Visual field

Practical medical physiology Visual field
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12- Visual field
Introduction:
The visual field of each eye is the portion of the external world visible out of eye
when the eye is directed forward. Theoretically, it should be circle, but actually it is
cutoff medially by the nose and superiorly by the roof of the orbit. The 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.
Testing visual fields assesses the function of the peripheral and central retina, the
optic pathways and the cortex. Visual fields can be estimated quickly by the
method of confrontation or measured accurately using perimeters. Red-hat pin is
particularly useful object for detecting scotomas.
Objective:
To examine visual field of the eyes.
Materials and instruments:
Confrontational test or Perimeter.
Methods:
1. Confrontational test (figure 12-1):
? Sit directly opposite and facing the patient.
? Examine each eye separately first.
? Ask the subject to cover one eye and look at the examiner’s opposite eye.
? Examine the outer aspect of the visual fields with a moving finger or
preferably with a red-hat pin.
? Bring the finger or the red-hat pin into the field of vision. Approach from the
periphery at several points on the circumference of the upper and lower,
nasal and temporal quadrants of visual fields
? Ask the patient to respond as soon as the test object is observed.
? Test for visual inattention by asking subject to report when fingertip is
moved on one or both sides simultaneously.
Figure 12-1: confrontation testPractical medical physiology Visual field
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2- Perimeter: The chart of field of vision perimetry is visual area seen by an eye at
given instant. Subject looks with one eye toward a central spot directly in front of
eye then small dots of light are flashed in all area of field of vision. The person
indicates when the spot of light can be seen or not or sometimes he is asked to
identify the number of flash lights. The field of vision for the left eye is then plotted
as shown in Figure 12-2
Figure 12-2. Perimeter (top) and perimetry chart (buttom).Practical medical physiology Visual field
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Common abnormalities of visual fields (Figure 12-3):
Visual field defect - a portion of the visual field is missing
Scotoma - this is a type of visual field defect. It is a defect surrounded by normal
visual field.
Hemianopia - a binocular visual defect in each eye s hemifield.
Central visual fields defect can occur in age-related macular degeneration and optic
neuropathy. Peripheral defects can occur in glaucoma and retinal detachment.
Figure 12-3 Visual field abnormalities by the anatomical location of the lesion of the
optic pathway.