Applied Visual Science, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
J Neural Eng. 2017 Oct;14(5):056013. doi: 10.1088/1741-2552/aa7d5c. Epub 2017 Jul 4.
Suprachoroidal-transretinal stimulation (STS) is a stimulation method for retinal prostheses. For STS-type retinal prostheses, we developed a new type of stimulating electrode called a femtosecond laser-induced porous electrode (FLiP electrode). To verify the safety of the FLiP electrode for STS, we investigated the characteristics of STS-induced retinal injury.
Sixteen eyes of pigmented rabbits were studied in this in vivo study. For each examined eye, we implanted a single-channel FLiP electrode (diameter, 0.5 mm; height, 0.3 mm; geometric surface area, 0.43 mm) in a scleral pocket created at the posterior pole of the eye. A return electrode (diameter, 0.5 mm; length, 3 mm) was inserted into the vitreous cavity. The eyes were divided into five groups, and each group was stimulated with a different current intensity. The stimulus intensities and the number of eyes in each group were as follows: 1.0 mA (n = 2), 1.5 mA (n = 3), 2.0 mA (n = 3), 2.5 mA (n = 4), and 3.0 mA (n = 2). Continuous biphasic pulses (0.5 ms/phase) were applied under general anesthesia at a frequency of 20 Hz for 48 h. Fundus photography, fluorescein angiography (FA), and optical coherence tomography were performed before and after applying the electrical stimulation to evaluate the retinal injury.
The 1.0 mA and 1.5 mA groups showed little or no retinal damage. Fluorescent dye leakage in FA and punctate pigmentation in the fundus were observed around the stimulation site with stimulation of 2.0 mA (1/3), 2.5 mA (1/4), and 3.0 mA (2/2).
Our findings indicate that the threshold current for inducing retinal damage is greater than that for eliciting electrical phosphenes (<1 mA) with STS observed in human trials. Therefore, STS by the FLiP electrode is a safe and feasible stimulation method for retinal prostheses as long as it is used with these pulse parameters.
脉络膜-视网膜经皮电刺激（STS）是一种用于视网膜假体的刺激方法。对于 STS 型视网膜假体，我们开发了一种新型刺激电极，称为飞秒激光诱导多孔电极（FLiP 电极）。为了验证 FLiP 电极用于 STS 的安全性，我们研究了 STS 诱导的视网膜损伤的特征。
本体内研究纳入了 16 只色素性兔眼。对于每只检查眼，我们在前极部巩膜袋中植入了单个通道的 FLiP 电极（直径 0.5mm；高度 0.3mm；几何表面积 0.43mm）。一个返回电极（直径 0.5mm；长度 3mm）插入玻璃体腔。将眼分为五组，每组用不同的电流强度进行刺激。刺激强度和每组的眼数如下：1.0mA（n=2），1.5mA（n=3），2.0mA（n=3），2.5mA（n=4）和 3.0mA（n=2）。在全身麻醉下，以 20Hz 的频率连续施加双相脉冲（0.5ms/相）48h。在施加电刺激前后进行眼底照相、荧光素血管造影（FA）和光相干断层扫描，以评估视网膜损伤。
1.0mA 和 1.5mA 组显示视网膜损伤很小或没有。在 2.0mA（1/3）、2.5mA（1/4）和 3.0mA（2/2）刺激时，在刺激部位周围的 FA 中观察到荧光染料渗漏和眼底点状色素沉着。
我们的发现表明，引起视网膜损伤的阈值电流大于在人类试验中观察到的 STS 诱发电幻视的电流（<1mA）。因此，只要使用这些脉冲参数，FLiP 电极的 STS 是一种安全可行的视网膜假体刺激方法。
