15immo10

kalyan srinivas,B

O.PHYSIOLOGY

CONTENTS

• INTRODUCTION

• EVOLUTION

• THEORIES

• DEFECTS

• TESTS

• ??

COLOR VISION!!How many colors can the human eye see??

A:This may seem like a lot, and when u consider the human eye cant even see that many colors. we are capable of distinguishing between different colors at best, with some estimates reaching as high as 10 million, but certainly not 16.8

million…

Which cells are responsible for color vision??

A:Color vision is an illusion created by the interactions of billions of neurons in our brain. There is no color in this external world; it is created by neural

programmes and projected into outer world we see …

INTRODUCTION!! People with normal color perception have three different

types of cones . Each type of cone is tuned to percievepredominantly long wavelengths(reddish),middle wavelengths(greenish), or short wavelengths (bluish). Referred to as L-,M-,S-Cones.the cone cells on the retina are crucial physical components of seeing color. Our minds determine what color we are seeing by determining the ratio between signals from different types of cones .

EVOLUTION OF COLOR VISION• Color vision is approximate adaptation of the vision sensory

modalaity,allows for the discrimination of light passed on its wavelength components

• INVERTEBRATES: Color vision requires a number of opsinmolecules with different absorbance peaks , and at least three opsins were present in the ancestor of chelicerates and pan crustaceans , members of both theses groups today posses color vision.

• VERTEBRATES:Researchers found that opsin genes are responsible for color vision pigments have long known that 4 photopigments opsin exist in birds,reptiles and teleost fishes , this indirectly denotes that these group ancestors have tetrachromatic vision i.e ability to see four dimensions of colors

EVOLUTION

THEORIES OF COLOR VISION!!There are two major theories that explain and guide research on color vision :the

trichromatic theory also known as the Young Helmholtz theory and the opponent process theory . These two theories are complementary and explain process that operate at different levels of the visual system .

TRICHROMATIC THEORY:

Evidence for the trichromatic theory comes from colour matching and colour mixing studies.

. This finding led to the hypothesis that normal colour vision is based on the activity of three types of receptors, each with a different peak sensitivity. Consistent with the trichromatic theory, we now know that the overall balance of activity in S (short wavelength), M (medium wavelength), and L (long wavelength) cones determines our perception of colour!!

OPPONENT PROCESS THEORY: Developed by Edwald Heiring

According to this theory states that the cone photoreceptors are linked together to form three opposing color pairs

i.e Blue/Yellow and Red/Green and Black/White.

The opponent-process theory was first developed by Ewald Hering. He noted that there are color combinations that we never see, such as reddish-green or yellowish-blue. Opponent-process theory suggests that color perception is controlled by the activity of three opponent systems.

DEFECTS OF COLOR VISION!!

The two principal color defects are

Congenital color defect

Acquired color defect

CONGENITAL:

The congenital color defects are inherited genitically and without any other abnormalities!!

I. The congenital color defects are non patghological and are incurable

II. The defect is the same in each eye with regard to both type and severity

III. And this defect is completely permanent in their life

IV. The most common are red green defects which are inherited as an x-chromosome linked recessive trait

V. They are more prevalent in males then females

TYPES OF CONGENITAL CV DEFICIENCY• The congenital color vision deficiencies are of two types:

1. Dyschromatopsia

2. Achromotopsia

DYSCHROMOTOPSIA(Types) : 1.Anamolous trichromacy

2.Dichromacy

Anomalous trichromacy:

The anomalous trichromacy is a common type of congenital color vsiondeficiency , occurring when one of three cone pigments are altered in its spectral sensitivity, whicj is of 3 types:

1. Protanomaly

2. Deuteranamoly

3. tritanamoly

• PROTONAMALY:

Protonamaly is a mild vision defect in which photopic sensitivity for red wavelength is low.

As compared with normal vision , protonamaly requires more red light in a color match.

It is hereditary sex linked and present in 1 percent of males

DEUTERONOMALY:

It is most common type of clor vision deficiency in which photopic sensitivity is normal.

