Asthenopia (Eye strain)

Japanese: 眼精疲労 - がんせいひろう（英語表記）Asthenopia (Eye strain)
Asthenopia (Eye strain)

What is the disease?

Continuous use of the eyes, such as when reading, can cause not only eye fatigue and a feeling of pressure on the eyes, but also general body fatigue, headaches, stiff shoulders, nausea, etc. This is commonly known as eye strain.

What is the cause?

There are many possible causes of eye strain. It is often difficult to identify the cause, so we will eliminate possible causes one by one and investigate them.

The causes of eye strain are roughly divided into four categories: 1) eye-related causes, 2) systemic causes, 3) psychological causes, and 4) environmental causes.

① Causes related to the eyes

A. Refractive errors

The most common cause of eye strain seems to be refractive errors such as farsightedness, nearsightedness, and astigmatism. In either case, you cannot see things properly, so you try to adjust your eyes to see them more easily, which causes eye strain.

Hyperopia is more likely to occur in people in their late 30s to 40s when the ability to accommodate begins to decline, but it can also occur in people in their 20s.

When presbyopia first begins, even those without hyperopia may experience eye strain. In this case, the patient will not realize that the eye strain is due to presbyopia, as they will be able to read small letters smoothly.

In the case of myopia, when getting glasses made at an optician, some patients choose lenses that allow them to see things in the distance, and as a result, they sometimes complain of eye strain. Glasses that allow you to see things in the distance well are not necessarily the best, so you should get a prescription for the right glasses from an ophthalmologist.

b. Caused by strabismus , etc.

Strabismus is a condition in which one eye is in the center of the eye, but the other eye is off-center, so both eyes cannot see at the same time. On the other hand, even if you can usually see with both eyes, if you cover one eye with your hand, the position of the eye becomes misaligned. Oblique ( sir ) It is called.

If the strabismus is fixed and binocular vision is not possible, eye strain will not occur, but in the case of strabismus, etc., eye strain is more likely to occur because of the effort to achieve binocular vision. Fusion ( Yuzo ) Because the width of the visual field (which combines the images reflected by both eyes into one) is narrow, abnormalities in the vertical eye position are more likely to cause eye fatigue.

c . Aniseikonia​

When there is a large difference in the refractive index of the two eyes, in other words, when the lens strength is significantly different between the left and right eyes, the size of the image perceived by the left and right eyes is different, which can cause eye strain. In this case, wearing contact lenses seems to reduce eye strain.

d. Other eye diseases

It can also be caused by inverted eyelashes, conjunctivitis, keratitis, etc. Recently, dry eyes have been recognized as an important cause of eye fatigue.

Glaucoma ( Powerful ) can also cause eye strain. In the early stages of glaucoma, the ability to adjust may decrease, which can lead to people mistaking it for early onset of presbyopia. In addition, in the case of chronic angle-closure glaucoma, which is a type of glaucoma, people may sometimes see things as if they are foggy, which can cause eye strain.

② Causes related to the whole body

Systemic illnesses can also cause eye strain, including high blood pressure, low blood pressure, diabetes, Graves' disease, anemia, autonomic nervous system imbalance, and menstrual disorders.

3) Mental

Workplace incompatibility, psychosomatic disorders, and neurosis can also contribute to eye strain.

4. Environmental

Some are caused by light stimuli such as ultraviolet rays, infrared rays, and excessive lighting, but in recent years, eye strain caused by VDT work has been attracting attention, and is known as VDT syndrome.

Mechanical stimuli include air conditioner wind and dust, while chemical stimuli include gases and organic solvents, and recently there has been a lot of attention given to sick house syndrome (column) which occurs in newly built homes.

How symptoms manifest

At first, your eyes may feel heavy, then they may start to hurt, sting, become blurred, or become sensitive to light, red, or teary.

General symptoms include headaches, stiff shoulders, and nausea.

Testing and diagnosis

Vision, visual field, intraocular pressure, Slit lamp ( Final stage ) The above-mentioned causes will be ruled out through general ophthalmologic examinations such as microscopy and fundus examination, but the most important test is accommodation testing.

If the cause is not thought to be eye-related, a thorough examination will be conducted to look for the causes mentioned above, including a full-body examination.

Treatment methods

The appropriate treatment for eye strain varies greatly depending on the cause, so identifying the cause is the most important thing.

What to do if you notice an illness

If you suspect that the cause of your eye strain is one of the psychological or environmental factors mentioned above, rule that out first. If not, first see an ophthalmologist, then an internist.

