Ophthalmoscopic detectability of the parafoveal annular reflex in the evaluation of the optic nerve : An experimental study in rhesus monkeys

Abstract

Objective To evaluate whether assessment of the ophthalmoscopic visibility of the parafoveal annular reflex is helpful in the detection of optic nerve fiber and optic nerve damage. Design Experimental animal study. Animals The study was performed in rhesus monkeys, divided into four study groups, with no significant difference in ages of the animals in the various groups. Three of these groups had (1) experimental chronic high-pressure glaucoma (n = 37 monkeys), (2) experimental temporary occlusion of the central retinal artery (n = 19 monkeys), and (3) systemic atherosclerosis and arterial hypertension (n = 13 monkeys). The fourth group was the normal control group (n = 10 monkeys). Methods In 60-degree color fundus photographs, taken at baseline and at the end of the study, the ophthalmoscopic detectability of the parafoveal annular reflex was graded, the visibility of the retinal nerve fiber layer was assessed, and neuroretinal rim and parapapillary atrophy were measured. Main outcome measures Ophthalmoscopic detectability of the parafoveal annular reflex; visibility of the retinal nerve fiber layer; neuroretinal rim area; size of parapapillary atrophy. Results The parafoveal annular reflex was significantly ( P < 0.0001) better detectable at baseline of the study than at the end of the study. In all study groups, detectability of the parafoveal annular reflex decreased significantly ( P < 0.0001) with decreasing visibility of the retinal nerve fiber layer. In the glaucoma group, parafoveal annular reflex detectability additionally decreased significantly ( P < 0.001) with increasing area of beta zone of parapapillary atrophy and with decreasing neuroretinal rim area. In the normal group, the parafoveal annular reflex detectability decreased with increasing age, parallel to a loss in the visibility of the retinal nerve fiber layer. In 23 of 25 (92%) eyes with a complete loss of the visibility of the retinal nerve fiber layer at the end of the study, the parafoveal annular reflex was no longer detectable. Conclusions The findings suggest that evaluation of the detectability of the parafoveal annular reflex in routine ophthalmoscopy is a useful additional tool in the qualitative assessment of the retinal nerve fiber layer and optic nerve.