Optical coherence tomography highlights retinal changes post-implantation
medwireNews: Researchers have used optical coherence tomography to reveal the development of a fibrosis-like hyper-reflective tissue at the interface between the electronic array and retina in patients who have undergone electronic retinal prosthesis implantation.
In the majority of patients this progressed to retinal schisis but was not associated with any deterioration in the patients’ visual performance, Laura Cinelli (University of Florence, Italy) and co-authors report in JAMA Ophthalmology.
The findings are based on an analysis of 20 eyes from 20 patients (mean age 57.4 years, 60% men) who underwent Argus II Retinal Prosthesis System implantation (Second Sight Medical Products Inc, Sylmar, California, USA) between October 2011 and June 2017. The patients were evaluated with a comprehensive ophthalmic examination before, and at regular intervals after surgery.
Optical coherence tomography showed that 50% of the implanted eyes developed a fibrosis-like hyper-reflective plaque, which was limited to the interface between the array and retina, between 2 and 33 months post-implantation (mean onset, 11.0 months).
Fibrosis began as a thin hyper-reflective band that was not present immediately postsurgery but thickened over time. This developed in 54% of 11 patients who had a mean electrode-to-retina distance below 100 μm, in 50% of four patients who had a distance of more than 100 μm but less than 300 μm, and in 40% of five patients in whom the distance between the electrode and retina was more than 300 μm.
Nine of the 10 patients with fibrosis eventually developed retinal schisis, with a mean onset time of 21.3 months after surgery and a range of 6–36 months.
The researchers note that “the retinal schisis seemed to appear when the mean thickness of the fibrosis was equal to or greater than approximately 100 μm as if this were the limit beyond which there may be a tractional force capable of inducing the onset of schisis.”
Cinelli and team also evaluated the effect fibrosis had on visual performance using the square localization and direction of motion tests but observed no deterioration in these patients following fibrosis onset.
Furthermore, none of the 10 patients who developed fibrosis reported any deterioration in their visual perception during the course of the study.
The investigators suggest that this may be because the electronic prosthesis system “can be custom programmed to optimize performance, and the changes in the patient perception may be counterbalanced with custom electrical stimulation measures (frequency, inter- phase gap, and pulse width).”
In an accompanying commentary, Julia Haller, from Wills Eye Hospital and Thomas Jefferson University in Philadelphia, Pennsylvania, USA, stresses the importance of careful tracking of the long-term safety and efficacy of new therapies in ophthalmology.
She writes: “It is reassuring that despite the fibrotic changes and schisis that developed in 50% of eyes in this carefully monitored series from Italy, the Argus II implant, harnessing the evidently intact ganglion cells superficial to the schisis, retained its connections and function.”
By Laura Cowen
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