Color Vision PDF

Color Vision Ariette Acevedo, O.D. PPO1 Color Vision • Color vision is the ability to distinguish between different wavelength of light. • Human retina has the ability to perceive light ranging from ~380nm to 700nm. • Retina is composed of 2 photoreceptors • Cones • Rods Color Vision • Scotopic...

Color Vision Ariette Acevedo, O.D. PPO1 Color Vision • Color vision is the ability to distinguish between different wavelength of light. • Human retina has the ability to perceive light ranging from ~380nm to 700nm. • Retina is composed of 2 photoreceptors • Cones • Rods Color Vision • Scotopic Vision: low levels of illumination • • • • Rod predominant Light sensitive retina allow for object detection Ability to recognize details is poor Color vision is absent, objects are seen in shades of gray • Photopic Vision: • • • • Cone predominant Bright illumination necessary for sharp visual acuity and color discrimination Retina is responsive to a broader range of light wavelength S-Cones, M-Cones, L-Cones Color Vision • S-Cones: Short λ • ~420nm • Blue Light • M-Cones: Medium λ • ~531nm • Green Light • L-Cones: Long λ • ~588nm • Red Light Color Vision Testing • Color Vision (CV) testing is part of a basic optometric examination. • Main concerns when testing CV: • Children: early detection of congenital R-G anomalies • Adult: early detection of an acquired CV anomaly, which may indicate ocular pathology. • Purpose of CV testing is to screen for R-G and B-Y anomalies. • Several test available: • Pseudoichromatic plates • Anomaloscopes • Dichotomous tests Acquired CVLoss • Many conditions of the choroid, retina and optic nerve can result in acquired CV loss. • As a general rule: • Choroidal conditions: B-Y anomalies • Retinal conditions: R-G or B-Y anomalies • Optic nerve conditions: R-G anomalies • Examples: • • • • • Choroiditis ARMD Optic neuritis Stargardt’s Glaucoma Inherited CVLoss • Several conditions, with an inherited component may also present with CV loss. • Examples: • • • • Cone dystrophy Cone-Rod Dystrophy Achromatopsia Leber’s Congenital Amaurosis • Depending on the genetic mutation condition may be progressive or stationary. • If progressive, visual acuity may decrease to legal blindness (20/200 or worse) Color Vision • For a person to have normal color vision, they must have three primary colors to match any color stimulus: • Red, Green, Blue • All colors can be matched with a combination of these 3 primary colors. • All spectral hues are matched by a mixture of the 3 primary colors. Color Vision Anomalies R-GAnomalies • Trichromatics: normal color vision • Use the same proportion of the 3 primary colors to match a given color sample. • Anomalous Trichromats: “color deficient” due to a mutation in a specific color wavelength cone. • Have a decreased ability to see color or differences in color. • Will match a given stimulus with different proportions of the 3 primary colors. Anomalous Trichromats • 3 different type: • Protanomalous (Red weak or red-cone defective) • Have a mutated form of the long-wavelength (red) pigment • Deuteranomalous (Green weak or green-cone defective) • Have a mutated form of the medium-wavelength (green) pigment • Tritanomalous (Blue/Yellow defective) • Tritanomalous is a form of anomalous trichromatism. • Have a mutated form of the short-wavelength (blue) pigment Red-Green Anomalies • Protanomalous (red weak): • Required more amount of red in a red-green combination • Less sensitive to red light than a color-normal, therefore is less able to discriminate colors. • Darkening of the red end of the spectrum, might mistake for black. • Poor discrimination of small differences in hues in the red, orange, yellow, green region of the spectrum. Red-Green Anomalies • Deuteranomalous (green weak or green cone defective) • Require more amount of green in a red-green combination. • Less sensitive green area of the spectrum • In the evening, dark green can appear to be black. • Poor at discriminating small differences in hues in red, orange, yellow, and green area of the spectrum. Red-Green Anomalies • Dichromats: individuals who require only 2 primary colors to match any given color stimulus. • They lack one of the three photopigments • 2 major types: • Protanope (red deficient) • Deuteranope (green deficient) • For dichromats, R-G stimulus appear to be the same color. Protanopia • Lacking red cones for long-wavelength. • Unable to distinguish between colors in the G-Y-R area of the spectrum. • Brightness of red, orange and yellow are reduced compared to normal (abnormal dimming) • Reds may be confused with black or dark gray • Red traffic lights may appear to be extinguished Protanopia • They have to learn how to distinguish reds from yellows mainly on their apparent brightness or lightness (not by hue) • Colors with some red components are difficult to distinguish from shades of blue (violet, lavender, purple, pink). • Protanopia is rare and very few are unilateral. • If unilateral, patient will not complain of CV loss. Deuteranopia • Deuteranopia: Lacking green cones for medium wavelengths. • Unable to distinguish