Pupillometry objectively confirmed the observation by full-field psychophysics of retained rod function. Families of TPLR responses elicited with brief stimuli in a representative normal subject are shown for comparison with those from a patient with
AIPL1-LCA (
Fig. 4B). In the normal subject, the TPLR threshold was near −4 log
10 scot-cd · m
−2. With increasing stimulus luminance there was an increase in amplitude and shortening of the latency to reach a 0.3-mm criterion response, and a retardation of the dilation phase. For each intensity, TPLR responses to the green stimulus (
Fig. 4B, black traces) were nearly identical with those elicited by the scotopically matched orange stimulus (
Fig. 4B, gray traces), supporting rod mediation of the normal dark-adapted TPLR. The response family in patient F6,P1 illustrates the abnormalities encountered in
AIPL1-LCA (
Fig. 4B). The TPLR threshold response in the patient was elevated by ∼3 log
10 units (to about −0.6 log
10 scot-cd · m
−2) compared with that of the normal subject. With increasing stimulus intensity, amplitude increased, latency was shortened to criterion response, and the dilation phase was retarded. At the highest intensity (+2.3 log
10 scot-cd · m
−2) TPLR response amplitude only reached ∼60% of normal (
Fig. 4B). At each stimulus intensity, responses in the patient resembled normal responses evoked by a ∼3-log
10-units dimmer stimulus, indicating that loss of sensitivity may explain, at least in part, the differences in TPLR kinetics between the patient and the normal subject. As in the normal subject, pairs of responses elicited by scotopically matched green and orange stimuli were similar, supporting the notion that the responses are mediated by a rod photoreceptor mechanism and confirming the rod mediation determined by psychophysics in this patient (
Fig. 4A).