Color Vision Test and interpretation in human eye

I'm an Optometrist and I want to share my knowledge about How to perform Color Vision Test.

1. COLOR VISION Bimal Kumar Thakur Consultant Optometrist

2. WHAT IS C O L O R ?? Visible spectrum contains wavelength of 380 – 760nm. All the colors are derived from three primary colors. All primary colors mixed in equal proportion results white. Admixture of these primary colors in different proportion results millions of colors.

3. WAVELENGTH OF COLOR AND PERCEPTION Short wavelength (400-500 nm ) SWS BLUE Medium wavelength(500-600 nm ) MWS GREEN Long wavelength (600-700 nm ) LWS RED

4. WHAT IS COLOR VISION ? Ability of the eye to discriminate between different colors excited by light of different wavelengths. An individual with normal color vision is known as Trichromats. Better appreciated in photopic vision. In scotopic vision all colors seen as gray-called Purkinje shift.

5. HOW COLOR VISION WORKS ON RETINA The rods, located in the peripheral retina, give us our night vision, but can not distinguish color. Cones, located in the center of the retina (called the macula), are not much good at night but do let us perceive color during daylight conditions. Cones (color sensitive receptors) containing single visual pigments selective for red, green, and blue light, are present in the normal human eye.

6. The photopigment in rod cells is called rhodopsin . The photopigment present in cone cells are iodopsin protein and a chromophore , which is a derivative of vitamin A. Photon absorption by the pigment molecules causes a change in the shape of the chromophore , which initiates the processes that lead to vision.

7. VON HELMHOLTZ THEORY. Young-Helmholtz Theory , or the Trichromatic theory says that there are three fundamental color (hue) sensations in human vision, namely red, green, and violet (or blue), and that there are three different kinds of color receptors, one for each of these colors. Equal excitation of all three receptor types leads to the sensation of white light, whereas the appropriate amounts of excitation of red and green receptors yields the sensation of yellow, and so on.

8. NORMAL R G B VISION The human retina has cone cells which see mainly red , green and blue . Other colors are interpreted as mixtures of these. If the red and green cones are triggered, then the brain thinks " yellow ". OUR BRAINS SEES= BLACK WHITE RED YELLOW GREEN BLUE RED OFF ON ON ON OFF OFF GREEN OFF ON OFF ON ON OFF BLUE OFF ON OFF OFF OFF ON

9. OTHER THEORY Channel Theory CIE Color System Munsell Color System

10. COLOR VISION DEFICIENCY Color Deficiency is a defect in vision that makes it difficult/impossible for a person to distinguish between colors.

11. WHAT COLOR VISION DEFICIENCY IS……. Color vision deficiency is a condition in which certain colors cannot be distinguished, and is most commonly due to an inherited condition. Those who are not color blind seem to have the misconception that color blindness means that a color blind person sees only in black and white or shades of gray. While this sort of condition is possible, but it is extremely rare.

12. symptoms The symptoms vary. some people may be able to see every color but not distinguish red or green. Other may not be able to see blue or yellow. Lastly, some people may not be able to see color at all. They may just be able to see shades of black, white and gray. This however is very rare.

13. CLASSIFICATION OF COLOR VISION DEFECTS Congenital defects. Acquired defects.

14. CONGENITAL ACQUIRED Type and severity of defect is same in each eye. Defect is constant throughout life. No change in results with change in testing conditions. Red green defects common. Colors of familiar objects correctly named. Test results reliable and easy to diagnose and categorize. No other signs and symptoms. More prevalent in males. Defect in one eye more or absent in relation to the other. Defect changes with primary cause. Test results influenced with testing conditions. Blue-yellow defects common. Changes in color appearance of familiar objects. Differences in test results and difficult to categorize. Defect is associated with disease , toxicity and trauma. Equally prevalent in males and females.

15. Dyschromatopsia Achromatopsia (monochromatism) Anomalous trichromatism Dichromatism PROTANOMALY DEUTERANOMALY TRITANOMALY PROTANOPIA DEUTERANOPIA TRITANOPIA complete incomplete Rod(typical) Cone(atypical) CONGENITAL

16. ANOMALUS TRICHROMATISM PROTANOMALY -RED ELEMETNT DEFECT. DEUTRANOMALY- GREEN ELEMENT DEFECT. TRITANOMALY – BLUE ELEMENT DEFECT.

17. DICHROMATISM PROTAN OPIA – RED ELEMENT ABSENT DEUTERAN OPIA –GREEN ELEMENT ABSENT TRITAN OPIA – BLUE ELEMENT ABSENT One of the element is absent..

18. MONOCHROMATISM All the spectrum perceived as gray of differing brightness.. rod Monochromacy : associated with reduced VA, nystagmus , etc cone monochromatism : normal VA

19. “Rules” of inheritance Color-defective fathers cannot pass the defect on to their sons. All daughters of color-defective fathers are carriers( at least). For a women to be color-defective, both father & her maternal grandfather must have a color vision defects. Sons of a color defective women always have a color vision defect and all daughters will be carriers.

