HUMPHREY FIELD ANALYSER (HFA)
1.Perimetry should be performed in a distraction-free environment, to enable the patient to concentrate on the perimetric test.
2.The perimeter is automatically calibrated each time it is turned on. Ideally, patient data (date of birth, refraction, etc.) are entered before the patient enters the room.
3.Before putting the patient onto the machine, the requirements of the test itself are clearly explained and the patient is instructed as follows.
4. Before fully positioning the patient, the eye not being tested should be covered with an eye patch that allows the patient to blink freely.
INSTRUCTIONS TO PATIENT
Perimetry tests your central and peripheral vision
Be relatively still once positioned
Always look straight ahead at the fixation target. Do not look around the bow for stimuli.
Press the response button whenever you see the stimulus
The stimulus in a flash of light
Only one stimulus is presented at a time
The stimulus might appear from anywhere. Some stimuli are very bright. Some are very dim and sometimes no stimulus is presented. You are not expected to see all stimuli
Do not worry about making mistakes
Blink regularly to avoid discomfort. Don't worry about missing a point the device does not a measure while you blink
If you feel uncomfortable or are tired close your eye for a moment the test will automatically stop. The test will resume once you open your eye.
If you have a question, keep the response button pressed this will pause the test
5. The patient is positioned appropriately and comfortably against the forehead rest and chin rest. The lens holder should be as close as possible to the patient’s eye to prevent artefacts.
6.The Analyser projects a series of white light stimuli of varying intensities (brightness), throughout a uniformly illuminated bowl.
7.The patient uses a handheld button that they press to indicate when they see a light. This assesses the retina's ability to detect a stimulus at specific points within the visual field. This is called retinal sensitivity and is recorded in 'decibels' (dB).
8.The Analyser currently utilises the Swedish Interactive Thresholding Algorithm (SITA); a complex mathematical formula which allows the fastest and most accurate visual field assessment to date.
For more information, see the youtube video (link below)
Written by our guest author - Jignesh Bhadarka
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