between colors in the G-Y-R area of the spectrum. • They also have hue discrimination problems, as protanopes, but do not have a dimming effect. • Purple colors all appear similar • Affects 1% of males Tritanomaly and Tritanopia • Blue-Yellow color anomalies • Affects the S cone • Tritanomalous is a form of anomalous trichromatism where there is a mutation for the short-wavelength (blue) pigment • Tritanopia is a form dichromatism • Both types have difficulty discriminating between blue and green hues, as well as red and yellow hues. Tritanomaly and Tritanopia • Tritanopia is known as B-Y color blindness • Lacking the short-wavelength cones • Blue-green colors are drastically dimmed and some may not be identified. • Blue, indigo, violet • Yellow is indistinguishable from pink • Purple colors are perceived as various shades of red. • Both are inherited in males and females, but prevalence is very low. • AR inheritance rather than sex-linked. Monochromatism/Achromatopsia • Monochromatism or Achromatopsia is rare • 1 in 1 million • All the colors appear the same • Only one primary color to match any color in the spectrum • Presents in 2 forms: Typical or Atypical Monochromatism/Achromatopsia • Typical monochromatism: • • • • Present at birth No foveal cones (only rods) Poor VA and presence of a central scotoma This is also known as rod monochromatism (achromatopsia) • Atypical monochromatism: (S-cone, Blue) • • • • • Only one type of cones Also known as cone monochromatism They only have one type of foveal cone May have better VA but it is still poor (20/50-20/400) Also present with nystagmus and photophobia Monochromatism/Achromatopsia • These patients are photophobic and have a decreased contrast sensitivity • Management is mainly for symptom relief • Filter glasses or contact lenses, red or brown tinted, to help reduce photophobia and to improve contrast sensitivity. • Low vision aids, such as high-powered magnifiers for reading • Routine examinations Inherited CVAnomalies • Most are X-Linked • Some are Autosomal • Prevalence: • 8% in males • 5% deuteranomalous • 0.50-0.64% in females • Achromatopsia prevalence 1 in 1,000,000 Testing Anomaloscope, Pseudoisochromatic Plates, Dichotomous Tests Nagel Anomaloscope • An instrument used to differentiate between an anomalous trichromat and a normal trichromat. • Patient will match a yellow stimulus with a mix of red and green. • Color-normal: will use the correct amount of Red and Green to match the Yellow stimulus in the same proportions. • Color-anomalous: • Protanomalous trichromats: will require more red • Deuteranomalous trichromats: will require more green Nagel Anomaloscope • Most effective test to detect a R-G color anomaly and provides a differential diagnosis. • But it is very expensive for an equipment that diagnoses an untreatable condition. • Pseudoisochromatic plates are less expensive and provide a quick screening. • Ishihara, HRR, Color Vision Testing Made Easy • Farnsworth D15 Test • Determine which type, but it is more expensive. Pseudoisochromatic Plates • Standard screening tests • A book with a variety of color plates that have different patterns (numbers, figures or winding paths) within a series of dots that vary in hue and brightness from the background. • To a color-normal person the patterns are easily distinguishes but to someone with dichromacy no figure will be seen. Pseudoisochromatic Plates • Ishihara and Dvorin tests are intended to be used a a screening tool for R-G anomalies. • American Optical Hardy-Rand-Rittler (HRR) book differentiates between R-G and B-Y anomalies. • Each plate has a ∆, ○, or □ in any four locations on the page. • The patient responds to what figure is seen and where. • Easily administered to children with the use of a brush and asking them to “paint“ the figures. Illumination • To be valid these tests would be performed under daylight illumination. • Natural light is defined as light from the northern sky. • But offices do not provide for daylight illumination, in this case the correct illumination to be used should be Macbeth Illuminant C-Lamp. • Uses a tungsten bulb to filter specific blue light. • If this lamp is not available daylight fluorescent tube lighting has the illumination similar to Macbeth Lamp. • The worst option to use will be a bare tungsten bulb (such as an overhead lamp) • Contains too much yellow Farnsworth D15 Color Test (Dichotomous Test) • Short screening test to identify color deficient persons. • Consists of 15 color samples that a patient needs to arrange in sequence. • The results are plotted in a recording sheet, which provides the type of color anomaly. • Very commonly used by military service, educational and vocational centers. Color Vision Testing Made Easy • Developed by Terrance Waggoner, O.D. • Simple objects and symbols • Good for children, patients with disabilities and non-communicative patients. • Consists of 2 parts with 14 different cards • Part I: simple symbols (circle, star, and square) • Part II: easily identified objects (dog, balloon and boat) • Performed at 30in or 76cm. Ishihara Procedure • Patient wears habitual or near correction • Patient needs to have better than 20/200 BCVA • • • • • • • Performed at 30in or 76cm Light: full room illumination, no headlamp 1st plate is for reliability: everyone needs to see it First test OD then OS If 10 or more plates are read normally, CV is regarded as normal. If 7 or less plates are read normally, CV is regarded as deficient. Report as # plates seen/# plates shown • Ex: CV cc OD 10/14 Ishihara Plates 1. 