角膜后表面散光

眼球的散光主要包括角膜散光和眼内散光(即晶状体的散光),角膜散光由角膜前后表面散光组成.角膜后表面散光大小约0.3D,主要为逆规散光(占85％～96.1％).角膜后表面非球面性并非完全由前表面的非球面性决定,它与年龄呈负相关.随年龄增长前表面散光由顺规向逆规漂移明显;后表面散光的趋势则相反,但总体变化很小.同时角膜前后表面半径比与年龄也呈负相关.后表面散光对前表面的补偿作用随年龄增加而减小.因此,对于青年人,后表面散光减小总角膜散光;对于老年人,后表面散光则增加总角膜散光.忽略后表面散光可能会导致总角膜散光的错误估计,测量角膜后表面散光以进一步准确计算角膜总散光是白内障屈光手术临床应用的迫切需求.     

老年性白内障患者中角膜后表面散光对总角膜散光的影响

目的　研究老年性白内障患者模拟角膜曲率计散光和总角膜散光大小及轴位的差异,评价角膜后表面散光对总角膜散光的影响。方法　８０例老年性白内障患者（１０５眼,左４７眼,右５８眼）手术前行Ｐｅｎｔａｃａｍ检查,记录角膜前后表面散光,并对角膜前后表面散光行相关性分析。模拟角膜曲率计散光用屈光指数１．３３７５及角膜前表面曲率半径计算,总角膜散光由前后表面散光在角膜后表面的矢量合计,计算模拟角膜曲率计散光和总角膜散光的矢量差Ｅ→、大小差Ｅ和轴位差Ａ。结果　角膜前表面散光和后表面散光大小间无明显相关性（Ｐ＝０．９８）,后表面散光对前表面散光的平均补偿作用为５．７９％。总角膜散光及模拟角膜曲率计散光大小分别为（１．１２±０．６５）Ｄ和（１．０７±０．６４）Ｄ,差异具有统计学意义（ｔ＝－２．４０,Ｐ＝０．０２）;两者轴位分别为（６７．９３±５６．５０）°和（６８．９０±５９．６８）°,差异无统计学意义（ｔ＝－０．２７,Ｐ＝０．７９）。散光值大小及轴位差异的算术均值分别是（０．０５±０．２３）Ｄ和（－０．５７±１３．０２）°,绝对值是（０．１９±０．１５）Ｄ和（７．００±１０．９７）°。两者散光大小差别大于０．５０Ｄ或轴位差别大于１０°的有３０眼,占２８．５７％。结论　老年性白内障患者忽略角膜后表面测量可能会导致具有临床意义的角膜散光值估计的差异。     

Surgical induction of corneal astigmatism

Summary The aim of all ocular surgery is to preserve or restore optimal visual function. Reduction of excessive postoperative astigmatism after keratoplasty, cataract extraction, or other anterior segment operations has been obtained in clinical surgery by corneal wedge resection. The purpose of this experimental investigation was to quantify and evaluate the results of different microsurgical techniques in crescentic resection of a corneal wedge. Twenty-five rabbits were operated and the induced changes of corneal curvature measured by keratometry. The immediate and long-term results are presented. The effect of wedge resection was a steepening of the meridian perpendicular to the resection and a flattening of the meridian parallel to the resection. The astigmatism induced was less pronounced than the changes obtained in human surgery. There were no postoperative ocular complications and all corneas remained clear. It is suggested that the operation be performed in all cases of severe corneal astigmatism uncorrected by lenses.     

Surgical correction of corneal astigmatism after corneal graft]

We performed Troutman's technique of corneal wedge resection in 6 patients who had substantial astigmatism after penetrating corneal grafts. The astigmatism was reduced by 5 to over 15 dioptres, and was stable for up to 36 months. The visual acuity was considerably improved in 5 of the 6 cases. However we could not neither predict the amount of correction nor the axis of the residual astigmatism with this technique. We stress the importance of using a keratometer when performing a penetrating corneal graft.     

Posterior corneal surface toricity and total corneal astigmatism.

