There’s a lot of talk about *potentially* using hydroxychloroquine to treat COVID. This is the most relevant I’ve been in weeks, so here’s a thread which addresses HCQ associated retinal toxicity...
Personally, I love HCQ consults. They make me feel smart because a rheumatologist is asking me for help, but keep in mind the risk of retinal tox is low, so low in fact that routine screening is not recommended until a patient has been on it for 5 yrs, unless pt has certain RFs
The American academy of ophthalmology recommends a dose of <5mg/kg/day (real BW) to minimize risk of tox. Most patients taking 200-400mg per day fall under this threshold. The treatment being proposed for COVID is 600mg/day, but this would presumably be a short course (<1 month)
There are case reports of toxicity occurring after ~1.5 months but this would be exceedingly rare. Vast majority of toxicity cases occur after 20 years on HCQ. Other toxicity RFs:
Cumulative dose > 1,000g
Renal disease
Tamoxifen use
Pre-existing retinal disease like AMD
Cumulative dose > 1,000g
Renal disease
Tamoxifen use
Pre-existing retinal disease like AMD
That said, I have never heard of retinal toxicity occurring within 1 month regardless of risk factors. That would be reportable. Just don’t pump your patient with 1,000 grams of HCQ (2,500% of normal dose) unless you want to kill the virus and everything it’s attached to
I’ve been asked for details on screening. We do a baseline visual field test and picture of the retina when a patient starts HCQ. Normal examples of these look like this 
In a patient with no risk factors for toxicity (see tweet above), we will resume these tests in 5 years. We will still see the patient once a year for dilated exams, but repeating the visual field and OCT isn’t necessary given the low risk
After 5 years, we repeat the tests yearly. This is an example of a patient with toxicity. Large central blind spots (black is bad) and photoreceptor atrophy. Unfortunately, those rods and cones don’t come back
What really sucks is that even after we see toxicity and stop the med, the retinal damage can still progress for a while and there’s nothing we can do about it. This is why it’s so important to have yearly exams to monitor for this, especially once you’ve been on HCQ FOR 10+ yrs
