OCT Angiography Demonstrates Retinal Involvement in Amblyopia

By Will Boggs MD

July 07, 2020

NEW YORK (Reuters Health) - Optical coherence tomography angiography (OCT-A) could play a role in diagnosing and understanding the pathogenesis of amblyopia, researchers in Hong Kong report.

"Our study, utilizing high-resolution imaging with OCT-A in a population-based cohort, confirmed the presence of retinal microvasculature abnormalities in amblyopic eyes, inferring retinal involvement in the development of amblyopia," Dr. Jason C. Yam of The Chinese University of Hong Kong and Hong Kong Eye Hospital told Reuters Health by email.

While the pathophysiology of amblyopia, one of the most common ophthalmic conditions in children, is not well understood, recent studies using OCT-A have reported abnormal microvasculature in amblyopic eyes in children.

Dr. Yam and colleagues used a fully automated program to measure several unitless OCT-A metrics from OCT angiograms in order to quantify the extent of microvascular damage in children from first to third grade. The study included 30 children with amblyopia and 1,045 controls.

The mean foveal avascular zone (FAZ) circularity was significantly lower in the amblyopic group than in the control group, indicating an irregular shape of the FAZ in eyes with amblyopia, the researchers report in JAMA Ophthalmology.

Amblyopic eyes had a lower mean fractal dimension (FD) than did control eyes, but there was no significant difference between amblyopic eyes and control eyes in mean FAZ area or mean vessel density.

Poorer visual acuity was associated with reduced FAZ circularity and increased vessel diameter index, whereas best-corrected visual acuity was not significantly associated with OCT-A metrics.

"OCT-A is a useful tool for high resolution, noninvasive imaging in ophthalmology; however, the interpretation of OCT-A results require caution," Dr. Yam said. "OCT-A metrics can be affected by multiple confounders and not all indices are reproducible and repeatable between machines. With proper image-analysis techniques, skilled technician and adjustment of confounders, OCT-A can be a very useful tool in multiple ophthalmic diseases, and has potential to serve as a quantitative tool for visual assessment in amblyopia."

"This noninvasive test is ideal in children, offering an objective tool on top of visual acuity to guide treatment plans," he said.

"Our study is limited by the cross-sectional nature of the data; hence, a causal relationship cannot be inferred in relation to the findings and visual acuity in amblyopia," Dr. Yam cautioned. "Data from future prospective studies to examine the effect of amblyopia treatment on retinal microvasculature and the reversibility of such changes will provide further useful information."

Dr. Tock H. Lim of the National Healthcare Group Eye Institute and Tan Tock Seng Hospital, in Singapore, who coauthored an invited commentary on the results, told Reuters Health my email, "Amblyopic eyes appear normal on routine ophthalmic examination, but the visual acuity is significantly lower. It is currently a diagnosis of exclusion, (i.e. when no other cause is found) in the presence of one or more potential amblyogenic cause(s)."

"The new OCT-A findings may be very helpful for the positive diagnosis of amblyopia, potentially saving expensive diagnostic tests to rule out other causes, e.g., MRI to exclude compressive optic neuropathy," he said.

"I would encourage researchers to design studies to see if the findings are replicable on other OCT-A platforms and in other age and racial groups," Dr. Lim said.

Dr. Eric Gaier of Boston Children's Hospital and Harvard Medical School, who recently reviewed insights about amblyopia from OCT studies, told Reuters Health by email, "There seems to be considerable overlap between (albeit statistically significantly different) OCT-A parameters for amblyopic and control eyes, so using these parameters to distinguish amblyopic eyes from normal eyes is problematic."

"Second, this is a solution with no problem - diagnosis of amblyopia (identification of an amblyogenic risk factor such as anisometropia and/or strabismus) including accurate measurement of visual acuity is not challenging in the 6-8 year age group," he said. "It's unclear to me that identification of these OCT-A parameters adds anything useful to our diagnostic toolbox; thus, I am skeptical these results will significantly influence clinical practice."

"That said, these findings carry a high scientific impact by identifying new OCT-A parameters associated with visual dysfunction in amblyopia," Dr. Gaier said. "Traditionally thought of as a cortical disorder, amblyopia is becoming increasingly recognized as a more complex entity than previously thought."

SOURCE: https://bit.ly/2BT78uT and https://bit.ly/38hLvQU JAMA Ophthalmology, online June 25, 2020.