New findings published in the American Journal of Ophthalmology assessed whether age-related macular degeneration (AMD) patients with concomitant amblyopia are more likely to have both diseases diagnosed on the ipsilateral or on the contralateral side.
Give me some background first.
A study in 2020 evaluated the recovery of visual function in amblyopic eyes after the loss of the fellow eye as a result of AMD; it demonstrated that out of 10 patients, all but one had AMD in the non-amblyopic eye.
Why is this significant?
This led to investigators concluding that either the amblyopic eye may be protected from AMD or that amblyopic patients do not notice AMD when it affects the amblyopic eye and, consequently, do not seek further care.
Gotcha. Now talk about this study.
In this retrospective cross-sectional study, a research team analyzed the medical records of patients who visited the Department of Ophthalmology at the Medical University Graz in Austria, between December 1996 and June 2021.
Patients with AMD diagnosed in one eye were used for further analysis, and spectral-domain optical coherence tomography (SD-OCT) was used to confirm the lateral asymmetry of AMD.
Findings?
In total, investigators identified 5,284 patients (1.61%) with amblyopia and 16,236 patients (4.96%) with AMD.
Further, 163 patients (3.3%) with AMD diagnosed on one side also had unilateral amblyopia (odds ratio [OR]=1.21, 95% confidence interval [CI] 1.04-1.42).
Of this patient group, 126 patients had AMD and amblyopia on opposite sides (OR=0.93, 95% CI 0.78-1.11), and 37 patients had both AMD and amblyopia on the same side (OR=0.27, 95% CI 0.19-0.37).
Anything else?
For the 5,051 patients with unilateral amblyopia, the research team noted:
- 130 patients (2.6%) were diagnosed with AMD in the amblyopic eye (OR=0.51, 95% CI 0.43-0.60).
- 219 patients (4.3%) were diagnosed with AMD in the non-amblyopic eye (OR=0.87, 95% CI 0.76-1.00).
Lastly, of 233 patients with bilateral amblyopia, three (1.3%) had co-occurent AMD in both eyes (OR=0.25, 95% CI 0.08-0.78).
What causes this relationship between amblyopia and AMD?
While the mechanism behind amblyopia’s protective effect on AMD remains unclear, the study authors highlighted a previous study where strabismus led to reduced metabolic activity in the visual cortex in a monkey model.
And this lead to …
They hypothesized that “amblyopia may also lead to reduced metabolic activity in the retina, causing less accumulation of degradation material like lipofuscin, which would otherwise contribute to AMD pathogenesis by oxidative stress-induced damage to the retinal pigment epithelium.”
Take home.
Patients with asymmetrical AMD and co-occurrent amblyopia were more likely to have the two diseases diagnosed on opposite sides than on the same side.
Additionally, in cases of concomitant amblyopia and AMD, the amblyopic eye tends to be less affected by AMD, though the protective effect of amblyopia in AMD disease progression is still not well understood.