When the data from all the experimental animals were pooled, there was a tendency for large interocular differences in contrast sensitivity to be associated with large degrees of anisometropia at the end of the lens-rearing period (
Fig. 9 ; ANOVA, F = 3.16,
P = 0.06). However, examination of the refractive errors within a given treatment group suggests that these experimentally induced refractive errors did not have a strong influence on the degree of form-deprivation amblyopia. In particular, within a given group there was no clear relationship between the degree of anisometropia at the end of the lens-rearing period and the depth of amblyopia. For example, the monkeys that were allowed 1 hour of unrestricted vision each day (
Fig. 9 , filled diamonds;
Fig. 8 , second row) showed a six to sevenfold range in their interocular contrast sensitivity function ratios, but the range of anisometropias at the end of the lens-rearing period was quite small (+0.8 to −1.3 D). In contrast, the degree of anisometropia at the end of the lens-rearing period in the monkeys in the 2-hour group (
Fig. 9 , filled circles;
Fig. 8 , third row) varied from +0.8 to −4.4 D, but they all exhibited relatively similar interocular differences in contrast sensitivity. Thus, potential differences in the quality of the retinal image related to refractive error during the daily periods of unrestricted vision did not appear to contribute to differences in the degree of amblyopia between animals. Also, the longer recovery times associated with larger anisometropias at the end of the lens-rearing period did not appear to influence the degree of form-deprivation amblyopia. For example, in the continuous form deprivation group, MKY LIS exhibited a smaller myopic anisometropia that recovered much faster than the anisometropia in MKY JAS (
Fig. 8 ; top row); however, MKY LIS demonstrated more severe form deprivation amblyopia. Similarly, MKY ULR in the 2-hour group (
Fig. 8 ; row 3) exhibited faster refractive error recovery than MKY NEL, but more severe amblyopia. Finally, although a number of the treated animals had significant anisometropias that developed well after the end of the diffuser-rearing period, these anisometropias did not overshadow the effects of the period of form deprivation or the protective effects provided by the daily periods of unrestricted vision. For example, monkeys MIG (continuous group), HAL (1-hr group), XYL (2-hour group), and NIN (4-hour group), all had significant anisometropia after approximately 250 days of age. However, each of these monkeys exhibited mild contrast sensitivity deficits within their respective treatment groups.