Human Eye and Colourful World

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The human eye is one of the most valuable and sensitive sense organs. It enables us to see the wonderful world and the colours around us

The main parts of the human eye include:

Cornea: transparent tissue covering the front of the eye that lets light travel through

Iris: a ring of muscles in the colored part of the eye that controls the size of the pupil

Pupil: an opening in the center of the iris that changes size to control how much light is entering the eye.

Sclera: the white part of the eye that is composed of fibrous tissue that protects the inner workings of the eye

Lens: located directly behind the pupil, it focuses light rays onto the retina

Retina: membrane at the back of the eye that changes light into nerve signals

Optic Nerve: a bundle of nerve fibers that carries messages from the eyes to the brain

Macula: a small and highly sensitive part of the retina responsible for central vision, which allows a person to see shapes, colors, and details clearly and sharply.

Choroid: The choroid is a layer of blood vessels between the retina and sclera; it supplies blood to the retina.

Ciliary muscle: it changes the shape of the lens - (this is called accommodation). It relaxes to flatten the lens for distance vision; for close work, it contracts to round out the lens.

Aqueous homour: A water like fluid, produced by the ciliary body, it fills the front of the eye between the lens and cornea and provides the cornea and lens with oxygen and nutrients. It drains back into the bloodstream through the canals of schlemm.

Vitreous homour: The space between the lens and retina filled with the gel like Vitreous Humor.

The minimum distance at which objects can be seen most distinctively without strain.

1. For a normal adult eye, its value is 25 cm.
2. The range of human vision – 25 cm to infinity.

Accommodation: The ability of the eye lens to adjust its focal length is called accommodation. Focal length can be changed with the help of ciliary muscles.

A normal eye can see all objects over a wide range of distances i.e., from 25 cm to infinity. But due to certain abnormalities, the eye is not able to see objects over such a wide range of distances and such an eye is said to be defective. Some of the defects of vision are,

1. Hypermetropia or long sightedness
2. Myopia or short-sightedness and
3. Presbyopia