• Stereopsis

  • Stereopsis: the perception of 3-D visual space due to binocular disparity cues (disparities of the two retinal images)

  • Stereoacuity: ability to discriminate very fine differences of objects in space by using binocular vision

    • Stereo acuity is not the same as depth perception

    • Must have some level of binocular vision to appreciate stereo acuity

    • Requires changes in both vergence and accommodation

  • Monocular cues to depth perception must be learned

    • Retinal image size, linear perspective, texture density, luminance variations, aerial perspective, overlay, motion parallax, kinetic depth, myosensory cues from muscles controlling accommodation and convergence

  • Each point on the retina has a local sign or directional value

    • Fovea: principal visual sign (straight ahead)

    • Corresponding retinal points: pairs of points in each eye that have the same local sign (point in one eye corresponds to an area in the other eye)

    • Objects that stimulate a pair of corresponding points appear to be single and located at the same position in space

  • Stereo Tests Designs

    • Local stereopsis (line or contour)

      • Targets have edges that are separated on background to produce disparity

      • Smaller separation defines better stereopsis

      • Howard Dolman Peg Test

        • Thresholds stereopsis

        • Most accurate

        • Two types of testing: null threshold and JND

      • Titmus Stereofly

        • Linear polarized test

        • 3 Parts: “fly” for gross stereo (3,000’’), “animal” test (400’’-100’’), Wirt circles (800’’-40’’)

      • Stereo Reindeer

    • Global stereopsis

      • Matrix of black dots on gray background

      • Lateral shift in central pattern

      • NO monocular cues

      • Random Dot

        • Uses 3-D cross polarized spectacles

        • Right side: 8 random dot figures-- 500 sec of arc on top and 250 sec of arc on bottom-----must identify which cell is empty

        • Left side: modified circles (400’’ – 20’’), animals (400’’ – 100’’)

  • Procedure

    • Present test perpendicular to LOS at a distance of 40 cm (16 in)**

    • Spectacles are placed over habitual

    • Score last number correct after 2 errors

    • Record sec of arc @ test distance, test used and note cc or sc

• Color Vision

  • Three types of cones responsible for color vision

    • Each contain photopigments that maximally absorb different wavelengths

      • Red (long), green (middle), blue (short)

  • Defects

    • Protan: red wavelength (L cones)

    • Deutan: green wavelength (M cones)

    • Tritan: blue wavelength (S cones)

  • Inherited color deficiencies

    • Anomalous trichromat (3 cone pigments)

      • Protananolmalous: red weak

      • Deutananolmalous: green weak

      • Tritananolmalous: blue weak

    • Dichromat ( 2 cone pigments)

      • Protanopia

      • Deutanopia

      • Tritanopia

    • Monochromat

      • Rod

        • True color blindness (may have few cones but abnormal in shape) and poor vision

      • Cone

        • Variation of color blindness (only one cone type present)

Inherited	Acquired
Permanent (not correctable)	Changes with progression or regression of primary cause
Test result relatively stable	Test results strongly influenced with changes in test conditions
Defect same in each eye in both type and severity	Severity may be greater in one eye, or one eye could be normal and the other not
More prevalent in males	Equally prevalent in males and females
Always binocular	Can affect only one eye
Almost always red/green	Most are blue/yellow
Transmitted via X chromosome	Caused by medications (plaquinel), disease, toxic effects of chemicals, aging

• Prevalence

  • Overall 4%

    • Males 8%

      • Protanomaly 1% Protanopia 1%

      • Deuteranolamly 5% Deutranopia 1.1%

      • Tritanopia 0.002%

    • Females 0.5%

• Patient selection

  • Children at an early age

  • Patients at initial office visit

  • Unexplained decreased in VA

  • Report changes in color vision

  • Abnormal fundus findings

• Types of color vision tests

  • Color Naming

  • Color Mixing

    • Anomaloscope

      • Assess ability to make metameric matches

      • Change mixture of monochromatic red and green

  • Color Confusion

    • Pseudoisochromatic plates (PIC)

      • Diagnostic plates: figure is isochromatic for one defect but not for another so it identifies type of deficiency

      • Vanishing figure: normal sees, defective does not see

      • Transformation: normal and defective see different figures

      • Hidden digit/symbol: defective sees, normal does not see

      • Screening mostly for inherited defects

    • HRR

      • Detects inherited and acquired defects

      • Can be used on illiterate patients (symbols used)

    • Ishihara

      • Screen for inherited red/green anomalies

  • Color Matching (arrangement)

    • Detects inherited or acquired

    • Farnsworth D-15

      • Quantifies depth of defect (mild/severe)

      • Used only as diagnostic (not screener)

    • Farnsworth-Munsell 100-Hue

      • Good for detecting/classifying early acquired color deficiencies caused by ocular disease

      • Detects subtle color discrimination

  • Occupational

    • PIC, D-15, Farnsworth Lantern test (FALANT), ISCC Color Matching Aptitude test

• Procedure

  • Use “standard” illumination “C”

    • MacBeth Easel Lamp

    • Incandescent lighting inadequate

  • HRR

    • Plates perpendicular to LOS at 75 cm

    • Use correction unless tinted and test monocular!

    • Ask patient how many symbols, what are they, and have trace where they are with brush

    • Time limit: 20 sec/page

    • Record check marks when correct for screening plates 5-10

      • If ALL 6 correct: normal CV

      • Only plate 5 or 6 missed test plates 21-24: B/Y defect

      • Only 1 or more plates 7-10 missed test plates 11-20: R/G defect

  • Ishihara

    • Plates perpendicular to LOS at 75 cm

    • Use correction unless tinted and test monocular!

    • Ask patient what do they see

    • Time limit: 3 sec/plate

    • Record number plates correct over number tested with pass/fail noted and the numbers said if missed

      • Normal if 10/1l

      • If </= 7 correct, test plates 12,13,14 to classify whether protan or deutan

  • Farnsworth D-15

    • Caps should be 45 deg to patient’s LOS at 50 cm

    • Use correction unless tinted and test monocular

    • Instruct patient to place caps in chromatic order

    • No time limit

**When recording, note the test used and if cc or sc**