20. ACQUIRED DEFICIENCY Type I >> R-G defect Progressive, begins with color confusion, reduced VA – likely due to macular cone degeneration Type II >> R-G defect Non progressive, mild color confusion. Type III >> B-Y defect Mostly due to age related changes of ocular media such as NS, AMD, glaucoma.

21. Conditions and Color Defect R-G Defect Diseases Optic Neuritis, Papillitis Leber’s Optic Atrophy Toxic Amblyopia Optic Nerve Lesion CME, Stargardt Fundus Flavimaculatus Medicine Oral antidiabetics Tuberculosis B-Y Defect Diseases Glaucoma, DRP, RD ARMD, Chorio -retinitis Papilloedema Medicines Erythromycin Indomethacin Chloroquine Oral contraceptives

22. Clinical color vision tests Basic four types Pseudoisichromatic The most common, easy to perform, mostly for R-G screening Arrangement Test Sequence of different hue, saturation & lightness Useful for both inherited and acquired, permits diagnosis of type Anomaloscope The most accurate, requires fair amount of skill Occupational Test For vocational purposes

23. Guidelines for testing Small paint brush use as a pointer. Common sense is helpful in clarifying may testing problems. Tinted spects or contact lens not allowed. Use score sheet designed for the test.

24. Pseudoisochromatic plate There exist four different types of plates:  Vanishing design: Only people with good color vision can see the sign. If you are colorblind you won’t see anything.  Transformation design: Color blind people will see a different sign than people with no color vision handicap.  Hidden digit design: Only colorblind people are able to spot the sign. If you have perfect color vision, you won’t be able to see it.  Classification design: This is used to differentiate between red- and green-blind persons. The vanishing design is used on either side of the plate, one side for deutan defects and the other for protans .

25. How to perform the test ? The test plates should be held under adequate daylight or room illumination. The plates are held at 75 cms from the subject and tilted so that the plane of the paper is at right angle to the line of vision. The time given to read each plate should not be more than 3 secs .

26. Vanishing figure Simplest design. Color defective person does not see any figure because the color of the figure & the background fall on a confusion line/zone.

27. Transformation figure A more clever design Four different color are used. Both normal and color defective person see a figure, different ones. Normal person see as background & defective person see part of figure.

28. Hidden symbol Only defective person see Figure and background each consist of three different color

29. Ishihara plates (interpretation) NORMAL - 17 or more plates read DEFICIENT -13 or less plates read ABNORMAL -18,19,20,21 read as 5,2,45,75 If normal answer is between14-16 , such case require the other color test

30. Why can colorblind people see something which is not visible for people with perfect color vision? If you are colorblind you are not distracted by hue differences along the confusion lines. You will be more focused on lightness differences. These two different facts are used to design the hidden or invisible plates.

31. Farnsworth-Munsell 100 Hue (ARRANGEMENT TEST) Very sensitive to color perception. Has black plastic cap stacked with different hues Munsell Paper. 85 different caps in 4 trays (15 caps removed from the series). Patient has to arrange the color caps is sequential order of colors.

32. Panel D-15 (Arrangement) Not as sensitive as 100-Hue test but fair enough to diagnose and easier, still better than pseudoisochromatic tests Contains 15 color caps of diff hues Application is same as in 100-Hue test The form contains sequence of numbers arranged in circular order Numbers are connected according to the cap arranged by patient

33. ANOMALOSCOPE The anomaloscope provides the most accurate possibility to test the severity of color blindness and distinguish between dichromats and anomalous trichromats . It is based on the Rayleigh match: A mixture of red and green light sources has to be matched with a yellow light source. Some of the anomaloscopes also include the Moreland match (blue-green) to test for tritan defects.

34. IN MIXER FIELD: 546 nm (green) + 670 nm (red) mix. IN TEST FIELD: 590 nm (yellow). CONFIGURATION OF THE NAGEL ANOMALOSCOPE.. MMIXTURE FIELD TEST FIELD

35. If you are a dichromat you will be able to make a match for all red-green mixture ratios. Anomalous trichromats don’t accept the normal match and the distance of their match indicates the severity of their deficiency. On the other side, if you suffer a protan vision deficiency you will use much more red to match the colors compared to people with a deutan defect, which use more green in their mixture.

36. Occupational Test Use of Color Lantern – Army. Use of color piece of cloths. City University color vision Test – color plates to be matched.

37. Optokinetic techniques Used for research purpose. Determinate infant have congenital red-green defect. Stimulus consisted of two oppositely drifting red-green grating present in a computer controlled TV screen.

38. IS THERE A CURE FOR COLOR BLINDNESS ?? The simple and easy answer is “NO”.. As of today there is no known traetment which can heal your color blindness. Color vision deficiency is in most cases a congenital disease based on some corrupted chromosomes. In this case only some gene therapy could give you back normal color vision.

39. PATIENT MANAGEMENT Communication Listening. Counseling. Adults advice career limitations. Driving-traffic signals must rely on other clues.