間欠性外斜視における水平直筋付着部の形態および年齢による変化

Age-related changes in horizontal extraocular muscles in intermittent exotropia

要約　目的：外眼筋の形態は斜視発症の一因となりうる。内直筋（MR）の筋肥大が間欠性外斜視（IXT）症例の手術中に確認されることがある。そこで今回，手術症例を対象とし，術中の水平直筋の所見を検討した。

対象と方法：手術となったIXT患者25例，および斜視のない網膜剝離（RD）患者30例において，術中にMRおよび外直筋（LR）の輪部から付着部の距離（付着部距離），付着部の幅（付着部幅）を計測し比較した。年齢による変化については，30歳（対象の年齢中央値）以下，および31歳以上の2群に分けて比較した。

結果：IXT群とRD群間でLR付着部距離に差はなかったが，IXT群のMRおよびLRの付着部幅はRD群に比べて大きかった（p＜0.05）。年齢の影響について，MRおよびLRの付着部距離および付着部幅は，RD群では両年齢群間で差はなかった。IXT群では，MRの付着部距離が30歳以下群に比べ31歳以上群で短かった（p＜0.05）。また，31歳以上群では，IXT群のMR付着部距離がRD群のそれよりも短かった（p＜0.01）。IXT群のLR付着部幅は両年齢群でRD群のそれに比較して大きく，MR付着部幅は31歳以上群のみでより大きかった（p＜0.05）。

結論：IXTの発症には広いLR付着部幅が関与すると思われた。眼位の外方偏位を代償するため長期に内転を活性させた結果，年齢が上がるに従ってMRの付着部が短くなり，筋幅が大きくなったと考えられた。

Abstract　Purpose：The conformation of horizontal extraocular muscles is possibly correlated with abnormal ocular alignment. Enlargement of the medial recti（MR）has been observed during surgeries on intermittent exotropia（IXT）. In this study, the conformation and the association with age of lateral recti（LR）and MR were investigated during IXT surgeries.

Subjects and methods：The study included 55 patients who underwent surgery for strabismus（IXT group）and retinal detachment（RD group）. The distances between the limbus and the insertion of horizontal extraocular muscles（LI distance）and widths on insertion（insertion width）were measured intraoperatively. Statistical analysis was performed to investigate the differences between IXT and RD groups. To evaluate the association with age, two age subgroups were compared, under and over 30 years of age, which was the median of age among participants.

Results：There were no differences in the LI distances of MR and LR between IXT and RD groups, whereas the insertion widths of both MR and LR were larger in IXT group（p＜0.05）. Among IXT, the LI distances of MR in patients over 31 years were shorter than those in the subgroup under 30 years（p＜0.01）while there were no differences between the two age subgroups in RD group. The LR insertion widths were larger in the IXT group than in the RD group in both age subgroups（p＜0.05）while MR widths were larger only in patients over 31 years（p＜0.05）.

Conclusion：Larger insertion width is suggested to correlate with the occurrence of IXT. To maintain normal ocular alignment, reactivity of adduction is suggested to compensate for the relatively powerful abduction in IXT. According the long-term reactivities of MR, the LI insertions become shorter and the insertion widths become larger with age.