Evaluation of phosphenes elicited by extraocular stimulation in normals and by suprachoroidal-transretinal stimulation in patients with retinitis pigmentosa.
BACKGROUND
To determine the efficient parameters to evoke electrical phosphenes is essential for the development of a retinal prosthesis. We studied the efficient parameters in normal subjects and investigated if suprachoroidal-transretinal stimulation (STS) is effective in patients with advanced retinitis pigmentosa (RP) using these efficient parameters.


METHODS
The amplitude of pupillary reflex (PR) evoked by transcorneal electrical stimulation (TcES) was determined at different frequencies in eight normal subjects. The relationship between localized phosphenes elicited by transscleral electrical stimulation (TsES) and the pulse parameters was also examined in six normal subjects. The phosphenes evoked by STS were examined in two patients with RP with bare light perception. Biphasic pulses (cathodic first, duration: 0.5 or 1.0 ms, frequency: 20 Hz) were applied through selected channel(s). The size and shape of the phosphenes perceived by the patients were recorded.


RESULTS
The maximum PR was evoked by TcES with a frequency of 20 Hz. The brightest phosphene was elicited by TsES with a pulse train of more than 10 pulses, duration of 0.5-1.0 ms and a frequency of 20 to 50 Hz. In RP patients, localized phosphenes were elicited with a current of 0.3-0.5 mA (0.5 ms) in patient 1 and 0.4 mA (1.0 ms) in patient 2. Two isolated or dumbbell-shaped phosphenes were perceived when the stimulus was delivered through two adjacent channels.


CONCLUSIONS
Biphasic pulse trains (> or =10 pulses) with a duration of 0.5-1.0 ms and a frequency of 20-50 Hz were efficient for evoking phosphenes by localized extraocular stimulation in normal subjects. With these parameters, STS is a feasible method to use with a retinal prosthesis even in advanced stages of RPs.
Fujikado
Takashi
T
Department of Applied Visual Science, Osaka University Graduate School of Medicine, Osaka, Japan. fujikado@ophthal.med.osaka-u.ac.jp
Morimoto
Takeshi
T
Kanda
Hiroyuki
H
Kusaka
Shunji
S
Nakauchi
Kazuaki
K
Ozawa
Motoki
M
Matsushita
Kenji
K
Sakaguchi
Hirokazu
H
Ikuno
Yasushi
Y
Kamei
Motohiro
M
Tano
Yasuo
Y
D000328:Adult; D000368:Aged; D001187:Artificial Organs; D004558:Electric Stimulation / Q000379:methods; D004599:Electric Stimulation Therapy; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010719:Phosphenes / Q000502:physiology*; D012025:Reflex, Pupillary / Q000502:physiology; D012160:Retina / Q000503:physiopathology*; D012174:Retinitis Pigmentosa / Q000503:physiopathology*