The human visual field refers to the entire area an individual can see without moving their head or eyes. It encompasses both direct focus and peripheral awareness. The “degrees” describe this area using angular measurements. This fundamental sensory input allows for continuous perception and navigation of surroundings.
Dimensions of the Human Visual Field
The human visual field is not a perfect circle; its dimensions vary horizontally and vertically due to anatomical constraints. A healthy human visual field spans approximately 160 to 180 degrees horizontally when both eyes are open, with overlapping vision contributing to a broader total span.
The vertical range is narrower, extending between 120 to 135 degrees, influenced by structures like the brow ridge and cheekbones. Within these dimensions, vision is divided into central vision, providing sharp detail within about 30 to 60 degrees, and peripheral vision, detecting motion and shapes at the edges. The macula, responsible for central vision, corresponds to about 17 degrees of the visual field.
How Visual Field is Measured
Visual field degrees are assessed through perimetry, which measures sensitivity to light across the field of vision. Automated perimetry is a common method in clinics. During this test, an individual looks at a central target on a screen with one eye covered.
Light spots appear at different locations. The patient presses a button when detected. This process maps the extent and sensitivity of vision, identifying areas where light perception is reduced or absent, and can test up to 120 degrees of the visual field.
Conditions That Affect Visual Field
Several medical conditions can lead to changes or loss in visual field degrees, impacting an individual’s ability to see fully. Glaucoma, a disease affecting the optic nerve, can cause visual field defects, often leading to “tunnel vision” where peripheral sight is gradually lost. Early changes frequently occur within the central visual field.
Stroke can result in hemianopia, a condition where vision is lost in one half of the visual field in both eyes due to damage to the brain’s visual pathways. Retinal detachment, where the retina pulls away, can also cause areas of vision loss. Optic nerve damage, such as from optic neuritis or atrophy, disrupts visual information to the brain, leading to field defects. Brain tumors, particularly those pressing on the optic nerve, optic chiasm, or occipital lobe, can cause various vision problems, including blurred vision, double vision, or blind spots, and can lead to gradual or peripheral vision loss.
Living with Visual Field Changes
Reduced visual field degrees can impact daily activities, necessitating adaptations. Driving becomes difficult, especially if both eyes are affected. Activities requiring broad visual awareness, like walking in crowded areas or navigating unfamiliar spaces, may also pose challenges. Reading can also be affected, as eyes may need smaller, more repetitive movements to compensate for missing information.
Various strategies and assistive devices are available to help individuals adapt. Visual rehabilitation, including visual therapy, can train individuals to scan their environment more effectively to compensate for lost vision. Low vision aids, such as magnifying glasses, and electronic devices with text-to-speech or high-contrast displays, can enhance remaining vision. Simple home modifications like reducing clutter, using contrasting colors for objects, and consistent placement of items can improve safety and independence.