is highly sensitive to cumulative exposure to elevated pressure in the eye. Stress emanating from the optic nerve head can induce not only distal axonopathy with aspects of dying back neuropathy, but also Wallerian degeneration of the optic nerve and tract and a proximal program involving synaptic and dendritic pruning in the retina. Balance between progressive and acute mechanisms likely varies with the level of stress placed on the unmyelinated axon as it traverses the nerve head, with more acute insult pushing the system toward quicker disassembly. A constellation of signaling factors likely contribute to the transduction of stress to the axon, so that degenerative events along the length of the optic projection progress in retinotopic fashion. This pattern leads to well-defined sectors of functional depletion, even at distal-most sites in the pathway. While ganglion cell somatic drop-out is later in progression, some evidence suggests that synaptic and dendritic pruning in the retina may be a more dynamic process. Structural persistence both in the retina and in central projection sites offers the possibility that intrinsic self-repair pathways counter pathogenic mechanisms to delay as long as possible outright loss of tissue.