terminology and guidelines for glaucoma ii - Kwaliteitskoepel

1.4 - VISUAL FIELD
The field of vision is defined as the area that is perceived when both eyes are open. Clinically, each eye is assessed independently.
Please see FC II, III, IV.
There are two main methods of testing the visual field (VF):
A) Kinetic perimetry: a stimulus is moved from a nonseeing area of the visual field to a seeing area along a set meridian.
The procedure is repeated with the same stimulus along other meridians, usually spaced every 15°. The luminance
and size of the target is changed in order to plot areas of different light sensitivity.
B) Static perimetry: the size and location of the test target remain constant. The retinal sensitivity or threshold at a specific
location is determined by varying the brightness of the test target. The shape of the hill of vision is defined by
repeating the threshold measurement at various locations in the field of vision.
In this chapter we refer mainly to Humphrey and Octopus perimeters, which are the most popular in Europe; several
other brands offer similar examination capabilities.
1.4.1 - APOSTILBS & DECIBELS
In perimetry the luminance of the test target is measured in Apostilbs (asb).
1 asb = 0.3183 candela/m2 = 0.1 millilambert
The decibel scale is a relative scale created by the manufacturers of automated perimeters to measure the sensitivity
each tested point of the hill of vision. It is an inverted logarithmic scale. Zero decibels is set as the brightest stimulus
Apostilbs Humphrey Decibels Octopus Decibels
0.1 50 40
1 40 30
1000 10 0
10000 0 -
1 bel = 1 log Unit = tenfold change in intensity
1 decibel = 0.1 log Unit
Decibel = dB
that each perimeter can produce. The decibel scale is not standardised because the maximal luminance of the stimulus
varies between instruments.
It is important to note that:
1) “0” dB do not correspond to the same stimulus luminance for Humphrey and Octopus
2) “0” dB does not mean a blind area but rather an area where the sensitivity of the retina to the stimulus is below the
maximum brightness for a given perimeter.
1.4.2 - STATIC VISUAL FIELD EXAM
1.4.2.1 - Reference tests for glaucoma
1.4.2.1.1 - Conventional techniques
Humphrey Perimeter, programs 24-2 or 30-2, or Octopus 32 measure the retinal sensitivity at 54 or 76 points in the
Ch. 1 - 24 EGS