As compared with normal vision deuteronomaly requires more green light in color match .

It is hereditary sex-linked.

Present in 0.25 % females and 05% of males.

TRITONAMALY

It is a rere color deficiency in which blue sensitive retinal pifgnment is deficient

As compared with normal vision, tritonamaly requires more blue light in a colrmatch

It is hereditary but not sex linked

Less than 0.01% affected

• DICHROMACY: Dichromacy is a moderately severe color vision defect in which one of the

three basic color mechanisms is absent or non functioning.

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

It can be defined as a type of color blindness.

PROTONOPIA:

It is a severe type of color deficiency caused by complete ebsence of red retinal photoreceptors.

It is aform of dichromatism in which red appears black

Hence are reds are confused with blacks

Heridetary and present in 1% of males

• DEUTERONPIA: It is a color vision deficiency syndrome in which green retinal

photoreceptors are absent

It is a form of dichromatism in which there are only two cone pigments present.

It is hereditary, sex linked and affecting predominantly males

Usually in deuteronopia and protonopia patients show same symptoms.

When a mixture of green and red is presented to them they are unable to spot either one of the colors

TRITANOPIA:

Only two pigments are present amd total absence of blue retinal receptor.

Unable to distinguish btw yellow and blue

It is hereditary and least dangerous

• ACHROMOTOPSIA:

Achromotopsia or monochromacy or total color deficiency.

Lack of distuinguishing colors caused by cone defect or its absence

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

Mainly It is of two types:

Complete achromotopsia

Incomlete achromotopsia

X-LINKED INHERITENCE!!X-linked inheritance (sex linked ) genes follows criss cross inheritance i.e.

the type of inheritance in which a parent passes the traits to grand child of the same sex but through the opposite sex..

GRAND FATHER-DAUGHTER-GRAND SON:DIA-ANDRIC INHERITENCE

GRAND MOTHER-SON-GRAND DAUGHTER:DIA GYNIC INHERITENCE

SEX LINKED RECESSIVE TRAITS IN HUMANS:

A. COLOR BLINDNESS

B. MYOPIA

C. NIGHT BLINDNESS

D. DM DYDTROPHY

E. HAEMOPHILIA

F. AE DYPLASIA

• ACQUIRED COLOR DEFECTS:

• A change in color vision may leads to serious ocular and systematic conditions and testing may be provides for an early diagnosis.

• It changes over time in both type and severity

• The severity of the defect may be greater in one eye then in other or an eye could be normal other not

• These effects are equally prevalent in males as well as females,

TYPES:

TYPE 1 Acquired in protonopia

TYPE 2 Acquired deuteronopia

TYPE 3 Acquired tritanopia

• DIAGNOSTIC TESTS:

ISIHARA TEST

ANAMALOSCOPE

D-15 TEST

FM_100 HUE TEST

I. Isihara test:

Test for red_green colr deficiencies

Most popular test and it comes from 16 plates, 24 plates, 38plates..

The relative visibility of the digit is asseses by asking the patient which numeral is brihter or easier to see.

• The full set of tests has a variety of figure background combinations, and enables diagnosis of which particular defect is present.

• Anamaloscope:

• Gold standard

• Extra ordinarily sensitive

• In this test the SUBJECT is asked to mixed red and green colors in such a proportion that the mixture should match the YELLOW color disc

• Indication of defect is relative amount of red and green required..

• D 15 TEST:

Abridged version

Patients are asked to arrange 15 coloured caps in sequential order.

Intended for screening color vision deficiency only,

Used to detect color vision defects such as red-green and blue- yellow deficiencies as opposed to color acuity

FM-100 HUE TEST

• Very sensitive reliable and effective method of determining color vision defect

• The test consisits of 88 movable color samples arranged in 4 boxes and 22 colours

• Subject has to arrange 88 color chios in ascending order

• The color vision is judged by the error score

• They results are recored in a circular graph

Circular graph representing hue test!!

Does this group of people really have color blindness?????@ ALBINOS^