Visual Fields

Equipment:

• Humphrey 740 Series Visual Fields Analyser (x2)

• Goldman Visual Field Analyser

Procedures:

• Humphrey SITA and Full Threshold Testing
  

The Humphrey Visual Field is an industry standard test which allow us to look for defects in the sensitivity of the eye. For example, the central vision of the eye may be good, but the periphery of the visual field may be severely damaged. It is important to detect change in the visual field in order to maintain the function of the eye. As a good eye is able to compensate for poor vision in the other eye, the effects of visual field damage are often unnoticed by the patient until there is significant damage to the vision. The Humphrey visual field tests is designed to pick up the earliest changes to the function of the eye.

The test works by displaying flashes of light around a bowl with a fixed background light level. The machine aims to find the dimmest light that the eye is able to detect at various locations in the visual field.

The Humphrey Visual Field Analyser has become an industry standard machine for the diagnosis and monitoring of glaucoma and other ocular and neurological diseases. Like all visual field tests, the machine tests the patient's response to a visual stimulus. The machine may be set to run one of many optimised programs.

Threshold Visual Fields:

Threshold testing of visual fields identifies the limit of the sensitivity of the eye at programmed locations in the visual field.
The most common Humphrey test is the 24-2, which tests the central 24° of vision. The Humphrey 10-2 test permits monitoring of patients with very restricted fields and the 30-2 has more peripheral points.

The following strategies are available for the 24-2, 10-2 and 30-2 tests:

Full Threshold - makes the least assumptions about the patient's vision. The bightness of the stimulus is varied at each location in order to find the threshold value. The results are based on the last point seen at each location, so patient fatigue may affect the accuracy.

SITA Standard - (Swedish Interactive Threshold Algorithm). With the benefit of research into visual fields, the SITA test is able to make predictions of threshold values by analysing the patient's previous responses. By analysing the data in this way the length of the test is reduced, often less than half the length of a similar full-threshold test. The results are calculated using all of the data collected , so errors may be identified and corrected automatically.

SITA Fast - the fastest threshold test. Best used with reliable subjects.

Stimulus Size - Full threshold tests may be carried out using different stimulus sizes. These equate to the stimulus sizes used by the Goldmann Perimeter. Humphrey tests are normally carried out with stimulus size III, but patients with poor vision may be tested with a size V stimulus. Please note the SITA tests are only possible with a size III stimulus.

Stimulus Colour - the Humphrey test is normally carried out using a white stimulus against a white background. However, the stimulus colour may be changed when monitoring colour dependent changes.

Goldman Visual Fields:

• Testing of entire field of vision

• Kinetic rather than static testing

• Better reliability in some cases

• Comparison with previous Goldman tests