What is hydroxychloroquine? How does it affect the eye?
Hydroxychloroquine is a common anti-inflammatory drug used in stabilizing rheumatologic conditions such as systemic lupus erythematosis. Given at higher doses over a long period of time, however, it can lead to retinal toxicity. Early toxicity may be asymptomatic and patients may complain of color vision or other visual symptoms only when the toxicity is more advanced. Given that retinal toxicity is usually irreversible and may even progress after stopping intake of hydroxychloroquine, early detection of retinal toxicity and cessation of the hydroxychloroquine is the best approach.
Corneal and ciliary body toxicity can be seen as well but these are not as worrisome as retinal toxicity. The former is also completely reversible with cessation of hydroxychloroquine intake.
What are the risk factors for retinal toxicity?
Risk for toxicity is the least with doses of less than 6.5 mg/kg/day. Current recommended maximum daily dose is 5 mg/kg/day. Patients are at low risk during the first 5 years of treatment. Cumulative dose of 250 grams and above increases the risk for toxic retinopathy. Other risk factors include kidney or liver disease, older age, other retinal disorders and concomitant use of tamoxifen. Obesity can be a risk factor as well in that the drug does not penetrate lipid-rich tissues and the calculated dose may be higher than the true amount that is safe for the patient. This has to be taken into consideration during dose calculations.
High risk patients have a 5% chance of developing toxic retinopathy. Another way to look at risk is: 5-year risk <1%; 10-year risk <2%; 20-year risk about 20%.
What does screening involve and how often should it be performed?
A complete eye examination is required before starting on hydroxychloroquine treatment. Your eye doctor will assess your visual acuity, colour vision and central visual field. In addition, specific tests such as the fundus auto-fluorescence test and retinal nerve fibre layer thickness test are useful adjuncts that have the potential to detect early toxicity.
Follow-up may be infrequent in the first five years. However, from the fifth year on, it is advisable to have your eyes screened on a yearly basis to detect early toxicity and halt treatment before any further damage occurs.