Optical Coherence Tomography Imaging for Glaucoma - Today and Tomorrow

OCT Intensity of the Region between Outer Retina Band 2 and Band 3 as a Biomarker for Retinal Degeneration and Therapy

Optical coherence tomography (OCT) is widely used to probe retinal structure and function. This study investigated the outer retina band (ORB) pattern and reflective intensity for the region between bands 2 and 3 (Dip) in three mouse models of inherited retinal degeneration (Rs1KO, TTLL5KO, RPE65KO) and in human AMD patients from the A2A database. OCT images were manually graded, and reflectivity signals were used to calculate the Dip ratio. Qualitative analyses demonstrated the progressive merging band 2 and band 3 in all three mouse models, leading to a reduction in the Dip ratio compared to wildtype (WT) controls. Gene replacement therapy in Rs1KO mice reverted the ORB pattern to one resembling WT and increased the Dip ratio. The degree of anatomical rescue in these mice was highly correlated with level of transgenic RS1 expression and with the restoration of ERG b-wave amplitudes. While the inner retinal cavity was significantly enlarged in dark-adapted Rs1KO mice, the Dip ratio was not altered. A reduction of the Dip ratio was also detected in AMD patients compared with healthy controls and was also positively correlated with AMD severity on the AMD score. We propose that the ORB and Dip ratio can be used as non-invasive early biomarkers for retina health, which can be used to probe therapeutic gene expression and to evaluate the effectiveness of therapy.

Association of SIX1-SIX6 polymorphisms with peripapillary retinal nerve fibre layer thickness in children

PURPOSE

Association of SIX1-SIX6 variants with peripapillary retinal nerve fibre layer (p-RNFL) thickness had been reported in adults. This study aimed to investigate these associations in children, with further explorations by spatial, age and sex stratifications.

METHODS

2878 school children aged between 6 and 9 years were enrolled from the Hong Kong Children Eye Study. Three single-nucleotide polymorphisms (SNPs) at the SIX1-SIX6 locus were genotyped. The association of each SNP with p-RNFL thickness (including global and sectoral thickness) were evaluated using multiple linear regression.

RESULTS

SNPs rs33912345 (p=7.7×10^-4) and rs10483727 (p=0.0013) showed significant associations with temporal-inferior p-RNFL thickness. The C allele of rs33912345 was associated with a thinner temporal-inferior p-RNFL by an average of 2.44 µm, while rs10483727-T was associated with a thinner temporal-inferior p-RNFL by 2.32 µm. The association with temporal-inferior p-RNFL was the strongest in the 8-9 year-old group for rs33912345 (p=5.2×10^-4) and rs10483727 (p=3.3×10^-4). Both SNPs were significantly associated with temporal-inferior p-RNFL thickness in boys (p<0.0017), but not in girls (p>0.05). In contrast, rs12436579-C (β=1.66; p=0.0059), but not rs33912345-C (β=1.31; p=0.052) or rs10483727-T (β=1.19; p=0.078), was nominally associated with a thicker nasal-inferior p-RNFL.

CONCLUSIONS

Both rs33912345 and rs10483727 at SIX1-SIX6 were associated with p-RNFL thickness in children, especially at the temporal-inferior sector, with age-dependent and sex-specific effects. SNP rs12436579 was associated with nasal-inferior p-RNFL thickness. Our findings suggested a role of SIX1-SIX6 in RNFL variation during neural retina development in childhood.

Automated iris volume analysis and trabecular meshwork length using anterior segment optical coherence tomography - Application in pseudoexfoliation and pseudoexfoliation glaucoma

Purpose:

The aim of this study was to evaluate differences in the iris and angle parameters in psuedoexfoliation syndrome (PXF) and pseudoexfoliation glaucoma (PXG) using anterior segment optical coherence tomography (ASOCT).

Methods:

Patients with PXF or PXG were compared using ASOCT with primary open-angle glaucoma POAG eyes as controls in this noninterventional comparative study conducted at a tertiary eye care center in East India. All angle parameters, TM length, and iris thickness were analyzed from the enhanced depth imaging (EDI) single scans obtained. Quadrant scans were used for the calculation of iris volume using a custom-built in-house software. In particular, the software performs multiple operations including edge detection, connected components, and thresholding to localize and segment the iris. Differences in the iris volume/thickness and TM length in PXF and PXG with POAG were analyzed.

