Retinal camera unlocks back-of-the-eye secrets

Reviewed by Dr Paola L. Oquendo.

An adaptive optics (AO) retinal camera has been used to measure photoreceptors preoperatively and following macular hole (MH) surgery to accurately assess any changes in cone density, according to research presented by Dr Paola L. Oquendo at the 2022 Canadian Ophthalmological Society Annual Meeting and Exhibition held in Halifax, Nova Scotia, Canada.

“We hypothesised that cone density will change following macular hole closure,” said Dr Oquendo, a vitreoretinal clinical research fellow at St Michael’s Hospital Toronto and the Department of Ophthalmology and Vision Sciences at the University of Toronto in Canada. “This is because it is likely that the temporal retina stretches to close the macula hole. This could possibly result in a reduction of cone density temporally.”

Discussing MH and photoreceptor changes using high-resolution imaging with adaptive optics, Dr Oquendo described the results of a small study that used an AO retinal camera (rtx1, Imagine Eyes) and spectral-domain optical coherence tomography (SD-OCT) to evaluate the photoreceptors in patients with various morphologies of MH and the changes following surgical closure.

The study included individuals presenting to the Kensington Vision and Research Centre in Toronto with idiopathic MH needing pars plana vitrectomy and membrane peeling. Patients underwent extensive imaging before surgery and at 3 months postoperatively, according to Dr Oquendo.

Assessing cone mosaics

In terms of results with eight patients (eight eyes) with idiopathic MH, cone density before surgery was 11,793.92 mm3,and at 3 months postoperatively it was 12,181.6 mm3. In addition, average preoperative spacing was 24.2%, and postoperatively it was 23.1%.

Preoperative regularity was 85.8%, and postoperative regularity was 85.1%. Five patients had stage 2 MHs, three had stage 3 and one had stage 4. All had successful closure of their MHs.

“There was no statistical difference in cone density, regularity or dispersion when comparing pre- and postoperatively,” Dr Oquendo explained. “The sample size was relatively small, but the study demonstrated that AO (rtx1 retinal camera) may be a useful method of assessing integrity of the cone mosaic following macular hole repair.”

Dr Oquendo noted that the sample size in this study was small. “We would like to continue recruiting patients to enlarge the sample size and get more meaningful data,” she said. “This initial study was a pilot project to assess the cone mosaic before and after surgery, and larger studies will be useful to assess AO imaging biomarkers with variations in surgical technique for macular hole closure.”

Dr Oquendo explained that the significance of the study is that it looked at the effect on cone mosaic following MH surgery. “It is well reported that there is a shift of the retina after surgical repair of the macular hole,” she said. “However, there are very few studies that describe the cone mosaic after surgical repair of MHs.”

Moreover, she pointed out, this is the first study describing the change in cone mosaic from baseline. “It is important to know the integrity and changes in the cone mosaic in macular hole to better understand the mechanism of closure and identify imaging biomarkers that may be associated with better functional outcomes,” Dr Oquendo said. “Eventually this could lead to improved surgical techniques.”

Limitations

One of the limitations of the technology is that its use can be time-intensive for clinicians, explained Dr Rajeev H. Muni. The senior author on the study, Dr Muni is a vitreoretinal surgeon at St Michael’s Hospital, Toronto and Kensington Eye Institute, and vice-chairman of clinical research in the Department of Ophthalmology and Vision Sciences at the University of Toronto, Canada.

“There is some training that is required before learning how to efficiently obtain images,” Dr Muni explained. “However, if the patient moves or does not fixate on the target, it can be difficult to acquire images. As a result, in some cases the image acquisition process is time-consuming. Furthermore, depending on the objective, performing imaging in many quadrants and several eccentricities will take more time.”

Dr Muni noted that the AO retinal camera will probably have an adjunctive imaging role to SD-OCT. “Both machines are different, and this is not a replacement for SD-OCT,” he added. “This imaging device provides a very high-resolution image of the cone mosaic, and I think it will be complementary to SD-OCT. Currently, I believe it has a lot of potential in research, as we discover novel imaging biomarkers that are associated with functional outcomes in various diseases.”

Dr Muni noted that the AO retinal camera has been used for conditions other than MH. “There are several applications in both medical and surgical retina, and these will keep expanding as we learn more and get more experience,” he pointed out.

“There has been a lot of research already in diabetic retinopathy and hereditary eye disease. It is also very good for measuring the vessel wall thickness in various vascular conditions. The best images can be acquired in younger phakic patients with no media opacity and a good tear film with a good ability to fixate.”

Paola L. Oquendo, MD

P: (001) 416/978-4321

Dr Oquendo had no relevant financial disclosures related to this content.

Rajeev H. Muni, MD

P: (001) 416/928-2132

Dr Muni is a consultant for Alcon, Bausch + Lomb, Bayer, Novartis and Roche. He has received grants/research funding from Bayer, Novartis and Roche.