visual field and colour vision

?The entire area that can be “seen” by the subject
without movement of the head and with the eyes fixed on a single spot.
oThe area seen to the nasal side is called nasal field of vision and area seen to the lateral side is called the temporal field of vision.
•The small, circular, insensitive region in the retina where fibers of the optic nerve emerge from the eyeball. It has no rods or cones. Also called optic disk and physiological scotoma.
?It 15° to the temporal side of the visual field of each eye On the horizontal meridian.
1.Direct confrontation method (bed side method ( .
?Sit or stand in front of subject about 1 meter away.
?First both you and pt ..Should keep your eyes open.
?Test both lt and Rt fields at the same ime.
?Then the subject covers one eye and fixes his gaze on your eye. Bring your finger slowly into view from out of the subject view.
?The finger should be kept more than midway between you and subject.
? Each of upper and lower temporal, upper and lower nasal quadrant are tested separately.
»Subject looks with one eye toward a central spot in perimetry chart directly in front of eye then small dot of light is moved in all area of field of vision. The person indicates when the spot of light can be seen or not.
?Cone cells, or cones, are one of the two types of photoreceptor cells that are in the retina of the eye which are responsible for color vision .
?Cone cells are densely packed in the fovea centralis.
?In humans, there are three types of cones sensitive to three different spectra, resulting in trichromatic color vision.
?Trianopia = color blindness; refer to defect of red, green and blue cone system
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Objective
To differentiate between subjects with normal and abnormal color vision.
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Materials
1- Subjects.
2- Ishihara pseudo isochromatic plates(These are coloured spots forming numbers or pictures(.
?The color blindness is an inherited sex-linked recessive condition which occurs in 8% of male Caucasian population. The most common anomalies of color vision are various types of red-green deficiency.
?People with blue-yellow deficiency and total color blindness are rare. These abnormalities are due to abnormal gene on the X chromosome.