In contrast, chicks fitted with −7 D lenses and exposed to an ambient illumination of 15,000 lux for 5 hours per day showed a significantly slower rate of compensation, with full compensation not achieved until day 6 (change in refraction −7.0 ± 0.5 D;
Fig. 1,
Table 1). ANOVA testing, followed by a Student's
t-test with Bonferroni correction, indicated a significant difference in refraction between the two light groups at days 3 (
P < 0.02), 4 (
P < 0.03), and 5 (
P < 0.01). Axial length was measured only at the commencement, day 3, and the cessation of treatment. Axial lengths of negative-lens–treated eyes from chicks raised under an ambient illumination of 15,000 lux were significantly shorter than axial lengths of lens-treated eyes of chicks kept under 500 lux at day 3 (8.73 ± 0.08 mm vs. 8.92 ± 0.04 mm,
P = 0.02), but, as expected, were not significantly different at the commencement or cessation of treatment (
P = 0.70,
P = 0.52, respectively). It should be noted, however, that the rate of axial elongation observed in this study in response to negative lenses, when compared with the rate of change in the axial length of contralateral control eyes, is significantly higher than normally reported in the literature.
26 This appears to be related to a lower rate of elongation in the contralateral control eyes than that normally observed. Changes in axial length represented changes in vitreous chamber depth (
y = 0.80
x − 1.63,
r 2 = 0.96,
Table 1), rather than alteration in anterior chamber depth (
Table 1). Refraction (
F = 2.28
P = 0.17) and axial length (
F = 3.93,
P = 0.10) of the contralateral eyes, exposed to normal vision, were unaffected by the treatment regimens, although, as mentioned, the rate of axial elongation was slower than that normally seen over the first 3 days of treatment.