Knighton Robert W, Huang Xiang-Run, Cavuoto Lora A
Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, 1638 NW Tenth Avenue, Miami, FL 33136, USA.
Opt Express. 2008 Sep 1;16(18):13738-51. doi: 10.1364/oe.16.013738.
Corneal birefringence affects polarization-sensitive optical measurements of the eye. Recent literature supports the idea that corneal birefringence is biaxial, although with some disagreement among reports and without considering corneas with very low values of central retardance. This study measured corneal retardation in eyes with a wide range of central corneal retardance by means of scanning laser polarimetry (GDx-VCC, Carl Zeiss Meditec, Inc.), which computes the retardance and slow axis of the cornea from images of the bow tie pattern formed by the radial birefringence of the macula. Measurements were obtained at many points on the cornea by translating the instrument. Data were compared to calculations of the retardation produced by a curved biaxial material between two spherical surfaces. Most corneas showed one or two small areas of zero retardance where the refracted ray within the cornea aligned with an optical axis of the material. The retardation patterns in these corneas could be mimicked, but not accurately described, by the biaxial model. Two corneas with large areas of low retardance more closely resembled a uniaxial model. We conclude that the cornea, in general, behaves as a biaxial material with its fastest axis perpendicular to its surface. Some locations in a few corneas can be uniaxial with the optical axis perpendicular to the surface. Importantly, corneal birefringence varies greatly among people and, within a single cornea, significantly with position.
角膜双折射会影响眼睛的偏振敏感光学测量。近期文献支持角膜双折射为双轴性的观点，尽管各报告之间存在一些分歧，且未考虑中央延迟值非常低的角膜。本研究通过扫描激光偏振仪（GDx-VCC，卡尔蔡司医疗技术公司）测量了中央角膜延迟范围广泛的眼睛的角膜延迟，该仪器根据黄斑径向双折射形成的领结图案图像计算角膜的延迟和慢轴。通过平移仪器在角膜上的多个点进行测量。将数据与两个球面之间弯曲双轴材料产生的延迟计算结果进行比较。大多数角膜显示出一两个延迟为零的小区域，角膜内的折射光线与材料的光轴对齐。这些角膜中的延迟模式可以被双轴模型模拟，但不能准确描述。两个具有大面积低延迟的角膜更类似于单轴模型。我们得出结论，一般来说，角膜表现为双轴材料，其最快轴垂直于其表面。少数角膜中的一些位置可以是光轴垂直于表面的单轴。重要的是，角膜双折射在人与人之间差异很大，并且在单个角膜内，随位置显著变化。
