Hydroxychloroquine Retinopathy With a Normal 24-2 Field
A 63-year-old woman with rheumatoid arthritis has taken hydroxychloroquine 400 mg daily for 8 years. She weighs 70 kg. She reports trouble reading in dim light and "brownish" central vision. Best-corrected acuity is 6/6 in each eye. Slit-lamp and dilated fundus examination are unremarkable. Humphrey 24-2 visual fields are reliable but show no definite defect; 10-2 testing shows a paracentral ring scotoma in the right eye and a partial ring in the left. SD-OCT shows perifoveal loss of the ellipsoid zone with a preserved foveal centre. Multifocal ERG shows reduced amplitudes in the paracentral rings. She asks whether she can stop the drug herself and whether the tests prove toxicity.
1. Calculate her weight-based daily hydroxychloroquine dose and identify her risk factors for retinopathy.
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400 mg/day divided by 70 kg = 5.7 mg/kg/day, which exceeds the commonly recommended 5 mg/kg/day real-body-weight threshold. Duration is 8 years, well beyond the 5-year mark after which risk rises. Cumulative dose is 400 mg x 365 x 8 = 1,168,000 mg, or about 1.17 kg. Additional risk factors include age over 60, possibly renal function (not given), and the presence of symptoms. The dose and duration alone put her in a higher-risk group, so annual screening and a low threshold for objective testing are appropriate. A normal fundus examination does not exclude toxicity, because the earliest changes can be subtle and may be missed without field and OCT testing.
2. Interpret the screening tests. Does she meet criteria for hydroxychloroquine retinopathy, and what is the role of the 24-2 versus 10-2 field?
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The 10-2 field shows a paracentral ring scotoma, SD-OCT shows perifoveal ellipsoid-zone loss with foveal sparing, and multifocal ERG shows reduced paracentral amplitudes. This pattern is characteristic of hydroxychloroquine retinopathy, which preferentially affects the parafoveal photoreceptors and ganglion cells. The 24-2 field can miss this because its test points are spaced 6 degrees apart and the parafoveal ring may fall between points; the 10-2 uses 2-degree spacing and is more sensitive. The normal 24-2 does not exclude toxicity. With objective structural and functional abnormalities, she meets criteria for probable or definite toxicity and should be managed as such. The preserved foveal centre explains why her acuity remains 6/6 despite parafoveal damage.
3. Formulate a plan for communication with the rheumatologist and the patient. Include whether to stop the drug, how to monitor, and why abrupt self-discontinuation is a problem.
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I would not advise her to stop the drug on her own. Hydroxychloroquine discontinuation is a rheumatologic decision because abrupt cessation can precipitate a flare of rheumatoid arthritis. I would contact her rheumatologist the same day, share the 10-2 fields, OCT, and multifocal ERG, and recommend discontinuation or substitution if toxicity is confirmed. Monitoring should continue after stopping because retinopathy can progress for months to years. I would arrange repeat testing in about 6 months and document the discussion. The patient should understand that early discontinuation improves the chance of stabilizing vision, but that the final decision is coordinated with her rheumatologist. She should also be told to report any new central visual symptoms promptly.