Ethnic Variability of the Vasculature of the Optic Disc in Normal and in Glaucomatous Eyes

Abstract

Purpose

Although disc pallor is associated with glaucoma, the structural macro-anatomy of the disc vasculature has received little attention, and possible ethnic differences have not been considered. Accordingly we studied the distribution of blood vessels crossing the rim of the optic disc.

Methods

Thirty normal controls, and 50 glaucomatous cases with a unilaterally impaired visual field were studied. The sample populations included white Caucasian, and African and Afro/Caribbean volunteers. A b/w photographic method of imaging the blood vessels crossing the rim of the optic disc was used, the illuminant being green. The prints used in the analysis had been masked during their exposure to enhance contrast. The numbers of vessels, grouped into large (~60nm), medium (~30nm), and small (~10nm) lumina, were counted, the disc images being divided radially into eight equal sectors.

Results

While the large vessels crossed the rim mainly along the vertical, the small ones did so mainly in the horizontal. The distribution of the medium vessels was unpolarized but their crossings predominated on the nasal side. The vessel patterns differed significantly between the two ethnic groups as regards both number and distribution along the rim of the disc, the smaller vessels being more numerous in Caucasian eyes (p~0.02). Rim crossings by vessels were smaller in glaucomatous eyes in both ethnic groups. In normal eyes there was a statistically significant age-related decline in the number of small vessels after the age of 20 years.

Conclusions

There exists a statistically significant inverse relation between the number of capillaries crossing the disc rim and the vertical cup/disc ratio. Caucasian rims show the larger number of capillaries crossing.