Transcorneal Electrical Stimulation Shows Neuroprotective Effects in Retinas of Light-Exposed Rats

Abstract

PURPOSE.To examine the effects of transcorneal electrical stimulation (TES) on retinal degeneration of light-exposed rats.METHODS. Thirty-three Sprague Dawley albino rats were divided into three groups: STIM (n ¼ 15) received 60 minutes of TES, whereas SHAM (n ¼ 15) received identical sham stimulation 2 hours before exposure to bright light with 16,000 lux; healthy animals (n ¼ 3) served as controls for histology. At baseline and weekly for 3 consecutive weeks, dark-and light-adapted electroretinography was used to assess retinal function. Analysis of the response versus luminance function retrieved the parameters Vmax (saturation amplitude) and k (luminance to reach ½Vmax). Retinal morphology was assessed by histology (hematoxylin-eosin [HE] staining; TUNEL assay) and immunohistochemistry (rhodopsin staining).RESULTS. Vmax was higher in the STIM group compared with SHAM 1 week after light damage (mean intra-individual difference between groups 116.06 lV; P ¼ 0.046). The b-wave implicit time for the rod response (0.01 cd.s/m 2 ) was lower in the STIM group compared with the SHAM group 2 weeks after light damage (mean intra-individual difference between groups 5.78 ms; P ¼ 0.023); no other significant differences were found. Histological analyses showed photoreceptor cell death (TUNEL and HE) in SHAM, most pronounced in the superior hemiretina. STIM showed complete outer nuclear layer thickness preservation, reduced photoreceptor cell death, and preserved outer segment length compared with SHAM (HE and rhodopsin).CONCLUSIONS. This sham-controlled study shows that TES can protect retinal cells against mild light-induced degeneration in Sprague Dawley rats. These findings could help to establish TES as a treatment in human forms of retinal degenerative disease. (Invest Ophthalmol Vis Sci. 2012;53:5552-5561)

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 …”

Transcorneal Electrical Stimulation in Patients with Retinal Artery Occlusion: A Prospective, Randomized, Sham-Controlled Pilot Study

“…The mechanism for these positive effects has been suggested to be a favorable regulation of neurotropic factors; electrical stimulation has been linked to the upregulation of neurotrophins in the central and peripheral nervous systems [16–18], whereas in animal experiments, electrical stimulation has been shown to be beneficial for the survival of photoreceptors in Royal College of Surgeon’s rats [19] promoting the survival of photoreceptors and improving retinal function in rhodopsin P347L transgenic rabbits [20], rescuing ganglion cells after optic nerve injury in Wistar rats [21, 22], and preserving retinal cells after light-induced retinal damage in Sprague–Dawley rats [23–25]. …”

Neuroprotective Effects of Low Level Electrical Stimulation Therapy on Retinal Degeneration

“…This configuration differs from TES and SES in that the applied electrical field, and thus the currents, are more uniformly distributed through the entire eye. It should be noted that this review will classify some studies identified as TES in the literature as WES due to reference electrode placement away from the cornea [8,9]. Neuroprotective current levels for TES and WES appear in the range of 1.5 to 1000 µA.…”

“…After WES stimulation every 3 days for 14 days with a contact lens electrode referenced to the opposite eye, albino rats exposed to bright light had significantly preserved a-and b-wave amplitudes [16]. EST for 2 h with a DTL fiber on the cornea (location of reference electrode not described) prior to a milder light exposure temporarily preserved b-wave amplitudes and some photoreceptors and rod outer segments after 3 weeks [8]. These effects were not as great as that reported by Ni et al [16], possibly due to the different electrode configuration and the absence of repeated EST sessions.…”