Evaluation of phosphenes elicited by extraocular stimulation in normals and by suprachoroidal-transretinal stimulation in patients with retinitis pigmentosa

  • Takashi FujikadoEmail author
  • Takeshi Morimoto
  • Hiroyuki Kanda
  • Shunji Kusaka
  • Kazuaki Nakauchi
  • Motoki Ozawa
  • Kenji Matsushita
  • Hirokazu Sakaguchi
  • Yasushi Ikuno
  • Motohiro Kamei
  • Yasuo Tano
Clinical Investigation



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.


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.


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.


Biphasic pulse trains (≥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.


Artificial retina Retinitis pigmentosa Phosphene Pupillary reflex Suprachoroidal-transretinal stimulation 



The authors thank Yozo Miyake, Satoshi Suzuki, Mineo Kondo Yutaka Fukuda, Hajime Sawai and Tomomitsu Miyoshi for advice and discussion.

Commercial interest

Hiroyuki Kanda and Motoki Ozawa are employees of the Nidek Company.

Financial support

This study was supported by Health Sciences Research Grants (H16-sensory-001) from the Ministry of Health, Labor and Welfare, Japan.


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Takashi Fujikado
    • 1
    • 4
    Email author
  • Takeshi Morimoto
    • 1
  • Hiroyuki Kanda
    • 1
    • 2
  • Shunji Kusaka
    • 1
  • Kazuaki Nakauchi
    • 1
  • Motoki Ozawa
    • 2
  • Kenji Matsushita
    • 3
  • Hirokazu Sakaguchi
    • 3
  • Yasushi Ikuno
    • 3
  • Motohiro Kamei
    • 3
  • Yasuo Tano
    • 3
  1. 1.Department of Applied Visual ScienceOsaka University Graduate School of MedicineOsakaJapan
  2. 2.Nidek Co.Gamagori, AichiJapan
  3. 3.Department of OphthalmologyOsaka University Graduate School of MedicineOsakaJapan
  4. 4.Department of Applied Visual ScienceOsaka University Graduate School of MedicineOsakaJapan

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