Correlation Of Optic Disc Changes With Visual Field Defects In Primary Open Angle Glaucoma – A Cross Sectional Study

Abstract

BACKGROUND ABSTRACT Primary open angle glaucoma ( POAG ) is a progressive chronic optic neuropathy in adults where intraocular pressure ( IOP ) and other currently unknown factors contribute to damage and in which in the absence of other identifiable causes, there is characteristic acquired atrophy of the optic nerve and loss of retinal ganglion cells and their axons with a corresponding visual field loss. This loss is usually very insidious and starts in the Bjerrum’s area and leaves the patients asymptomatic in the early stages. The importance of the correlation of the optic disc changes with the visual field defects in primary open angle glaucoma cannot be stressed enough and is the need of the hour to help in detecting the glaucomatous changes early in the course of the disease and thereby help prevent blindness. OBJECTIVES 1. To correlate the optic disc parameters with the visual field defects in primary open angle glaucoma patients using magnified photographs of the optic disc and Humphrey Field Analyzer. 2. To look for the features of the optic disc commonly associated with early visual field loss by Humphrey Visual Field Analyzer II using Swedish Interactive Threshold Algorithm program. METHODS This was a cross sectional study in which 96 eyes of 48 patients of primary open angle glaucoma who met the inclusion criteria were included. After obtaining written informed consent, all patients underwent a detailed optic disc evaluation by slit lamp biomicroscopy and visual field analysis with SITA Standard algorithm using Humphrey Visual Field Analyzer II - i series perimeter. VI RESULTS On correlating the type of NRR notching with the visual field defects ( scotomas) using Kappa statistics, the agreement of the visual field defects with the morphometric optic disc parameter ( NRR notching ) was good ( 0.959) and statistically significant p < 0.001. When the increasing mean deviation ( dB ) was correlated with the larger cup:disc ratio using chi square test, it was found to be statistically significant with p < 0.001, χ² = 76.753, DF = 6. When the increasing IOP was correlated with larger C:D ratio, p value was found to be < 0.001 which indicates statistically significant good correlation between IOP and C:D ratio. CONCLUSION The optic disc parameter neuroretinal rim notching correlated best with the visual field defects and is a optic disc variable superior to the cup/disc ratio in correlation with visual field defects. The earliest glaucomatous disc change is inferior neuroretinal rim notching and is a good optic disc parameter to differentiate between ocular hypertensives and POAG patients. A large cup/disc ratio is not necessarily a sign of visual field loss. However, the correlation between increasing cup/disc ratio and increasing IOP is good, suggesting that concentric enlargement of the optic cup is largely pressure dependent. The mean deviation by HFA correlates well with the cup/disc ratio in advanced glaucoma more than in early glaucoma.