Abstract
Purpose :
Transcorneal electrical stimulation (TES) is applied as therapy in degenerative retinal diseases and to assess retinal functions. Furthermore, electrostimulation of the ciliary muscle (CM) was reported to cause short-term improvement of accommodative ability (Gualdi et al. 2017). Possible effects of TES on the CM morphology are yet unknown. In a pilot study, we aimed to assess whether monocular TES leads to morphological and functional CM changes and whether central accommodation control is affected.
Methods :
Monocular ipsi- and contralateral TES using a DTL electrode and biphasic rectangular pulses was performed on the same day in the morning and afternoon in random order. A prior phosphene threshold determination served to select individual TES current amplitude (50-100µA). Before and during TES, optical coherence tomography (OCT; ZEISS Visante) images of the right eye’s ciliary muscle were taken. During imaging, subjects fixated targets at 4m distance and refraction was simultaneously recorded with eccentric IR-photorefraction. Custom-developed software (Wagner et al. 2018) was applied for OCT image analysis and CM thickness (CMT) assessment. CMT and refractive values before vs. during TES were analyzed in a paired t-/Wilcoxon signed rank test.
Results :
10 healthy near-emmetropic volunteers (age 26.3±3.6years, 4 females, monocular Snellen VA ≥20/25) participated. CMT profile analyses revealed that, compared to the non-stimulated CM, both ipsi- and contralateral TES induced increased CMT (Fig.1). Assessment of selective CMT readings (n=10) confirmed a significant increase with ipsi- (31±30µm; p=.010) and contralateral (25±16µm; p=.001) stimulation, while refraction was not significantly affected (ipsi- [n=5]: median Δw/-w/o=0D; contralateral [n=7]: Δw/-w/o=0.13D).
Conclusions :
CMT increase during ipsilateral TES might derive from anatomical changes like enhanced CM blood supply or increased interstitial fluid. However, the finding of CM thickening with contralateral TES indicates an effect on the central control circuits of accommodation and requires further experiments. Assessing the accommodation responses before and after TES would clarify whether CM thickening is associated with an increased amplitude or improved accuracy of accommodation. This would open a perspective to apply TES in children with accommodation insufficiencies and in myopia management (e.g. combined with multifocal CL).
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.