Association between hydroxychloroquine intake and damage to the outer nuclear layer in eyes without manifest retinal toxicity

Background: Hydroxychloroquine (HCQ) is widely used to treat various autoimmune diseases but carries a risk of retinal toxicity, particularly with prolonged use. Despite advancements, uncertainty persists regarding optimal screening methods. Recent advances in OCT have enabled early detection of retinal damage, with studies suggesting that thinning of specific retinal layers may be an early indicator of toxicity. However, there is a gap in research on outer nuclear layer (ONL) thinning in HCQ users without apparent retinal toxicity. This information is crucial for improving screening and identifying the ONL as a reliable biomarker for screening. Therefore, this study aimed to investigate the association between HCQ intake and ONL damage in eyes without manifest retinal toxicity.

Methods: A case‒control study was conducted at the ophthalmology department of Eye and Ear Hospital International from July 2022 to June 2023. The study included 20 individuals on HCQ and 20 age-matched controls. The data were obtained through chart reviews, and participants underwent comprehensive ophthalmic assessments.

Results: A total of 80 eyes were analyzed. Patients on HCQ exhibited significantly thinner perifoveal, parafoveal, and overall ONL compared to controls (P < .001, P < .012, and P < .004, respectively). Similarly, this association was found in the nasal, inferior, and temporal quadrants of both the inner (region 3: P < .01, region 4: P < .001, and region 5: P < .03) and outer zones (region 7: P < .04, region 8: P < .001, region 9: P < .02), most pronounced in the inferior regions. The cumulative dose was weakly associated with decreased ONL thickness only in the nasal quadrant of the inner zone (region 3: P < .047). Correlation analysis of the initial and most recent OCT scans in the same individuals revealed a weak association with ONL thinning in the central zone (region 1: P < .0048).

Conclusion: The thickness of the ONL can significantly decrease in patients taking HCQ, even in the absence of of manifest retinal toxicity. This study is the first to evaluate this association in eyes with negative screening and diagnostic tests for HCQ retinopathy. The findings suggest that ONL thickness could serve as an early diagnostic indicator for HCQ retinal toxicity.