Effects of corneal thickness distribution and apex position on postoperative refractive status after full-bed deep anterior lamellar keratoplasty

Abstract

Objective

To investigate the effects of corneal thickness distribution and apex position on postoperative refractive status after full-bed deep anterior lamellar keratoplasty (FBDALK).

Methods

This is a retrospective analysis of patients who were diagnosed with advanced keratoconus between 2011 and 2014 in our hospital. The base of the cone in all patients did not exceed the central cornea at a 6-mm range. The FBDALK was performed by a same surgeon. All patients had a complete corneal suture removal and the follow-up records were intact. Patients who had graft-bed misalignment or who were complicated with a cataract or glaucoma were excluded. Uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA), and Pentacam examination data were recorded at two years postoperatively. The recorded data included the superior-inferior (S-I) and nasal-temporal (N-T) corneal thickness differences in 2, 4, 6, and 8 mm diameter concentric circles with the corneal apex as the center (S-I_{2 mm}, S-I_{4 mm}, S-I_{6 mm}, S-I_{8 mm}, N-T_{2 mm}, N-T_{4 mm}, N-T_{6 mm}, and N-T_{8 mm}), the linear, X-axis, and Y-axis distance between the corneal pupillary center and the cornea apex, total corneal astigmatism at a zone of 3 mm diameter from the corneal apex (TA_{3 mm}), the astigmatic vector values J₀ and J₄₅, and the corneal total higher-order aberration for 3 and 6 mm pupil diameters (HOA_{3 mm} and HOA_{6 mm}). Statistical analysis was performed by SPSS 15.0.

Results

A total of 47 eyes of 46 patients met the criteria and were included in this study. The mean follow-up time was (28±7) months. The mean UCVA was 0.45±0.23 (logMAR) (MAR: minimum angle of resolution) and the mean BSCVA was 0.19±0.15 (logMAR), which were all significantly positively correlated with postoperative TA_{3 mm} and HOA_{3 mm}. The mean S-I corneal thickness differences were (44.62±37.74) μm, and the mean N-T was (38.57±32.29) μm. S-I_{2 mm} was significantly positively correlated with J₀ (r=0.31), J₄₅ (r=0.42), HOA_{3 mm} (r=0.37), and HOA6 mm (r=0.48). S-I4 mm and S-I_{8 mm} were significantly positively correlated with HOA_{3 mm} (r=0.30, r=0.40) and HOA_{6 mm} (r=0.46, r=0.35). The X-axis distance between corneal pupillary center and corneal apex was significantly positively correlated with J₄₅ (r=0.29).

Conclusions

In patients with advanced keratoconus after FBDALK, the unevenly distributed thickness at corneal pupillary area and the misalignment of corneal apex and pupillary center might cause significant regular and irregular astigmatism, which affected the postoperative visual quality.

中文概要

目的

探讨全植床深板层角膜移植术后角膜厚度的分布及顶点的位置对术后屈光状态的影响。

创新点

角膜移植术后的高度散光或不规则散光都会严重影响患者的术后视力, 部分患者甚至成为无法矫正的低视力。角膜移植术后植片和植床厚度的偏倚及顶点位置的偏倚可能会导致明显散光, 目前并没有相关的研究报道。

方法

回顾性分析相关病例, 严格纳入标准, 记录进展期圆锥角膜的患者全植床深板层角膜移植术后的裸眼视力、最佳矫正视力及Pentacam检查结果, 包括各个区域的角膜厚度差值、角膜瞳孔中心距角膜顶点的距离及散光矢量值、高阶像差, 进行相关数据分析。

结论

进展期圆锥角膜的患者经全植床深板层角膜移植术后, 角膜瞳孔区厚度分布的不均匀及角膜顶点偏离瞳孔中心, 都可能会造成明显散光, 包括规则和不规则散光, 从而影响术后的视觉效果。