(NEWSER) – The prescription drugs Avastin and Lucentis both fight blindness in the elderly, and they're both made by the same company, Genentech, at what experts say is a similar production cost. The key difference between them: While an Avastin injection costs $50, a shot of Lucentis goes for $2,000. And more than half a million times per year, doctors opt for Lucentis, running up an extra $1 billion tab for Medicare, the Washington Post reports. Genentech generates a far bigger profit from Lucentis, and it "continues to maintain that Lucentis is the most appropriate medicine" for "wet age-related macular degeneration," saying it costs "significantly" more than Avastin to make. But doctors can also see a financial benefit from providing Lucentis, since Medicare rules reimburse them for the drug plus 6% of its price tacked on top. Genentech also gives doctors rebates when they use large amounts of Lucentis.