Results:

A total of 225 eyes were included, which included 75 PXG and 98 PXF cases and 52 POAG with a mean age of 67 ± 9.7 years at presentation. The algorithm repeatability and reproducibility was also established with correlation coefficients more than 99% which was substantiated with Bland-Altman plots. The iris volume (calculated in 197 images of 225 eyes) did not differ significantly in PXF and PXG eyes, although both had significantly greater volume compared to POAG eyes. The iris volume or other angle parameters including TM length did not correlate with clinical variables such as IOP, age, or visual field indices.

Conclusion:

Iris parameters or TM length do not explain pathogenesis of glaucoma in pseudoexfoliation.

Progression of Macular Vessel Density in Primary Open-Angle Glaucoma: A Longitudinal Study

PURPOSE

To evaluate the rate of progression of macular vessel density (mVD) in primary open-angle glaucoma (POAG) and explore the relationship between the progression of mVD and macular ganglion cell-inner plexiform layer (mGCIPL) thickness and parapapillary retinal nerve fiber layer (pRNFL) thickness.

DESIGN

Prospective cohort study.

METHODS

In this study, 102 eyes with POAG were followed for 36.6 ± 6.4 months. The rates of progression were estimated by linear models. The agreement of progression detection among the 3 parameters was evaluated with Kappa statistics. The influence of baseline measurements on the rates of progression of mGCIPL thickness, pRNFL thickness, and mVD was investigated by linear mixed modeling. Kaplan-Meier survival analysis was adopted to calculate the survival probabilities.

RESULTS

The respective rate of progression by linear regression was -0.102 ± 0.054 μm/month, -0.160 ± 0.086 μm/month, and -0.199 ± 0.073 %/month for mGCIPL thickness, pRNFL thickness, and mVD. The agreement in detection of progression among them was poor with the Conger's Kappa coefficient of 0.098 (95% confidence interval: -0.025~0.220, P = .116). The significant factors influencing the rate of progression of mVD were baseline mGCIPL thickness, baseline pRNFL thickness, and baseline mVD (P ≤ .001), while baseline mVD was not a significant factor influencing the rates of progression of mGCIPL thickness and pRNFL thickness (P ≥ .659). Also, pRNFL thickness had a better survival probability compared with the other 2 parameters (P = .025).

CONCLUSIONS

The mGCIPL thickness, pRNFL thickness, and mVD decreased over time in POAG eyes. The rate of reduction of mVD was significantly influenced by the baseline measurements of mGCIPL thickness, pRNFL thickness, and mVD.

Smaller Anterior Chamber Volume Is Associated With Higher Risk of Intraocular Pressure Elevation After Laser Peripheral Iridotomy: A 1-Year Follow-Up Study

PURPOSE

The aim of this study was to analyze the predictive value of swept-source optical coherence tomography (SS-OCT) derived anterior-segment volumetric parameters such as anterior chamber volume (ACV) in the long-term follow-up of primary angle closure disease (PACD).

DESIGN

Longitudinal observational study.

METHODS

In this single-center longitudinal observational study, PACD patients undergoing laser peripheral iridotomy (LPI) were recruited. Anterior segment images of the patients were captured using SS-OCT before LPI, and at 1 week, 1 month, 3 months, 6 months, and 1 year after LPI. Ninety eyes of 81 subjects were enrolled, and 72 eyes of 72 subjects finished the 1 year follow-up. Data of all the 81 subjects were included for analysis. Intraocular pressure (IOP) elevation was defined as IOP >21 mm Hg at any time point after LPI. The association between baseline trabecular-iris space area 750 μm from scleral spur (TISA750), ACV and iris volume (IV), and IOP elevation were analyzed using logistic regression.

RESULTS

Eighty-one subjects were included, 59 were female, and 22 were male, with a mean age of 60.98± 9.44 years. IOP elevation appeared in 14 eyes. Mean TISA750 was negatively associated with IOP elevation (OR = 0.94, P = 0.02). The correlation of TISA750 with IOP elevation varies across quadrants and there was only significant association in temporal TISA750 (OR = 0.98, P = 0.046), whereas in the other 3 quadrants, there was no significant association. Greater ACV was associated with lower risk of IOP elevation (OR = 0.80, P = 0.031), whereas IV was not associated with IOP elevation.

