color vision

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a presentation regarding color vision assessment by Optom. Naheel B. Ma'rouf


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Presentation Transcript

Definitions : 

Definitions Color vision: Is the capacity of an organism or machine to distinguish objects based on the wavelengths or frequencies of the light they reflect or omit. Color blindness or deficiency: A condition in which certain colors cant be distinguished due to absence or deficiency in color receptor cones.

Definitions : 

Definitions Hue Is the identification of color. Brightness Is the intensity of color. Saturation Is the purity of a color.

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Color vision is the function of 3 populations of cones. Tritan blue at 414-424nm. Deutran green522-539nm. Protan red 549-570nm. The principle of color vision

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-Short wavelengths causes the green receptor to fire. - As the wavelength gets longer and closer to 580 nm the red begins to fire, surpassing the green. The principle of color vision

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Therefore, color vision is the consequence of unequal stimulation of the 3 types of cones. In a specific ratio. Example : If you stimulate all 3 types of cones about equally the result is white or no color. Color wheel principle The principle of color vision

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Color vision abnormality :is either congenital or acquired. Congenital color vision defect: is equal and non progressive. more common in males than females. -X linked and almost red green. Abnormal color vision

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Acquired color vision defect -Is progressive or regressive. - Often involves loss of blue sense. -Visual acuity is affected. -Common cause is exposure to drugs or toxins as xanthopsia from cardiac glycosides. Abnormal color vision

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At any cone pigment may deficient, Or absent totally. Trichromatism (Normal sight) Which person can differentiate all colors. -All 3 cones although not necessary functioning perfectly. Anomalous trichomatism can differentiate all colors but on reduced or displaced sensitivities. - Protanomaly red displaced sensitivity. - Deutranomaly green displaced sensitivity. - Tritanomaly blue displaced sensitivity . Types

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Dichromatism absence of one cone - Tritanopia blue is missing (red ,green and present). - Deutranopia green is missing (red and blue are present) - Protanopia red is missing while blue and green are present. Monochromatism totally unable to dedifferentiate colors of equal brightness. Types

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Note: Patient with tritanopia confuse in yellow and blue orange and violet. - Most congenital color vision defects are trichromats and use abnormal proportions of 3 colors to match those in spectrum . Types

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This is what a normal person would see as the colours of the rainbow This is the same picture viewed by someone with protanopia. This is the same picture viewed by someone with deuteranopia How rainbow is seen? These are the colours of the rainbow and also what they would look like if you were colour blind

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This is the same picture viewed by someone with tritanopia This is the same picture viewed by someone with Monochromacy which Is full colour blindness How do we see rainbow?

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Pseudoisochromatic color confusion charts. Like Ishihara. Hue arrangement task Like Fransworth Munsell 100 hue test Farnsworth pand D 15,lanthony desaturated D15. Lantern detection tests Edridge green. All tests determines congenital and acquired disorders . Needs more investigations like anomaloscope. Types of Color Vision tests

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Notes for color vision testing - Use proper illumination (day light). - Explain test for the patient. - In screening for congenital diseased test is done binocularly and monocularly for acquired abnormality. - Patient should use his or her near correction. - Avoid tinted spectacles or contact lenses. How To Do Tests..!

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-Named by Dr shinobo Ishihara at Tokyo university. -Pseudoisochromatic color plates which are circles in multiple patterns. Ishihara Test

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The test consists of 25-30 plate in the complete group. - The first plate is for demonstration and malingerers. - Plates from 2-9 are transformation . - Plates from 10-17 are vanishing. - Plates from 18-21 are hidden . Procedure: - Test is done at 75 cm at day light at right angle of the visual plane. Ishihara Test

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Allow the patient to see just in 3 sec. If the subject is unable to read numbers on plates 1-17 traces with x endings are used. Recording -Write the number of correct attempted as 12/16 correct. Interpretations -Normal see them all except hidden digits(18-21). -Red green defect cant see vanishing plates(10-17) but apart of hidden and transforming. Ishihara Test

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-Plates (22-25) to distinguish deutrans and protans. -Purple blue plates are not seen by deutrans. -Red purple are not seen by protans. Ishihara Test

Ishihara Test : 

Ishihara Test

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Procedure - Test is done at 35 cm at day light at right angle of the visual plane. - It consists of 10 plates each contains four peripheral colored dots with one on the centre. - The patient is asked to select the peripheral that most closely matches the central one - Results are written as Top(T), Bottom (B),Right (R),Left (L) and score paper is present to analyze defect due to patient response. The City University test TCU

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- Most sensitive test for congenital and acquired but rarely used. - Consists of 85 hue caps not like named, are in 4 separate racks in each of 2 end caps are fixed while others are loose to be randomized by examiner. - The box is then closed ,turned upside-down ,then opened so that markers of the inside caps are visible. Fransworth- Munsell 100 hue test

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Recording -The findings are recorded in cumulative manner on circular chart . - Each of 3foerms of dichromatism is characterized by failure in specific meridian of the chart. Fransworth- Munsell 100 hue test

Protan result : 

Protan result - Test is similar to Farnsworth- Munsell100 hue test but with 15 caps used. - Test is done at 50 cm on a table. FransworthD 15

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Can detect the 3 types of color defects. Pseudoisochromatic Subset Book for Red/Green test . contains two demonstration plates, four screener plates, and 10 diagnostic series for a total of 16 plates. - Each of these plates has its own tab for easy and clean page selection. Harady –Rand-Ritter Hardy-Rand- Ritter(HRR)

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-The test also includes a set of instructions in English and a laminated copy of the score sheet. -The score sheet can then be copied directly onto the patient's record or copies can be made locally. A pad of score sheets is available separately. Hardy-Rand- Ritter(HRR)

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- The test is very similar to ishihara . Recording Place x on the missed plate and write the number of blue yellow ,red green defects If only plate no 4 is missed then repeat the plate. Interpretations Ignore mistakes on plate no 3and 6 because the are difficult and mostly missed. People over 60 fails the BY part with 2or more errors people less than 20 years old fails the BY 2 or more are missed. Standard pseudoisochromatic plates part 2 SPP-2

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