Lecture 4 Color Vision Stereopsis

Photoreceptors allow us to see

Rods – scotopic (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

develop color vision around what age? whats the visible spectrum of light?

Develop around 5 months of age  Visible spectrum of light  400nm-700nm

Monochromats – 1 type of cone

Does not see color  Rare  May also have reduced VA

Dichromats – 2 primary cone types

Protanopia – unable to distinguish red/green hues  Brightness of red/orange/yellow is diminished  1/100 males (1%)

Deuteranopia – unable to distinguish red/green hues  Does not have the diminished brightness  1/100 males (1%)

(Tritanopia – unable to distinguish blue/yellow hues  (0.001%)

Trichromats – 3 primary cone types

Anomalous trichromacy – one or more of the peak sensitivity of the pigments isn’t right  Protanomaly (protanomalous)  Reduced sensitivity of red  Colors shifted towards green  1/100 males (1%)  Deuteranomaly (deuteranomalous)*  Reduced sensitivity of green  Colors are shifted towards red  5/100 males (5%)  Tritanomaly  Reduced sensitivity to blue © Neiman, Rev Fall 20240.0001%

Anomalous trichromacy –

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

Dichromats

absolute color deficient

examples of Dichromats

Protanopia – red deficient - 1% males  Deuteranopia – green deficient - 1% males  Tritanopia – blue deficient - 0.001% males

Trichromats

– Partial color deficient

examples of trichoromats

Protanomaly – red weakness – 1% males  Deuteranolmaly - green weakness - 5% males  * most common  Tritanomaly – blue weakness – 0.0001% males

Red/Green deficiencies

Sex linked – X chromosome  Recessive trait  Males mostly affected (8%)  Females (0.4%)

Congenital Color Vision Defects

 Present since birth  Stable  Bilaterally symmetric  Throughout the visual field  Patient is asymptomatic

Acquired Color Vision Defects

Present secondary to ocular or visual pathway disease  Asymmetric in one or both eyes  May affect only a portion of the visual field  May progress or regress  Highly symptomatic

Once thought: Kollner

Optic Nerve Disease = red/green  Retinal disease = blue/yellow

However, too many exceptions: Verriest

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 shift in peak spectral sensitivity to shorter wavelengths  Type IV = ill-defined or not classifiable

autorefrac use near infared

out of light we can see

Color Vision – Why test

All new patients  Rule out congenital color deficiencies  Rule out acquired color deficiencies

 Support ocular signs of disease  Optic nerve, macula problem…

Color vision necessary for professions  Airline pilot  Air traffic controller  Firefighter  Police officer  Train conductor  Some ranks in the armed forces  Some electrical/electronic engineers

Color Vision - Tests

Identify numbers/shapes  Ishihara – Red/Green  HRR – Red/Green and Blue /Yellow

color vision tests

Arrange colors in an orderly spectral sequence  D 15  Farnsworth-Munsell 100 Hue test

Color Vision – Ishihara

Tests for Red-Green color deficiencies  Identify numbers  Abbreviated test/full test  Plate #1 – demonstration plate  Plates #2 – 15 – screening plates  Plates #16 – 17 – diagnostic plates  Plates # 18 – 24 – illiterate plates

Color Vision - Ishihara requirments

Pt must have 20/200 acuity to test  Pt wears their glasses  Lighting – C-daylight  Bulb vs glasses*  Overhead on full  Stand light projected toward the plates  75 cm testing distance  Demonstration plate – first plate “12”  Anyone that has 20/200 acuity or better should see this – malingerer  Does not count in your recording

testing for Color Vision - Ishihara

testing for Color Vision - Ishihara pt 2

Color Vision - HRR purpose

 Tests for Red-Green and Blue-Yellow color deficiencies  Identify shapes  Plates #1 – 4 – demonstration plates  Plates #5 – 10 – screening plates  #5-6 blue yellow  #7-10 red green  Plates #11– 24 – diagnostic plates  #11-20 red green  #21-24 blue yellow

HRR color vision screening plates

Color Vision – D-15

Place chips of color in order from stationary chip  Plot out on paper to determine deficiency

Anomaloscope

An instrument that requires the patient to adjust the knob to match a ‘test’ field  Patient adjusts the red/green color until it matches  Provides the examiner with type of color vision deficiency depending on the amount of colors used

Stereopsis

The perception of nearness or farness of object points obtainable from disparate, but fusible, retinal images  Due to binocular horizontal retinal disparity  Lateral displacement of our eyes – different views of the same object.

Important indicator for the binocularity of your patient

simultaneous perception

1-3 months

flat fusiion

3 months

stereopsis

3-5 months

 1-3 months – simultaneous perception

Determine presence/absence or degree of stereopsis  Look for suppression  Screen for constant strabismus/microstrabismus  Requirement for professions  Aid in prognosis/treatment of vision therapy

Reduced Stereopsis

Constant strabismus – does NOT have binocularity, unable to appreciate stereopsis  Intermittent strabismus – will have binocularity and appreciate stereopsis but may be reduced  Reduced acuity in one or both eyes  Small central suppression scotoma  Unequal refractive errors – changes image size on the retina – may reduce stereopsis

Monocular Clues for Depth

 Relative Size  Interposition  Linear perspective  Aerial Perspective  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

aeriel perspective

objects in the distance have less contrast and less saturated color

Monocular Clues  Light and shade

can provide info about depth

monocular clues Monocular Movement Parallax

hold up your fingers  Close objects move ‘against’  Far objects move ‘with’

Randot Stereotest

Randot circles – local stereopsis/contour targets  Two similar targets that are laterally displaced  The finer the stereoacuity (secs of arc), the smaller the lateral displacement (localization acuity)  Monocular clues are present that may help your pt.  Stereo-acuity – finer measurement  Seconds of arc

Random-dot stereotargets (gross forms) –

global stereopsis

 Geometric shapes made from dots that are laterally displaced  Minimal monocular clues  Higher order form of stereo  Can only be achieved with bi-foveal fixation

randot stereotest precedure

randot stereotest/interpretation and recording

interpretation of randoty stereo