ARAVIND EYE CARE SYSTEM A R A V I N D E Y E H O S P I T A L & Postgraduate Institute of Ophthalmology Madurai, India ARAVIND EYE CARE SYSTEM A R A V I N D E Y E H O S P I T A L & Postgraduate Institute of Ophthalmology Madurai, India Colour vision P.S.SelvakumarFaculty Aravind School of Optometry

A R A V I N D E Y E C A R E S Y S T E M What is colour vision?  An ability to distinguish certain colors.  Presents only in day light / bright light conditions & absent at night / dark.  Maximum sensitive color cones are considered.  Normal person can match the 3 primary colors with all spectral hues called, Trichromatic.

A R A V I N D E Y E C A R E S Y S T E M Light sensitive receptors  Rods (120 million)  Located in peripheral retina.  Responsible for night vision.  Cones ( 7 million)  Responsible for color vision,day vision and sharper vision.  Located around fovea region.

A R A V I N D E Y E C A R E S Y S T E M Types of cones  Red, Blue and Green  74% red cones.  16% blue cones.  10% green cones.  Color discrimination occurs through the integration of all cones.  Yellow perceives from red and green combination.  White perceives from inputs of all cones.

A R A V I N D E Y E C A R E S Y S T E M Color vision defects / deficiencies  Due to absence / defects of cones.  Unable to interpret the signals to brain.  Classified as either hereditary or acquired.  Affects about 8% of men & 0.5% women.  Abnormal color matching and color confusions may be result.  Grass may appear in orange color.

A R A V I N D E Y E C A R E S Y S T E M Types of color vision defects  Trichromatic – all cones present – normal vision.  Dichromatic – one cone completely absent  Monochromatic – only one cone present.  – no functioning cones.  Achromatic – no functioning cones.

A R A V I N D E Y E C A R E S Y S T E M Dichromacy  Two cone receptors for matching with all spectral hues.  Three types.  Red and green defects  Are sex-linked.  Protanopes - lack of red receptors.  Deutranopes – lack of green receptors.  Blue and yellow confusion due to  Tritanopes – lack of blue receptor  CIE Chromaticity diagram useful to identify dichromats.

A R A V I N D E Y E C A R E S Y S T E M Protanopia  Red (erytholabe) is absent and replaced by green (chlorolabe).  Protanopes confuses red and green.  Blue become less saturated until 492nm,as wavelengths increases. (Neutral point is white).  1% males & 0.02% of females are protanopes, approximately.

A R A V I N D E Y E C A R E S Y S T E M Deuteranopia  Green(chloralabe) is replaced with red (erythrolabe).  Confuse red and green.  Blue perceived below 498nm and yellow above it.  Neutral point of deuteranope is higher than protanope. ( 498 vs. 492nm)

A R A V I N D E Y E C A R E S Y S T E M Tritanopia  Blue(cyanolabe) may be absent.  Sensitive to yellow and blues.  Neutral point occurs at 570nm.  Very rare condition (0.002% of males and 0.001% of females.)

A R A V I N D E Y E C A R E S Y S T E M Problems in daily life  Many works depends on color discrimination.  Defects may affect an individual ‘s ability.  Color defects could be costly even disastrous.

A R A V I N D E Y E C A R E S Y S T E M Tests for color vision  Many tests are currently used to detect certain color vision defects.  All vary in popularity and reliability.  Most common tests are  Ishihara pseudo- isochromatic plates.  American Optical plates. (HRR test)  The City University test  The Farnsworth Munsell D15 test.  The Farnsworth- Munsell 100 hue test (FM 100 hue)  Color Arrangement Tests  The Anomaloscope Test

A R A V I N D E Y E C A R E S Y S T E M Ishihara pseudo- isochromatic plates.

A R A V I N D E Y E C A R E S Y S T E M Ishihara pseudo- isochromatic plates.  Widely used and efficient test for red-green color deficiency.  Contains 38 plates (25 numerals and 13 plates pathways).  Of the 25 plates,  one is for demonstration of the visual task,  20 are for red-green screening, and  four are for classification of red and green cone deficiencies.  three plates intended for use with nonverbal subjects.  Dichromate and anomalous trichromats fail to distinguish the number.  slight protanopes and deutranopes read some plates correctly.

