No eye disease was detected in over 900 rheumatoid arthritis patients treated with less than 4.0 mg/kg per day of chloroquine or less than 6.5 mg/kg per day of hydroxychloroquine for a mean of about seven years. I therefore consider these dosage rates safe, since they are below the threshold of retinal toxicity. This is based on more than 6,000 patient-years of drug exposure. That dosage threshold for retinopathy appears to be 5.1 mg/kg per day for chloroquine and 7.8 mg/kg per day for hydroxychloroquine according to my studies with these compounds. The daily dosage rate, rather than total drug accumulation, seems to determine the development of eye disease. To prevent overdosage, dosing should be calculated not on the actual weight of the patient but on ideal (lean) body weight. Furthermore, the patient's renal and liver function should also be taken into account to avoid overdosage. Since exposure to light amplifies the risk of retinopathy in patients treated with antimalarials, dark sunglasses are recommended for patients spending much time in sunlight.