Optic disc cup slope and visual field indices in normal, ocular hypertensive and early glaucomatous eyes

Current literature suggests that a significant degree of optic nerve fibre loss precedes visual field defect formation in patients with glaucomatous optic neuropathy. ^{1- 3} A study by Sommer et al ⁴ found that nerve fibre layer defects were detectable up to 6 years before visual field loss could be clinically demonstrated. In order to examine for optic nerve head changes, the confocal scanning laser ophthalmoscope (SLO) has become a useful tool in the morphological assessment of the optic nerve head. ⁵ Area and volume derived topographic parameters have been studied extensively for their ability to discriminate normal eyes from those with glaucoma, ^{6- 8} but only a handful of studies have examined the slope measurement parameter of the optic disc cup. Dong et al , ⁹ using sector based slope, and Caprioli et al , ¹⁰ using peripapillary slope measurements, have examined this function in separating normal from glaucomatous eyes. However, the correlation between visual field indices and slope values have not been previously examined. In the knowledge that disc slope changes may occur before visual field change, this study examines for the relation between this parameter and visual field indices in a population of normal, ocular hypertensive, and early glaucoma patients, all having a visual field mean deviation better than -4 dB.

PATIENTS AND METHODS

Three age and sex matched white groups consisting of normal subjects (n = 22) and patients with ocular hypertension (OHT) (n = 21) and primary open angle glaucoma (POAG) (n = 50) were recruited at Bristol Eye Hospital. Patients with OHT and POAG were recruited from the glaucoma clinic, while normal subjects were recruited following advertisements in the local media. These had an age range from 49 to 89 years. The mean age for each group was 62 years (normal), 67 years (ocular hypertensives), and 68 years (glaucoma) respectively. This prospective cross sectional study was approved by the ethics committee for the United Bristol Healthcare Trust and informed consent was obtained from all of the patients. One eye was randomly selected from each subject before entry into the study and only eyes with a spherical equivalent between -5 and +5 dioptres were included.

Normal subjects were included in the study if there was no family history of...