Argon laser photocoagulation can reduce the risk of severe vision loss in patients with age-related macular degeneration, ocular histoplasmosis, and idiopathic neovascularization. Early detection of neovascularization soon after the onset increases the likelihood of identifying patients with a new vessel membrane in a potentially treatable position. Patients with one or both eyes at risk for the development of a new vessel membrane should assess their central visual fields on a daily basis by occluding first one eye and then the other. Any disturbance in distance vision or reading vision or the appearance of distortion in the patient's field or on the Amsler grid should prompt an eye examination at the earliest feasible time, in an effort to detect neovascularization in a treatable position.