Electrical Stimulation Parameters in Normal and Degenerate Rabbit Retina

서지정보

· 발행기관 : 한국의학물리학회
· 수록지 정보 : 의학물리 / 19권 / 1호 / 73 ~ 79페이지
· 저자명 : 진계환, 구용숙

초록

Retinal prosthesis is regarded as the most feasible method for the blind caused by retinal diseases such as retinitis
pigmentosa (RP) or age related macular degeneration (AMD). Recently Korean consortium launched for
developing retinal prosthesis. One of the prerequisites for the success of retinal prosthesis is the optimization
of the electrical stimuli applied through the prosthesis. Since electrical characteristics of degenerate retina are
expected to differ from those of normal retina, we performed voltage stimulation experiment both in normal and
degenerate retina to provide a guideline for the optimization of electrical stimulation for the upcoming prosthesis.
After isolation of retina, retinal patch was attached with the ganglion cell side facing the surface of microelectrode
arrays (MEA). 8×8 grid layout MEA (electrode diameter: 30μm, electrode spacing: 200μm, and impedance:
50 kΩ at 1 kHz) was used to record in-vitro retinal ganglion cell activity. Mono-polar electrical stimulation was
applied through one of the 60 MEA channel, and the remaining channels were used for recording. The electrical
stimulus was a constant voltage, charge-balanced biphasic, anodic-first square wave pulse without interphase
delay, and 50 trains of pulse was applied with a period of 2 sec. Different electrical stimuli were applied. First,
pulse amplitude was varied (voltage: 0.5∼3.0 V). Second, pulse duration was varied (100∼1,200μs). Evoked
responses were analyzed by PSTH from averaged data with 50 trials. Charge density was calculated with Ohm’s
and Coulomb’s law. In normal retina, by varying the pulse amplitude from 0.5 to 3 V with fixed duration of 500
μs, the threshold level for reliable ganglion cell response was found at 1.5 V. The calculated threshold of charge
density was 2.123 mC/cm². By varying the pulse duration from 100 to 1,200μs with fixed amplitude of 2 V,
the threshold level was found at 300μs. The calculated threhold of charge density was 1.698 mC/cm². Even
after the block of ON-pathway with L-(1)-2-amino-4-phosphonobutyric acid (APB), electrical stimulus evoked
ganglion cell activities. In this APB-induced degenerate retina, by varying the pulse duration from 100 to 1200
μs with fixed voltage of 2 V, the threshold level was found at 300μs, which is the same with normal retina.
More experiment with APB-induced degenerate retina is needed to make a clear comparison of threshold of
charge density between normal and degenerate retina.

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