The Degree of Intereye Asymmetry of Retinal Nerve Fiber Layer and Its Association with Other Structural and Functional Parameters Differences Between Eyes in Glaucoma.

Abstract

Purpose : This study aims to evaluate the intereye asymmetry of selected structural and functional parameters in glaucoma and normal eyes between groups divided by the degree of circumpapillary retinal nerve fiber layer (cRNFL) thickness asymmetry between eyes.

Methods : Subjects with glaucoma and normal controls were included. Patients underwent 24-2 perimetry and Spectral Domain Optical Coherence Tomography (SD-OCT). Parameters analyzed were: cRNFL, average circumpapillary choroidal thickness (cChoroid), the hypotenuse of the vertical optic nerve head cup (HVOC) and VF mean deviation (MD). cChoroid was calculated as the mean between the measurements at 0^o, 90^o,180^o and 270^o of the circular B-scan. For calculating HVOC the length and depth of the optic nerve cup were used as the sides of a right triangle. The length was measured as the distance between the innermost portion of the descending RNFL tissue at the Bruch’s membrane opening level plan. The depth was measured as distance between the former line and the maximum depth of the anterior prelaminar tissue. Patients were divided into 3 groups based on the degree of asymmetry of cRNFL between eyes.Statistical analysis was performed using general estimate equations (GEE), One-way ANOVA and Tukey HSD test.

Results : 110 eyes (55 subjects) qualified for the study. The mean (SD) age was 65 (13.38) years. The number of subjects was 49 in the glaucoma and 6 in the control group. Three groups were divided by the terciles of the cRNFL difference between eyes: 1: ≤ 4 µm (n=21, 4 controls); 2: 5-13 µm (n=18, 2 controls) and 3: ≥14 µm (n=16, no controls). The mean (SD) cRNFL asymmetry within the groups was: 2.71 (1.35) µm, 9.28 (2.90) µm and 25.31 (12.56) µm (p<0.001), respectively. The average of the parameters in each group are depicted in table 1 showing that MD, cRNFL and HVOC were worse in the group with more intereye asymmetry. The MD, cRNFL and HVOC average differences between eyes comparing the 3 groups were significant (p<0.001)(Table 2).

Conclusions : The ONH parameter HVOC and the VF MD demonstrated significant intereye differences between the groups based on the degree of intereye asymmetry of the cRNFL. Evaluating additional SD-OCT parameters asymmetry may provide additional biomarkers and strategies for the diagnosis and monitoring of glaucoma.

This is a 2021 ARVO Annual Meeting abstract.