The field of vision is the entire area a person can see while their gaze is fixed on a single point without moving their eyes. This encompasses everything from the sharp, focused center to the edges of what can be detected. Human sight relies on both high-resolution direct sight and the broader surrounding area.
The Dimensions of Normal Vision
The normal field of vision is measured in degrees away from the central point of fixation. When using a single eye (monocular vision), the field is an irregular oval shape with varying limits. A healthy eye typically extends approximately 60 degrees inward toward the nose (the nasal field) and much farther outward, reaching about 90 to 100 degrees toward the ear (the temporal field). This difference is due to the anatomical obstruction of the nose and brow ridge. Vertically, the monocular field extends roughly 60 to 70 degrees above the center and 70 to 80 degrees below the center.
The combined visual field (binocular vision) results from the overlap of both monocular fields. This creates a much wider horizontal perception, often spanning a total of about 190 to 200 degrees. The central overlap area is approximately 120 degrees wide and allows for stereopsis, or the perception of depth. The total vertical span is more limited, covering roughly 130 degrees from top to bottom.
Peripheral Vision and the Blind Spot
The total field of vision is divided into central and peripheral components. Central vision, corresponding to the macula and fovea, is responsible for fine detail, color perception, and reading acuity. Peripheral vision is the surrounding area, which is less acute but plays a substantial role in environmental awareness. It is highly effective at detecting motion, which is crucial for orientation and reacting to objects entering the side view. This vision relies heavily on rod photoreceptors, which function well in low light.
Within this broad field, there is a distinct, non-seeing area known as the physiological blind spot. This natural blind spot is located about 15 degrees temporal to the center of fixation and corresponds to the optic disc. The optic disc is the point where the optic nerve and blood vessels exit the eye, meaning there are no light-sensing photoreceptors there. We do not notice this gap because the brain fills in the missing visual information. Additionally, the blind spot of one eye falls within the functional visual field of the other eye, ensuring a complete binocular image.
How Field of Vision is Tested
Eye care professionals use specialized procedures to determine if a person’s vision falls within the expected normal range. The most common method is perimetry, which systematically maps the sensitivity of the entire field of vision.
Automated Static Perimetry
This prevalent technique requires a patient to fix their gaze on a central target while brief, dim lights appear at various locations. The patient presses a button each time a light is seen, and a computer records the sensitivity threshold at different points.
Kinetic Perimetry
In this method, a light target of a specific size and brightness is moved from the non-seeing periphery toward the center until the patient first detects it. This technique maps the outer boundary of the field, defining lines called isopters.
Simpler screening methods are also used, such as the confrontation visual field test, where the examiner compares the patient’s field to their own. The Amsler grid, a square pattern of intersecting lines, is used to test the central 10 to 20 degrees of vision. Distortion or missing areas on the grid can indicate a problem in the macula.
Signs of Abnormal Field of Vision
Patterns of visual field loss are described using specific terminology. A scotoma is a localized blind spot or area of reduced vision that is not the physiological blind spot. Scotomas vary widely in size and shape, such as a central scotoma affecting the primary focus point or a paracentral scotoma located near the center.
A more extensive loss pattern is hemianopia, which describes the loss of vision in half of the visual field. This loss is often sharply defined and respects the vertical midline. Quadrantanopia is a similar pattern, but the loss is limited to only one quarter of the visual field.
Another identifiable pattern is concentric constriction, often referred to as tunnel vision, where the peripheral field gradually shrinks inward. This results in a narrow, circular field of view, making it difficult to detect objects outside of the central focus. Identifying these specific patterns of loss is a crucial step in diagnosing the underlying condition.