Maloof A J, Ho A, Coroneo M T
Department of Ophthalmology, University of New South Wales, Australia.
Invest Ophthalmol Vis Sci. 1994 Apr;35(5):2592-8.
Light incident at the temporal cornea is focused by the peripheral anterior eye to the nasal limbus, the usual site of pterygium formation. Parameters that may contribute to observed individual variations in the degree of limbal light focusing were assessed.
Computer-assisted optical ray tracing techniques were applied to a human anterior segment model. The angle of incident light (theta, 95 degrees to 108 degrees posterior to the sagittal plane), corneal central radius of curvature (ro, 7.2 to 8.4 mm), and shape factor (p) were varied, and the effect on distal limbal intensity (I) was calculated.
The magnitude of intensity peaks (Ipeak) is dependent on theta and ro. Steeper corneas have higher intensity peaks (Ipeak approximately 21.5X at ro = 7.2 mm, p = 0.75), and flatter corneas have lower intensity peaks (Ipeak approximately 8X at ro = 8.4 mm, p = 0.75) (cf Ipeak approximately 14X for a standard cornea, ro = 7.8 mm, p = 0.75). Anteroposterior location of intensity peaks is dependent on theta and ro. Steeper corneas have intensity peaks situated more anteriorly, whereas flatter corneas have more posteriorly placed peaks. Distal light distribution profiles demonstrate that intensity peaks are not always centrally located. At lower angles of incidence (theta = 100 degrees, ro = 7.8 mm, p = 0.75), peak intensity is located approximately 1 mm above and below the horizontal plane. The overall distribution (envelope) of light at the distal limbus is apparently independent of corneal shape.
Differences in corneal topography can account for the clinical observation of individual variation in the degree of limbal light focusing. Whether individuals with corneas capable of developing intense limbal foci may be more predisposed to developing pterygium requires further study.
入射到颞侧角膜的光线被眼前节周边部聚焦到鼻侧角膜缘，这是翼状胬肉形成的常见部位。对可能导致观察到的角膜缘光线聚焦程度个体差异的参数进行了评估。
将计算机辅助光线追踪技术应用于人体眼前节模型。改变入射光角度（θ，矢状面后95度至108度）、角膜中央曲率半径（ro，7.2至8.4毫米）和形状因子（p），并计算对远端角膜缘强度（I）的影响。
强度峰值（Ipeak）的大小取决于θ和ro。角膜较陡时强度峰值较高（ro = 7.2毫米，p = 0.75时，Ipeak约为21.5倍），角膜较平时强度峰值较低（ro = 8.4毫米，p = 0.75时，Ipeak约为8倍）（相比之下，标准角膜ro = 7.8毫米，p = 0.75时，Ipeak约为14倍）。强度峰值的前后位置取决于θ和ro。角膜较陡时强度峰值位置更靠前，而角膜较平时峰值位置更靠后。远端光分布曲线表明强度峰值并不总是位于中心。在较低入射角（θ = 100度，ro = 7.8毫米，p = 0.75）时，峰值强度位于水平面上方和下方约1毫米处。远端角膜缘处光的总体分布（包络）显然与角膜形状无关。
角膜地形图的差异可以解释角膜缘光线聚焦程度个体差异的临床观察结果。角膜能够形成强烈角膜缘焦点的个体是否更易患翼状胬肉，需要进一步研究。
