Abstract
Purpose :
Recent advances in the design of retinal implants have required to develop a method of measuring the electroretinogram (ERG) and the visual evoked potential (VEP) in eyes implanted with a retinal prosthesis in an animal model. Most retinal prosthesis are sensitive in the visible and also in the infrared spectrum beyond the sensitivity of the native photoreceptors. It is therefore important to develop to study the neural response to the visual stimulus of visible and infrared light stimulus. Furthermore, this setup can then be used to evaluate the ability of a retinal prosthesis to produce a neural response.
Methods :
We modified an existing electroretinogram device by modifying the stimulus generation and stimulus delivery. We replaced the Ganzfeld stimulator in the conventional setup with a slitlamp delivery system. In addition, we used a laser diode to create the light stimulus. The laser diodes (532 and 850 nm) were mounted in a temperature controlled mount and driven by combination laser diode current and temperature driver. The light was coupled into a multimode fiber and delivered via a Haag-Streit slitlamp. The retinal spot size can be varied between 600-5,000 µm. We used Dutch pigmented rabbits (n=12) for our experiment. The focal ERG was recorded with a Burian-Allen contact lens. The VEP was recorded with transcranial screw electrodes as previously described [Makowiecki et al. TVST 4:15;2015 PMC4413925]. Maximum permissible exposure limits were calculated according to ANSI standard. A custom Faraday cage was constructed.
Results :
The results show good reproducibility of the VEP recording within the same day and a decrease in VEP amplitude with decreasing spot size. As expected, infrared light was not able to generate a detectable VEP in normal retina even at the highest power setting. The VEP generated by the implant when stimulated with infrared light showed a cortical response.
Conclusions :
This setup allows selection of different laser diode light sources with accurate stable light output and triggered by commercial ERG equipment. Light delivery through the slit lamp allows accurate monitoring of the stimulus location. It allows for ERG and VEP testing in animals with a retinal prosthesis and allowed us to evaluate the focal response of the neural retina in normal and diseased retinal regions as well as the performance of a retinal prosthesis.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.