Vision occurs when light from all angles of the visual fields hit the retina, the photosensitive lining of the back of the eye. However, in some cases the light from the periphery (the sides) is not seen, resulting in tunnel vision. Specifically, tunnel vision is a visual field defect where peripheral (side) vision is lost while keeping visual acuity in the central regions. If the peripheral vision is slowly lost over a period of time, a person may not realize that he or she has tunnel vision. That is why it is important to have vision checked every year by an optometrist or ophthalmologist. Glaucoma is one of the many causes of tunnel vision, which becomes more prevalent in persons over the age of 40. Glaucoma is a severe condition that can lead to blindness if left untreated.
Causes, Signs, and Symptoms
Tunnel vision can be a result of damage to the optic nerve (cranial nerve II, which is the primary nerve used for sight and connects the eyes to the brain), the retina, or the occipital lobe (part of the brain that processes visual input). When the damage is to the optic nerve it is called optic neuropathy. A specific type of optic neuropathy is optic neuritis, which is the inflammation of the optic nerve. It can occur at any length of the optic nerve and its cause is unknown. Scientists have suggested that optic neuritis may be a type of autoimmune disorder, where the body’s immune system abnormally attacks itself.
Other noninflammatory causes of optic neuropathy may include glaucoma, which is associated with increased pressure within the eye; reduced blood flow to the eye; neurological diseases such as diabetes; tumors along the optic nerve; deficiencies in nutrition; and excessive tobacco or alcohol use, just to list a few. Since there are several causes of tunnel vision, this entry will only discuss the most common causes: cataracts, glaucoma, and retinitis pigmentosa (a degenerative eye disease that damages the retina).
Cataracts are a clouding of the lens within the eye. This clouding decreases normal vision as if a film were over the eye. Cataracts increase in probability as a person ages, but some infants can be born with cataracts (congenital cataracts). Cataracts are the most common cause of blindness and can be surgically corrected.
The term glaucoma refers to several conditions that cause damage to the optic nerve. It is a slow but steady loss of peripheral vision and can lead to blindness if not treated. The most common type of glaucoma is an abnormal increase in eye pressure, called intraocular pressure. This may happen when too much fluid is produced within the eye or if the natural drainage (outflow channels called trabecular meshwork) of this fluid is blocked. Glaucoma may also occur with normal eye pressure but there is reduced blood flow to the optic nerve. Glaucoma must be treated as soon as possible to reduce the chances of permanent blindness.
Finally, retinitis pigmentosa is a rare degenerative disease that is first identified when a person complains of night blindness. This tends to be followed by several years or even decades later of slow peripheral tunnel vision loss. This vision loss is caused by the death of photoreceptors (rods and cones) in the retina. Since these neurons are unable to regenerate, retinitis pigmentosa, an inherited disease, affects both eyes and often leads to blindness.
It is very important to see a doctor as soon as possible if a person is experiencing tunnel vision. As in most cases, treatment for tunnel vision depends on the underlying cause. If glaucoma is detected in the early stages, medical intervention can stop the loss of peripheral vision altogether. Glaucoma is usually treated with eye drops, lasers, and/or surgery to prevent further loss of vision. Additionally, vitamin A derivatives may be beneficial in improving retinal degenerative diseases such as retinitis pigmentosa.
Patricia A. Bloomquist
See also: Optic Nerve; Retina; Visual Fields; Visual Perception; Visual System
Davis, Jennifer C., Heather McNeill, Michael Wasdell, Susan Chunick, & Stirling Bryan. (2012). Focusing both eyes on health outcomes: Revisiting cataract surgery. BMC Geriatrics, 12, 50.
National Eye Institute. (2014). Facts about retinitis pigmentosa. Retrieved from http://www.nei.nih.gov/health/pigmentosa/pigmentosa_facts.asp
Perusek, Lindsay, & Tadao Maeda. (2013). Vitamin A derivatives as treatment options for retinal degenerative diseases. Nutrients, 5(7), 2646—2666.