Peripheral vision loss (PVL) is the reduction or complete inability to see objects outside the direct line of sight, often described as tunnel vision. While central vision allows for sharp focus and detail recognition, peripheral vision is the broad awareness that detects motion and spatial surroundings. This side vision is important for daily safety and function, aiding in balance, coordination, and preventing accidents. A loss of this wide field of view makes simple tasks such as driving, navigating crowded areas, or seeing well at night significantly more difficult. Peripheral vision loss is a symptom, not a disease itself, and it signals damage to some part of the complex visual pathway. This damage can originate in the eye’s internal structures, the light-sensing tissue at the back of the eye, or the brain’s processing centers.
Damage Caused by Eye Pressure
The most common cause of permanent peripheral vision loss is glaucoma, a group of conditions that damages the optic nerve. This nerve transmits visual information from the eye to the brain. Glaucoma often begins when the intraocular pressure (IOP) inside the eye becomes too high.
This elevated pressure happens when the eye’s natural fluid, called the aqueous humor, cannot drain properly from the anterior chamber. In primary open-angle glaucoma, the drainage angle is open, but the microscopic meshwork is partially blocked, leading to a slow pressure increase. This chronic pressure steadily compresses the nerve fibers where they exit the back of the eye.
The initial fibers damaged are those responsible for peripheral vision, which is why the condition progresses subtly. Angle-closure glaucoma, a less common form, involves a sudden rise in IOP because the iris blocks the drainage angle entirely. The damage to the optic nerve fibers creates blind spots that narrow the visual field. Because this process is painless and affects the edges of vision first, a person may not notice the loss until significant vision is already gone. Regular eye examinations are necessary to measure IOP and check for early signs of optic nerve damage.
Issues Originating in the Retina
The retina, the light-sensitive layer of tissue lining the back of the eye, is a common site for damage that causes peripheral vision loss. Photoreceptor cells in the retina capture light and send signals to the optic nerve. Damage to this tissue can result from sudden physical trauma or long-term degenerative disease processes.
A retinal detachment occurs when the retina separates from its underlying supportive tissue and blood supply. When the retina is pulled away, the light-sensing cells are deprived of oxygen and nutrients, leading to a sudden, acute loss of vision. Patients often describe this vision loss as a shadow or curtain moving across their field of view, frequently starting in the periphery.
Retinitis Pigmentosa (RP) is a group of inherited disorders that cause the slow degeneration of photoreceptor cells. The rod cells, which are concentrated in the outer retina and are responsible for peripheral and night vision, are affected first. As these cells progressively die, patients first experience difficulty seeing in low light, known as night blindness, followed by a gradual inward constriction of the side vision.
Diabetic Retinopathy, a complication of diabetes, damages the retina by affecting the blood vessels. High blood sugar levels weaken the vessel walls, causing them to leak fluid, swell, or close off entirely. In advanced stages, the eye may grow new, abnormal blood vessels that are fragile and prone to bleeding and scarring. This leads to blockages and distortion in the peripheral visual field, creating blank spots.
Vision Loss Stemming from the Brain
Peripheral vision loss can occur even when the eyes and optic nerve are healthy, indicating a problem with the brain’s ability to process visual information. Visual signals travel along complex pathways to the visual cortex, primarily located in the occipital lobe at the back of the brain. Damage to these pathways or the cortex itself can result in specific patterns of vision loss.
Strokes, caused by a blockage or rupture of a blood vessel, interrupt blood flow to a specific region of the brain. If a stroke affects the visual processing centers, it can cause homonymous hemianopia, a loss of the same half of the visual field in both eyes. For instance, a person might lose the entire right side of their visual world, even though their eyes are still transmitting the full image.
Brain tumors or other mass lesions can also cause peripheral vision loss by compressing the visual pathways. The specific pattern of vision loss depends on the tumor’s size and location along the pathway. Ocular migraines present a temporary cause, involving visual disturbances called auras that may include a temporary loss of peripheral vision.