Abstract
Purpose: :
Parapapillary atrophy (PPA) is an important feature of glaucomatous optic neuropathy. PPA can be divided into two types, alpha and beta zone. In beta zone PPA, the retinal pigment epithelium (RPE) is absent revealing large choroidal vessels and sclera. In alpha zone PPA, there is hypo- or hyperpigmentation of the RPE. Beta zone PPA is more specific for glaucoma but can be difficult to definitively differentiate clinically from alpha zone PPA. As beta zone PPA represents RPE absence, we hypothesize that light passed behind the RPE via the optic nerve would result in parapapillary transillumination defects, akin to iris transillumination defects. In this study we demonstrate a new technique for the detection and documentation of beta zone PPA.
Methods: :
Twenty-six eyes (15 patients) with varying degrees of PPA were selected. Ten eyes (5 patients) with no PPA were controls. Standard optic nerve head photographs were taken using the Topcon TRC 50EX Retinal Camera (Topcon Co., Tokyo, Japan). Next, a circular 1 mm2 to 4 mm2 beam of light illuminated the optic nerve head (avoiding the parapapillary retina) and photographed using a Zeiss 90 diopter indirect lens and Nikon AS-15 slit-lamp camera (Nikon Co., Tokyo, Japan). The standard and transillumination photographs were evaluated for photographic quality as well as the presence, absence and location of beta or alpha zone PPA. The reviewer evaluated the photographs in a randomized and masked fashion.
Results: :
In 10 control eyes no PPA was visualized on standard optic nerve head photography and no transillumination defects were visualized using the new technique. In 26 eyes with PPA on standard photographs, transillumination defects corresponded with the region of PPA in 100% (26/26). In 8 eyes with alpha zone PPA, faint transillumination defects were visualized adjacent to the optic nerve but not contacting the scleral rim (Figure 1a and 1b). In 20 eyes with beta zone PPA, transillumination defects were visualized adjacent to the scleral rim (Figure 1c and 1d).
Conclusions: :
This report is the first to demonstrate that defects of the RPE found in PPA can be documented using optic nerve transillumination. Further study would ideally resolve the pathological underpinnings corresponding to regions of PPA.
Keywords: retinal pigment epithelium • optic disc • imaging/image analysis: clinical