Constriction amplitude

Figure 7.2 After high doses of the experimental drugs, changes (from baseline) in initial (p re stimulus) pupil diameter, constriction velocity, and constriction amplitude varied as a function of the drug condition and time.

The constriction amplitude of the light reflex differed significantly among the treatment conditions (Figure 7.2). A two-way ANOVA indicated significant differences among drug conditions... 

Drug Dose Pupil Diameter Constriction Amplitude Constriction Velocity Dilation Velocity... 

Shown in Table 7.2 are the mean and standard deviation of the four parameters collected on subjects (n = 6) on days (minimum of 10) when their urine was negative for drugs of abuse compared to days when their urine was positive for abused drugs. Although the mean values are similar, the variability increased (larger standard deviation) for ID, CL, and SV on urine-positive days. The variability in the measures obtained for constriction amplitude was similar regardless of the presence of illicit drugs in the urine. 

Figure 7.1 Pupil diameter before (A) and after a light stimulus (S). Constriction (B) and dilation (D) velocities are determined from a least square fit of the slope. Amplitude of constriction (C) represents the maximal difference in diameter before and after the flash.

In the elastic range, the Poisson s ratio, Vei = —/, can be used to relate the amplitude of transverse constriction with axial strain. The volume strain depends on this material coefficient by = (1 — 2vei)e - Similarly, for nonlinear materials, the tangent Poisson s ratio Vt = —d i/d 3 may be introduced at large strain, so that coefficient is also obtained from the instantaneous slope of the volume strain versus axial strain from (1 — 2vt ) = d v/d 3. In this paper, the latter slope will be called dilatation rate (or damage rate ) and denoted by the variable A. 

In eight patients with visual field constriction, who were examined 4-6 years after they had stopped taking vigabatrin visual field constriction was unchanged [42T]. The amplitude of the 30 Hz flicker response was still reduced. The authors concluded that vigabatrin causes permanent retinal damage. 

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