Retinal camera unlocking back-of-the-eye secrets

Reviewed by Paola L. Oquendo, MD

The AO Retinal Camera has been used to measure photoreceptors pre-operatively and following macular hole (MH) surgery to accurately assess any changes in cone density, according to research presented by Paola L. Oquendo, MD, at the annual meeting of the Canadian Ophthalmological Society held recently in Halifax, Nova Scotia, Canada.

“We hypothesized that cone density will change following macular hole closure,”

said Oquendo, a vitreoretinal clinical research fellow, St. Michael’s Hospital/Unity Health Toronto, Department of Ophthalmology and Vision Sciences University of Toronto in Toronto, 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 macular hole and photoreceptor changes using high-resolution imaging with adaptive optics, Oquendo described results of a small study that used Adaptive Optics (AO) RTX-1 retinal camera and Spectral Domain Optical Coherence Tomography (SD-OCT) to evaluate the photoreceptors in patients with various morphology of macular hole and to evaluate changes following surgical closure.

Subjects presenting to the Kensington Vision and Research Center in Toronto with idiopathic MH needing pars plan vitrectomy (PPV) and membrane peeling were included in the study. Patients underwent extensive imaging (SD-OCT, IOL Master, Optos, and AO testing) before surgery and at 3 months postoperatively, according to Oquendo.

In terms of their results with 8 patients (8 eyes) with idiopathic MH, they saw the cone density before surgery was 11,793.92mm3 and at 3 months post-operatively was 12,181.6mm3. In addition, pre-operative spacing was 24.2% and post-operatively it was 23.1%. Pre-operative regularity was 85.8% and post-operative regularity was 85.1%. Five patients had MH Stage 2, 3 patients had Stage 3, and 1 patient had Stage 4. All had successful closure of the MH.

“There was no statistical difference in cone density, regularity or dispersion when comparing pre- and post-operatively,” Qquendo explained. “The sample size was relatively small, but the study demonstrated that AO (RTX-1 retinal camera) may be a useful method of assessing integrity of the cone mosaic following macular hole repair.”

Oquendo noted the sample size was small and future research will involve a bigger sample.

“We would like to continue recruiting patients to enlarge the sample size and get more meaningful data,” Oquendo pointed out. “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.”

The significance of the study is that it looked at the effect on cone mosaic follow MH surgery, explained Oquendo.

“It is well-reported that there is a shift of the retina after surgical repair of the macular hole,” Oquendo added. “However, there are very few studies that describe the cone mosaic after surgical repair of MHs.”

Moreover, Oquendo pointed out, this is the first 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,” Oquendo said. “Eventually this could lead to improved surgical techniques.”

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

“There is some training that is required before learning how to efficiently obtain images,” 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.”

The AO retinal camera will likely have an adjunctive imaging role to SD-OCT, Muni noted.

“Both machines are different, and this is not a replacement for SD-OCT,” Muni 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.”

An advantage of the AO retinal camera is that it is user-friendly and not a challenging technology, according to Oquendo.

“The learning curve is rapid,” Oquendo added. “It is not difficult to use although it can be challenging to obtain high quality imaging in some cases. Some training is certainly required to understand the system and learn how best to obtain high-quality images.”

Moreover, the AO retinal camera has been used for conditions other than MH, Muni explained.

“There are several applications in both medical and surgical retina, and these will keep expanding as we learn more and get more experience,” Muni 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: 416/978-4321

Oquendo had no relevant disclosures.

Rajeev H. Muni MD

P: 416/928-2132

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