The optic disc in glaucoma.

SIR, The article by Hitchings and Wheeler' demonstrates the difficulty in recognising nerve fibre layer loss in glaucoma. Except for a single case they noted no difference in the visibility of the nerve fibre layer between normotensive eyes and hypertensive mates of 10 patients with uniocular hypertension. Yet another case, illustrated in Fig. 4 of their article, clearly shows this difference. Nerve fibre layer striations are far more apparent in the normotensive than the hypertensive eye. The loss of nerve fibre layer is confirmed by the sharper definition of major vessels in the hypertensive eye. These changes are most apparent in the area of the superior temporal vein. Nerve fibre layer loss can be recognised by slit-like defects,2 but also by thinning of the nerve fibre layer as it crosses the temporal rim3 and as a general loss of striations and prominence of the major vessels near the disc.2 4 Unfortunately these changes are often difficult to recognise. Better, more reproducible techniques for visualisirig the nerve fibre layer and its abnormalities are clearly needed. Wilmer Ophthalmological Institute, ALFRED SOMMER 600 N Wolfe Street, Baltimore, Maryland 21205, USA.