Basics of Glaucoma

Basics of Glaucoma

Visual Field Testing

Various tests can determine the extent, if any, or progression of peripheral visual field loss as a result of

glaucoma. Visual field is defined as the “full extent of the area visible to an eye that is fixating straight

ahead.”

This measurement is “perimetry,” and although a person’s visual field is perceived using both

eyes together, testing is done on each eye independently.

Visual field tests are either

kinetic

static

. Kinetic tests are those in which the stimulus is moved from

inward until the patient is able to see it. A static test is defined by the changing intensity of the stimulus

until the patient is able to perceive its presence. Once the patient acknowledges the stimulus, its location

changes. Modern static testing (e.g., Humphrey) does not test one location at a time, but uses a computer

to analyze the data from the all the locations at the conclusion of the test.

The following sections describe the various types of testing for peripheral field of vision:

TYPES OF VISUAL FIELD TESTING

Confrontation visual fields

Tangent screen

Goldmann perimetry

Automated visual fields

Confrontational visual fields:

The gross screening measurement of a patient’s visual field is the

confrontational visual field and is often performed by the ophthalmic technician during a comprehensive

workup. In this kinetic test, the tester’s eye is used as the patient’s fixation point, and the tester’s fingers

are the peripheral stimulae. In order to approximate the patient’s visual field, it is important that the

technician’s eyes be on the same plane as the patient’s and that the tester has closed the eye opposite

the patient’s closed eye. The finger stimulae should be equidistant between the patient and the

technician, and given in all quadrants of vision. Should a defect be identified, it should be recorded in the

chart, and the physician will determine if further visual field testing will be necessary.

Tangent screen:

This test measures the central 30 degrees of a patient’s visual field. Seated

approximately 1 meter from the black felt tangent screen, the patient is asked to identify a white, circular

target attached to the end of a black wand. This target travels along the meridians of the screen, which

are separated by 30 degrees. Depending on the patient’s visual acuity, the target will vary in size from 1

to 50 millimeters. When the stimulus is acknowledged, the tester will note the point on a chart using a pin,

later transferring the results to a recording chart. This test is rarely used in today’s highly technological

environment, but when used, provides a gross screening of peripheral field of vision. This can be used as

well to document non-physiologic (not real) loss of vision.

Goldmann perimetry:

This bowl-like instrument is constructed so the patient’s eye is centered in the

hemisphere. The test object is moved from the periphery towards the center of the bowl either

mechanically or manually until the patient signals having seen it; defining it as a kinetic test. The patient’s

responses are then mapped onto the recording chart along with the size of the stimulus, its color, test

distance (33 centimeters), patient cooperation, and reliability. This is often used with low-vision patients,

or those physically unable to perform automated testing.

Automated visual field testing:

Included in this group of static testing instruments are the Humphrey

and Octopus machines. With the fellow eye patched, patients are instructed to fixate straight ahead and

indicate when they see the stimulus. The stimulus will be presented in each location at different intensities

until the threshold intensity is determined at each location. The “threshold” intensity is the intensity at

which the stimulus is visible 50 percent of the time. For this reason, the same points are tested multiple

times during each test. This test is based on the premise that as the brightness of the stimulus increases,

the likelihood of detection by the patient increases. Different computer algorithms (e.g., SITA Standard

Cassin, Barbara; Dictionary of Eye Terminology 4

Edition; Triad Publishing Company; p. 276