National Health and Medical Research Council Centre for Clinical Eye Research, Discipline of Optometry and Vision Science, Flinders Medical Centre and Flinders University of South Australia, Adelaide, Australia.
Ophthalmic Physiol Opt. 2013 May;33(3):215-26. doi: 10.1111/opo.12056.
Young eyes compensate for the defocus imposed by spectacle lenses by changing their rate of elongation and their choroidal thickness, bringing their refractive status back to the pre-lens condition. We asked whether the initial rate of change either in the ocular components or in refraction is a function of the power of the lenses worn, a result that would be consistent with the existence of a proportional controller mechanism.
Two separate studies were conducted; both tracked changes in refractive errors and ocular dimensions. Study A: To study the effects of lens power and sign, young chicks were tracked for 4 days after they were fitted with positive (+5, +10 or +15 D) or negative (-5, -10, -15 D) lenses over one eye. In another experiment, biometric changes to plano, +1, +2 and +3 D lenses were tracked over a 24 h treatment period. Study B: Normal emmetropisation was tracked from hatching to 6 days of age and then a defocusing lens, either +6 D or -7 D, was fitted over one eye and additional biometric data collected after 48 h.
In study A, animals treated with positive lenses (+5, +10 or +15 D) showed statistical similar initial choroid responses, with a mean thickening 24 μm h(-1) over the first 5 h. Likewise, with the low power positive lenses, a statistically similar magnitude of choroidal thickening was observed across groups (+1 D: 46.0 ± 7.8 μm h(-1); +2 D: 53.5 ± 9.9 μm h(-1); +3 D 53.3 ± 24.1 μm h(-1)) in the first hour of lens wear compared to that of a plano control group. These similar rates of change in choroidal thickness indicate that the signalling response is binary in nature and not influenced by the magnitude of the myopic defocus. Treatments with -5, -10 and -15 D lenses induced statistically similar amounts of choroidal thinning, averaging -70 ± 15 μm after 5 h and -96 ± 45 μm after 24 h. Similar rates in inner axial length changes were also seen with these lens treatments until compensation was reached, once again indicating that the signalling response is not influenced by the magnitude of hyperopic defocus. In study B, after 48 h of +6 D lens treatment, the average refractive error and choroidal changes were found to be larger in magnitude than expected if perfect compensation had taken place, with a + 2.4 D overshoot in refractive compensation.
Taken together, our results with both weak and higher power positive lenses suggest that eye growth is guided more by the sign than by the magnitude of the defocus, and our results for higher power negative lenses support a similar conclusion. These behaviour patterns and the overshoot seen in Study B are more consistent with the behaviour of a bang-bang controller than a proportional controller.
年轻的眼睛通过改变眼轴的伸长率和脉络膜的厚度来补偿眼镜镜片带来的离焦，使它们的屈光状态恢复到戴镜前的状态。我们想知道，在眼结构或屈光度的初始变化率是否与所戴镜片的屈光力有关，如果存在比例控制器机制，这将是一个一致的结果。
进行了两项独立的研究；均跟踪了屈光不正和眼尺寸的变化。研究 A：为了研究镜片屈光力和符号的影响，在小鸡一只眼戴上正（+5、+10 或+15 D）或负（-5、-10、-15 D）镜片后的第 4 天，跟踪其变化。在另一个实验中，在 24 小时的治疗期间，跟踪了平面、+1、+2 和+3 D 镜片的生物测量变化。研究 B：从孵化到 6 天龄跟踪正常的正视化，然后在一只眼上戴上+6 D 或-7 D 的离焦镜片，在 48 小时后收集额外的生物测量数据。
在研究 A 中，接受正透镜（+5、+10 或+15 D）治疗的动物在前 5 小时内表现出统计学上相似的初始脉络膜反应，平均增厚 24 μm/h。同样，在低屈光力正透镜组中，在戴镜的第一个小时内，观察到各组之间脉络膜增厚的幅度相似（+1 D：46.0±7.8 μm/h；+2 D：53.5±9.9 μm/h；+3 D：53.3±24.1 μm/h），与平面对照组相比。这些在脉络膜厚度上相似的变化率表明，信号反应本质上是二元的，不受近视离焦程度的影响。-5、-10 和-15 D 透镜治疗引起统计学上相似的脉络膜变薄，在 5 小时后平均减少 70±15 μm，在 24 小时后减少 96±45 μm。这些透镜治疗也观察到类似的眼内轴长变化率，直到达到补偿，再次表明信号反应不受远视离焦程度的影响。在研究 B 中，在接受+6 D 透镜治疗 48 小时后，发现屈光度和脉络膜的变化幅度比完全补偿时预计的要大，屈光补偿的超调为+2.4 D。
总的来说，我们用弱和高屈光力正透镜的结果表明，眼球生长更多地受到离焦的符号而不是大小的影响，我们用高屈光力负透镜的结果也支持了类似的结论。这些行为模式和研究 B 中观察到的超调现象与 bang-bang 控制器的行为更为一致，而不是比例控制器的行为。
