Single and multiple stimulus static perimetry in glaucoma; the two phases of perimetry

Abstract

In the 'method of constant stimuli' a stimulus is presented a number of times at various luminance levels and the subject is asked to react the moment he sees the stimulus. For a given stimulus value a percentage of positive reactions is obtained as compared with the total number of times the stimulus is presented.This information is usually plotted as a 'frequency-of-seeing curve', in which the abscissa is the logarithm of the luminance and the ordinate the percentage of positive reactions (Fig. 1). The result is an S-shaped curve between 0~ and 100 ~ frequency of seeing. 5 lOO 83 66 50 33 l 16 %o / / J 0.0 0.1 The factors which influence the level and variation of the difference threshold can be subdivided into the following 5 groups: t. Physical characteiistics of the stimulation; 2. Preretinal factors; 3. Receptor and neural factors; 4. Psychological factors; 5. General health.In Table I an attempt has been made to show the relationship between these factors. The stimulation passes from left to right through the optic system of the eye and gives rise to an electrical impulse in the receptors, which is integrated by the neural system.The stimulus and the background are usually easily measurable physical quantities. The preretinal factors, the optical system of the eye, determine the final stimulation at the retinal level. These factors will be discussed after the normal visual field has been described. 7The distribution of the receptors over the retina and their function are considered under the subheading receptor mechanisms. The transmission and integration of impulses generated by light stimulation of the receptors through the cells of the retina, geniculate body and the cortex will be considered under the subheading neural mechanisms. Psychological factors will be considered only in connection with the multiple-stimulus method. Finally, the subject's general 8 The reverse order (i.e. suplaliminal to liminal) has certain disadvantages which will be described later. 7 Chapter IX. 10 a