SSLC NOTES (chapter 2 )

Eye

Eye socket	depressions in the skull
External eye muscles	fix the eye balls in the orbit
Eyebrow	Protects from dust and sweet
Eyelashes	Protects from dust and
Eyelids	Protects from dust and and external shocks
Conjunctiva	Secretes mucus which protects the anterior portion of the eye ball from being dry.
Tears	Clean and lubricate the anterior part of the eye ball. Lysozyme, the enzyme present in tears, destroys germs that enter the eyes.

The fluids in the eye
Aqueous humor	Vitreous humor
The water like fluid filled in the aqueous chamber between the lens and the cornea. It is formed from blood, and is reabsorbed into blood. Provides oxygen and nourishment to the tissues of the eye.	The jelly like substance seen in the vitreous chamber between the retina and the lens. Helps in maintaining the shape of the eye.

 

The entry of a large amount of light is harmful to the tissues of the eye. Iris and the aperture at its Centre called pupil regulate the amount of light falling on the eyes.

The size of the pupil is regulated by the action of circular muscles and radial muscles. When the radial muscles contract in dim light, the size of the pupil increases. When the circular muscles contract in intense light, the size of the pupil decreases. Thus the amount of light falling on the lens is regulated according to the intensity of light.

Formation of Image

The curvature of the cornea and the lens help light rays which reflect from an object to get focused on the retina.

While viewing nearby objects	While viewing distant objects
Ciliary muscles contract	Ciliary muscles relax
Ligaments relax	Ligaments stretch
Curvature of lens increases	Curvature of lens increases
Focal length decreases	Focal length decreases

The ability of the eye to adjust the focal length of the lens by changing its curvature in accordance to the distance of the object from the eye and form the image on the retina is called the power of accommodation of the eye

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