Optic Nerve Head Drusen With and Without Visual Field Loss: A Quantitative Analysis of Optic Disc Parameters Using Heidelberg Retinal Tomography

Abstract

Abstract: : Purpose: Optic nerve head drusen occur in 0.3% clinically and 2% histopathologically, of Caucasian patients. Drusen consist of calcified hyaline like material located in the substance of the optic nerve anterior to the lamina cribrosa. They have been associated with visual field loss, subretinal neovascularization, progressive optic atrophy and anterior ischemic optic neuropathy. It has been theorized that damage to nerve fibers as a result of compression by the drusen result in visual field loss. The purpose of this study is to determine if any disc parameters on Heidelberg Retinal Tomography( HRT) are associated with visual field loss and to evaluate HRT as a method to evaluate and follow patients with optic nerve head drusen. Methods: Six patients with optic nerve head drusen confirmed by ophthalmoscopy , B scan ultrasonography or neuroimaging underwent evaluation with the HRT. The HRT provides 13 different optic nerve parameters for quantitative analysis of the optic nerve cup, disc, as well as, the retinal nerve fiber layer. Two of the twelve eyes which had visual field loss were compared to the remaining ten eyes in all HRT parameters. The mean optic disc values in eyes with visual field loss were statistically compared using ANOVA to the mean values in eyes without visual field loss. Results: The mean disc area of eyes with optic nerve drusen with visual filed loss was 3.8500+0.25600 mm². The mean disc area of eyes with optic nerve drusen without visual field loss was 2.5252+0.13141 mm². This difference was statistically significant (t(10)=-4.166, p=0.002). Similarly, the mean rim area of eyes with optic nerve drusen with visual field loss was 3.8420+0.26400 mm². The mean rim area of eyes with optic nerve drusen without visual field loss was 2.4296+0.16033.This difference was also statistically significant (t(10)=-3.682, p=0.004). All other parameters were not found to be statistically significantly different. Conclusions: The HRT allows for a three-dimensional view of the optic nerve head and surrounding area, as well as quantitative measurements that can be used to compare depth, area, and contour changes over time. The disc and rim areas of eyes with optic nerve drusen with visual field loss were significantly larger than those of eyes with optic nerve drusen without visual field loss. It is hypothesized that these drusen must first reach a critical size at which compression of nerve fibers and subsequent field loss occur.

Keywords: drusen • neuro-ophthalmology: optic nerve • imaging/image analysis: clinical