Vision testing machines, such as optecs, phoroptors and slit-lamps, examine the eye using various lenses, magnifiers, lights and measuring devices to check the vision strength and overall condition of the eye, as well as scan for diseases. Hand-held devices, including ultra-violet scanner lights, illuminate the surface tissue of the eye, showing abrasions or debris.
Optec machines are used for basic vision tests, and measure the limits to which the eye can focus, decipher objects, letters and colors. These machines also measure muscle balance within the eye. Tests are performed by having a patient look into the machine with both eyes open, and looking in specific directions, at certain objects, or reciting what is seen or read. This machine determines vision standards for possible further testing. A vision standard of at least 20/40 is required for passing without the need for corrective lenses.
Phoropters are used when optec machines determine a need for corrective lenses. Phoropters measure levels of far-sightedness and near-sightedness; this test is known as refraction. The machine is positioned in front of the face, with lenses placed in the center of the eyes. Patients are then asked to read a line of letters or numbers that are projected across the room, and sample lenses are increased or decreased until the patient is able to read the smallest line. This process allows optometrists to prescribe the most precise eyeglass or contact lens strength.
Eye health is examined by machines called slit-lamps. Slit-lamps highly magnify the external tissues and internal structures of the eye. Orange dye is placed in each eye to highlight any problem areas before the optometrist examines the eyes using a device called an ocular. An ocular shines a light into the eyes while functioning like a microscope, diagnosing corneal ulcers, cataracts and retinal diseases or injuries.