The Evaluation of Retinal Function in Each Layers of The Macula in Retinitis Pigmentosa

Abstract

Purpose: : To investigate the correlation between focal electroretinograms (ERG) and retinal thickness in each layers of the macula in patients with retinitis pigmentosa.

Methods: : All 16 patients (49.9±19.3 years) with retinitis pigmentosa had a good best corrected Snellen visual acuities of 30/20 to 14/20, no visible macular cysts and no epiretinal membrane. We recorded focal ERGs and optical coherence tomography (OCT) in the macular regions from 16 eyes (16 patients). Spectral-domain optical coherence tomography (RTVue-100) was used to measure outer and inner retinal layer thickness in fovea, parafovea and perifovea. Focal ERGs were elicited by a 15 degrees stimulus centered on the fovea and monitored by an infrared fundus camera. The amplitudes and implicit times of the a- and b-waves and oscillatory potentials (OPs) were compared with the retinal thickness of inner and outer layer in the fovea, parafovea and perifovea, respectively.

Results: : We recorded a- and b-waves and OPs in 16 eyes of all 16 patients. The mean amplitudes (±S.D.), respectively, were: a wave, 0.9±0.5 µV; b wave, 2.3±1.2 µV and OP, 0.6±0.3 µV. The mean implicit times (±S.D.), respectively, were: a wave, 21.9±1.8 ms; b wave, 42.3±3.5 ms and OP, 34.0±1.9 ms. The average retinal thickness (±S.D.) were 162.5±10.1 µm, 76.4±13.7 µm; 165.8±13.8 µm, 115.8±11.6 µm; 139.5±17.3 µm, 98.8±12.1 µm in outer layer and inner layer, respectively, in fovea, parafovea and perifovea. The a-wave amplitude showed a significant correlation with the retinal thickness in outer layer not in inner layer in perifovea (r² = 0.30, p<0.05) but not in fovea and parafovea. The b-wave and OP amplitude showed a significant correlation with the retinal thickness in outer layer not in inner layer in parafovea (r² = 0.32, p<0.05; r² = 0.41, p<0.005, respectively) and in outer layer and inner layer in perifovea (r² = 0.37, p<0.01 and r² = 0.33, p<0.05; r² = 0.52, p=0.001 and r² = 0.43, p<0.005; in the b-wave and OP, respectively). There were no significant correlation between the implicit times and retinal thickness.

Conclusions: : These results suggest that focal ERG is associated with the outer retinal function in parafovea and perifovea rather than fovea in early stage of retinitis pigmentosa.

Keywords: retinal degenerations: hereditary • electroretinography: clinical