Knapp変法を行った先天monocular elevation deficiencyの1例

A case of congenital monocular elevation deficiency treated with modified Knapp's procedure

要約　目的：先天monocular elevation deficiency（MED）は，片眼の上転障害をきたす疾患である。筆者らはKnapp変法が奏効したMEDの1例を経験したので報告する。

症例：0歳6か月，女児。生後まもなく家族が左眼上斜視に気づき受診した。初診時，眼位はHirschberg法において左眼固視時で右下斜視15度，右眼固視で左上斜視30度であった。また，右偽眼瞼下垂を認めた。右眼の上転不全があり，Bell現象が消失していた。なお，左眼の眼球運動とBell現象は正常だった。1歳6か月時に右眼MEDに対してKnapp変法を施行した。内・外直筋を2分割して上直筋付着部の両側へ移動し，内・外直筋の上半分を上直筋付着部から後方6.0mmの筋腹縁に縫着した。術後の眼位は交代プリズム遮閉試験で右下斜視12Δとなり，残余斜視角に対してプリズム眼鏡を処方した。術後1年経過した現在も良好な眼位を維持している。

考按：Knapp変法は水平直筋全筋上方移動術（Knapp法）に比べて，外眼筋の半分を切断・移動するため前房虚血のリスクが低くなる。さらに，移動した内・外直筋を上直筋の筋腹縁に縫着したことで矯正効果を増大できた。本症例は早期手術を施行し，残余斜視角をプリズム眼鏡で矯正しており，両眼視の獲得も期待できる。先天MEDに対してKnapp変法は有効な術式と思われた。

Abstract　Purpose：Congenital monocular elevation deficiency（MED）is a condition characterized by a unilateral elevation impairment. Here we report a case of MED successfully treated with a modified Knapp's procedure.

Case report：A 6-month-old female infant was brought to our clinic with left eye hypertropia noticed by her parents shortly after birth. On the first visit, pseudoptosis and 15°right hypotropia were evident during fixation with the left eye, while 30°left hypertropia was evident during fixation with the right eye. An elevation deficiency and lack of Bell's phenomenon were noted on the right eye, while extraocular movement and Bell's phenomenon were normal on the left eye. A modified Knapp's procedure was performed on the right eye for MED at the age of 1 year and 6 months as the symptoms progressed. The medial and lateral rectus muscles were bisected and moved to either side of the superior rectus muscle insertion. The transposed medial and lateral rectus muscles were sutured to the muscle belly of the superior rectus muscle at 6.0 mm behind the insertion. Postoperatively, ocular alignment measured using the alternate prism cover test revealed 10Δ right hypotropia, and prism glasses were prescribed to address the residual strabismus. The ocular alignment has remained unchanged for 1 year postoperative.

Discussion：The modified Knapp's procedure carries a lower risk of anterior chamber ischemia compared to the horizontal full tendon upward transposition procedure（Knapp procedure）because it involves only one half of the transposed extraocular muscle. Additional sutures of the transposed medial and lateral rectus muscles at the muscle belly of the superior rectus muscle enhance its effects. In this patient, early surgery and correcting the residual deviation with prism glasses could lead to binocular vision acquisition. The modified Knapp's procedure is an effective surgical technique for correcting congenital MED.