VISUAL DEFECTS 3 COLOR BLINDNESS - PowerPoint Presentation

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VISUAL DEFECTS 3

COLOR BLINDNESS

Inability to see specific colors

The term ‘color blind’ does not mean that objects are seen only in black and white.

Total

color blindness is very rare.

There

are many types and degrees of color blindness.

The

most appropriate term for color blindness is

deficiency of color vision.

The

Trichromatic

theory explains this phenomenon very well

Color blindness or color vision deficiency is the inability to perceive differences between some of the colors that others can distinguish.

It is most often of genetic nature, but may also occur because of eye, nerve, or brain damage, or exposure to certain chemicals

.

Two types ; Acquired and Inherited

Congenital

/ inherited deficiencies

are due to the inborn abnormality of cone photoreceptor cells

Acquired

deficiencies results any time after birth___ occur due to the disorders that affect the eye or/ and the brain

In

both of these deficiencies, people experience colors differently from those with normal

trichromatic

color vision

CAUSES FOR ACQUIRED COLOR BLINDNESS

1. Trauma

Injury

to eye due to accidents or strokes results in

color blindness

.

2. Chronic Diseases

Color

blindness is caused by chronic diseases such as:

i

. Glaucoma

ii

. Degeneration of macula of eye iii. Retinitis

iv

. Sickle cell anemia

v

. Leukemia vi. Diabetes

vii

. Liver diseases

viii

. Parkinson disease ix. Alzheimer disease

x

. Multiple sclerosis.

3. Drugs

Frequent

use of some drugs leads to color blindness:

i

. Antibiotics

ii

. Antihypertensive drugs iii.

Anti-tuberculosis drugs

Barbiturates

v

. Drugs used to treat psychological

problems and

neural disorders.

4. Toxins

Industrial

toxins or strong chemicals cause color blindness. Common substances causing color blindness are:

i

. Fertilizers

ii

. Carbon monoxide

iii

. Carbon disulfide

iv

. Chemicals with high lead content.

5. Alcoholism

Chronic

alcoholism results in color blindness.

6. Aging

Color

blindness can occur after 60 years of age due

to various

changes in eye.

There

are three types of inherited or congenital color vision deficiencies:

monochromacy

,

dichromacy

,

anomalous

trichromacy

.

Monochromacy

,

It is also

known as "total color blindness," is the lack of ability to distinguish colors; caused by cone defect or absence.

Monochromacy

occurs when two or all three of the cone pigments are missing and color and lightness vision is reduced to one dimension.

Rod

monochromacy

(

achromatopsia

) is an exceedingly rare,

nonprogressive

inability to distinguish any colors as a result of absent or nonfunctioning retinal cones.

It is associated with light sensitivity (photophobia), involuntary eye oscillations (

nystagmus

), and poor vision.

Cone

monochromacy

is a rare total color blindness that is accompanied by relatively normal vision,

electoretinogram

, and

electrooculogram

.

Dichromacy

It is

a moderately severe color vision defect in which one of the three basic color mechanisms is absent or not functioning.

It is hereditary and, in the case of

Protanopia

or

Deuteranopia

, sex-linked, affecting predominantly males.

Dichromacy

occurs when one of the cone pigments is missing and color is reduced to two dimensions.

Protanopia

is a severe type of color vision deficiency caused by the complete absence of red retinal photoreceptors.

It is a form of

dichromatism

in which red appears dark. It is hereditary, sex-linked, and present in 1% of males.

Deuteranopia

is a color vision deficiency in which the green retinal photoreceptors are absent, moderately affecting red-green hue discrimination.

It is a form of

dichromatism

in which there are only two cone pigments present.

It is likewise hereditary and

sexlinked

.

Tritanopia

It is a very rare color vision disturbance in which there are only two cone pigments present and a total absence of blue retinal receptors.

Anomalous

trichromacy

is a common type of inherited color vision deficiency, occurring when one of the three cone pigments is altered in its spectral sensitivity. This results in an impairment, rather than loss, of

trichromacy

(normal three-dimensional color vision).

Protanomaly

is a mild color vision defect in which an altered spectral sensitivity of red retinal

receptors.

perception for red is weak. So to appreciate red color, the person requires more intensity of red than a normal person.

It

is hereditary, sex-linked, and present in 1% of males.

Deuteranomaly

, caused by a similar shift in the green retinal receptors, is by far the most common type of color vision deficiency, mildly affecting red-green hue discrimination in 5% of males. It is hereditary and sex-linked.

Tritanomaly

is a rare, hereditary color vision deficiency affecting blue-yellow hue discrimination. Unlike most other forms, it is not sex-linked.

TESTS FOR COLOR

BLINDNESS

Three

methods are available to determine the color blindness:

1. By using Ishihara color charts

2. By using Holmgren colored wool

3

. By using

Edridge

-Green lantern.