Ancillary Testing in Screening for Hydroxychloroquine and Chloroquine Retinopathy

The most important purpose of 4-aminoquinoline retinopathy (4AQR) screening, detecting overdosing, requires no ancillary testing. However, a subsidiary purpose, detecting the rare occurrence of 4AQR among properly dosed patients, requires ancillary testing, because clinical examination is insensitive. In Bayesian reasoning, the sensitivity and specificity of an ancillary test interact with the estimated prior probability of disease to determine the estimated posterior probability of the disease. For a condition of low prior probability a single test is rarely dispositive for management. Instead, the common role for each test is to adjust the clinician’s estimate of the probability of 4AQR before applying another test, until a level of certainty is achieved indicating that the 4-aminoquinoline (4AQ) will be stopped or continued. Testing with 10-2 visual fields, multifocal electroretinography, spectral domain optical coherence tomography (SD-OCT), and fundus autofluorescence is useful for this purpose when applied selectively rather than universally. SD-OCT is especially helpful because it has the lowest test variability, the highest specificity, and similar sensitivity to the other tests.