Volume of visual field assessed with kinetic perimetry and its application to static perimetry

Abstract

Background: The purpose of this study was to quantify the volume of the kinetic visual field with a single unit that accounts for visual field area and differential luminance sensitivity.

Methods: Kinetic visual field perimetry was performed with a Goldmann perimeter using I4e, I3e, I2e, and I1e targets. The visual fields of 25 normal volunteers (17 women, eight men) of mean age 33.9 ± 10.1 (range 17-64) years were obtained and digitized. Isopter areas were measured with a method devised to correct cartographic distortion due to polar projection inherent in perimetry and are expressed in steradians. The third dimension of each isopter represents sensitivity to target luminance and was calculated as log (target luminance(-1)). If luminance is expressed in cd/m(2), the values for the third dimension are 0.5 for I4e, 1.0 for I3e, 1.5 for I2e, and 2.0 for I1e. The resulting unit is a steradian (log 10(3) (cd/m(2))(-1) which is referred to as a Goldmann. In addition, the visual fields of four patients with representative visual defect patterns were examined and compared with normal subjects.

Results: Mean isopter areas for normal subjects were 3.092 ± 0.242 steradians for I4e, 2.349 ± 0.280 steradians for I3e, 1.242 ± 0.263 steradians for I2e, and 0.251 ± 0.114 steradians for the I1e target. Isopter volumes were 1.546 ± 0.121 Goldmanns for the I4e target, 1.174 ± 0.140 Goldmanns for I3e, 0.621 ± 0.131 Goldmanns for I2e, and 0.126 ± 0.057 Goldmanns for I1e. The total mean visual field volume in our study for the I target was 3.467 ± 0.371 Goldmanns.

Conclusion: The volume of the island of vision may be used to quantify a visual field with a single value which contains information about both visual field extension and differential luminance sensitivity. This technique may be used to assess the progression or stability of visual field defects over time. A similar method may be applied to static perimetry.

Keywords: cartographic distortion; kinetic perimetry; static perimetry; steradian; visual field.

Figure 1

The assignment of a vertical dimension for luminance sensitivity reinterprets the island of vision for a particular target size (I) from the classical planar figure that is used in kinetic perimetry (1a) to a three-dimensional form (1b).

Figure 2

Four representative visual field defects obtained with Goldmann perimetry. 2a) demonstrates concentric contraction in a patient with gyrate atrophy and 2b) represents temporal hemianopia in a patient with craniopharyngioma. 2c) reveals a field with a central scotoma in a patient with macular dystrophy and 2d) an arcuate scotoma in a patient with glaucoma.

Figure 3

Three-dimensional illustration of 30-2 Humphrey perimetry in a normal subject. The small area of depression seen in the normal visual field corresponds to the blind spot.