Review of retinal morphology around optic disc in Peripapillary atrophy by using Spectralis Optical Coherent Tomography.

Sir,

In 2010, we studied the clinical and optical coherent tomography (OCT) findings of 32 eyes of 16 patients (9 male and 6 female) with paripaillary optic atrophy (PPA) at eye unit of King Faisal University hospital. Two medical retina specialists and one ophthalmic technician examined patients with clinical PPA. Cycloplegic refraction of each eye of the participants was carried out. To have stereoscopic view of retina and optic nerve head (ONH), we used slit lamp bio-microscope (Topcon–Japan) and +90D fundus lens (Volk–Germany). For assessment of posterior segment, we also used indirect binocular ophthalmoscope (Keelar, UK) with + 20D fundus lens. The retinal area temporal to the ONH were evaluated with Spectralis OCT. The outer Alpha zone of PPA around ONH was defined as an irregular hypo- and hyper-pigmentation of the retinal pigment epithelium. The inner beta zone of PPA was identified with area of marked atrophy of the retinal pigment epithelium and choriocapillaris with thinning of the chorioretinal tissues and good visibility of the large choroidal vessels and sclera.[1]

Retinal examination and digital photograph using red free filter suggested that more prominent crescent on the temporal side of ONH had two zones. The alpha zone was large, whereas inner smaller zone had visible sclera and large chorio-retinal vessels [Figure 1]. The OCT of same area showed larger alpha zone characterized by a disruption of the photoreceptor and underlying pigment epithelium layers. The smaller beta zone was characterized by termination of photoreceptor and retinal pigment epithelium layers [Figure 2].

Figure 1

Digital image of optic nerve head showing paripapillary optic atrophy

Figure 2

Optical coherent tomography of retina temporal to the optic nerve head (a) Alpha zone and (b) Beta zone

OCT findings correlated well with the digital image of the retina near ONH in all cases. The alpha zone matched with the thinning of neuro-epithelium, whereas beta zone signified absence of neuro-epithelium and pigment epithelium making the large choriodal vessels and sclera clearly visible on fundus examination.

The findings of our study matched with the histopathological findings of Curcio et al. They demonstrated loss of photoreceptors and alteration of Bruc's membrane in PPA.[2] The functioning of photo receptor in alpha zone was demonstrated by the presence of a relative scotoma compared with the absolute scotoma corresponding to the beta zone while testing the field of vision.[3] PPA and its correlation to the ONH changes could enable the glaucoma expert to reach diagnosis even in early stages.[4]

Manjunath et al demonstrated usefulness of spectrum OCT in eyes with PPA to confirm clinical diagnosis of different retinal conditions. Both optic disc morphology and RNFL around optic disc were showing significant changes in glaucoma, age related macular degeneration, high myopia, and other conditions of retina.[5]

Our findings demonstrate that alpha zone is caused by disruption of the photoreceptor and underlying pigment epithelium layer and the beta zone was caused by a termination of photoreceptor and retinal pigment epithelium. Further study with a larger sample is recommended to review correlation of clinical and OCT findings in different ocular conditions.