CONCLUSIONS

ACV is a reliable and accurate predictor for the outcome of PACD. Due to its 3-dimensional nature, the robustness of ACV is greater than traditional angle width parameters such as TISA750.

One year structural and functional glaucoma progression after trabeculectomy

We evaluated the changes in visual field mean deviation (VF MD) and retinal nerve fibre layer (RNFL) thickness in glaucoma patients undergoing trabeculectomy. One hundred patients were examined with VF and spectral-domain optical coherence tomography (OCT) before trabeculectomy and 4 follow-up visits over one year. Linear mixed models were used to investigate factors associated with VF and RNFL. VF improved during the first 3 months of follow-up (2.55 ± 1.06 dB/year) and worsened at later visits (−1.14 ± 0.29 dB/year). RNFL thickness reduced by −4.21 ± 0.25 µm/year from 1st month of follow-up. Eyes with an absence of initial VF improvement (β = 0.64; 0.30–0.98), RNFL thinning (β = 0.15; 0.08–0.23), increasing intraocular pressure (IOP; β = −0.11; −0.18 to −0.03) and severe glaucoma (β = −10.82; −13.61 to −8.02) were associated with VF deterioration. Eyes with VF deterioration (β = 0.19; 0.08–0.29), increasing IOP (β = −0.09; −0.17 to −0.01), and moderate (β = −6.33; −12.17 to −0.49) or severe glaucoma (β = −19.58; −24.63 to −14.52) were associated with RNFL thinning. Changes in RNFL structure and function occur over a 1-year follow-up period after trabeculectomy. Early VF improvement is more likely to occur in patients with mild/moderate glaucoma, whereas those with severe glaucoma show greater decline over one year. Our findings indicate that progression is observable using OCT, even in late-stage glaucoma.

Glaucoma detection using image processing techniques: A literature review

The term glaucoma refers to a group of heterogeneous diseases that cause the degeneration of retinal ganglion cells (RGCs). The degeneration of RGCs leads to two main issues: (i) structural changes to the optic nerve head as well as the nerve fiber layer, and (ii) simultaneous functional failure of the visual field. These two effects of glaucoma may lead to peripheral vision loss and, if the condition is left to progress it may eventually lead to blindness. No cure for glaucoma exists apart from early detection and treatment by optometrists and ophthalmologists. The degeneration of RGCs is normally detected from retinal images which are assessed by an expert. These retinal images also provide other vital information about the health of an eye. Thus, it is essential to develop automated techniques for extracting this information. The rapid development of digital images and computer vision techniques have increased the potential for analysis of eye health from images. This paper surveys current approaches to detect glaucoma from 2D and 3D images; both the limitations and possible future directions are highlighted. This study also describes the datasets used for retinal analysis along with existing evaluation algorithms. The main topics covered by this study may be enumerated as follows.

Volumetric parameters-based differentiation of narrow angle from open angle and classification of angle configurations: an SS-OCT study

BACKGROUND

To evaluate the diagnostic ability of volumetric parameters to differentiate narrow angle from open angle and distinguish different configurations of narrow angle.

METHODS

The current study was composed of two parts. In the first part, with gonioscopy as reference standard, we tested power of each parameter to differentiate narrow angle from open angle. In the second part, we evaluated the efficacy of different parameters to distinguish angle configurations which were subclassified into type 1 (pupillary block) and type 2 (non-pupillary block and multiple mechanisms) based on ultrasound biomicroscopy (UBM) images.

RESULTS

In part 1, the training set was composed of 117 narrow-angle eyes and 60 open-angle eyes, and the validation set included 38 narrow-angle eyes and 37 open-angle eyes. Anterior chamber volume (ACV) outperformed all the other parameters with an area under the curve (AUC) of 0.988. The sensitivity and specificity of the cut-off value 98.1 mm³ in the validation set were 90.0% and 97.1%, respectively. In part 2, training set was composed of 96 eyes of 88 patients with primary angle-closure disease, with 49 diagnosed as type 1 and 47 as type 2 configuration. 32 eyes were used for validation. A model comprised of iris volume (IV), iris thickness (IT) 2000 µm from the scleral spur and angle open distance (AOD) 750 µm from the scleral spur was found to have an AUC of 0.793 (95% CI, 0.695 to 0.870). Sensitivity and specificity of the model were 82.6% and 77.8% respectively in the validation set.

