Pre-treatment using a xanthin carotenoid (preferably 3R,3′R-zeaxanthin) can improve the benefits and efficacy of photodynamic therapy (PDT), which uses a light-activated drug (such as verteporfin) in patients who suffer from unwanted retinal blood vessel growth, including the “wet” (exudative) form of macular degeneration. Before a PDT treatment, patients are given a regimen of orally-ingested zeaxanthin for a period of at least 1 and preferably at least 2 to 3 weeks, at dosages of at least 3 and preferably at least 10 milligrams per day. Since zeaxanthin imparts a yellowish color to the macula, a preferred dosage should increase a patient's macular pigment density before the PDT treatment is performed.