Human eye and the colourful world (copy)

Myopia

The eye defect where a person can see near by objects distinctly but cannot see the objects at a distance.

Hypermetropia

The eye defect where a person can see distant objects Clearly but can't see nearby objects clearly.

Presbyopia

This is an eye defect which happens with aging, in this eye defect a person can't see neither distant objects nor objects that are nearby.

Lens in the eye

Convex or converging

Corrective lens for myopic eye

Concave lens or diverging lens

Corrective lens for hypermetropic eye

Convex lens or converging lens

Cataract

The crystalline lens people at old age becomes milky and cloudy which causes partial or complete loss of vision.

Cataract defect can be cured by

Cataract surgery

Corrective lens for presbyopia is

Bi focal lens

Lens forbi focal lenses

Upper portion is concave lens and lower portion is convex lens

Length of diameter of the eyeball

2.3

The lens system of human eye forms an Image on a light sensitive screen which is a delicate membrane having enormous number of light-sensitive cells called

Retina

Light enters the eye throught a thin membrane called

Cornea

Refraction of light rays entering the eye occurs at

The outer surface of the Cornea

A dark muscular diaphragm that controls the size of pupil is called

Iris

Which part of the eye regulates and controls the amount of light entering the eye

Pupil

Near point for the normal eye

25 cm

Farthest point for normal eye

Infinity

The farthest point upto which the eye can objects Clearly is called

Far point of the eye

The minimum distance at which objects can be seen most distinctly without strain is called

Near point of the eye

When light is very bright

The iris contracts the pupil to allow less light to enter the eye

When the light is dim

The iris expand the pupil to allow more light to enter the eye

The ability of eye lens to adjust its focal length is called

power of accommodation

When the Ciliary muscle are relaxed

The lens becomes thin,the curvatureof eye lens decreases and the focal length increases

When the ciliary muscles contract

The lens becomes thick, the curvature of eye lens increases and the focal length decreases

The cells in retina that respond to brightness or intensity of light

Rod shaped cell

The cells in retina that respond to colour of light that enables us to distinguish between different colors

Cone shaped cells

Reasons for myopic defect

1. Increase in the length of eye ball/ distance of retina and eye ball Increases

2. Decrease in the focal length in the eye lens when the eye is fully relaxed

In myopia the image forms

Infront of retina

In hypermetropia the image forms

Behind the retina

Cause for hypermetropic defect

1. Eye ball is too small

2. the focal length of the eye lens is too long

The eye lens forms which type of image

Real and inverted

Function of vitreous humour

Maintain the shape of the eye ball