Visual complications of warfarin

To the Editor: Warfarin is frequently used in the same population that is at risk of age-related macular degeneration (ARMD), the commonest cause of blindness in the elderly. A recent report has suggested that warfarin may cause severe intraocular haemorrhage and loss of vision in the minority of patients who have the neovascular form of ARMD.1 We have also seen this occur in patients taking warfarin. There are methodological imperfections in the report, and the association is certainly not proven. Nevertheless, it would seem prudent to exercise some caution in the use of warfarin in patients who are or may be at risk. Our preliminary recommendations (pending a prospective study) are:

• If a patient has only one functioning eye (for whatever reason), an ophthalmologist's opinion should be sought as to the risk of neovascular ARMD in the seeing eye before or soon after commencing warfarin therapy. Low-risk patients are easily identified and warfarin use in these patients should have no visual sequelae. In patients considered at high risk of neovascular ARMD, the use of warfarin may carry a (currently unquantifiable) risk of visual loss. Alternatives to warfarin should be considered, and the possible risks of taking, or not taking, warfarin should be discussed with the patient.

• If a patient has two seeing eyes, the risk of bilateral visual loss from warfarin must be exceedingly small, and indeed there have not even been anecdotal reports of such an event. Warfarin can be used in such patients without regard to ocular status.

• Ophthalmologists should ask all patients they examine whether they take warfarin and should communicate to the treating doctor the presence or absence of factors that put this patient at high risk of neovascular ARMD.