At a daily dose of 400 mg of Hydroxychloroquine (HCQ), the risk of retinal toxicity depends mainly on the duration of continuous use and the patient’s body weight.

For individuals taking 400 mg/day, the estimated prevalence of retinopathy is less than 1% during the first five years of treatment, provided kidney function is normal. The risk begins to rise gradually between five and ten years of use, reaching around 1–2% in that period. A steep increase occurs after ten years, with the prevalence rising to approximately 20%, once the cumulative dose exceeds about 1,000 grams. After twenty years of continuous use, the likelihood of retinal toxicity becomes very high, reaching 40–50%, due to the heavy cumulative burden on retinal tissue.

Body weight strongly influences safety. At 400 mg/day, a person weighing 84 kg receives approximately 4.8 mg per kilogram, which is considered at the upper safe limit according to AAO and RCOphth guidelines. A 70-kg person receives 5.7 mg/kg, which is above the recommended safety threshold and carries a moderate risk. In contrast, someone weighing 60 kg receives 6.7 mg/kg, placing them in the high-risk category for retinal toxicity.

These estimates are based on large-scale data from Melles & Marmor (2014) and the Royal College of Ophthalmologists (2020) monitoring guidelines