The influence of posterior corneal surface toricity upon total corneal astigmatism was investigated in 60 young subjects (mean age 22.04 +/- 3.24 years). Both surfaces were found to be flatter horizontally than vertically. Astigmatism arising from the anterior corneal surface was therefore reduced by astigmatism of the opposite sign arising from the posterior surface. Had the toricity of the posterior corneal surface been purely governed by that of the anterior surface this reduction would have amounted to about 5%. However, the posterior surface was found to exhibit additional toricity bringing about a greater reduction of total corneal astigmatism amounting to approximately 14%.     

不同年龄段前角膜散光和后角膜散光相关性的横断面研究

目的：以不同年龄段分组评估前角膜散光(ACA)和后角膜散光(PCA)。同时分析各年龄段ACA、PCA之间散光程度、散光轴的相关性。

方法：横断面研究，包括381眼。将临床测得的散光数值转换为向量记法，以分析ACA和PCA。在整体人群和四个不同年龄段(5～19， 20～39， 40～59， 和≥60)中评估ACA和PCA之间散光程度、散光轴的关系。使用随机效应线性回归模型评估ACA、PCA散光程度之间的关系。

结果：在5～9岁儿童中，ACA平均散光度最高为3.59D，PCA为0.50D。总体上来说，ACA在1～10.0D，PCA在0～3.5D。在较年轻的分组中(5～19岁)，ACA和PCA显著相关(r=0.85， P<0.001)。在60岁以上组中，ACA每增加1D，PCA增加0.04D(95%CI： 0.005， 0.07； P=0.03)，增加程度相比其余组最少。

结论：在60岁以上人群中，相比仅仅依靠经验公式，通过ACA数据计算IOL度数，更为谨慎的方法是同时测定后角膜散光度和散光轴。     

个体化准分子激光上皮瓣下角膜磨镶术矫治角膜不规则散光的临床研究

目的评价眼前节全景仪引导的个体化准分子激光上皮瓣下角膜磨镶术(laser subepithelial keratomileusis,LASEK)治疗偏中心切削所致不规则散光的效果,并比较术前和术后不同时间角膜不规则状态的变化。方法收集10例(18眼)因行屈光手术而发生偏中心的患者,伴有严重的不良视觉症状,行眼前节全景仪引导的个体化LASEK治疗。所有患者在术前和术后1个月、3个月和6个月均行眼前节全景仪检查,并对手术前后所有患者的裸眼视力(uncorrected visual acuity,UCVA)、最佳矫正视力(best corrected visual acuity,BCVA)、角膜表面非球面性(Q值)、角膜表面变异指数、角膜表面垂直不对称指数等进行比较。结果 UCVA由术前0.26±0.15变为术后6个月0.85±0.11,BCVA术前0.69±0.20变为术后6个月1.02±0.04,UCVA、BC-VA与术前相比差异均有显著统计学意义(均为P=0.00)。Q值术前为0.56±0.29,术后1个月、3个月时分别为0.21±0.52、0.36±0.42,差异均有统计学意义(均为P<0.05);术后6个月为0.54±0.48,与术前相比差异无统计学意义(P>0.05)。角膜表面变异指数术前为65±11,术后6个月降低为59±8,差异有统计学意义(P<0.05)。角膜表面垂直不对称指数术前为0.78±0.12,术后6个月降低为0.24±0.18,差异也有统计学意义(P=0.04)。术后切削区中心偏移明显改善,光学区居中,并且光学区较术前有所扩大。结论眼前节全景仪引导的个体化LASEK手术矫治偏中心所致的角膜不规则散光安全、有效,能整体上改善角膜不规则状态。     

The effect of posterior corneal flat meridian and astigmatism amount on the total corneal astigmatism estimated from anterior corneal measurements

Background

To evaluate the effects of posterior corneal astigmatism and the absolute flat meridian difference between anterior and posterior corneal surfaces (AMD_Ant-Post) on the estimation of total corneal astigmatism using anterior corneal measurements (simulated keratometry [K]).

Methods

Ninety-nine eyes of 99 healthy participants were enrolled. Anterior, posterior, and total mean corneal power, cylinder power, flat meridian, and vector components J₀, and J₄₅ measured by a dual Scheimpflug camera were analyzed. The correlation between the posterior corneal cylinder power, AMD_Ant-Post, and the difference in the cylinder power between simulated K and total cornea (cylinder power difference_SimK-Tot) were evaluated.

