Argon laser trabeculoplasty, or ALT, is a treatment for open angle glaucoma. Open angle glaucoma occurs because the pressure in the eye increases. Eye pressure is normally regulated by fluid flow out of the eye. Fluid drains out of the eye from the Trabecular Meshwork. Over production or insufficient drainage causes an imbalance in the eye's ability to regulate pressure. Most patients with open angle glaucoma must use eye drops daily to lower eye pressure. ALT is an outpatient procedure. Using a special lens, to aim the laser, your doctor will fire the laser into the drainage area. With each pulse, the laser will 'open up' the drainage system.