Chloroquine is an antimalarial drug. Hydroxychloroquine is a derivative of the drug that is more commonly used in the United States. These antimalarials have properties that downregulate the immune system and are now commonly used as immunomodulatory therapy for diseases such as rheumatoid arthritis, discoid and systemic lupus erythematosus, dermatomyositis, lichen planopilaris, and erosive vulvovaginal lichen planus.

Prolonged use of antimalarials can cause toxicity to the retina, specifically the macula. The toxicity is known as a bull's-eye maculopathy and is usually bilateral and symmetric. Chloroquine causes direct toxicity to the retinal pigment epithelium (RPE), causing loss of outer retinal photoreceptors. The photoreceptor degradation spares the fovea, giving it the classic bull's-eye appearance. Retinal changes are irreversible.

Patients may not experience any symptoms in early toxicity, but more progressive toxicity can cause color vision changes or paracentral scotomas.

Very rarely, hydroxychloroquine lipid deposits can occur in the corneal epithelium, causing a vortex keratopathy. This has been commonly reported in cancer patients requiring high doses of hydroxychloroquine (more than 400 mg daily). Unlike the retinal toxicity, however, the vortex keratopathy rarely causes visual changes and is reversible once the drug is discontinued.

The prevalence of hydroxychloroquine-induced retinopathy is estimated to be around 4%-13%. Risk factors for its development include drug dosage and chronicity. Ideally, the dose should be 5 mg/kg actual body weight/day or less for hydroxychloroquine and 2.3 mg/kg actual body weight/day or less for chloroquine. Toxicity usually occurs after chronic use and with doses above the recommended amount. However, if the daily dosage of hydroxychloroquine is 5 mg/kg per day or less, the risk of retinopathy is reported to be less than 2% for use of 10 years, or less than 5% for each subsequent year. Other risk factors for development of retinopathy on antimalarials include kidney disease due to impaired excretion of drug and concomitant use with other medications, such as tamoxifen.

Prognosis can be good with early detection and discontinuation of the drug. However, even after discontinuation, retinal toxicity can continue to occur.

Keratopathy is reversed once medication is stopped and does not cause long-term damage to the cornea.