Retinal vessel density from optical coherence tomography angiography to differentiate early glaucoma, pre-perimetric glaucoma and normal eyes.

PURPOSE: To evaluate optic nerve vascular density using swept source optical coherence tomography angiography (OCTA) in patients with early primary open angle glaucoma (POAG), pre-perimetric glaucoma and normal eyes. METHODS: This is a prospective, observational study including 56 eyes in total and divided into 3 groups; 20 eyes with mild POAG, 20 pre-perimetric glaucoma eyes, and 16 age-matched normal eyes as controls. The optic disc region was imaged by a 1050-nm-wavelength swept-source OCT system (DRI OCT Triton, TOPCON). Vessel density was assessed as the ratio of the area occupied by the vessels in 3 distinct regions: 1) within the optic nerve head; 2) in the 3 mm papillary region around the optic disc; and 3) in the peripapillary region, defined as a 700-µm-wide elliptical annulus around the disc. The potential associations between vessel density and structural, functional measures were analyzed. RESULTS: There was a statistically significant difference for the peripapillary vessel density, optic nerve head vessel density, and papillary vessel density among all the groups (p<0.001). Control eyes showed a significant difference for all measured vessel densities compared to glaucomatous eyes (p values from 0.001 to 0.024). There was a statistically significant difference between control and pre-perimetric glaucoma eyes for peripapillary, optic nerve head and papillary vessel density values (p values from 0.001 to 0.007). The optic nerve head vessel density, superior and inferior papillary area vessel density (Pearson r = 0.512, 0.436, 0.523 respectively) were highly correlated with mean overall, superior and inferior RNFL thickness in POAG eyes (p = 0.04, p = 0.02 and p = 0.04 respectively). Multiple linear regression analysis of POAG group showed that optic nerve head vessel density in POAG group was more strongly linked to RNFL thickness than to any other variables. CONCLUSIONS: Eyes with mild POAG could be differentiated from pre-perimetric glaucoma eyes, which also could be differentiated from normal eyes using OCTA-derived retinal vessel density measurements.

Quantitative analysis of retinal structures using spectral domain optical coherence tomography in normal rabbits.

PURPOSE: The purpose of this study is to quantify the normal retinal thickness (RT) and retinal nerve fiber layer thickness (RNFLT), and to obtain cross-sectional area measurements of the main retinal artery and vein in the rabbit animal model using spectral domain optical coherence tomography (SD-OCT). MATERIALS AND METHODS: Fifteen eyes of 15 adult rabbits were used to obtain SD-OCT scans. RT, RNFLT and cross-sectional areas of the main retinal artery and vein were measured with a custom-made software grading tool (OCTOR) on selected B-scans at the edge of the optic nerve head and at 1, 2, 3 and 4 mm from the nerve. Statistical comparisons were made using the analysis of variance test with post hoc comparison. RESULTS: In the nasal and temporal retina, the average RT and RNFLT decreased significantly with eccentricity from the optic disc. There was a statistically significant greater RT and RNFLT at the edge of the optic disc as compared with values at 1, 2, 3 and 4 mm from the disc edge (p < 0.01). Mean cross-sectional area of the primary retinal vein was significantly larger than the retinal artery (p < 0.01). CONCLUSIONS: We have quantified the cross-sectional dimensions of RT, RNFLT and the major retinal vessels in the rabbit retina with SD-OCT. These findings are novel anatomic features of the rabbit retina, which should be considered in any studies using this animal model.