A R A V I N D E Y E C A R E S Y S T E M American Optical plates. (HRR test)  To identify protan, deutan and tritan defects, and to grade their severity.  Consists of 24 plates containing symbols and employs neutral colours.  4 introductory plates,  6 plates for colour vision screening, and  14 plates for grading the severity of protan,deutan and tritan defects.  Best for the detection of moderate or severe tritan defects.  Not possible to distinguish dichromats and severe anomalous trichromats.  HRR plates for estimating the severity of colour deficiency and for tritan screening.

A R A V I N D E Y E C A R E S Y S T E M The City University test  Derived from the D-15 panel.  Contains ten plates(Each plate displays a central colour & 4 peripheral colours.  Observer must select the peripheral colour which looks most similar to the central colour.  3 colours are typical iso-chromatic confusions for protan,deutan and tritan deficiency.  4 th colour is an adjacent colour in the D-15 sequence and is the normal.  Classification of congenital protan and deutan defects is imprecise due to the limited choice of confusion color.  Grading test not a screening test.  Used to identify the severity of the colour defect.

A R A V I N D E Y E C A R E S Y S T E M Farnsworth Munsell D15 test

A R A V I N D E Y E C A R E S Y S T E M Farnsworth Munsell D15 test.  Consists of 15 loose caps and one fixed cap (the reference cap) in one box.  Each cap hue is chosen so that adjacent caps have approximately equal hue differences.  If caps are arranged in order out of their box forms a hue circle to detect errors  Standard D15 test divides people into two groups.  people with normal colour vision and slight colour deficiency  people with moderate and severe colour vision deficiency.  Typical results obtain in congenitalprotan,deutan,andtritan colour deficiency.  Not designed for screening.  It separates  sufficiently affected deutans from protans.  sufficiently affected deutans and moderate protans.

A R A V I N D E Y E C A R E S Y S T E M The Farnsworth-Munsell 100 hue test (F-M 100 hue)  To detect all types of abnormality from the mildest red-green defect to total achromatopsia.  It separates persons with normal colour vision from various color discrimination and  Measures the axes or zones of colour confusion in those with defective colour vision.  Consists of 85 caps which form a perfect hue circle of the visual spectrum.  The hue circle is divided into four parts for the testing.  Each has an additional fixed or pilot cap at either end of the box and 22 or 21 loose caps.  4boxes render it impossible to confuse reds with greens, or blues with yellows.  Most comprehensive type tests, giving both differential diagnosis and progression of the disease.  Used to screen for any type of colour vision loss.  Takes long time to complete for an acquired loss patients

A R A V I N D E Y E C A R E S Y S T E M Anomaloscope Test Anomaloscope Test Nagal anamaloscope  Commonly used in the diagnosis of red-green deficiencies.  Assesses the observer’s ability to make a specific colour match.  Patient looks into the anomaloscope via eyepiece to view a bipartite colour field.  A mixture field composed of red and green wavelengths is presented in the top half of the display, the bottom half of the test field is yellow.  Patient adjusts the mixture field to match the colour of the test field.  Distinguish between dichromatic and anomalous trichromatic vision by measuring the balance of red and green wavelengths in the mixture field.

A R A V I N D E Y E C A R E S Y S T E M Who may be affected?  Corneal ulcer  Diplopia.  Eye haemorrhages.  Myopia  Ophthalmoplegia  Optic atrophies.  Optic neuritis.  Retinal detachment.  Diabetic retinopathy.  Retinitis pigmentosa

A R A V I N D E Y E C A R E S Y S T E M

Enhancing the color defect performances  Colored filters  absorb the selected wavelengths  help to differentiate stimuli based on their relative brightness.  help to differentiate stimuli based on their relative brightness.  For example,  A red object viewed through a green filter or a green object viewed through a red filter will appear much darker.  A red object viewed through a green filter or a green object viewed through a red filter will appear much darker.  X-chrome lens wears on one eye that absorbs shorter wavelengths and passes longer ones.  X-chrome lens wears on one eye that absorbs shorter wavelengths and passes longer ones.  Dichromat's ability to distinguish red from green can be enhanced.  Dichromat's ability to distinguish red from green can be enhanced.  While such monocular comparisons may be useful in specific applications, the user remains a dichromatic and is unlikely to find the approach practical for everyday use.

A R A V I N D E Y E C A R E S Y S T E M Thank You