CONCLUSIONS

With ACV, we can detect patients with narrow angle from open angle faster and more easily than AOD and anterior chamber depth. Then, for patients with narrow angle, the combination of IV, IT and AOD750 measured by swept-source optical coherence tomography could further classify configurations of angle closure compared with UBM.

Automatic Assessment of Biometric Parameters in Optic Nerve Head Area by "Zhongshan ONH Calculator (ZOC)"

PURPOSE

To test the repeatability and reproducibility of the Zhongshan ONH Calculator (ZOC) software in terms of selected optic nerve head (ONH) parameters commonly used in clinical research of glaucoma.

MATERIALS AND METHODS

Forty-two horizontal single-line scans were selected to test the repeatability and reproducibility of the ZOC software. Clinically relevant 2D parameters of the ONH area were selected to test repeatability of ZOC, including length of BMO, minimum rim thickness on both sides (RIML and RIMR), optic cup depth (OCD), and depth of the anterior surface of the LC (ALCD).

RESULTS

Intraobserver test showed higher the intra-class correlation coefficient (ICC) of BMO ((0.991 vs. 0.777), RIML (0.988 vs. 0.890), RIMR (0.972 vs. 0.846), OCD (0.997 vs. 0.992), and ALCD (0.993 vs. 0.949) by single researcher using ZOC software than manual measurement. BA analysis showed acceptable agreement between automatic and manual measurements. SDs and limits of agreement (95% CI) of BMO, RIML, RIMR, OCD, and ALCD were 0.05 (-0.13, 0.07), 0.03 (-0.05, 0.05), 0.03 (-0.06, 0.07), 0.015 (-0.035, 0.024), and 0.04 (-0.07, 0.08), respectively.

CONCLUSION

This study presented the design and development of software for the automatic measurement of OCT images of ONH area with good reproducibility. In the future, with advances of OCTs and improvements to the resolution of the LC, ZOC will become a powerful tool in glaucoma research.

The Role of Microglia in Retinal Neurodegeneration: Alzheimer's Disease, Parkinson, and Glaucoma

Microglia, the immunocompetent cells of the central nervous system (CNS), act as neuropathology sensors and are neuroprotective under physiological conditions. Microglia react to injury and degeneration with immune-phenotypic and morphological changes, proliferation, migration, and inflammatory cytokine production. An uncontrolled microglial response secondary to sustained CNS damage can put neuronal survival at risk due to excessive inflammation. A neuroinflammatory response is considered among the etiological factors of the major aged-related neurodegenerative diseases of the CNS, and microglial cells are key players in these neurodegenerative lesions. The retina is an extension of the brain and therefore the inflammatory response in the brain can occur in the retina. The brain and retina are affected in several neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and glaucoma. AD is an age-related neurodegeneration of the CNS characterized by neuronal and synaptic loss in the cerebral cortex, resulting in cognitive deficit and dementia. The extracellular deposits of beta-amyloid (Aβ) and intraneuronal accumulations of hyperphosphorylated tau protein (pTau) are the hallmarks of this disease. These deposits are also found in the retina and optic nerve. PD is a neurodegenerative locomotor disorder with the progressive loss of dopaminergic neurons in the substantia nigra. This is accompanied by Lewy body inclusion composed of α-synuclein (α-syn) aggregates. PD also involves retinal dopaminergic cell degeneration. Glaucoma is a multifactorial neurodegenerative disease of the optic nerve, characterized by retinal ganglion cell loss. In this pathology, deposition of Aβ, synuclein, and pTau has also been detected in retina. These neurodegenerative diseases share a common pathogenic mechanism, the neuroinflammation, in which microglia play an important role. Microglial activation has been reported in AD, PD, and glaucoma in relation to protein aggregates and degenerated neurons. The activated microglia can release pro-inflammatory cytokines which can aggravate and propagate neuroinflammation, thereby degenerating neurons and impairing brain as well as retinal function. The aim of the present review is to describe the contribution in retina to microglial-mediated neuroinflammation in AD, PD, and glaucomatous neurodegeneration.