Ocular muscle palsy

Japanese: 眼筋麻痺 - がんきんまひ（英語表記）Ocular muscle palsy

What is the disease?

When we follow an object with our eyes, the muscles around the eyes are activated. Extraocular muscles ( Foreign cancer ) In the horizontal direction, Medial rectus muscle ( No payment )・Lateral rectus muscle ( Foreign currency ) Two types, vertical Superior rectus muscle ( Government subsidy )・Superior oblique muscle ( Public transport )・Inferior rectus ( Corporate )・Inferior oblique muscle ( Cashier ) There are a total of six types of muscles:

When these muscles stop moving for some reason, it is called extraocular movement disorder or external ophthalmoplegia, or more commonly simply called ophthalmoplegia. The severity of ophthalmoplegia ranges from mild to severe.

What is the cause?

Broadly speaking, there are cases where the condition is caused by damage to the extraocular muscles themselves, and cases where the condition is caused by damage to the nerves that control the extraocular muscles.

The lateral rectus muscle is the abducens nerve, and the superior oblique muscle is pulley ( Kassha ) The nuclei of these nerves are Brain stem ( Noukabu ) The nuclei of the oculomotor and trochlear nerves are in the midbrain, and the abducens nerve is in the bridge ( today ) Each nerve nucleus is controlled by a center in the brain stem, which is further controlled by the motor area of the frontal cortex.

Therefore, if any part of these nerves is damaged, the muscles will eventually stop working and ophthalmoplegia will occur.

For example, if there is an abnormality in the connection between the nerves and muscles (neuromuscular junction abnormality), stimuli are not transmitted to the muscles, resulting in ophthalmoplegia. A typical example is myasthenia gravis, which will be discussed in the next section. This is an autoimmune disease that develops when autoantibodies attack the neuromuscular junction.

Other causes of nerve damage include inflammatory diseases such as multiple sclerosis, brain tumors, and orbital tumors that put pressure on the nerves. infiltration ( Shinjun ) When this happens, the nerve nutrient vessels cerebral infarction ( Noise ) etc. may cause problems.

Diseases that affect the extraocular muscles themselves include genetic muscular dystrophy and mitochondrial myopathy, which cause muscles to stop working, and autoantibodies that attack the extraocular muscles. Thyroid eye disease ( Factory competition ) and diseases such as extraocular myositis.

How symptoms manifest

When we look at an object, we have the ability to see it with two eyes. This is called binocular vision. The positions of the two eyes are well adjusted depending on the position of the object.

However, if the alignment is not done properly due to some illness, you will see two objects. Double vision ( Reconstruction ) This is the most common symptom of ophthalmoplegia.

In cases of mild ophthalmoplegia, double vision occurs when the eyes are moved widely, but in severe cases, patients may see two objects even when facing straight ahead.

Ophthalmoplegia can sometimes be accompanied by pain behind the eye. Eyelids ( Hard work ) Swelling (of the eyelids) or drooping eyelids Ptosis ( Fighting hard ) In addition, various neurological symptoms may appear depending on the site of the nerve damage.

Testing and diagnosis

To examine the nature of diplopia, ophthalmologists will visually examine the eyelids and eye position, and then observe changes in eye movement. With both eyes open, they will observe binocular conjugation (movement of both eyes at the same time), and then observe monocular movement. This will determine roughly which extraocular muscle is insufficient or paralyzed. In addition, a Hess chart test will be performed to quantitatively record eye movement disorders.

Next, we observe the muscles and nerves in order to determine where the abnormality is occurring, and assume the location from peripheral to central, and then use neuroimaging tests such as CT or MRI to diagnose both the location and the cause.

Treatment methods

If the ophthalmoplegia is clearly inflammatory, systemic corticosteroids are effective, whereas if it is noninflammatory and caused by a tumor, surgery is required.

If the cause is other than ischemia, the condition will be monitored. If the condition remains stable after 4 to 6 months of monitoring, surgery to correct the frontal position will be performed. correction ( Resilience ) will do.

If diplopia becomes a concern during follow-up, prism-based eyeglass correction will be used. However, in cases of ophthalmoplegia with disconjugate eye movements, the prisms may not be aligned properly, and one eye may be displaced. Shielding ( Shahei ) Cosmetically, one eye can be covered with a contact lens.

