Patient Fixation; Trial Lenses - Zeiss HUMPHREY 720i User Manual

TEST RELIABILITY

Patient fixation

Trial lenses

REV. B 02/03 PN 51680-1
Improper or erratic fixation may make test results meaningless. The perimetrist can play an
important role by emphasizing fixation while explaining the test procedure.
Tips for improving patient fixation:
• Choose a fixation target that is appropriate for the patient. When you tell the patient
to look at the yellow fixation light, verify that they can see the light by asking, "Do you
see the yellow light? Is it clear?". If the light is not clear, consider modifying the trial
lens correction. If the patient cannot see the light, for example, due to macular
disease, change to the small or large diamond to help the patient fixate throughout
the test.
• Use the Demo test to make sure the patient understands the test and is responding
properly. Re-instruct the patient as necessary, especially if they are inclined to look
around for stimuli.
• Fixation is more difficult with a dry cornea. Encourage the patient to blink normally
whenever they press the response button. Lack of blinking can cause part of the
visual field to "white out" for some patients.
• Inform your patient in advance that it is normal for the background to seem to
change or for the fixation target to seem to move. Barring other problems, they
should not let these phenomena distract them. Encourage them to take breaks and
pause the test by holding down on the response button if fatigue is a problem.
• Observe the patient by means of the video eye monitor. Encourage correct behavior.
• Record any observations that are relevant to reliability by entering your comments on
the patient data screen, or by writing your comments directly on the printout.
Using trial lenses incorrectly or using none when one is needed is another source of unreliable
test results.
Things to remember about trial lenses:
• Use a trial lens, when necessary. Use only the thin, wire-rimmed variety. Let the
automatic calculation program (see Section 3: "Inputting Trial Lens Data") deter-
mine the correct lens power to use. Verify with the patient that the fixation light is not
blurred.
• Use trial lenses only for central tests (within 30°), or the central part of a full field
test. Remove trial lenses and lower the trial lens holder for peripheral tests (beyond
30°). You cannot start the peripheral part of a full field test until the trial lens holder
has been lowered.
• Place the sphere correction in the slot closest to the patient's eye and the cylinder
lens behind the sphere. Adjust the trial lens holder so that the lenses are as close to
the patient's eye as comfort will allow, without touching any lashes.
• Tell the patient that it is important to stay close to the trial lens and centered behind
it. Model 750i owners should use Head Tracking and Vertex Monitoring to help keep
the trial lens centered and set at the proper distance (see Section 5).
HUMPHREY FIELD ANALYZER II -
6-3
i
series