Table 3 Interpretation of Humphrey visual field parameters

Fixation Losses

Fixation is plotted, if the patient moves and the machine re-tests and patient sees spot then a fixation loss is recorded.

Fixation losses above 20% may significantly compromise the reliability of the test.

OD- Right eye;

OS – Left eye.

Note the longer the test time the more tired the patient will be.

False POS (Positive) Errors

Patient responds to the normal whirr noise of the computer when it sounds as if is about to present a light but does not.

High false positive score occur in a “trigger happy” patient. < 33% is an unacceptable test.

False NEG (Negative) Errors

A brighter light is presented in an area in which the threshold has already been determined and the patient does not respond to it.

High false negative score occurs in fatigued or inattentive patients. < 33% is an unacceptable test.

Glaucoma Hemifield Test (GHT)

This assesses clusters of points above and below the horizontal meridian for any significant difference.

It describes the field as “Within normal limits”, “Borderline” or “Outside normal limits”

24–2 denotes the test strategy (24 degrees temporally and 30 degrees nasally and tests 54 points).

VFI

Mean deviation (MD)

A measure of overall field loss

Pattern standard deviation (PSD)

Measure of focal loss or variability within the field taking into account any generalised depression.

An increased PSD is more indicative of glaucomatous field loss than MD.

Probability values

These indicate the significance of the defect < 5%, < 2%, < 1% and 0.5%.

The lower the p value the greater its clinical significance and the lesser the likelihood of the defect occurring by chance.