Scotoma - Anten

A localized visual field defect (part that cannot be seen) in the visual field, and a physiological one is called a blind spot. Scotoma can be classified into various categories according to their nature. Among the dark spots, those that can be felt as spots are called solid scotoma, and those that cannot be felt are called imaginary scotoma. Blind spots are physiological imaginary scotoma. A scotoma that appears in the center of the visual field is called a central scotoma, and is often circular or near-circular in shape and is accompanied by a decrease in visual acuity. A blind spot (Marriott's blind spot) connected to a central scotoma is called a central blind spot scotoma, and is caused by a disease of the optic nerve and the papillomacular fiber bundle. In addition, a scotoma near the point of fixation is called an accessory central scotoma, and a ring-shaped visual field defect is seen in between the central and peripheral visual fields that remain is called a ring scotoma. A scotoma in which the test target is not visible at all during a visual field test is called an absolute scotoma, and a scotoma in which the target appears unclear and blurred, or a scotoma that appears a different color in a color target is called a comparative scotoma.

[Yasuo Ohta]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

視野中にある限局性の視野欠損（見えない部分）をいい、その生理的なものを盲点という。暗点は性質によっていろいろに分類できる。暗色のうち、斑点(はんてん)として自覚できるものを実性暗点といい、自覚できないものを虚性暗点という。盲点は生理的な虚性暗点である。視野の中心に現れる暗点を中心暗点といい、円形や類円形のものが多く、視力の低下を伴う。盲点（マリオットの盲斑(もうはん)）と中心暗点が連結したものを盲点中心暗点といい、視神経と乳頭黄斑線維束の疾患によっておこる。そのほか、注視点の付近にある暗点を副中心暗点、中心部と周辺部の視野が残っていて、その中間に輪状の視野欠損がみられるものを輪状暗点という。また、視野検査で検査視標のまったく見えない暗点を絶対暗点、視標が不鮮明にぼけて見え、あるいは色視標では異なった色に見える暗点を比較暗点という。

［太田安雄］

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