Colour Vision OPTM 1051 - PDF

# Colour Vision ## OPTM 1051 ### **Dr Kingsley Ekemiri** ## 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 c...

# Colour Vision ## OPTM 1051 ### **Dr Kingsley Ekemiri** ## 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**.  ## 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.  ## 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.  ## 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.  ## Types of color vision defects * **Trichromatic** - all cones present - normal vision * **Dichromatic** - one cone completely absent * **Monochromatic** - only one cone present. * **Achromatic** - no functioning cones. ## 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  ## Dichromats and Anomalous Trichromats  ## 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.  ## 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)  ## 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.)  ## Problems in daily life * Many works depends on color discrimination. * Defects may affect an individual's ability. * Color defects could be costly even disastrous.  ## 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  ## 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.  ## 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 color 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.  ## 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. * 4th 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.  ## 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 congenital **protan, deutan, and tritan** colour deficiency. * Not designed for screening. * It separates * sufficiently affected **deutans** from **protans**. * sufficiently affected **deutans** and moderate **protans**. ## 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  ## 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.  ## Who may be affected? - Corneal ulcer - Optic atrophies. - Diplopia. - Optic neuritis. - Eye haemorrhages. - Retinal detachment. - Myopia - Diabetic retinopathy. - Ophthalmoplegia - Retinitis pigmentosa ## Enhancing the color defect performances - **Colored filters** - absorb the selected wavelengths - 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. - **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. - 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.  ## Thank You