Evaluation of residual retinal function by pupillary constrictions and phosphenes using transcorneal electrical stimulation in patients with retinal degeneration

Abstract

The safety and the efficacy of TES to estimate the residual inner-retinal function in patients with retinal degeneration indicate that TES can be used as one of the most important test to select candidates for retinal prostheses.

Electrical Stimulation as a Means for Improving Vision

“…38 Schatz et al 36 also reported minor conjunctiva irritation after intraocular pressure measurements. Other clinical TES studies reported slight corneal superficial punctuate keratopathy, 41 transient superficial keratitis, 39 and foreignbody sensations in three patients. 43 Adverse effects after TES in animal studies have not been reported; however, one study addressed this concern and reported no negative effects up to 35 hours after application.…”

“…The results showed that all functional parameters were slightly improved or remained constant in the 150% group, whereas there was no marked tendency in the 66% group. Compared to normal subjects, Morimoto et al 41 showed that patients with RP and cone-rod dystrophy demonstrated significantly higher electrical thresholds (ie, T1, threshold current for initial phosphene; T2, threshold for eliciting a phosphene extending into the central field; and P, threshold for a relative pupillary constriction !3%). The authors concluded that TES could be used as one of the most essential tests to select candidates for retinal prostheses.…”

Phosphene Thresholds Elicited by Transcorneal Electrical Stimulation in Healthy Subjects and Patients with Retinal Diseases

“…In those studies electrical stimulation for eliciting phosphenes is applied in a different manner: transcorneal, 19,20 suprachoroidal, 21 transscleral, 22 epiretinal, [23][24][25] and subretinal. [26][27][28][29] Recently, the noninvasive determination of electrically evoked phosphene thresholds (EPTs) has been used as a screening test for visual prosthesis candidates, providing a safe way to assess electrical excitability in patients before invasive surgical procedures are performed.…”

“…[26][27][28][29] Recently, the noninvasive determination of electrically evoked phosphene thresholds (EPTs) has been used as a screening test for visual prosthesis candidates, providing a safe way to assess electrical excitability in patients before invasive surgical procedures are performed. 19,20,[29][30][31] Moreover, studies have shown that electrical stimulation produced by visual prostheses can have neuroprotective effects in degenerated retinae, 27,[32][33][34] potentially delaying the disease progress. Some data link electrical stimulation with the upregulation of neurotrophins in the central and peripheral nervous systems.…”

“…In all, 117 individuals participated: healthy subjects (n ¼ 20) and patients with retinitis pigmentosa (RP, n ¼ 30), Stargardt's disease (STG, n ¼ 14), retinal artery occlusion (RAO, n ¼ 20), nonarteritic anterior ischemic optic neuropathy (NAION, n ¼ 16), and primary open-angle glaucoma (POAG, n ¼ 17). EPTs were determined at 3,6,9,20,40,60, and 80 Hz with 5 þ 5-ms biphasic current pulses using DTL electrodes. Subjects were examined twice (test-retest range: 1-6 weeks).…”