BACKGROUND Glaucoma is a chronic progressive optic neuropathy characterised by optic nerve head changes and field defects due to apoptosis of ganglion cells, with raised intraocular pressure being the most important risk factor. Traditionally Armaly's cup/disc (C/D) ratio was considered as a standard method of evaluation of optic nerve head. The Disc Damage Likelihood Scale DDLS relies on the optic nerve as a direct indicator of disease. Because the scale divides glaucomatous progression into 10 stages, it can also aid to monitor the disease progression. DDLS helps in quantification of the amount of damage that the optic nerve has sustained. This study correlates the DDLS score with the visual field indices establishing a structural and functional correlation. We wanted to analyse Disc Damage Likelihood Ratio in patients with established open angle glaucoma and to correlate it with field defects and to thereby obtain an anatomical versus functional correlation. This study also evaluates the diagnostic ability of disc damage likelihood scale in glaucoma. METHODS 50 cases of established open angle glaucoma were included in this study. For all cases visual fields were recorded by Octopus 301 using G1 program and TOP strategy. After field testing, DDLS scores were calculated after dilatation. The DDLS score and field parameters of the patients were analysed. RESULTS Of the 50 patients included in this study, 70% were on topical antiglaucoma medications and 30% had undergone trabeculectomy. DDLS score and average loss variance showed a strong positive correlation as the r value was 0.95. CONCLUSIONS Disc diameter evaluation is an important part of optic nerve head evaluation. In cases with asymmetry of the cup disc ratio between two eyes, asymmetry of the disc size should also be considered if the neuroretinal rim is healthy. Disc Damage Likelihood Scale (DDLS) is a better indicator of optic nerve head status and has strong positive correlation with visual field indices. KEYWORDS Disc Damage Likelihood Scale, Automated Perimetry, Field Defects in Glaucoma. HOW TO CITE THIS ARTICLE: Chitra MR, Ramanathan A. Correlation of disc damage likelihood scale with field defects in established glaucomas-an anatomical versus functional correlation.

BACKGROUND Glaucoma is the second leading cause of blindness globally. Intraocular pressure and vascular risk factors have been proposed to be important risk factors in the development of glaucoma. The aim of this study is to describe the variation of ocular perfusion pressure and intraocular pressure in normal subjects, glaucoma suspects, which include Ocular Hypertension (OHT) suspects and Normotensive Glaucoma (NTG) suspects and established primary open-angle glaucoma patients over a period of 24 hours. MATERIALS AND METHODS A cross-sectional study was conducted for 24 hours at the glaucoma services of a tertiary eye care hospital at Chennai. Totally, 30 eyes (right eye) of 30 patients were included and they were categorised into four groups-Group A (normal)-Subjects with normal IOP, fields and normal optic nerve head and RNFL on fundus examination; 12 eyes were included. Group B (ocular hypertension suspects)-Subjects with normal fields and normal optic nerve head on fundus examination, but with elevated IOP; 8 eyes were included. Group C (normotensive glaucoma NTG suspects)-Subjects with normal IOP and fields, but with optic nerve head changes like increased cup disc ratio, focal notching, focal NRR thinning or RNFL wedge defects; 8 eyes were included. Group D (primary open-angle glaucoma)-Subjects with increased IOP, typical glaucomatous field defects and optic nerve head and RNFL changes suggestive of glaucoma; 7 eyes were included. A thorough baseline investigation including applanation tonometry with central corneal thickness correction, gonioscopy and fields by automated perimeter (Octopus 301 perimeter) were done. Intraocular pressure and blood pressure were recorded at 12 p.m., 6 p.m., 12 a.m. and 6 a.m. The systolic, diastolic and mean ocular perfusion pressures were calculated. RESULTS Four parameters viz. intraocular pressure, systolic perfusion pressure, diastolic perfusion pressure and mean perfusion pressure were analysed over a period of 24 hours. The intraocular pressure fluctuation over 24-hour period in Group A was minimal with a standard deviation of 1.15. In group B, the mean intraocular pressure was lowest during 12 a.m. and the fluctuations were more with standard deviation of 1.63. Maximum fluctuations in IOP were found in Group C with standard deviation of 4.76. Systolic, diastolic and mean ocular perfusion pressures were lowest in POAG group with a dip at 12 a.m. In POAG group, diastolic perfusion pressures were as low as 35 mm Hg. CONCLUSION This study has demonstrated that the mean and diastolic ocular perfusion pressure is significantly lower in primary open-angle glaucoma group and NTG suspects when compared to other groups. This study also shows that large diurnal fluctuation of IOP is an important risk factor in open-angle and normotensive glaucomas.