The eye doctor will start by asking a series of questions about your medical and eye health history, including any noticeable eye problems. Visual acuity (vision) is determined in each eye using the Snellen Chart. This chart consists of random letters of different sizes. The letters for normal vision (20/20) are 3/8-inch tall, viewed at 20 feet. People with normal vision can read these letters. A refraction test may also be performed (the doctor puts several lenses in front of the eyes to determine if glasses are needed). Eye movement (see extraocular muscle function ) and peripheral vision (see visual fields ) are tested by moving a light or object through the field of vision. The eye's reaction to light (pupillary response) is also measured. Color blindness is tested using multicolored dots that form numbers (see color vision test ). Colorblind people are not able to detect certain numbers or may see a different number than people who are not colorblind. Glaucoma testing (tonometry ) is performed with a puff of air directed at the eye or using a blue circle of light that comes very close to the eye. Evaluation of the cornea (the clear surface of the eye)and the front part of the eye is performed while you are seated at a slit lamp, a device that magnifies the doctor's view. The retina, fundus (back of the eye), retinal vessels, and optic nerve head (optic disc) are viewed with an ophthalmoscope (a magnifier with a light). This procedure is known as an ophthalmoscopy. Drops that dilate the pupil allow more of the fundus to be viewed.
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