Norton Thomas T, Siegwart John T, Amedo Angela O
Department of Vision Sciences, University of Alabama at Birmingham, 924 S. 18th Street, Birmingham, AL 35294, USA.
Invest Ophthalmol Vis Sci. 2006 Nov;47(11):4687-99. doi: 10.1167/iovs.05-1369.
To examine the ability of hyperopic defocus, minimal defocus, and myopic defocus to compete against a myopiagenic -5-D lens in juvenile tree shrew eyes.
Juvenile tree shrews (n > or = 5 per group), on a 14-hour lights-on/10-hour lights-off schedule, wore a monocular -5-D lens (a myopiagenic stimulus) over the right eye in their home cages for more than 23 hours per day for 11 days. For 45 minutes each day, the animals were restrained so that all visual stimuli were >1 m away. While viewing distance was controlled, the -5-D lens was removed and another lens was substituted with one of the following spherical powers: -5 D, -3 D (hyperopic defocus); plano (minimal defocus); or +3, +4, +5, +6, or +10 D (myopic defocus). Daily noncycloplegic autorefractor measures were made on most animals. After 11 days of treatment, cycloplegic refractive state and axial component dimensions were measured.
Eyes with the substituted -5- or -3-D-lens developed significant myopia (mean +/- SEM, -4.7 +/- 0.3 and -3.1 +/- 0.1 D, respectively) and appropriate vitreous chamber elongation. All animals with the substituted plano lens (minimal defocus) during the 45-minute period showed no axial elongation or myopia (the plano lens competed effectively against the -5-D lens). Variable results were found among animals that wore a plus lens (myopic defocus). In 11 of 20 eyes, a +3-, +4-, or +5-D lens competed effectively against the -5-D lens (treated eye <1.5 D myopic relative to its fellow control eye). In the other eyes (9/20) myopic defocus was ineffective in blocking compensation; the treated eye became more than 2.5 D myopic relative to the control eye. The +6- and +10-D substituted lenses were ineffective in blocking compensation in all cases.
When viewing distance was limited to objects >1 m away, viewing through a plano lens for 45 minutes (minimal defocus) consistently prevented the development of axial elongation and myopia in response to a myopiagenic -5-D lens. Myopic defocus prevented compensation in some but not all animals. Thus, myopic defocus is encoded by at least some tree shrew retinas as being different from hyperopic defocus, and myopic defocus can sometimes counteract the myopiagenic effect of the -5-D lens (hyperopic defocus). However, it appears that minimal defocus is a more consistent, strong antidote to a myopiagenic stimulus in this mammal closely related to primates.
研究远视性离焦、最小离焦和近视性离焦在幼年树鼩眼中对抗致近视的-5D镜片的能力。
幼年树鼩（每组n≥5只），采用14小时光照/10小时熄灯的时间表，每天在其饲养笼中右眼佩戴单眼-5D镜片（一种致近视刺激）超过23小时，持续11天。每天有45分钟，将动物固定，使所有视觉刺激距离>1米。在控制观察距离的同时，取下-5D镜片，替换为以下球面屈光度之一的另一镜片：-5D、-3D（远视性离焦）；平光（最小离焦）；或+3、+4、+5、+6或+10D（近视性离焦）。对大多数动物进行每日非散瞳自动验光测量。治疗11天后，测量散瞳屈光状态和眼轴各部分尺寸。
佩戴替换的-5D或-3D镜片的眼睛出现了显著近视（平均值±标准误，分别为-4.7±0.3D和-3.1±0.1D）以及相应的玻璃体腔延长。在45分钟时间段内佩戴替换平光镜片（最小离焦）的所有动物均未出现眼轴延长或近视（平光镜片有效对抗了-5D镜片）。佩戴正镜片（近视性离焦）的动物出现了不同的结果。20只眼中有11只，+3D、+4D或+5D镜片有效对抗了-5D镜片（治疗眼相对于对侧对照眼近视<1.5D）。在其他眼中（9/20），近视性离焦在阻止代偿方面无效；治疗眼相对于对照眼近视超过2.5D。在所有情况下，+6D和+10D替换镜片在阻止代偿方面均无效。
当观察距离限制在>1米的物体时，通过平光镜片观察45分钟（最小离焦）可始终防止因致近视的-5D镜片而导致的眼轴延长和近视的发展。近视性离焦在一些但并非所有动物中阻止了代偿。因此，至少一些树鼩视网膜将近视性离焦编码为与远视性离焦不同，并且近视性离焦有时可抵消-5D镜片（远视性离焦）的致近视作用。然而，在这种与灵长类密切相关的哺乳动物中，最小离焦似乎是对抗致近视刺激的更一致、更强有力的解药。
