Psychophysical testing in glaucoma.

Glaucoma can be diagnosed as a group of conditions that share a characteristic topographic change at the optic nerve head (glaucomatous cupping) and pattern of visual loss (glaucomatous visual field defect). Usually the intraocular pressure (IOP) lies above the normal range. For a common complaint, the existence of which has been known for centuries, we ophthalmologists are not good at identifying its early stages or recognising progression of the established disease. We are quite good at measuring IOP but, with progression still occurring despite IOP levels within the normal range, quantification of optic disc and visual field changes are essential to good glaucoma management. The recognition of optic disc'2 and retinal nerve fibre change23 predating observed visual loss has led to enormous efforts being made to characterise these features. Although we can record and describe them2"7 we are not good at measuring them.4' It is to be hoped that the current research with scanning laser ophthalmoscopes can resolve this problem, both for the optic disc and the peripapillary nerve fibres. In the absence of objective measurement data on optic disc change, the ability of visual psychophysics and electro-physiology to quantify visual change has an increasing, importance. Tests which examine specific aspects ofretinal sensitivity-for example, in the discrimination of spatial or temporal stimuli, coloured stimuli, or stimuli ofvarying contrast, have frequently been advocated in the study of glaucoma."' Recent studies on experimental models of ocular hyper-tension, such as those described by Ofri et al in this issue of the journal and in more detail elsewhere'2 have provided good electrophysiological evidence for abnormal retinal sensitivity before the onset of clinical and/or pathological signs. It is the purpose of this editorial to assess the current position. Quantification of visual performance took a major leap forward with the harnessing of computer driven software to the bowl perimeter. Current programs provide raw data which can be subjected to intense analysis. The cost of this development has been the capital expenditure, reduced patient throughput, and patient alienation. Inadequate training has led to the ophthalmic equivalent of 'garbage in, garbage out,' with medical dependence on 'the printout,' negating clinical skills and burying true visual field change. With training and test repetition the quality ofdata improves, allowing reliance to be placed on the results of data analysis. The earliest sign ofdisease remains focal depression of¢5 dB at two or more contiguous locations repeated on retesting once or preferably …