Although previous studies have shown structural/functional abnormalities in the lateral geniculate nucleus and cortical neurons in those with amblyopia, retinal involvement remains to be elucidated. Advanced imaging technologies have allowed researchers to examine anatomical abnormalities in the eyes of those with amblyopia.
Researchers now say patients with unilateral amblyopia demonstrate intraocular differences in retinal microstructure. In a study published in the Journal of American Association for Pediatric Ophthalmology and Strabismus, patients’ foveal avascular zone’s (FAZ) shape was increasingly irregular and related to the severity of the condition, which ameliorated and became more regular following amblyopia treatments that improve visual acuity.
The researchers initially recruited 70 Chinese children aged between 4 and 12 years, of whom 33 finished follow-up assessments after 6 months of treatment for amblyopia. Children exhibited anisometropic, strabismic, and mixed amblyopia. The investigators found that the central thickness, thickness of the ganglion cell-inner plexiform layer, and vessel density index were higher in the amblyopic eyes compared with those of control eyes (P <.001, P <.001, P <.001, respectively). In amblyopic eyes, the area and circularity of the FAZ was decreased (P =.014, P <.001, respectively).
Improved visual acuity was demonstrated with greater circularity of the FAZ in eyes with amblyopia only, and the circularity rose following bilateral amblyopia treatment, with changes in circularity relating to visual-acuity improvements. Macular thickness, with measures including central-retinal thickness and ganglion cell and inner plexiform layer thickness, was higher in amblyopic eyes compared with that of control eyes.
“The shape of the FAZ could be a sign of the arrested development of the macular fovea. In our study, lower FAZ circularity was found in amblyopic eyes than in fellow eyes,” researchers report.
Improved visual acuity is positively associated with FAZ circularity. FAZ is a metric that was initially employed to assess the severity of retinal geographic atrophy, and is currently used to quantify the disruption of the terminal capillary ring at the fovea. FAZ is linked to disease progression in vascular maculopathy.
Treatment for amblyopia seems to mediate retinal microvasculature to a greater extent than it does retinal thickness. Because the shape of the FAZ changes after birth, the study authors hypothesize that clearer visual stimulation mediated by optical therapy may facilitate macular-vascular pruning in amblyopic eyes, thus boosting FAZ circularity.
Limitations of the current study include the small sample size of strabismic patients, which impaired the ability to differentiate statistically significant microstructural differences in the retina of the two types amblyopia. Another limitation is that the duration of amblyopia treatment could have been inadequate to facilitate significant structural change in the retina.
Huang X, Liao M, Li S, Liu L. The Effect of treatment on retinal microvasculature in children with unilateral amblyopia. J. AAPOS. Published online September 25, 2021. doi:10.1016/j.jaapos.2021.05.011