12: reliability test 2. CV normal sees 8, R-G deficient see 3. 3. CV normal sees 5, R-G deficient see 2. 4. CV normal sees 29, R-G deficient see 70. 5. CV normal sees 74, R-G deficient see 21. 6. CV can see, R-G cannot see 7. CV can see, R-G cannot see 8. CV normal sees 2, R-G deficient nothing. 9. CV normal cannot see, R-G deficient sees 2. 10. CV normal sees 16, R-G deficient nothing • CV deficient are unable to trace the line or trace a line different from the expected one. • No. 12. Normal subjects and mild R-G deficiencies see “35”. • Protanopia + strong protanomalous -“5” only. • Deuteranopia + deuteranomalous “3” only. • No. 13. Normal subjects and mild R-G deficiencies see “96” • protanopia + strong protanomalous read “6” only, • Deuteranopia + strong deuteranomalous “9” only. • No. 14. the Normal trace along the purple and red lines. • Protanopia + strong protanomaly only the purple line is traced • mild protanomaly both lines are traced but the purple line is easier to follow. • Deuteranopia + strong deuteranomalies only the red line is traced • mild deuteranomalies both lines are traced but the red line is easier to follow. HRR • Performed with habitual or near correction • Patient must have 20/200 or better VA • Test is performed at 30 inches (76 cm) • Illumination-Full Room illumination • No overhead lamp • 1st four plates are reliability plates: everyone needs to see them • Next 6 plates for screening CV anomalies • If patient fails one of these plates, must test corresponding CV group (R-G or B-Y) • 7-10: R-G color • 5-6 B-Y color AOHRR • If a patient missed one from the screening plates proceed to test specific color groups: • Plates 11-20 are for the R-G color defect (miss 7-10) • Plates 21-24 are for the B-Y color defect (miss 5-6) • Score the results from these plates • It is going to provide you with a CV defect and severity: • Mild, moderate or severe Scoring HRR • When testing: • For plates 7-20, the patient might see one figure and miss the other one. • If a patient got a figure correct mark it as OK • If missed that figure, mark with an X or a ✔️ • At the end tally the total of CORRECT ones in each column • The column with the highest CORRECT ones is the CV deficit. • The last error the patient got determines the severity. • Recording: # plates seen/ # plates shown • Ex: OD: 8/16: Strong deutan • OS: 9/16 Medium deutan • OD: 6/6, normal • OS: 6/10, Medium tritan Counseling • Parents of inherited anomalous trichromats should be told that their child will have only slightly greater trouble with colors than children with normal color vision. • The principal problems will be with discriminating between pastel shades or very dark tones. • Early School performance should not be greatly affected • Child is healthy Counseling • If a child has inherited protanopia or deuteranopia, the parents should understand that many of the color names used to describe hues (green, yellow, orange, red, and brown), will appear all the same to that child. • Encourage the parents to discuss this with the teachers, especially during preschool • Occupations: • Patient has to be aware of the condition. • Certain occupations can be safety hazards, such as firefighting, military , law enforcement and pilots. Acquired CVAnomalies Acquired CVAnomalies • Caused by a disease of the choroid, optic nerve or retina. • Could also be caused by certain medications • Ex: sildenafil citrate (Viagra), digoxin (Lanoxin), amiodarone (Cordarone), hydroxychloroquine (Plaquenil) and ethambutol (Myambutol) • Köllner’s Rule • Outer retinal disease and media changes result in B-Y color defects • Inner retina, optic nerve, visual pathway and visual cortex disease result in RG defects. • Exceptions: • Glaucoma: B-Y defect • Stargardt’s Disease: R-G defect Outer Retina and Media B-Y Defects Inner Retina, ONH, Visual Pathway and Cortex R-G Defects Acquired CVAnomalies Pearls • The presence of a unilateral CV anomaly may help the clinical determine if an optic nerve or retinal disease is present prior to progression to a stage where it could be detected by VA or visual field test. Congenital Defect Affects both eyes equally Acquired Defects May affect one eye or may present asymmetry Usually R-G defect Other visual functions are normal Stable through out lifetime B-Y or R-G defect Other visual functions are abnormal Variable, depend on test and disease condition Learned to adapt- can label objects More prevalent in males Cannot name color correctly One or more cones are absent Cones are present but work is decreased/altered Causes: diabetes, glaucoma, medication, gaining and chemical exposure Causes: X-linked recessive gene Equally prevalent in M and F