Human eye is an organ which makes us capable of viewing object in presence of light. Human eye has following major parts with function mentioned below.
- Choroid: It is outer cover of eye ball which protects all internal parts and gives shape.
- Cornea: It is front part of choroid which is dramatically transparent and light inters into eye from here.
- Iris: it is a muscular aperture of eye which controls the amount of light to inter inside eye
- Pupil: It is hole formed by iris from which light enters into eye. If light is bright pupil becomes small and if light is dim pupil becomes large
- Lens: It is clearly transparent muscular convex lens which focus light coming from object to retina and real inverted image is formed here.
- Retina: Real image is formed here and colors are processed to send to the brain
- Optic nerve: Information of image formed on retina is sent to brain by optic nerve.
- Aqueous humor and vitreous humor moisturize and give shape to eye ball.
- Ciliary muscle controls the focal length of lens
Accommodation of eye: The lens made by glass has fixed focal length but the single lens of eye is capable of focusing far as well as near object i.e. it has variable focal length. When we view near object ciliary muscle relaxes and hence focal length is decreased which can focus near object. Similarly when we view far object ciliary muscle contracts and lens becomes thin and focal length decreases. The least distance of distinct vision is that nearest distance at which eye can focus clearly. For healthy eye it is 25cm.
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