Figure 1 shows L-cone CFF (temporal acuity) data for the four observers with Tyr99Cys mutant GCAP1 plotted on a linear ordinate as a function of log
10 target radiance. The CFF at each target radiance is the highest frequency at that radiance at which the target appears to flicker. Data for GP1 to GP4, whose ages increase from GP1 to GP4, are shown in
Figure 1. The mean L-cone CFF data for 12 observers with normal vision are shown in
Figure 1 as red squares. Error bars in all figures (visible only when they are larger than the symbols) are ±1 SEM within observers for the affected individuals and between observers for the normal measurements.
In normal observers, L-cone CFF starts to rise at approximately 6.5 log
10 quanta s
−1 deg
−2. And above approximately 7.25 log
10 quanta s
−1 deg
−2 the CFF increases (on these coordinates) with a linear slope until at approximately 9.75 log
10 quanta s
−1 deg
−2 it begins to approach a plateau near 40 Hz.
33,34 By contrast, the L-cone CFF functions for all four observers with the Tyr99Cys mutant GCAP1 show substantial losses in CFF. Flicker is not detected in any of the affected observers until the mean 650-nm target radiance reaches at least 7.7 log
10 quanta s
−1 deg
−2, nearly 13 times more intense than that for normal observers. The differences suggest that the deficit involves a loss of at least 1.2 log
10 units of intensity. For the affected observers, as the radiance increases above 7.7 log
10 quanta s
−1 deg
−2, the CFF increases but, except for GP3, in whom no asymptote is apparent, approaches much lower asymptotic CFF values than normal. The CFF loss is greater the older the patient. The highest CFF for the mean normal observer is approximately 40 Hz but declines to 29, 23, 11, and 10 Hz for observers GP1 to GP4, respectively (see also
Fig. 3,
Table 3). In terms of temporal acuity, the four observers with the Tyr99Cys mutant GCAP1 show losses that increase with age.
There is a region both for the normal and for the affected observers over which the CFF is approximately linearly related to the logarithm of the target radiance. This linear relationship, known as the Ferry-Porter law,
35,36 holds, in normal observers, from approximately 7.25 to 9.75 log
10 quanta s
−1 deg
−2. For the affected observers, with the exception of GP1, the slope over the Ferry-Porter region is much shallower, and the range over which it occurs is displaced to higher radiances. We can quantify and compare the individual CFF data shown in
Figure 1 in terms of the slope. The blue straight lines fitted to each set of CFF data shown in
Figure 1 are the best fitting slopes over the Ferry-Porter regions for each observer. The best fitting slopes, their standard errors, and
R 2 values are given in
Table 2. The slopes for GP2 to GP4, which are between 2.91 and 4.42 Hz per decade, are much less than the normal slope of 8.57, yet, interestingly, the slope for GP1 at 18.79 Hz per decade is twice that of the normal slope. The high
R 2 values in
Table 2 suggest that the Ferry-Porter law is a plausible description of the data over the appropriate ranges. (The Ferry-Porter slopes are considered further in the Discussion.)