Direct microperimetry of alpha zone and beta zone parapapillary atrophy

Background: To examine the psychophysical correlate of alpha zone and beta zone of parapapillary atrophy. Methods: The study included 20 eyes of 10 patients affected by primary open-angle glaucoma and 12 normal eyes of six subjects. The parapapillary region was psychophysically examined by direct fundus microperimetry. The parapapillary atrophy was ophthalmoscopically differentiated into a peripheral alpha zone with pigmentary irregularities and a central beta zone characterised by a good visibility of the large choroidal vessels and the sclera. Results: The mean stimulus attenuation values in the beta zone of parapapillary atrophy measured 1.00 (SD 2.54) dB, corresponding to an absolute scotoma. In the alpha zone, the mean stimulus attenuation values was 6.29 (4.82) dB, corresponding to a relative scotoma. The difference in the stimulus attenuation between alpha zone and beta zone was statistically significant (p = 0.028). Conclusions: The psychophysical correlate of beta zone of parapapillary atrophy is an absolute scotoma, and the correlate of alpha is a relative scotoma. It agrees with the histological correlate of beta zone with a complete loss of retinal pigment epithelium cells and photoreceptors, and with the histological correlate of alpha zone with structural irregularities of the retinal pigment epithelium.