Provided is a method of treating or preventing age-related macular degeneration (AMD) in a patient subject to, or symptomatic of the disease, wherein the method comprises restoring normal lysosomal pH (pHL), or acidifying an abnormally elevated pHL, thus decreasing or preventing a damaging accumulation of lipofuscin or waste products in the retinal pigment epithelium (RPE) cells of the eye of the patient. Further, this method is achieved by modulating the action of the P2X7 and/or P2Y12 receptors of the RPE cells, specifically decreasing the acidity (pHL) of the RPE lysosomes by administering selected receptor antagonists affecting the action of the P2X7 and/or P2Y12 receptors of the RPE. Methods for selecting and quantifying the effectiveness of drugs to restore pHL and determine outer segment clearance rates is also provided using a high through-put screening protocol.