Visual field testing is important in the diagnosis and management of glaucoma. It is used to confirm that glaucoma has affected the visual field, to evaluate the severity, and to monitor for progression.

An automated instrument is used to map the visual fields.The patient looks straight ahead into a bowl-shaped area and the instrument's computer randomly flashes points of light around different places in the bowl. The patient clicks a switch whenever he/she sees the light, which varies in brightness.

All eyes have a normal blind spot in the side vision where the optic nerve enters at the back of the eye. The side vision map produced by the automated perimetry test shows exactly where different intensities of light were seen (or not seen) in the patient's field of vision. Visual field tests are usually performed once or twice a year after glaucoma is diagnosed to check the field of vision for any changes.

A visual field examination takes time and requires concentration. During visual field testing, it is best to relax and respond as accurately as possible. Performance results can vary from day to day; therefore, your doctor may ask that you repeat the test.

For many years the standard of care has been static automated perimetry. The IU School of Optometry Ocular Disease Service has made a commitment to acquiring the latest technology that will provide the most sensitive detection of early visual field defects. Our standard visual field testing for glaucoma is the Humphrey's 24-2 Sita Standard threshold strategy. This is only available on the Humphrey Field Analyzer II. We feel that this strategy may be even more sensitive than the original standard 24-2 threshold strategy and at the same time reduces patient fatigue.

There is, however, a limitation to the Humphrey's threshold testing strategy. This testing is relatively nonspecific when testing for early retinal ganglion cell damage because a great deal of overlap occurs in the receptive fields of ganglion cells. The unfortunate situation is that visual fields can appear to be normal, while there is observable glaucomatous optic nerve damage and/or loss of the nerve fiber layer. In order to overcome this limitation, the IU School of Optomery uses two perimetric tests that aid in the earlier detection of a visual field defect. The tests are the short-wavelength automated perimetry (SWAP) and the frequency doubling technology perimetry (FDP). These tests are designed to test a subset of retinal ganglion cells which will hopefully reduce the number of retinal ganglion cells evaluated, in turn reducing the overlap of the receptive fields, and thus allowing earlier detection of visual defects. Both of these tests have shown visual field loss in well-controlled studies when conventional testing has shown no loss.

• Short-Wavelength Automated Perimetry (SWAP) uses a large blue target (5nm) on a bright yellow background. This testing strategy is a separate program available on the HFA II and has a blue yellow statpac analysis. This more sensitive test, however, does require a longer testing time.

• The Frequency Doubling Perimetry (FDP) instrument was developed by Welch Allyn and introduced by Humphrey systems. It differs from the conventional bowl perimeters in that the patient is asked to look at a central black fixation dot on a video screen inside the instrument. The patient presses a button when shimmering bars appear anywhere in his/her field of vision. The bars appear for a brief second, disappear, and then present at another location. The contrast can be increased or decreased until the target is perceived.

  The FDP has proven to be an excellent screening device for glaucoma as well as other visual field defects (e.g., neurological defects, retinal defects). Because of this, the IU School of Optometry eye care center doctors perform the screening test during primary care exams. We use the full threshold mode that tests 19 locations and extends 30 degrees nasally. Where SWAP attempts to isolate the blue cones, the FDP technology isolates a subset of only a small number of retinal ganglion cells called M-y cells. By testing a sparse subset of the visual septum which seems to have a minimal amount of redundancy, the FDP can detect glaucoma early. The FDP is a small, portable lightweight device, is highly resistant to blur up to 6 diopters (thus, patients can wear their glasses), and has a rapid testing time of 3-5 minutes per eye.

It can be difficult to make an early diagnosis of glaucoma in a significant number of patients, so we often employ several tests on high risk glaucoma suspects (ocular hypertensive and/or suspicious optic cupping) whose visual fields test normal using the Humphrey's 24-2 Sita Standard threshold strategy. By using SWAP, FDP, and HRT--we can make an early diagnosis and detect progression of glaucoma more accurately which in turn allows us to provide better treatment.

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	URL: http://www.opt.indiana.edu/clinics/pteduc/glaucoma/vf.htm Revised: August 2, 2002
	IU Optometry home page: http://www.opt.indiana.edu/ Comments: Web Administrator Page design and coding: Terri Greene Copyright © 2002, The Trustees of Indiana University