Zeiss Humphrey II-i series, Руководство пользователя

Страница: 26 / 580

Introduction & Instrument Setup
Humphrey Field Analyzer II-
i
series User Manual 2660021145640 A
1-18
Normal Versus Pathologic Fields
The visual field normally extends more than 90
º
temporally, 60
º
nasally and superiorly, and about
70
º
inferiorly. That means a person can potentially perceive stimuli within this range while staring at
a fixed point.
60º
90º
60º
70º
Superior
Inferior
Nasal
Te
m
po
ra
l
Figure 1.2 The Boundaries of the Normal Visual Field
A more comprehensive understanding of the normal field takes into account that visual sensitivity is
not constant (or equal) throughout the range. As previously stated, vision is most acute at the fovea
and decreases toward the periphery of the retina. It is easy to see why the visual field is often
expressed as a “hill of vision in a sea of darkness”.
Blind Spot
Fovea
Figure 1.3 The Normal Hill of Vision
Several factors affect the normal hill of vision, causing variations in its overall height and shape.
Among them are a patient’s age, ambient light, stimulus size, and stimulus duration. In general,
deviations from the normal hill of vision are viewed as visual field defects and caused by some
pathological change.
A visual field defect, or scotoma, is categorized as either relative or absolute. A relative defect is an
area that has depressed vision or less than normal sensitivity; an absolute defect is an area where
the perception of light is absent. The point at which the optic nerve enters the retina is referred to as
the blind spot, and is an example of an absolute scotoma.