基于角膜地形图的泪膜视频预处理

在基于角膜地形图的泪膜稳定性评估中,针对眼动、睫毛反射和背景干扰,本文提出了一种泪膜视频的预处理算法。首先,利用索贝尔算子(Sobel operator)进行模糊图像检测,然后对灰度图像进行形态学开运算以获取环状图样凸显的目标图像,再通过霍夫圆检测以及快速傅里叶变换提取目标图像的环状图样频率,依据环状图样频率对目标图像进行带通滤波。最后,二值化及形态学闭运算用于确定环状图样区域。本文从数据库中随机选取10段泪膜视频,应用上述算法逐帧进行泪膜图像处理。实验结果表明,该算法有效地去除了视频序列中的无效图像,并实现了环状图样的定位,为后续泪膜稳定性的评估奠定了基础

Variation of axial and oblique astigmatism with accommodation across the visual field

In this study we investigated the impact of accommodation on axial and oblique astigmatism along 12 meridians of the central 308 of visual field and explored the compensation of corneal first-surface astigmatism by the remainder of the eye's optical system. Our experimental evidence revealed no systematic effect of accommodation on either axial or oblique astigmatism for two adult populations (myopic and emmetropic eyes). Although a few subjects exhibited systematic changes in axial astigmatism during accommodation, the dioptric value of these changes was much smaller than the amount of accommodation. For most subjects, axial and oblique astigmatism of the whole eye are both less than for the cornea alone, which indicates a compensatory role for internal optics at all accommodative states in both central and peripheral vision. A new method for determining the eye's optical axis based on visual field maps of oblique astigmatism revealed that, on average, the optical axis is 4.88 temporal and 0.398 superior to the foveal line-of-sight in object space, which agrees with previous results obtained by different methodologies and implies that foveal astigmatism includes a small amount of oblique astigmatism (0.06 D on average). Customized optical models of each eye revealed that oblique astigmatism of the corneal first surface is negligible along the pupillary axis for emmetropic and myopic eyes. Individual variation in the eye's optical axis is due in part to misalignment of the corneal and internal components that is consistent with tilting of the crystalline lens relative to the pupillary axis

Automatic Estimation of the Corneal Limbus in Videokeratoscopy

An algorithm for estimating the corneal limbus from videokeratoscopic images is proposed. After the image is transformed to a polar grid, a novel edge-detection procedure, suitable for the detection of the soft edge produced by the limbus, is used to locate the limbus. Outliers due to the eyelids, eyelashes, and videokeratoscopic rings are removed by taking advantage of the approximate circularity of the cornea. An ellipse which minimizes the sum of the squared algebraic errors is fitted to the remaining edge points. Comparisons between the proposed algorithm, a manual computer- based technique and an algorithm which uses conventional edge-detection techniques demonstrate the accuracy of the proposed algorithm