Zeiss Humphrey II-i series, Руководство пользователя

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Humphrey Field Analyzer II-
i
series User Manual 2660021145640 A
SITA Normative and GPA Databases K-1
(K) SITA Normative and GPA Databases
How SITA Works K-1
Normative and GPA Database Collection and Demographics K-3
Acknowledgements K-8
How SITA Works
To better explain how SITA works, we will use analogies. Think of perimetry testing as taking a
patient’s case history. Think of SITA as an experienced doctor. Think of previous perimetry strategies
as medical students. With these analogies in mind, we will describe how SITA reduces test time in
the following four ways:
1. SITA Asks Smart Questions
The importance of asking smart questions is familiar to any experienced doctor. When students take
a patient’s case history, they often ask questions that are off the mark and do not yield critical
information. They sometimes miss clues that the patient is offering— information which could lead
directly to the proper diagnosis if pursued. After many years of taking histories, however, experience
teaches practitioners precision and economy in framing their questions.
Good perimetry is similar to taking a good history. It is a matter of getting information from the
patient in a quick and efficient manner. In perimetry, the most critical factors are the following:
A. Start with stimuli at each point that are already very near the threshold, thus avoiding the long,
inefficient process of gradually brightening or dimming the stimulus while searching for the
threshold.
B. Make optimal use of the information contained in the patient’s responses to those stimuli. This is
important both in terms of calculating the threshold at the point being tested, and in terms of
determining how bright the initial stimulus should be at the next point to be tested.
SITA considers many factors in determining what stimuli to present at each point during the test.
These factors include age, normative data, detailed characteristics of abnormal and normal tests,
and patient responses so far in the test. They are combined and weighted into the SITA visual field
model, which continually updates calculations of the threshold at each point.
2. SITA Tailors the Testing Pace to the Individual
When taking a history, all doctors know that some patients are quick to respond to questions and
others are not. If they rush elderly patients, they will not get much good information. If they go too
slowly with young, bright patients they may lose both their interest and their cooperation.
In a threshold test, fewer than half of the stimuli will be seen. Thus, the perimeter must decide how
long to wait after stimulus presentation before moving to the next point. The test must allow a
reasonable amount of time between presentations, but waiting too long will prolong testing
unnecessarily and make the test uninteresting. Thus, it is very important to know how quickly a
particular patient reacts to stimuli and to make careful use of that information. If a test proceeds too
slowly, the patient may get frustrated and fatigued, and the results may, therefore, be inaccurate.