QUANTITATIVE-EVALUATION OF THE OPTIC-NERVE HEAD IN EARLY GLAUCOMA

Aims-Progressive loss of neuroretinal rim tissue is known to occur ear ly in glaucoma and measurement of the neuroretinal rim area is possibl e by magnification corrected analysis of optic disc photographs (plani metry). This study was performed to determine whether the facility to distinguish between glaucomatous and normal optic discs could be impro ved upon by: (a) taking into account the known relation between optic disc size and neuroretinal rim area, and (b) measuring rim area in a n umber of segments, in order to detect focal changes. Methods-Planimetr ic examination of the optic disc photographs of 88 control subjects an d 51 patients with early visual field defects was performed. In the co ntrol group, multiple linear regression analysis was performed between neuroretinal rim area and optic disc area, age, sex, eye side, refrac tion, and keratometry. This was repeated for the whole disc and for ea ch of twelve 30 degree segments. Normal ranges were defined by the 98% prediction intervals of the regression analysis and the sensitivity a nd specificity for correct identification of optic discs in the two gr oups determined. Results-Multiple linear regression demonstrated signi ficant associations between the neuroretinal rim area and optic disc a rea and age in normal subjects. Sensitivity and specificity for glauco ma diagnosis, using the cut off derived from the 98% prediction interv als, was 37.7% and 98.9% respectively when total neuroretinal rim area alone was considered, and 88.7% and 94.3% respectively when the 30 de gree segments were included. The most frequent pattern of neuroretinal rim loss was diffuse, followed by thinning in more than one sector an d then by thinning in the inferotemporal sector alone. Conclusions-Thi s method of optic disc analysis enables the examiner to identify glauc omatous optic discs at the stage of early perimetric loss with a high degree of precision. Optic disc photography is simple, and fundus came ras are widely available. This method for glaucoma case identification may therefore be suitable for the primary care setting as well as hos pital practice.