Characteristics of Retinal Reflectance Changes Induced by Transcorneal Electrical Stimulation in Cat Eyes

Abstract

Transcorneal electrical stimulation (TES) activates retinal neurons leading to visual sensations. How the retinal cells are activated by TES has not been definitively determined. Investigating the reflectance changes of the retina is an established technique and has been used to determine the mechanism of retinal activation. The purpose of this study was to evaluate the reflectance changes elicited by TES in cat eyes. Eight eyes of Eight cats were studied under general anesthesia. Biphasic electrical pulses were delivered transcornealy. The fundus images observed with near-infrared light (800–880 nm) were recorded every 25 ms for 26 s. To improve the signal-to-noise ratio, the images of 10 consecutive recordings were averaged. Two-dimensional topographic maps of the reflective changes were constructed by subtracting images before from those after the TES. The effects of different stimulus parameters, e.g., current intensity, pulse duration, frequency, and stimulus duration, on the reflective changes were studied. Our results showed that after TES, the reflective changes appeared on the retinal vessels and optic disc. The intensity of reflectance changes increased as the current intensity, pulse duration, and stimulation duration increased (P<0.05 for all). The maximum intensity of the reflective change was obtained when the stimulus frequency was 20 Hz. The time course of the reflectance changes was also altered by the stimulation parameters. The response started earlier and returned to the baseline later with higher current intensities, longer pulse durations, but the time of the peak of the response was not changed. These results showed that the reflective changes were due to the activation of retinal neurons by TES and might involve the vascular changes induced by an activation of the retinal neurons.

Topographic Quantification of the Transcorneal Electrical Stimulation (TES)–Induced Protective Effects on N-Methyl-N-Nitrosourea–Treated Retinas

“…23,33 Experimental and clinical studies have demonstrated protective effects of TES against traumatic-or geneticinduced retinal degeneration. [34][35][36][37] Retinitis pigmentosa is a heterogeneous group of retinal diseases characterized by progressive photoreceptor degeneration and visual disturbanc- The total firing rate in the sham group decreased significantly compared with that in normal controls.…”

Proteomic Study of Retinal Proteins Associated with Transcorneal Electric Stimulation in Rats

“…The stimulation system in this study, electric stimulation with 20 Hz, was different from a flicker 30 Hz light stimulation. Though 20 Hz was the best condition for neuroprotection in the retina [ 5 , 11 ], we should check differences in protein expression changes for various conditions of TES, that is, frequencies, in a future study.…”

“…TES also promoted the survival of retinal ganglion cells (RGCs) of rats after optic nerve injury [ 4 ]. Furthermore, the results of TES in cat eyes suggested that TES activated retinal neurons through vascular changes [ 5 ].…”

Electrical Stimulation as a Means for Improving Vision

“…However, beneficial effects of ES have been shown in one study using transorbital ES 14 and in several animal experiments using TES (Table 1). 15e35 These studies can be categorized as follows: i) healthy animals 17e19, 23,26,31,34 ; ii) transgenic animals 22,28 ; iii) animals as a disease model for RP 21 ; iv) animals with induced ischemic insult, 27,29,33 optic nerve crush, 15,16,20,32 and transected optic nerve 24,25 ; and v) animal cells isolated from the retina. 35 …”