日本人角膜鉄線の特徴―動画を応用した角膜鉄線撮影法による研究

Corneal iron line in the Japanese documented by slit-lamp videophotography

要約　背景：角膜鉄線の頻度は，日本人では4.4％，非日本人では29～69％とされている。目的：日本人での角膜鉄線の頻度を動画で検索した報告。対象と方法：眼科を受診した男性436名，女性564名の合計1,000名の角膜を動画として撮影し，Photoshop^®で自動処理をして角膜鉄線を検索した。結果：散乱光では瞳孔領の鉄線だけが写り，青フィルタを挿入すると虹彩域の鉄線と透明域が写った。直接光と反帰光では虹彩域の鉄線が写り，透明域は写らなかった。この写真をPhotoshop^®で処理すると虹彩域で透明域が現れ，鉄線の両端から輪部まで続いていた。鉄線と透明域を合わせた頻度は31.3％であった。鉄線の形は非日本人で報告されているそれと同じであった。結論：角膜鉄線は虹彩の色と記録法で検出率が違う。その頻度が日本人と非日本人とで異なるのは，手技の違いによると解釈される。

Abstract.　Background：The incidence of corneal iron line has been reported to be 4.4％ in the Japanese and 29 to 69％ in non-Japanese. Purpose：To report the incidence of corneal iron line as studied by videophotography. Method：This study was made on 1,000 outpatients at an eye clinic. The series comprised 436 males and 564 females. The cornea was documented by videophotography. The images were then processed by Photoshop^®. Results：By diffuse illumination,iron line was documented in the pupillary area. Iron line and transparent zone was documented when illuminated by blue light. Direct and retroillumination showed iron line in front of the iris and not transparent zone. By processing by Photoshop^®,transparent zone appeared in front of the iris and continued from both ends of the iron line up to the limbus. Shape of iron line was the same as reported in non-Japanese. Incidence of iron line and transparent zone was 31.3％. Conclusion：Incidence of iron line may differ depending on the method of documentation. This feature may be the major cause for the reported racial difference in its incidence.