Hydroxychloroquine (Plaquenil) belongs to the antimalarial class of drugs, and is used for a variety of rheumatic conditions including lupus. Its popularity stems from its relative efficacy and a very good safety profile.
The most worrying potential side effect is retinopathy. Classically, this is in the form of a Bull’s eye maculopathy. The macula is the central portion of the retina responsible for central vision. Bull’s eye maculopathy is so named because the lesion has a hyper-pigmented centre surrounded by a de-pigmented zone which in turn is surrounded by a hyper-pigmented ring. If detected early, mild maculopathy in the form of stippling of the retinal pigment epithelium (RPE) of the macula can be seen. This early form of damage may be reversible if the medication is ceased in time.
Patients with maculopathy often present with a paracentral scotoma before any detectable clinical change. Hence, ophthalmic screening is recommended in some countries. In others, the United Kingdom included, there is an argument that with proper dosing regimens, retinopathy is rare and therefore screening is not cost-effective. The proponents of screening argue that because dosing is based on lean-body weight, overdosing can still occur. In addition, it may be medicolegally advisable to offer screening.
A baseline examination is very useful within the first year of starting hydroxychloroquine. Parameters measured at this visit can include best-corrected visual acuity, dilated fundus examination, colour fundus photography, colour testing and Humphrey 10-2 automated visual field. Colour photography is particularly useful if there are retinal changes that could confuse with maculopathy at a later stage. It is also useful to detect congenital colour defects especially in males.
The frequency of subsequent examinations will depend on risk factors. These include a dosing of >6.5 mg/kg/day, being overweight (risk of over-dosing if dose not based on lean-body weight calculations), duration of treatment > 5 years, renal or liver disease (impaired metabolism and clearance) and retina susceptible to toxicity (including pre-existing macular disease and age >60 years). Screening intervals vary with each ophthalmologist and ranges from a few months in cases of possible maculopathy to yearly or less in low risk patients. Common review intervals are between 6 to 12 months.
Patient education is essential to ensure early detection and cessation of the medication. Patients can be taught to self-screen using an Amsler-grid to monitor for para-central scotomas about once a month. Any visual symptom should be taken seriously and referred for investigation.
