白内障術後角膜不正乱視の定量的検討

Quantitative assessment of irregular corneal astigmatism after cataract surgery

　角膜形状解析装置で測定した円周上の角膜屈折力を正弦曲線に近似し，回帰残差を計算する方法で，白内障手術後の角膜不正乱視を定量的に検討した。対象は白内障手術症例48例48眼で，6.5mm強膜切開創縫合閉鎖法（19眼），3.2mm強膜切開創自己閉鎖創法（18眼），3.4mm角膜切開創縫合閉鎖法（11眼）の3法で手術を行い，術前，術後1週，2週，2か月の4点で解析した。3群の不正乱視係数は，術後すべての測定点で有意な差を示し（p＜0.01，一元配置分散分析），6.5mm強膜切開創群の値は全期間を通じて3.2mm強膜切開創群より高く（p＜（0.05,Bonferroni多重比較），角膜切開創群は術後1週で3.2mm強膜切開創群より高い値を示した（p＜0.05）。Cravy法，Jaffe法，Holladay法で解析した正乱視の平均値は，いずれも群間で有意差のないものであった。以上の結果から，正弦曲線近似法により角膜不正乱視を正乱視から分離して解析することが可能であり，創口幅の小さい強膜切開創ほど角膜不正乱視に与える影響が小さいものと結論された。

We quantitatively analyzed the irregular corneal astigmatism in 48 eyes after cataract surgery using corneal topography. Circumferential refractive powers of the cornea were approximated with a sine curve, where the calculated final loss was used as a parameter for irregular astigmatism. Cataract surgery was performed with 6.5 mm scleral incision closed with a suture in 19 eyes, 3.2 mm scleral self-sealing incision in 18 and 3.4 mm clear-corneal incision closed with a suture in 11. Measurements were performed before surgery and 1,2 and 8 weeks after surgery. Postoperative irregular astigmatism differed among the 3 procedures throughout the study period (p＜0.01, one way analysis of variance). Significantly higher values were seen in 6.5 mm incision group than in 3.2 mm scleral incision group up to 2 months after surgery (p＜0.05, Bonferroni test). Values in clear-corneal incision group were higher than in 3.2 mm scleral incision group at 1 week postoperatively (p＜0.05). Degree of regular astigmatism calculated by Cravy's, Jaffe's and Holladay's methods showed no difference among the 3 procedures. Approximation of refractive power with a sine cure thus enabled the individual analysis of irregular astigmatism as difference from regular one. Smaller scleral incisions resulted in lesser irregular corneal astigmatism.