Katsunori Ohnishi

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

Japanese:

どんな病気か

　読書などのように眼を持続的に使うと、眼の疲労感、眼の重圧感だけでなく、全身にも疲労、頭痛、肩こり、吐き気などが起こることがありますが、これを一般的に眼精疲労といいます。

原因は何か

　眼精疲労の原因は、実にさまざまなものが考えられています。原因を特定することが難しい場合が多く、原因と考えられるものを一つ一つ除外して追及していきます。

　眼精疲労の原因は、大きく4つに分けて考えられています。①眼に原因があるもの、②全身に原因があるもの、③精神的なもの、④環境的なもの、です。

①眼に原因があるもの

a．屈折異常によるもの

　遠視、近視、乱視などの屈折異常が原因で起こる眼精疲労が最も多いようです。いずれも、物が適正に見えないために、それを無理に調節して見ようとして、眼を無理に働かせるために眼精疲労が発生します。

　遠視の場合は、調節力が低下し始める30代後半～40代にかけて起こりやすいのですが、20代でも起こります。

　老視の起こり始めには、遠視でなくても眼精疲労になることがあります。この場合は、小さな字でもすらすらと読めるので、本人は老視のための眼精疲労とはわかりません。

　近視の場合は、眼鏡屋さんで近視の眼鏡をつくる時に、遠方がより見えるレンズを自分で選び、そのために眼精疲労を訴える患者さんを時々みかけます。遠くがよく見える眼鏡が必ずしもよいわけではないので、眼科で適正な眼鏡の処方をしてもらいましょう。

b．斜視(しゃし)などによるもの

　斜視とは、片眼は眼の中心にあるのに他眼が中心からずれているため、両眼で同時に見えない状態です。一方、ふだんは両眼視できても、片眼を手で隠すなどすると眼の位置がずれる状態を斜位(しゃい)といいます。

　斜視が固定していて両眼視ができていない場合は、かえって眼精疲労は起こりませんが、斜位などの場合は両眼視をしようと努力するために眼精疲労が現れやすくなります。水平方向の眼位（眼の位置）の異常よりも、融像(ゆうぞう)（左右の眼に映った像をひとつにまとめてみるはたらき）の幅が狭いために上下方向の眼位の異常のほうが眼精疲労を起こしやすくなります。

c．不等像視(ふとうぞうし)によるもの

　両眼の屈折値の差が大きい時、つまり、レンズの度が左右で相当違う時などは、左右の眼に感じる映像の大きさが異なるので眼精疲労が起こります。この場合はコンタクトレンズにすると眼精疲労は起こりにくいようです。

d．その他の眼の病気によるもの

　さかさまつ毛、結膜炎、角膜炎などによっても起こります。最近では眼精疲労の原因として、ドライアイが重要視されています。

　緑内障(りょくないしょう)も眼精疲労の原因になります。緑内障の初期には調節力が低下してくることがあり、老視が早くきたかと思い違いすることがあります。また、緑内障の一種である慢性閉塞隅角(まんせいへいそくぐうかく)緑内障の場合は、時々、霧がかかったように見えたりして眼精疲労と感じることがあります。

②全身に原因があるもの

　全身疾患によっても眼精疲労が起こります。高血圧、低血圧、糖尿病、バセドウ病、貧血、自律神経失調症、月経異常など、さまざまな病気で眼精疲労が発生します。

③精神的なもの

　職場での不適合、心身症、神経症なども眼精疲労の一因となります。

④環境的なもの

　紫外線や赤外線、過度の照明などの光刺激によるものがありますが、近年注目されているのがVDT作業による眼精疲労で、VDT症候群と呼ばれています。

　また、機械的刺激によるものとしてクーラーの風やごみなどがあります。化学的刺激としては、ガスや有機溶剤によるものがあり、最近は新築の家などで起こるシックハウス症候群（コラム）が注目されています。

症状の現れ方

　最初は眼が重い感じがしますが、眼が痛くなり、じんじんし、かすんできたり、まぶしくなったり、眼が赤くなったり、涙が出たりします。

　全身的には頭痛、肩こり、吐き気などが起こります。

検査と診断

　視力、視野、眼圧、細隙灯(さいげきとう)顕微鏡検査、眼底検査などの眼科の一般検査で前記した原因を除外していきますが、調節検査が最も重要です。

　眼に原因がないと考えられる時は、全身検査を含めて前記した原因を精密検査します。

治療の方法

　眼精疲労の的確な治療はその原因によってまったく異なるので、原因追及が最も重要です。

病気に気づいたらどうする

　眼精疲労の原因が前記の精神的なもの、環境的なものと予想がついた時は、自分でそれをまず除外してください。そうでない時は、まず眼科医、その後に内科医の診察を受けるようにしましょう。

大西　克尚

出典　法研「六訂版 家庭医学大全科」六訂版 家庭医学大全科について　情報

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