Structure of Human Eye Eye Muscles Optic nerve

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 • Structure of Human Eye: – Eye Muscles, Optic nerve, sclerotic coat –

• Structure of Human Eye: – Eye Muscles, Optic nerve, sclerotic coat – Cornea, iris, pupil, , lens, retina, blind spot – aqueous humour, vitreous humour, ciliary muscle • Focusing – seeing near object ( near point ) – seeing distant object ( far point ) • Eye defects – Short sight – Long sight

Structure of human eye iris Retina Cornea pupil Blind spot lens Focusing muscles Vitreous

Structure of human eye iris Retina Cornea pupil Blind spot lens Focusing muscles Vitreous humour

 • Light entering the eye is focused successively by the len onto the

• Light entering the eye is focused successively by the len onto the retina. • The image formed on the retina is inverted but is interpreted as erect. • The retina contains many light sensitive cells sends signal along the optic nerve to the brain, causing the sensation of sight.

Focusing near object Light from near object Clear image

Focusing near object Light from near object Clear image

Focusing far away object Light from far away object Clear image

Focusing far away object Light from far away object Clear image

Accommodation

Accommodation

Near Point and Far Point • The average normal eye can focus objects easily

Near Point and Far Point • The average normal eye can focus objects easily from about 25 cm, i. e. , the near point, to infinity, i. e. the far point. • This range of distance of clear vision varies from one person to another and decreases with age.

Short sight Light from distant object blurred image in front of the retina The

Short sight Light from distant object blurred image in front of the retina The image is focused ______

 • The eyeball is too long. • The lens lacks the ability to

• The eyeball is too long. • The lens lacks the ability to accommodate for a distant object.

Correction of short sight Light from distant object Concave lens ( Diverging lens )

Correction of short sight Light from distant object Concave lens ( Diverging lens )

Long sight Light from near object blurred image behind the retina The image is

Long sight Light from near object blurred image behind the retina The image is focused ____

 • The eyeball is too short. • The lens lacks the ability to

• The eyeball is too short. • The lens lacks the ability to accommodate for a near object.

Correction of long sight Light from near object Convex lens ( Converging lens )

Correction of long sight Light from near object Convex lens ( Converging lens )

Class Practice 1. Which of the following statements about the lens is/are correct ?

Class Practice 1. Which of the following statements about the lens is/are correct ? (1) The image formed on the retina is real. (2) The pupil is smaller in bright light than in dim light. (3) When the object distance changes, the eye focuses an object by changing the focal length of the lens.

Class Practice 2. The near point of a long-sighted eye is 50 cm from

Class Practice 2. The near point of a long-sighted eye is 50 cm from the eye. A lens is used for correction. (a) What type of lens should be used ? (b) Find the focal length of the lens.