Schmid K L, Strang N C, Wildsoet C F
Centre for Eye Research, School of Optometry, Queensland University Technology, Brisbane, Australia.
Optom Vis Sci. 1999 May;76(5):320-5. doi: 10.1097/00006324-199905000-00021.
Young chicks can adjust their eye growth to compensate for both imposed hyperopia and myopia (using negative and positive spectacle lenses); the rate of eye elongation increases in the former and slows in the latter case. This emmetropizing behavior implies that the eye can distinguish the sign and magnitude of defocus, although the identity of the cue(s) involved is unknown. As the spectacle lenses used in these studies generally introduce significant retinal image size differences that are in opposite directions for negative and positive lenses (minification vs. magnification), we asked whether retinal image size might provide the required sign information.
This question was addressed by manipulating retinal image size while keeping lens power constant. We also investigated the effect of eliminating other potential cues, accommodation and chromatic aberration, under these conditions. Three negative "size" lenses of approximately -11 D optical power were used, with 2 of the lenses producing magnification rather than minification as typical of negative lenses (i.e. +1.9% and +6.9% compared to -2.9%). The lenses were fitted monocularly to 7-day-old chicks, which were subsequently measured at 9 and 11 days of age (refractive error and axial dimensions). The same lens-wearing schedule was applied to two other groups of chicks that had monocular ciliary nerve section surgery to prevent accommodation 2 days posthatching; one of these groups was reared under monochromatic yellow light instead of white light.
Near-perfect refractive compensation was seen by the end of the treatment period with all three lenses, for all three treatment groups, and there was also little difference in the rate of compensation among the various groups. In all cases, the typical responses of axial (mainly vitreous chamber) elongation and myopia were observed.
That manipulations to retinal image size, which either decrease or reverse the usual effects of negative lenses, did not disrupt compensation to the imposed hyperopic defocus, even in the absence of accommodation and chromatic aberration cues, argues against imposed retinal image size changes being the directional cue to defocus in experimental emmetropization.
幼雏能够调节其眼睛生长，以补偿人为施加的远视和近视（分别使用负透镜和正透镜）；在前一种情况下眼睛伸长率增加，在后一种情况下则减缓。这种正视化行为意味着眼睛能够辨别散焦的正负和程度，尽管其中涉及的线索尚不明确。由于这些研究中使用的透镜通常会导致视网膜图像大小出现显著差异，且负透镜和正透镜产生的差异方向相反（缩小与放大），因此我们探究视网膜图像大小是否能提供所需的正负信息。
通过在保持透镜屈光度不变的同时操控视网膜图像大小来解决这一问题。我们还研究了在这些条件下消除其他潜在线索（调节和色差）的影响。使用了三个屈光度约为 -11 D 的负“大小”透镜，其中两个透镜产生的是放大而非负透镜通常产生的缩小效果（即分别为 +1.9% 和 +6.9%，而典型负透镜为 -2.9%）。这些透镜单眼佩戴于7日龄雏鸡，随后在9日龄和11日龄时测量（屈光不正和眼轴尺寸）。相同的戴镜方案应用于另外两组雏鸡，这两组雏鸡在孵化后2天进行了单眼睫状神经切断手术以防止调节；其中一组在单色黄光而非白光下饲养。
在治疗期结束时，所有三个治疗组使用的所有三个透镜均观察到近乎完美的屈光补偿，并且不同组之间的补偿速率也几乎没有差异。在所有情况下，均观察到眼轴（主要是玻璃体腔）伸长和近视的典型反应。
对视网膜图像大小的操控，无论是减小还是逆转负透镜的通常效果，即使在没有调节和色差线索的情况下，都不会干扰对人为施加的远视性散焦的补偿，这表明在实验性正视化过程中，视网膜图像大小的人为改变并非散焦方向的线索。
