Department of Optometry and Vision Science, Faculty of Physics, Mathematics and Optometry, University of Latvia, 1 Jelgavas Str, Riga, LV-1004, Latvia.
BMC Ophthalmol. 2020 Nov 26;20(1):466. doi: 10.1186/s12886-020-01737-x.
To understand which irregular corneal parameters determine the visual quality in keratoconus subjects.
The cross-sectional study examined the eyes of 44 subjects, graded from the first to third keratoconus stages by Amsler-Krumeich classification. We obtained measurements in two ways: (a) by projecting two perpendicular axes onto a cornea (first, through the central point of the cornea and keratoconus apex; second, as the perpendicular axis) to read the elevation values at points on these axes as parameters characterising the corneal surface; (b) by projecting circles with different diameters around the central part of the cornea (1, 2, and 3 mm) and reading elevation values at points equally displaced on these circles as parameters characterising an anterior surface slope. Irregular corneal shape parameters' correlations with visual acuity and contrast sensitivity were determined in order to understand which corneal slope parameter has the strongest correlation with visual acuity and contrast sensitivity.
Parameters characterising the corneal surface's correlations with contrast sensitivity were from r = 0.25 (p = 0.03) at 3 cpd to r = 0.47 (p < 0.01) at 9 cpd for the highest elevation and from r = 0.33 (p = 0.09) at 5 cpd to r = 0.40 (p < 0.01) at 11 cpd for the lowest elevation in all subjects together, while for visual acuity the parameters were r = 0.30 (p < 0.01) for the highest elevation and r = 0.21 (p = 0.06) for the lowest elevation in all subjects together. The correlation between contrast sensitivity and the highest and lowest corneal point in all measured cornea was stronger for subjects with a peripheral corneal apex than for those with a central apex. In keratoconus subjects, contrast sensitivity displayed a strong correlation with slope in the central part of the cornea (with a radius of 1 mm) ranging from 0.48 (p < 0.01) at 3 cpd to 0.61 (p < 0.01) at 9 cpd.
Contrast sensitivity has a higher correlation with corneal shape parameters than with visual acuity. Subjects with a peripheral corneal apex had stronger correlations with visual acuity and contrast sensitivity than did subjects with a central apex. In keratoconus subjects, the strongest correlation was for contrast sensitivity and elevation (slope) in the region within a 1 mm radius of the corneal centre in the opposite direction of the keratoconus apex (direction (ax) CB).
了解哪些不规则角膜参数决定圆锥角膜患者的视觉质量。
这项横断面研究检查了 44 名受试者的眼睛，这些受试者根据 Amsler-Krumeich 分类被分为第一至第三级圆锥角膜。我们通过两种方式获得测量值：（a）通过将两个相互垂直的轴投射到角膜上（第一轴通过角膜中央点和圆锥角膜顶点；第二轴为垂直轴），读取这些轴上各点的高度值作为表征角膜表面的参数；（b）通过在角膜中央部分投射不同直径的圆（1、2 和 3mm），并读取这些圆上各点等距的高度值作为表征前表面斜率的参数。为了了解哪个角膜斜率参数与视力和对比敏感度相关性最强，确定了不规则角膜形状参数与视力和对比敏感度的相关性。
共同纳入所有受试者时，参数表征角膜表面的相关性在对比度灵敏度方面从 r=0.25（p=0.03）（在 3cpd 时）到 r=0.47（p<0.01）（在 9cpd 时），用于最高高度；从 r=0.33（p=0.09）（在 5cpd 时）到 r=0.40（p<0.01）（在 11cpd 时），用于最低高度。对于视力，参数为 r=0.30（p<0.01）（用于最高高度）和 r=0.21（p=0.06）（用于所有受试者的最低高度）。在所有测量角膜中，与周边角膜顶点的受试者相比，与中央角膜顶点的受试者相比，对比敏感度与角膜最高点和最低点之间的相关性更强。在圆锥角膜患者中，对比敏感度与角膜中央（半径 1mm）部分的斜率之间存在很强的相关性，范围从 3cpd 时的 0.48（p<0.01）到 9cpd 时的 0.61（p<0.01）。
对比敏感度与角膜形状参数的相关性高于与视力的相关性。与中央角膜顶点的受试者相比，周边角膜顶点的受试者与视力和对比敏感度的相关性更强。在圆锥角膜患者中，最强的相关性是对比敏感度与角膜中心（顶点相反方向）半径 1mm 范围内的角膜隆起（斜率）之间的相关性（方向（ax）CB）。
