Quantitative evaluation of the visual field measured by Goldmann perimetry as a solid angle
Baba, H.
Nippon Ganka Gakkai Zasshi 90(1): 210-214
1986
ISSN/ISBN: 0029-0203 PMID: 3706063 Document Number: 267924
Two types of program were made in order to measure the area of the isopter of Goldmann perimetry. The area was presented as cm2 in one programe and as a solid angle (steradian; sr) in the other. The area of the isopter was divided into small trapezoides in the former and it was divided into small traiangles in the latter. Analog data were gotten from a digitizer (BIT PAD ONE, MUTO, Tokyo) and analyzed by microcoputer (M100 ACE, SORD, Tokyo). The imput error from a digitizer was about 0.3% and the error derived from the program was 0.8%, because it was evaluated as the area of a polygon which was inscribed in the isopter. If the area of the isopter is measured as cm2, the peripheral area is overestimated, because it is elongated in the equatorial direction. However, when the area of the visual field was represented as a solid angle, the peripheral overestimation was cancelated. The overestimation of this type was 11.7% and 38.8% at the site of 30.degree. and 60.degree. respectively. When the area of the visual field is measured directly on the chart as cm2 or mm2, it should be evaluated as percentile reduction from the normal visual field. With this normalization, the peripheral overestimation was also eliminated. It was shown in two cases of glaucoma patients. However, as a further step when the volume of this visual island is estimated, the area of the isopter should be represented as a solid angle.