Achromatopsia Demonstrates Responsiveness to Low-Frequency Electrical Stimulation

Individuals with achromatopsia demonstrate peak pupillary responsiveness while undergoing low-frequency electrical stimulation (6-10 Hz), according to research published in Experimental Eye Research. This may potentially indicate retinal remodeling of the connections between the photoreceptors and bipolar cells, the report suggests. 

Researchers evaluated the retinal responsiveness to sinusoidal electrical stimulation in 14 patients (age range, 18-44 years; 8 women) with genetically confirmed achromatopsia who were evaluated at a single center between September 2020 and November 2021. The participants underwent electrical stimulation in 1 eye via corneal electrodes. The stimulus consisted of amplitude-modulated sine waves with variable carrier frequencies (4-30 Hz) and contained a steady low-frequency envelope. The research team calculated the retinal responsiveness across the spectrum according to the velocity and synchronicity of the electrically evoked pupillary oscillations. 

According to the report, patients with achromatopsia showed a characteristic peak in responsiveness in the 6-10 Hz range, and stimulus frequencies higher than 16 Hz elicited weak pupillary responses and phosphenes. Compared with the tuning curve of the healthy retina, responses to low-frequency stimulation appear to show rod activation and higher frequencies seem to activate cones, the researchers note.  

“In the present study, we provide further evidence that it is possible to selectively activate specific classes of retinal neurons (rods and cones) via specific stimulation frequencies. Specifically, rod activation appears to manifest as a strong peak in the retinal tuning curve in the range of 6 to 10 Hz,” according to the researchers. “The possibility to selectively activate specific cell populations and the retina via electrical stimulation and to evaluate the elicited responses non-invasively by means of electrically evoked pupillary responses might present a useful diagnostic tool for photoreceptor diseases such as [achromatopsia].” 

Study limitations include a small sample size, single center design, limited stimulation frequency range (4-30 Hz), and failure to identify significant differences (after Bonferroni-correction) between patients with achromatopsia and healthy individuals due to high interindividual variability among the patients.