Iris - English spelling: iris

Japanese: 虹彩 - こうさい（英語表記）iris

A disk-shaped membrane that constitutes the anterior part of the uvea. There is a circular pupil in the center, the pupil margin touches the anterior surface of the lens, and the peripheral part of the iris transitions to the ciliary body. The color of the iris is called eye color, and can be brown, blue, gray, etc. Functionally, it corresponds to the aperture of a camera, and adjusts the amount of light entering the eye. The amount and arrangement of melanin pigment in the iris determine the color of the iris. If there is little melanin pigment, external light leaks through the iris into the posterior chamber under strong light, resulting in a blurring of the image obtained through the pupil. In high latitude areas where sunlight is weak, even if the amount of melanin pigment in the iris is low, it does not affect vision, but in low latitude areas where sunlight is strong, vision is significantly weakened, which has a serious impact on survival. Blue or gray eyes with little pigment are common among people living in northern Europe, while the irises of people living in areas close to the equator, especially black people, are close to jet black. Japanese irises are brown, with some shades depending on the person. Blue eyes are characterized by the absence of pigment cells in all areas of the iris except the last layer. The lack of melanin pigment is closely related to the loss of pigment in the skin and hair.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

ブドウ膜の最前部を構成する円盤状の膜。中央に円形の瞳孔があり，瞳孔縁は水晶体前面に接触し，虹彩周辺部は毛様体に移行する。虹彩の色は眼色といわれ，褐色，青色，灰色などがある。機能的にはカメラの絞りに相当し，眼内への入射光線量を調節する。虹彩中のメラニン色素の多少と配列とが虹彩の色を決定する。メラニン色素が少ければ，強烈な光のもとでは虹彩を通して外光が後眼房に漏れ，結果として瞳孔を通じて得られた映像をぼかしてしまう。日光の弱い高緯度地帯では，虹彩のメラニン色素量が少くても視覚に影響をもたらすことはないが，日光の強い低緯度地帯では，視力は著しく弱まり，生存上重大な影響をもたらす。北ヨーロッパに住む人々の間では，色素量の少い青い眼や灰色の眼が一般的であり，赤道に近い地方に住む人々，特に黒人の虹彩は漆黒に近い。日本人の虹彩は褐色であり，人により若干の濃淡がある。青い眼は虹彩の最後層以外の部分に色素細胞が欠如している。メラニン色素の欠如傾向は，皮膚や毛髪の色素消失と深く関連する。

出典　ブリタニカ国際大百科事典小項目事典ブリタニカ国際大百科事典小項目事典について　情報

<<: Steel - Kozai

>>: Suburban Festival - Kousai (English)