光学离焦对雏鸡屈光状态的影响

目的观察远视、近视离焦对雏鸡屈光状态的影响，了解光学离焦视觉回馈在相当于人类近视发展的关键年龄对屈光状态发育的调控作用。方法年龄7d的健康罗曼氏小鸡（相当人类1～1．5岁）随机分为5组，每组10只。在白天12h的给光时段内，第1、2、3组雏鸡随机1只眼每天戴＋6．5D眼镜1h（依次分割成2、4、6次配戴）；其余11h戴-6．0D眼镜；第4、5组分别戴用＋6．5D、-6．0D眼镜12h。5d后，用带状光检影镜和游标卡尺测量实验眼和对照眼的屈光度和眼轴，进行统计分析。结果①实验眼和对照眼的眼轴、屈光度均有显著性差异。②戴负镜组（第5组）实验眼较对照眼更为近视，眼轴相对更长。③交替戴正负镜组（第1、2、3组）和戴正镜组（第4组）的实验眼较对照眼均表现为相对远视．眼轴相对更短；相同戴正镜时间分成的次数越多，产生远视度数越高，眼轴相对越短。结论远视性离焦导致近视，近视性离焦导致远视，短时的近视离焦可以完全抵消相当长时间的远视性离焦的效果，分成的次数和效果成正相关。

Effects of Experimentally Induced Optical Defocus on Refractive Status of Chicks

Objective To determine if optical defocus alters refractive development in chicks corresponding to the typically developed age of myopia in children.Methods Chicks wore +6.5 D lenses for 60 min/d,in two to six periods and wore-6.0 D lenses for the remainder of the 12 h daylight period.The chicks in other groups wore +6.5 D or-6.0 D lenses all of the 12 hour daylight period.Refraction and ocular length were performed after the 5day-long experiments.Result Wearing positive lenses for as little as 60 min/d(in two to six periods) and wore-6.0 D lenses the remainder of the 12 h daylight period caused eyes to become hyperopic and reduced the rate of ocular elongation.The eyes compensated for the positive lenses,as though the negative lenses had not been worn.Conclusion Brief periods of myopic defocus imposed by positive lenses prevent myopia caused by daylong wearing of negative lenses.This implies that periods of myopic and hyperopic defocus do not add linearly.If children are like chicks and if the hyperopic defocus of long daily periods of reading predisposes a child to myopia,regular,brief interruptions of reading might have use as a prophylaxis against progression of myopia.