Chance of visual field loss relatively small with ONHD

Iowa City-The rate of visual field loss in patients who had optic nerve head drusen (ONHD) was about 1.6% per year, approximately what would be expected for this condition, said Andrew G. Lee, MD, professor of ophthalmology, neurology, and neurosurgery at the University of Iowa Hospitals and Clinics, Iowa City.

Dr. Lee reported no correlation between the rate of loss and gender or age, although a correlation between older age and more severe visual field loss was detected in a separate cohort of patients. In a presentation at the American Academy of Ophthalmology annual meeting last year, he also stated that all of the patients had preserved central acuity after extended follow-up unless another ocular pathology was present.

Dr. Lee and co-author Miriam Bridget Zimmerman, PhD, conducted a retrospective chart review using the modified Esterman grid technique in which only the 14e isopter was identified and scored [Am J Ophthalmol 2005;139:1062-1066]. The rate of visual field loss was calculated as the difference between the initial and final Goldman visual fields (GVFs) divided by the number of years of follow-up.

All patients had at least 36 months of follow-up and two or more serial Goldman fields that could be directly compared.

Investigators began with 292 patients (584 eyes) with a diagnosis of ONHD who had been seen at the University of Iowa Hospitals and Clinics department of ophthalmology from 1990 to 2003. However, 158 patients (316 eyes) were excluded because of an insufficient follow-up period. An additional 73 patients were excluded because they had either an unreliable or no GVF, 10 patients were eliminated because of ischemic optic neuropathy, and 19 patients were excluded because of various eye diseases.

This left investigators with 32 patients; their mean age at entry was 46.4 years, mean follow-up was 90 months, and median follow-up was 67 months (range, 37 to 204 months).

Comparing the initial and the outtake GVF scores for these patients, investigators found that the rate of visual field loss was 1.58 ± 0.28 per year with a 95% confidence interval (CI) of 1.14 and 2.16.

There was no statistically significant difference based on gender (p = 0.74). The rate of visual field loss for women was 1.50 ± 0.30 (95% CI, 1.03 to 2.16) and was 1.67 ± 0.44 (95% CI, 0.99 to 2.71) for men.

To investigate the possibility of a correlation between age and visual field loss, investigators conducted a separate analysis of 180 patients who had an initial GVF performed.

"Presumably if you're older, you have more time to lose field," Dr. Lee explained.

Acknowledging that this was a different cohort from the one used for the rate analysis, which required two Goldman visual fields, Dr. Lee noted that investigators found a significant negative correlation between age and initial GVF (p < 0.0001). Older patients had lower GVF scores, a finding that would be expected with a slow, progressive condition. The younger patients tended to have normal visual fields or minimal loss, while older patients had moderate to severe visual field losses.

Based on their best GVF score, 48 patients (72%) had moderate or severe visual field loss, and 132 patients (73%) had mild, minimal, or no visual field loss despite visible or ultrasound-confirmed drusen.

Despite limitations such as the small sample size (n = 32), the study provides information that clinicians might find helpful in advising patients on the prognosis of ONHD, Dr. Lee said. Ophthalmologists can reassure patients that the likelihood of long-term, significant visual field loss is relatively small and that central acuity will be spared.