The retinal camera unlocks the secrets behind the eye
Reviewed by Paola L. Oquendo, MD
The AO Retinal Camera was used to measure photoreceptors before and after 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 recently held in Halifax, Nova Scotia, Canada.
“We hypothesized that cone density would change after the macular hole closed,”
said Oquendo, Vitreoretinal Clinical Investigator, St. Michael’s Hospital/Unity Health Toronto, Department of Ophthalmology and Vision Sciences, University of Toronto in Toronto, Canada. “This is because the temporal retina is likely to stretch to close the macula foramen. This could possibly lead to a temporal reduction in cone density.
Discussing macular hole and photoreceptor changes using high-resolution imaging with adaptive optics, Oquendo described the results of a small study that used the RTX-1 retinal adaptive optics (AO) camera and Spectral domain optical coherence tomography (SD-OCT) to assess photoreceptors in patients with various macular hole morphologies and to assess changes after surgical closure.
Subjects presenting to Kensington Vision and Research Center in Toronto with idiopathic MH requiring pars plan vitrectomy (PPV) and membrane peeling were included in the study. The patients underwent extensive imaging (SD-OCT test, IOL Master, Optos and AO) before surgery and at 3 months postoperatively, according to Oquendo.
In terms of results with 8 patients (8 eyes) with idiopathic HD, they saw that the cone density before surgery was 11,793.92 mm3 and at 3 months after surgery was 12,181.6 mm3. In addition, the preoperative spacing was 24.2% and postoperative it was 23.1%. Preoperative regularity was 85.8% and postoperative regularity was 85.1%. Five patients had stage 2 MH, 3 patients had stage 3, and 1 patient had stage 4. All successfully closed the MH.
“There were no statistical differences in cone density, evenness, or scatter when comparing pre- and post-operatively,” Qquendo explained. “The sample size was relatively small, but the study demonstrated that AO (RTX-1 retinal camera) can be a useful method to assess cone mosaic integrity after macular hole repair. “
Oquendo noted that the sample size was small and that future research will involve a larger sample.
“We would like to continue recruiting patients to expand the sample size and obtain more meaningful data,” Oquendo pointed out. “This initial study was a pilot project to assess 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 after HD surgery, Oquendo explained.
“It is well reported that there is retinal displacement after macular hole surgical repair,” Oquendo added. “However, there are very few studies that describe cone mosaic after surgical repair of MH.”
Additionally, Oquendo pointed out, this is the first description of the cone mosaic change from baseline.
“Knowing cone mosaic integrity and changes in the macular hole is important to better understand the closure mechanism 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 it can be time-consuming for clinicians to use, explained Rajeev H. Muni MD, lead study author and vitreoretinal surgeon at St. Michael’s Hospital/Unity Health Toronto and at the Kensington Eye Institute, Vice Chair for Clinical Research, Department of Ophthalmology and Vision Sciences, University of Toronto at Toronto.
“There is some training that is needed before you learn how to get images effectively,” Muni explained. “However, if the patient is moving or not focusing on the target, it can be difficult to acquire images. As a result, in some cases, the image acquisition process takes time. Also, depending on the objective, imaging in many quadrants and multiple eccentricities will take longer.
The AO retinal camera will likely have a complementary imaging role to SD-OCT, Muni noted.
“The two machines are different and it’s not a substitute 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 think it has a lot of potential in research, as we discover new imaging biomarkers associated with functional outcomes in various diseases.
One advantage of the AO retinal camera is that it is user-friendly and not difficult technology, according to Oquendo.
“The learning curve is steep,” added Oquendo. “It’s not difficult to use although it can be difficult to get high quality imaging in some cases. Some training is definitely needed to understand the system and how to best achieve high quality images.
Additionally, the AO retinal camera has been used for conditions other than HD, Muni explained.
“There are several applications in the medical and surgical retina, and these will continue to expand as we learn more and gain more experience,” Muni emphasized. “There has already been a lot of research on diabetic retinopathy and inherited eye diseases. It is also very good at measuring vascular wall thickness in various vascular conditions. The best images can be acquired in younger phakic patients without media opacity and a good tear film with good uptake ability.
Paola L. Oquendo, MD
Oquendo had no relevant disclosure.
Rajeev H. Muni MD
Muni is a consultant for Alcon, Bausch + Lomb, Bayer, Novartis and Roche. He has received research grants/funding for Bayer, Novartis and Roche.