Analysis of corneal curvature after pterygium excision: the impact of the surgical procedure objectively in our practice

Abstract Introduction: Pterygium is a centripetal proliferation of fibrovascular tissue, which proceeds from the bulbar conjunctiva towards the center of the cornea. Excision of the pterygium may cause visual acuity improvement and surgical excision aims to achieve a topographically regular ocular surface. The improvement of the visual acuity results from the alteration of the refractive corneal power, that is measured in the topography as alteration of the topographic astigmatism. The objective of this study was to evaluate the variation of the final topographic astigmatism after the pterygium excision surgery. Methods: A prospective study was carried out to follow up patients after pterygium excision surgery with corneal topography before and 1 month after the surgery. The population was of the non-probabilistic type of volunteers, with n of 74 eyes. Sampling was for convenience and participation was offered to patients from the ophthalmology residence outpatient service who underwent pterygium excision between July and December 2015. Results: A total of 74 surgeries were performed in the period and 44 were included in the statistical analysis. Mean values of topographic astigmatism (CYL) showed a statistically significant reduction from 2.715D to 1.448D (p = 0.0037). The change in the more curved meridian (Ks) showed no significant change from 45.60D to 45.32D (p = 0.1050), while the meridian plane at 90º Ks (Kf) showed a significant increase from 42.86D to 43,87D (p = 0.0052). Isolated analysis of the groups showed that only the group with grade 3 pterygia suffered a significant alteration of CYL from 7,12D to 1,82D (p = 0,0002). Conclusion: The surgery resulted in a significant reduction of topographic astigmatism only in patients with grade 3 pterygium, due to the reduction of the flattening caused by the pterygium.

摘要 引言：翼状胬肉（Pterygium）是一种纤维血管组织向心性增生病变，起源于球结膜（bulbar conjunctiva）并向角膜（cornea）中央进展。翼状胬肉切除术可改善患者视力，手术目标是获得地形学上规整的眼表。视力改善源于角膜屈光力的改变，该改变可通过角膜地形图（corneal topography）检测为地形图散光（topographic astigmatism）的变化。本研究旨在评估翼状胬肉切除术后最终地形图散光的变化情况。

方法：本研究为前瞻性研究，对接受翼状胬肉切除术的患者进行随访，分别在术前及术后1个月采集角膜地形图数据。研究对象为非概率抽样的自愿者，共纳入74只眼。采用方便抽样法，招募2015年7月至12月期间于眼科住院医师门诊接受翼状胬肉切除术的患者参与本研究。

结果：研究期间共完成74例手术，最终44例纳入统计分析。地形图散光的柱镜度数（CYL）平均值从2.715D显著降低至1.448D（p=0.0037），差异具有统计学意义。角膜最陡子午线（Ks）的数值从45.60D降至45.32D，差异无统计学意义（p=0.1050）；而90°子午线对应的最平屈光力值（Kf）则从42.86D显著升高至43.87D（p=0.0052）。分组单独分析显示，仅Ⅲ级翼状胬肉组的柱镜度数出现显著改变，从7.12D降至1.82D（p=0.0002）。

结论：本研究显示，翼状胬肉切除术仅可使Ⅲ级翼状胬肉患者的地形图散光显著降低，其机制为该类患者因翼状胬肉导致的角膜扁平化效应得以减轻。