Abstract
Purpose: :
In the Humphrey 30-2 and the 24-2 threshold tests, four paracentral points, located at the corners of a 9-degree rectangular, are initially tested (first threshold determination). Then, the threshold of these points is rechecked (second threshold determination). Finally, the rest of the field is tested. We studied the visual fields of 12 patients that presented with visual field defects involving solely any of these four points.
Methods: :
30 threshold visual field tests of 12 subjects with visual field scotoma at any of the the four paracentral points, located at the corners of a 9-degree rectangular, were studied. All visual fields were performed with the automated Humphrey Zeiss perimeter. Subjects were tested with Fastpac, either 24-2 (six cases) or 30-2 (six cases). Three of these patients had repeat visual field testing.
Results: :
In each visual field, the most significant threshold depression was expressed in at least two of the four paracentral points that were tested initially. The right eye (which was the first tested eye) was involved in 11/12 (92%) of the patients. The mean second threshold determination of the 4 paracentral points was significantly higher (p=0.001) than the first (mean 27.3DB and 21.8DB respectively). In 10/12 of the threshold fields, the second determination of the mean threshold for the 4 points was higher than the first determination by 3 DB or more. None of the patients had a higher first threshold determination. Information regarding history of visual field testing was available in nine cases. In all nine, this test was the first ever visual field test to be performed. Visual field testing had been repeated in three of the patients and was normal in all three.
Conclusions: :
When a field defect is restricted to any of the four paracentral points that are tested initially, a learning artifact should be suspected. It is important to recognize this artifact, since such a defect could be incorrectly interpreted as a scotoma in the Bjerrum area, and may lead to the false diagnosis of early glaucomatous damage. Normal visual field on repeat testing can confirm the nature of this visual field artifact.