COLOR VISION Presented by GAURAV BAJPAI INDIRA GANDHI

COLOR VISION Presented by GAURAV BAJPAI INDIRA GANDHI INSTITUTE OF PARAMEDICAL SCIENCES, MUNSHIGANJ AMETHI

Color Vision • It is the ability of the eye to differentiate between different colors excited by light of different wavelengths • In our eyes (Retina) two types of light sensitive cell are formed - rods and cones • The rods are responsible for vision in low illumination (active at night)) and peripheral vision whereas the cones are responsible for color vision and central vision (active at day light). • (Rods and cones translate the incoming light into nervous impulses)

Cone type There are three types of cones § L-cones sense long wavelength (red light) – (64%) § M-cones sense medium wavelength (green light) – (32%) § S-cones sense short wavelength (blue light) – (2%) (When we see an object, light enters our eye and stimulates the cone cells, our brain interpret the signals from the cone cell and enable us to see the color of object)

Color Vision Deficiency (color blindness) It is a decreased ability to see color or differences in color under normal lighting conditions. Faulty or missing cones are responsible for color deficiency/blindness. (I. e. they cannot transmit the information to the optic nerve)

Causes of Color Vision Deficiency The two principal color defects are Congenital color defect Acquired color defect Congenital Color Defects: • The congenital color defects are inherited and without any other abnormalities. • The congenital color defects are non-pathological and are incurable • The defect is the same in each eye with regard to type and severity • The most common are red green defects. • These are more common in males than females Acquired Color Defects: • By injury - Damage to the eyes, nerves, brain • Diabetes, • Glaucoma • Macular degeneration • Chronic illness • Exposure to industrial toxins

Types of Color Vision (based on number of cone types) Trichromacy = Normal Color vision, has 3 cones (Anomalous Trichromacy = See all three primary colors. One color is seen weakly (reduced function in 1 cone)) Dichromacy = missing 1 cone Monochromacy = missing 2 cones Achromatopsia = missing all 3 cones (Anomalous=defective, anopia=absent)

Types of Dichromancy Protanopia = absence of red cones Protanomaly = weakness of red cones Deuteranopia = absence of green cones Deuteranomaly = weakness of green cones Tritanopia = absence of blue cones Tritanomaly - weakness of blue cones

“Normal” Color Vision

Protanopia

Deuteranopia

Tritanopia

Tests for color vision Ishihara test (Pseudo-isochromatic chart test) – § This is the most common test for the detection of color deficiency. § Dr. Shinobu Ishihara is the inventor of this test. § Ishihara test is used to detect mainly red-green color blindness. § Ishihara chart comes in three different forms: 16 plates, 24 plates and 38 plates. § The plates have various dots which forms numbers or spiral lines or connector shapes in different colors. § Color blind person cannot detect the numbers or differences in lines. § Plates should be held at 75 cm under good illumination § Patients should be answered in not more than 3 sec. § Pathway tracing should be completed within 10 sec.

Ishihara test – Cont. (Assessment of the reading of plates § 1 to 15 -- normality of color vision § If 13 or more plates are read correctly, the color vision is regarded as normal. § If only 9 or less than 9 plates are read correctly, the color vision was regarded as red green deficient. § The plates 16 and 17 are used to differentiate protan and deutan types of color vision efficiency. ) § If the subject is unable to read numerals, plates 26 -38 are used and the winding lines between the two X’s are traced with the brush. Each tracing should be completed within ten seconds)

Other charts for color vision – City university color vision test Nagel’s Anomaloscope The Lantern test Treatment – There is currently no treatment. Color filters or contact lenses can be used to increase the brightness between some colors For acquired color vision deficiency, after treating the cause, vision may return to normal.