Glossary of Ocular Testing

Amsler Grid
A grid of 400 small squares (white separated by black lines or black separated by white lines), with a fixation dot in the middle, used to detect macular degeneration in an eye by the presence of curved, distorted, or broken lines in the grid.

Automated Visual Fields
Determines peripheral and central vision disorders.

Determines near and farsightedness and astigmatism.

Biomicroscope/Slit Lamp
Used to examine the cornea and the rest of the external eye for abnormalities.

A process by which the pupil is temporarily enlarged with special eye drops. Dilation allows the eye care specialist to better view the inside of the eye. By examining the entire inside of the eye, the doctor can see problems that you cannot feel or see until they impair your vision.

Depth Perception/Stereovision
A simple test to determine if both eyes work together to provide 3-D vision.

Intraocular Pressure
Pressure of the fluid inside the eye; normal IOP varies among individuals.

Intraocular pressure (IOP)
The pressure within the eyeball that gives it a round firm shape, regulated by the rate at which aqueous humor enters and leaves the eye

An instrument used to check the front curvature of the cornea’s surface. This test is important for anyone interested in contact lenses.

An instrument that allows an eye care professional to read a prescription directly from a pair of glasses.

A non-invasive, hand-held instrument the doctor uses to view the entire dilated eye. It has a bright light which illuminates and magnifies the eye’s interior.

The doctor examines the inside of your eyes with an instrument that illuminates and magnifies the interior of the eye. Conditions such as cataracts, diabetes or hypertension can be detected.

A mask-like instrument positioned so that each eye sees through a separate lens. It determines amount of vision correction necessary.

The degree of nearsightedness, farsightedness or astigmatism is determined during this test. As series of lenses are used and adjusted before your eyes to determine the best correction.

An instrument, such as a Goldmann tonometer or an “air puff” tonometer, used to measure the interior pressure of the eye in millimeters of mercury (mm Hg)

This test measures the internal pressure of the eye. High pressure of the eye may indicate the presence of glaucoma.

Visual Acuity Test
This test checks vision sharpness by presenting letters of graduated sizes to determine the smallest size that can be read at a standard distance (a 20/20 letter located 20 feet away from an eye); “normal” acuity in the human eye is 20/20, although some eyes are capable of 20/15 or even 20/10 acuity. The smaller the letters that can be distinguished, the better a patient’s visual acuity. Both distance and near vision are checked.