Results

The cylinder power difference_SimK-Tot was positively correlated with the posterior corneal cylinder power (rho?=?0.704 and P?Ant-Post (rho?=??0.717 and P?0 was strongly associated with the posterior corneal cylinder power and the AMD_Ant-Post. When corneal J₀ had a positive value, the cylinder power of simulated K tended to be larger than the total corneal cylinder power. In comparison, the opposite trend was presented in eyes with negative anterior corneal J₀. When anterior corneal J₀ was larger than 1.0 or smaller than ?0.9, the errors from estimating the total corneal cylinder power using anterior corneal measurements tended to be larger than 0.25 D.

Conclusion

Posterior corneal astigmatism should be considered for more accurate corneal astigmatism predictions, especially in eyes with anterior corneal astigmatism greater than 2.0 D of with-the-rule astigmatism or greater than 1.8 D of against-the-rule astigmatism.     

翼状胬肉与角膜散光的关系

目的:研究翼状胬肉大小与角膜散光的关系,探讨翼状胬肉手术的时机及必要性。方法:对61例82眼进行了视力、屈光度、角膜曲率及对胬肉进入角膜缘长度的测定,其中45眼进行了手术前后的比较。结果:其中74眼有不同程度的散光,与胬肉进入角膜长度正相关,以顺规性远视散光为主。术后3mo散光度数下降,视力提高。结论:翼状胬肉大小与角膜散光存在相关性,手术可使角膜散光得以改善,提高视力。     

Customized ablation for asymmetrical corneal astigmatism

PURPOSE: To evaluate laser in situ keratomileusis (LASIK) cases in which a customized ablation assisted by corneal topography was performed. SETTING: Instituto de la Visión, Buenos Aires, Argentina. METHODS: The study group comprised 23 cases with asymmetrical corneas; 17 had myopia and 6, hyperopia. Visual acuity, spherical equivalent (SE), and cylinder vectorial change measurements, along with keratometry and corneal topography, were performed in all cases preoperatively and postoperatively. RESULTS: In the myopic cases, the mean preoperative SE was -4.92 diopters (D) +/- 2.46 (SD); it was -0.38 +/- 0.66 D after a mean follow-up of 4.41 +/- 2.32 months. In the hyperopic cases, the preoperative SE was +3.54 +/- 1.57 D; it was +0.33 +/- 0.50 D after a mean follow-up of 3.42 +/- 3.23 months. Cylinder vectorial change, visual acuity, and the number of visual acuity lines gained or lost were also evaluated in both groups. CONCLUSION: Although some features of our algorithm for corneal-topography-assisted customized ablations should be modified, the results of our treatment of cases with asymmetrical astigmatism were encouraging.     

Pterygium‐induced corneal astigmatism

A significant degree of corneal astigmatism can be induced by the encroachment of a pterygium onto a cornea. The pterygium generally causes with‐the‐rule corneal astigmatism that is hemimeridional on the side of the pterygium. There is a significant correlation between the extension of the pterygium onto the cornea and the amount of induced astigmatism. However, there is a poor correlation between pterygium‐induced astigmatism measured topographically and that measured by manifest refraction. Successful pterygium surgery will reduce pterygium‐induced refractive astigmatism and improve visual acuity. This paper outlines the management of a patient with an advanced pterygium, in whom a large degree of corneal astigmatism was induced by the encroachment of a pterygium onto the cornea. Subsequent excision of the pterygium brought about a reversal of the pterygium‐induced corneal astigmatism.     

翼状胬肉大小与角膜散光的关系

目的:探讨翼状胬肉大小与角膜散光的关系。方法:选取64例70眼翼状胬肉患者纳入研究,测量裸眼视力、角膜曲率及胬肉侵入角膜缘长度,分析胬肉长度与角膜散光的相关度,对比翼状胬肉切除+角膜缘干细胞移植术手术前后裸眼视力。结果:术前69眼有不同程度的角膜散光,与胬肉侵入角膜长度相关,以循规性散光为主。术后1mo,其角膜散光明显下降,裸眼视力提高。结论:翼状胬肉可引起角膜循规性散光,散光程度与胬肉侵入角膜长度关系密切,手术可以使角膜散光改善、视力提高。