Compensation of corneal oblique astigmatism by internal optics: a theoretical analysis.
Compensation of corneal oblique astigmatism by internal optics: a theoretical analysis.
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内部光学补偿角膜斜散光：理论分析。
DOI：
10.1111/opo.12364
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Thibos,LarryN
中科院分区：
文献类型：
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作者：
Liu,Tao;Thibos,LarryN
目的斜散光是一种突出的周边视觉光学像差，由光线倾斜入射到角膜和晶状体的折射表面引起。我们询问从理论上讲，来自这两个来源的斜散光是否应该在不同的调节状态下在整个视野中具有相同或相反的符号。方法使用光学设计软件计算旋转对称示意图眼的中央视野中的斜散光。通过以与已发表的生物测定一致的方式改变双凸透镜的两个非球面表面的顶曲率半径和间隔来改变调节状态。在与调节晶状体相关的各种表面曲率和非球面值上，分别评估整个眼睛、角膜和孤立晶状体的斜散光。我们还通过从全眼斜散光中减去角膜斜散光来计算内斜散光。结果纳瓦罗模型中角膜斜散光的视野图遵循视野中各处径向轴的经典教科书描述。尽管在调节过程中表面特性发生了很大的变化，但准直光的孤立人类晶状体的固有散光也是径向定向的，并且在理论上和真实的眼睛中几乎独立于调节。然而，眼部斜散光的幅度小于单独角膜的散光幅度，表明内部光学器件进行了部分补偿。这意味着内斜散光（包括从角膜后表面到晶状体前表面的波前传播和内在晶状体散光）必须具有切向轴。内部散光的切向轴的这种非经典模式可追溯到角膜屈光力对撞击内部晶状体的光线的入射角的影响。结论内部光学器件对角膜散光的部分补偿主要是由于角膜折射导致入射到晶状体上的波前的高度会聚性质。补偿程度与偏心度成二次方关系，但预计会随着眼睛的适应而减小。通过折射率匹配来中和角膜会破坏内部补偿，从而揭示孤立晶状体中经典的径向倾斜散光。
PurposeOblique astigmatism is a prominent optical aberration of peripheral vision caused by oblique incidence of rays striking the refracting surfaces of the cornea and crystalline lens. We inquired whether oblique astigmatism from these two sources should be expected, theoretically, to have the same or opposite signs across the visual field at various states of accommodation.MethodsOblique astigmatism was computed across the central visual field for a rotationally‐symmetric schematic‐eye using optical design software. Accommodative state was varied by altering the apical radius of curvature and separation of the biconvex lens's two aspheric surfaces in a manner consistent with published biometry. Oblique astigmatism was evaluated separately for the whole eye, the cornea, and the isolated lens over a wide range of surface curvatures and asphericity values associated with the accommodating lens. We also computed internal oblique astigmatism by subtracting corneal oblique astigmatism from whole‐eye oblique astigmatism.ResultsA visual field map of oblique astigmatism for the cornea in the Navarro model follows the classic, textbook description of radially‐oriented axes everywhere in the field. Despite large changes in surface properties during accommodation, intrinsic astigmatism of the isolated human lens for collimated light is also radially oriented and nearly independent of accommodation both in theory and in real eyes. However, the magnitude of ocular oblique astigmatism is smaller than that of the cornea alone, indicating partial compensation by the internal optics. This implies internal oblique astigmatism (which includes wavefront propagation from the posterior surface of the cornea to the anterior surface of the lens and intrinsic lens astigmatism) must have tangentially‐oriented axes. This non‐classical pattern of tangential axes for internal astigmatism was traced to the influence of corneal power on the angles of incidence of rays striking the internal lens.ConclusionsPartial compensation of corneal astigmatism by internal optics is due mainly to the highly converging nature of wavefronts incident upon the lens resulting from corneal refraction. The degree of compensation is quadratically dependent on eccentricity but is expected to diminish as the eye accommodates. Neutralising the cornea by index‐matching defeats internal compensation, revealing classical, radially‐oriented oblique astigmatism in the isolated lens.