Forms strong bonds with melanin in the retinal pigment epithelium. This binding results in an accumulation of the drug in the retina, leading to toxicity. Color Vision Ishihara color plates are usually normal at early stages of toxicity. Usually not affected until after changes in visual acuity or the visual field have occurred. Automated visual fields and Amsler Grid testing are highly sensitive for detecting early hydroxychloroquine toxicity.
Early toxicity causes relative pericentral scotomas or metamorphopsia.
Severe toxicity can result in a large central scotoma. Changes in the visual field generally occur prior to a reduction in visual acuity. Electroretinogram Not clinically useful in detecting hydroxychloroquine toxicity. Essentially normal at all stages of toxicity. May or may not show a reduction in photoreceptor function during late stages of toxicity.