Human Eye:
The main parts of the human eye are :- Cornea, Iris, Pupil, Ciliary muscles, eye lens, Retina, Suspensory ligament and Optical nerve.
1. Cornea:-The cornea is the transparent front part of the eye that covers the iris, pupil and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately 2/3rd of the eye's total optical power. In human, the refractive power of the cornea is approximately 43 Dioptres.
2. Iris and Pupil:- The iris control the amount of light entering the eyes. The iris automatically adjusts the size of the pupil according to the intensity of light received by the eye.
- If the amount of light received by the eye is large(during the daytime) then iris controls the pupil(make the pupil small) and reduced the amount of light entering the eye.
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| When outside light is bright, pupil become small |
- If the amount of light received by the eye is small (as in a dark room or during night) the iris expands the pupil(makes the pupil large) so that more light may enter the eye.
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| When outside light is dim, pupil becomes large |
3. Retina:- The retina is the innermost, light sensitive layer of tissue of the eye of most vertebrates. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which translates that image into electrical neutral impulses to the brain to create visual perception.
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| Image form by Retina |
4. Ciliary Muscles:-
- Ciliary muscles help in changing the focal length of the eye lens.
- Ciliary muscles help the eye lens to focus the image of an object on the retina by increasing or decreasing the curvature of the eye lens.
5. Suspensory Ligament of Lens:It provides the support to the lens, or It holds the lens in their position.
Range of vision of a normal human eye:
- The farthest point from the eye at which an object can be seen clearly is known as the” far point” of the eye.
- The nearest point up to which the eye can see an object clearly without any strain is called the”near point” of the eye.
- The minimum distance at which an object must be placed so that a normal eye may see it clearly without any strain is called the least distance of distinct vision. The least distance of distinct vision for a normal human eye is about 25 cm.
- The range of vision of a normal human eye is from ∞ to about 25 cm.