What to do if you notice an illness

If you experience double vision, we recommend you visit an ophthalmologist. If it is monocular diplopia, it is purely an ophthalmological disorder, but if it is binocular diplopia, the cause must be diagnosed.

It is a good idea to first narrow down the cause and then get a referral to a specialist for that specific cause.

Kenji Matsushita

Source: Houken “Sixth Edition Family Medicine Encyclopedia” Information about the Sixth Edition Family Medicine Encyclopedia

Japanese:

どんな病気か

　私たちが物を眼で追いかける時には、眼のまわりについている筋肉がはたらきます。これを外眼筋(がいがんきん)といい、水平方向に内直筋(ないちょくきん)・外直筋(がいちょくきん)の2種類、垂直方向に上直筋(じょうちょくきん)・上斜筋(じょうしゃきん)・下直筋(かちょくきん)・下斜筋(かしゃきん)の4種類、合計6種類の筋肉がついています。

　これらの筋肉が何らかの理由で動かなくなった状態を、外眼筋運動障害あるいは外眼筋麻痺といい、一般には単に眼筋麻痺と呼んでいます。眼筋麻痺の程度は、軽いものから重いものまでいろいろです。

原因は何か

　大別して、外眼筋自体に障害が起こる場合と、外眼筋を支配している神経の障害によって起こる場合があります。

　外直筋は外転神経、上斜筋は滑車(かっしゃ)神経、それ以外は動眼神経に支配されています。さらに、これらの神経の核は脳幹部(のうかんぶ)にあり、動眼神経と滑車神経の核は中脳に、外転神経は橋(きょう)というところにあります。それぞれの神経核は、脳幹における中枢に支配されており、その中枢はさらに大脳前頭野の運動領に支配されています。

　したがって、これらの神経のどこの部分が障害を受けても、最終的に筋肉がはたらかなくなって眼筋麻痺が起こります。

　たとえば、神経と筋肉のつながりの部分に異常が起こると（神経筋接合部異常）、筋肉への刺激が伝わらなくなって眼筋麻痺になります。代表的な病気として、次項で述べる筋無力症(きんむりょくしょう)があります。これは自己免疫疾患のひとつで、自己抗体が神経筋接合部を攻撃することによって発症します。

　そのほか、神経障害の原因として、多発性硬化症のような炎症性疾患が関与する場合、脳腫瘍(しゅよう)や眼窩(がんか)腫瘍が神経に圧迫および浸潤(しんじゅん)する場合、神経栄養血管が脳梗塞(のうこうそく)などで障害される場合があります。

　外眼筋それ自体に障害を起こす病気としては、遺伝的に筋肉がはたらかなくなる筋ジストロフィーやミトコンドリアミオパチー、自己抗体が外眼筋を攻撃して起こる甲状腺眼症(こうじょうせんがんしょう)、外眼筋炎といった病気などがあります。

症状の現れ方

　私たちの眼は物を見る時、2つの眼で見る力があります。これを両眼視といいます。2つの眼の位置は、物がある位置によってうまく調節されています。

　しかし、何らかの病気で位置合わせがうまくいかないと、物が2つに見えてしまうことになります。これを複視(ふくし)といい、眼筋麻痺でいちばん多い症状です。

　複視の出方は、眼筋麻痺が軽い場合は大きく眼球を運動させた時に生じますが、重症になると正面を向いていても2つに見えるようになることがあります。

　眼筋麻痺は、時には眼の奥の痛みを伴うこともあります。眼瞼(がんけん)（まぶた）のはれや、まぶたが垂れてくる眼瞼下垂(がんけんかすい)を合併することもあります。そのほか、神経の障害の発生部位に応じて、いろいろな神経症状が現れます。

検査と診断

　複視の性状を調べるため、眼科では視診による眼瞼や眼球位置の観察のあと、眼球運動の変化を観察します。両眼を開いた状態で両眼の共同性運動（2つの眼球を同時に動かす運動）をみたあと、単眼での運動を観察します。ここまででおおよそ、どの外眼筋の不全または麻痺があるかわかります。さらに、眼球運動障害を定量的に記録するために、ヘスチャートという検査も行います。

　次に、異常がどこで生じているのかを筋肉、神経の順に観察し、末梢から中枢までの部位を想定し、CTやMRIなどの神経画像検査によって、部位診断から原因診断までを行います。