CS 1 Lecture 4 Color Vision and Stereopsis

rods

scoptic (dim) conditions

peripheral retina

Cones

photopic (bright) conditions - color

central retina - macula/fovea

Trichromatic vision

3 types of cones

red sensitive

green sensitive

blue sensitive

Color vision develops around age

5 months

Visible spectrum of light

400-700 nm

Monochromats

1 type of cone

does not see color

rare

may also have reduced VA

Dichromats

2 primary cone types

Protanopia

absence of red cones

difficulty distinguishing red/greens

brightness of red/orange/yellow is diminished

1/100 males (1%)

Deuteranopia

absence of green cones

difficulty distinguishing green/redns

does not have the diminished brightness

1/100 makes 1%

Tritanopia

absence of blue cones --> difficulty distinguishing blue/yellow hues

1/10000 male and female 0.01%

Trichromats

3 primary cone types

anomalous trichomacy

one or more of the peak sensitivity of the pigments isn't right

Protonomaly

reduced sensitivity to red light

colors shifted toward green

1% males

Deuteranomaly

reduced sensitivity of green

colors shifted toward red

5% males

Tritanomaly

reduced sensitivity to blue 1/500 - 1/10000 males =females

Which is the most commone

deuteranolmaly

Red/green deficiency genetics

sex linked - X chromosome

recessive trait

males mostly affected (8%)

females (0.4%)

congenital color vision defects

present since birth

stable

bilaterally symmetric

throughout visual field

patient is asymptomatic

Acquired color vision defects

present secondary to ocular disease

asymmetric in one or both eyes

may affect only a portion of the visual field

may progress or regress

highly symptomatic

Kollner's Rule

optic nerve diseases = red/green

retinal disease = blue/yellow

Not true

Verriest Rule

Type 1-4

Type I

red/green with shift in peak spectral sensitivity to shorter wavelengths

Type II

red/green with preservation of the spectral sensitivity

Type III

Blue/Yellow with the shift in peak spectral sensitivity to shorter wavelengths

Type IV

not classifiable

Why do we do color vision testing?

all new patients

rule out congential color deficiencies

rule out/monitor acquired deficiences

(optic nerve or macula problems)

Color vision necessary for professions

CV tests identifying numbers or shapes

ishihara - red/green

HRR - red/green and blue/yellow

CV tests arranging colors in an orderly spectral sequence

D15

farnsworth munsell 100 Hue test

Ishihara

Red/green

identify numbers

plate #1 - demonstration

plates #2-15 - screening

plates #16 - 17 - diagnostic

Plates #18 - 24 illiterate plates

what acuity must a patient have to test with ishihara

20/200

ishihara :does patient wear glasses?

yes

ishihara: lighting

C-daylight

overhead on full

stand light projected toward the plates

ishihara: testing distance

75 cm

ishihara: procedure

Monocular test

abbreviated test!

test plates #2-15

even plates OD

odd plates OS

Grade out of 7

if not 7/7

must do all plates

NEVER 6/7

ishihara: normal

up to 4 errors

if 5 or more errors,

use the diagnostic plates #16-17

SEE SLIDES AND READ MANUAL IM CONFSED SLIDE 16

HRR tests for

red/green and blue/yellow

identify shapes!

HRR: plates 1-4

demonstration plates

HRR: plates #5-10

screening

5-6 blue yellow

7-10 red green

HRR: plates 11-24

diagnostic plates

#11-20 red

#21-24 blue yellow

what is the set up for HRR

pt must have 20/200 or better

pt wearing glasses

light:

C day light

Stand toward book

overhead on full

75cm testing distance

separate recording sheet

test demonstration OU

what is the shape and wehere

test the screening monocular

if no errors on screening

normal color vision

if no errors on diagnostic

diagnostic normal

HRR: diagnostic plates

if pt is correct mark it

count up correct - one with most determines the color deficiency

the last error determiens the severity ppok

HRR color vision does NOT distinguish between

dichromat or trichromat

HRR color vision DOES distinguish between

deutan/protan/tritan

Color vision D-15

place chips of color in order from stationary chip

plot on paper to determine deficiency

Farsnworth-Munsell 100 Hue test

85 hues

place chips in order

plot on paper

duetranope/protanope/tritanope/acquired R/G

Anomaloscope

an intrument that requires the patient to adjust the know to match a test field

patient adjsuts the red/green color until it matches

TYPE of color vision deficiency

Rabin Cone Contract Test RCCT

computer based test using a controller

quantitive assement of sach cone type

detets color vision change

colored Landilt C/letters that gradually fade

Stereopsis

the perception of nearness or farness of object points obtainable from disparate but fusible images

How can we have stereopsis

due to binocular horizontal retinal disparity

lateral displacement of out eyes - diffèrent views of the same object

1-3 months

simultaneous perception

3 months

flat fusion

3-5 moths

stereopsis

Why do we test stereopsis?

determine the presence/absence or degree of stereopsis

look for suppression

screen for constant stabismus/microstrabismus

requirement for professions

aid in prognosis/treatment of vision therapy

Why may we have reduced steropsis

constant strabismus - no binocularity

intermittent strabismus - may be reduced

reduced acuity in one or botheyes

small central supression scotoma

unequal refractive errors

Monocular clues for depth

relative size

interposition

linear perspective

aerial persepctive

light and shade

monocular movement - parallax

Relative size

- perceive smaller objects as further away - size constancy

interposition

an object that is behind is further away

Linear perspective

parallel lines that converge as move away from you

aerial perspective

objects in the distance have less contrast and less saturated color

light and shade

can provide info about depth

Monocular Movement Parallax

hold up your fingeres

close objects move ahgainst

far objects move with

Randot circles

two similar targets that are laterally displaced

monocular clues

finer

the finer the stereoacuity (the secs of arc), the --- the lateral displacement (localization acuity)

smaller

Random-dot steretargets (gorss forms) - global stereopsis

geometric shapes made from dots that are laterally displaced

minimal monocular clues

higher order form of stereo

can ONLY be acheived with bi-foveal fixation

Randot stereotest set up

pt wears their near correction

pt wears polarized glasses over top

overhead on full/stand projection toward the test

pr hold the test at 40 cm

pt cannot tilt th test

Randot stereotest procedure