Zeiss Humphrey II-i series, User Manual

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Humphrey Field Analyzer II-
i
series User Manual 2660021145640 A
Introduction & Instrument Setup 1-19
Some defect patterns are characteristic of certain diseases, a fact which makes visual field testing a
valuable part of the diagnostic process. Furthermore, by having patients repeat the same tests at
later dates, practitioners gain insight into the progression of the disease and the effectiveness of
treatment.
Methods of Testing the Visual Field
Over the years, visual field testing devices have varied in size, complexity, and testing methodology.
The fundamental premise has remained the same, however; patients must respond when they see a
stimulus.
Static threshold testing evaluates retinal function. The term “static” refers to a stationary stimulus
being used. In static testing, predefined test locations in the visual field are probed. Through a series
of stimulus presentations of varying brightness intensities, the threshold value is determined for
each test point. When evaluating static test results, clinicians are looking at the topography or
contour of the hill of vision, and whether depressions are evident.
In a second type of retinal evaluation, called kinetic testing, a light stimulus of fixed characteristics
is moved into the visual field from a non-seeing area, until it is detected by the patient. Typically, the
stimulus is brought toward the center from several directions and the operator marks the location at
which the patient first detects the stimulus (threshold point).
Kinetic test results can only be reliably related to specific parts of the visual field if points are joined
to form an isopter, or ring of equal contrast sensitivity. Targets of varying size and brightness are
used during one kinetic test, and for each different target, a different isopter is mapped. When
reviewing several isopters, the clinician is visualizing different tiers in the hill of vision.
Patient Fixation and Test Reliability
In order for any visual field test to be useful clinically, it must yield reliable results. One important
factor affecting reliability is the steadiness of patient fixation. Unless the eye being tested fixates
accurately on the target while responding to stimuli, the results are unreliable.
Other factors adversely affecting reliability are:
• patient fatigue and anxiety
• poor test instructions
• patient discomfort
• improper near vision correction for central testing
Benefits of Computerized Perimetry
Certainly the advancements in microprocessor technology within the last 20 years have had a
profound effect on perimetry. Perimeters have evolved into a more precise measuring tool yielding
highly repeatable results.
These changes are better appreciated by examining the benefits computerized perimeters bring to
both patient and professional:
• Reproducible testing conditions
• Data storage capability; results can be compared over time and analyzed using expert-system
software