II Optic Nerve - Visual Fields
A. Peripheral visual field
(a) wiggling fingers
(b) counting fingers
(c) white pin
B. Central visual field
(a) red pin
- visual fields are assessed by confrontation , i.e.
the examiner compares the patients visual field
to their own and assumes that theirs is normal.
- first test each eye separately.
- test both eyes together with wiggling fingers.
- the examiner places himself approximately 1 meter
away from the patient and advises the patient to look
directly at the examiners eye for monocular
testing or nose for binocular testing. The test object
(either a wiggling finger, one or two fingers, or
a white pin head) is presented equidistant from the
patients and examiners eye and the patient
is asked either to state the number of fingers or
say "yes" when they first see a moving target.
- for central vision (the 20 degrees on either side
of the vertical meridian) a red pin is used. The patient
is instructed to state when they see the pin as red.
A red pin is also used to map the blind spot. Vision
in the center of the visual field is more detailed
than in the peripheral areas. This is because of both
the structure of the retina and the connections of
its neurons. Light rays from the center of the visual
field are focused on the macula in the center of the
retina. In the macula, the proportion of cones to
rods is high. Cones are important for color vision.
- the normal monocular visual field extends approximately
100 degrees laterally, 60 degrees medially, 60 degrees
superiorly and 75 degrees inferiorly. It is divided
into nasal and temporal halves and superior and inferior
altitudinal halves. A blind spot is located 15 degrees
temporal to fixation and just below the horizontal