What is What is the the

function function of this of this chart ?chart ?

What eye What eye defect you defect you may suffer may suffer if you see if you see the distant the distant object like object like

this? this?

Eye DefectsEye Defects& Their Corrections& Their Corrections

Short Sight

Long Sight

Colour Blindness

Short SightShort Sight

Light rays fromDISTANTDISTANT object

Definition: The image of DISTANTDISTANT object falls IN FRONT OFIN FRONT OF the retina.

Causes of Short Sight:

Corrections:

1. The lens is too CONVEXCONVEX.2. The eye ball is too LONGLONG.

Wearing CONCAVECONCAVE (diverging) lens→ divergediverge the light rays from the distant object onto the retina.

Corrections of Short SightCorrections of Short Sight

Light rays fromDISTANTDISTANT object

Concave lensConcave lens Light rays areLight rays aredivergeddiverged

Sharp imageSharp image

Long SightLong Sight

Light rays fromNEARNEAR object

Definition: The image of NEARNEAR object falls BEHINDBEHIND the retina.

Causes of Long Sight:

Corrections:

1. The lens is too THINTHIN.2. The eye ball is too SHORTSHORT.

Wearing CONVEXCONVEX (converging) lens→ convergeconverge the light rays from the near object onto the retina.

Corrections of Long SightCorrections of Long Sight

Light rays fromNEARNEAR object

Convex lensConvex lensLight rays areLight rays areconvergedconverged

Sharp imageSharp image

Colour-blindnessColour-blindnessWrite down what you see in each of the following chart!!

a.

b.

c.

d.

ChartChart

VisionVision a. b. c. d.NormalNormal

29 45 26Red-green colouRed-green colour-blindnessr-blindness

70 5 2 or 6Total colour-blindTotal colour-blindnessness

Are you suffering from colour-blindness?

Causes of Colour blindness:

Types of Colour blindness:

1. It is due to the absence of certain kind of cone cells.

2. It is a hereditaryhereditary defect. So, it cannot be corrected by wearing glasses.

1. RedRed-greengreen colour blindness.2. Total colour blindness.