MAR 08, 2012
Investigators reviewed the charts of all patients with optic nerve head drusen (ONHD) seen at their institution between 1989 and 2010. They found that ONHD are rare in blacks compared to whites, possibly due to the presence of a larger cup-to-disc ratio or a lack of predisposing genetic factors. Since approximately 50 percent of the patients examined at their institution are black, the disproportion is unlikely to be due to referral bias.
Of the 196 patients with confirmed ONHD, 10 (5.1 percent) were black. Six of the 10 patients had bilateral ONHD. The ONHD were buried in 11 of 16 eyes and exposed in five of 16 eyes. Fifteen of 16 eyes with ONHD had small cupless optic nerve heads. Visual fields were normal in four of 16 eyes with ONHD. In the remainder, visual field defects included an enlarged blind spot (five eyes), constricted field (five eyes), nasal defect (two eyes), central defect (one eye) and generalized depression (one eye). None of the patients were related, and none of their examined family members had exposed ONHD on funduscopic examination.
Although the percentage of patients with exposed ONHD who had visual field defects (80 percent) was slightly greater than that reported in prior studies (70 percent to 75 percent), the percentage of patients with buried ONHD who had visual field defects (72.7 percent) was substantially greater than that reported in prior studies (20 percent to 45 percent). While this could be a consequence of referral bias, it might also indicate that visual field defects are more likely to develop in black than in white patients with ONHD, possibly due to racial differences in the sensitivity of retinal ganglion cells to damage at the optic nerve head.
The authors conclude that while these results suggest that there is a low prevalence of ONHD in blacks compared with whites, a large population-based study with fundus examination or photography and B-scan ultrasonography would be required to determine the exact prevalence of ONHD in blacks.