gms | German Medical Science

Purpose: The success of retinal prosthesis to restore vision depends on the presence of physiologically intact retinal ganglion cells that can transmit visual signals to the brain. Therefore it is important to properly evaluate the degree of retinal integrity for patient selection. The purpose of study to investigate the relationship between the retinal thickness by optical coherence tomography (OCT) and the threshold current to evoke phosphene by transcorneal electrical stimulation (TES) in patients with advanced retinitis pigmentosa (RP).

Methods: Forty four eyes of 25 patients with RP (average age, 64.2 years) were examined. The best-corrected visual acuity (BCVA) ranged from 0 to HM (median, LP). Retinal thickness (RT) was measured by macular cube scan (512×128) of Cirrus HD-OCT. Phosphene threshold was obtained when the subject can reliably identify a visual sensation at the center of visual field during TES (10ms/phase,20Hz,20 pulses).

Results: The central phophene was elicited in 25 eyes but was not elicited with current less than 2 mA in 19 eyes. There was no significant difference in BCVA between in a group with central phosphene and in that without central phophene. The average RTs at three areas (center, central subfield, Maximum subfield) were significantly thicker in a group with central phosphene than that without central phosphene (center: 213 ±76 um vs 128 ± 65 um, P<0.05;central subfield: 271 ± 50 um vs 179 ± 81um, P<0.05; Maximum subfield: 252 ±34 um vs 184 ± 67 um, P<0.05). But no significant correlation was observed between RTs and thresholds of phosphene.

Conclusions: OCT provides an useful information to select a candidate for a retinal prosthesis, but the RTs did not proportionally correlate with the threshold of phosphene. It is necessary to examine patients by both OCT and TES in order to select patients suitable for a retinal prosthesis.