Chloroquine retinopathy can result in devastating loss of vision. To date, there are no effective and reliable methods of detecting the toxicity at an early stage when retinopathy may be reversible. Chloroquine is deposited in the retinal pigment epithelium, which forms part of the blood-retinal barrier (BRB). By vitreous fluorophotometry we have shown that there is breakdown of the BRB in chloroquine retinopathy. However, in asymptomatic patients who had received varying amounts of hydroxychloroquine (up to 1067 g), the BRB remained intact.