Kurt Scavelli, MD
Vitreoretinal Fellow
Vanderbilt Eye Institute
Dr. David W Parke II started off the 2021 Charles L Schepens MD Lecture by introducing speaker Dr. Mark S Humayun. Dr. Parke provided an overview of Dr. Mark S Humayun’s illustrious career including 138 patents along with numerous publications and book chapters.
Dr. Humayun’s talk was entitled “Advanced Retinal Implants.” The lecture opened with an overview of the unmet need in medicine for advances in visual restoration for patients with advanced retinal disease. He emphasized the challenge and complexity to provide visual restoration and the need for a multifaceted approach. The focus of his talk was on advances in bioelectronic implants and stem cell implantation utilized to restore vision in patients with advanced retinal degenerations.
Dr. Humayun provided an overview of the history of bioelectronic implants in patients with inherited retinal disease. He acknowledged the success of recent genetic therapies for the treatment of inherited retinal diseases, such as RPE65-related Leber’s Congenital Amaurosis; however, emphasized the majority of inherited retinal diseases have a myriad of genetic mutations that preclude targeted genetic treatment. Retinal prostheses have the advantage of bypassing damaged neurons within the retina to help restore vision. Dr. Humayun discussed a new epiretinal prothesis called IMIE 256. It is the first 256 electrode epiretinal human implant which is a substantial increase from the 60 electrodes present in the Argus II implant. An exciting clinical example was presented of a patient with advanced RP with the IMIE 256 Epiretinal Implant exhibiting 20/150 visual acuity and efficiently navigating a room under low light condition.
The second half of Dr. Humayun’s talk was on stem cell implantation in the treatment of advanced geographic atrophy in patients with AMD. An issue with current delivery methods for subretinal stem cell therapy is necessity for a retinotomy to deliver cells in the subretinal space resulting in reflux of cells and potential for ERM and PVR. Dr. Humayun’s lab has sought to navigate this challenge by bioengineering a foldable synthetic scaffold for allogenic RPE cells. The scaffold is derived from a Parylene substrate that is micromachined to have both a thick and thin texture allowing for strong mechanical support as well as permeability for nutritional diffusion to the RPE cells. The foldable nature of the membrane allows the surgical retinotomy to be around 1.5 mm in size. A Phase 1/2a clinical trial is currently underway and one-year results have been published in TVST. Dr. Humayun presented post-operative OCT images demonstrating remarkable reappearance of the external limiting membrane in patients with advanced geographic atrophy at two and six month follow up. Histologic analysis was provided on one patient that demonstrated survival of RPE cells on the Parylene membrane at 2 years. Of the 15 subjects who received the allogenic RPE cell implantation, 27% improved 7-15 letters at one year as compared to 80% of the 15 control patients who lost 8-21 letters.
In conclusion, Dr. Humayun outlined the unique issues related to bioengineering retinal implants. He emphasized how improvements in energy sources, materials, 3-D printing and nanoscale fabrication provide a promising avenue for future development of bioelectronic implants and stem cell implantation. The IMIE 256 prosthesis and allogenic RPE cell bioengineered implant are exceptional examples of this. We thank Dr. Humayun for his tremendous contributions to the field.
