Vision loss or visual loss is the absence of vision Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision . The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in where it existed before, which can happen either acutely This adjective is part of the definition of several diseases and is, therefore, incorporated in their name, for instance, severe acute respiratory syndrome, acute leukemia (i.e. abruptly) or chronically In medicine, a chronic disease is a disease that is long-lasting or recurrent. The term chronic describes the course of the disease, or its rate of onset and development. A chronic course is distinguished from a recurrent course; recurrent diseases relapse repeatedly, with periods of remission in between. As an adjective, chronic can refer to a (i.e. over a long period of time).
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Ranges of vision loss
Various scales have been developed to describe the extent of vision and vision loss based on visual acuity Visual acuity is acuteness or clearness of vision, especially for vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain.[1] Early editions of the World Health Organization The World Health Organization is a specialized agency of the United Nations (UN) that acts as a coordinating authority on international public health. Established on 7 April 1948, and headquartered in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health Organization, which had been an agency of the's ICD The International Statistical Classification of Diseases and Related Health Problems provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease. Under this system, every health condition can be assigned to a unique category and given a described a simple distinction between "legally sighted" and "legally blind".[1] The ICD-9 released in 1979 introduced the smallest continuous scale which consisted of three tiers: normal vision, low vision Low vision is a subspecialty within the professions of optometry and ophthalmology dealing with individuals who have reduced vision even when using the best possible spectacle or contact lens correction available. It can be a result of either congenital disease or acquired factors (such as in some forms of optic atrophy), and blindness Blindness is the condition of lacking visual perception due to physiological or neurological factors.[2]
Acute visual loss
Acute visual loss may be dramatic in presentation. It may be caused by media opacities, retinal The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These disease, optic nerve The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during embryonic development. Consequently, the fibres are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system disease, visual pathway disorders, or functional disorders, or it may be in fact an acute discovery of chronic visual loss.
Media opacity
Opacities of the clear refractive media of the eye Eyes are organs that detect light, and convert it to electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement. In higher organisms complex neural pathways exist that connect the eye, via the optic nerve to the visual cortex and other areas of the brain. Complex optical systems with resolving such as the cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. While the cornea contributes most of the eye', anterior chamber, lens The lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the, and vitreous humor The vitreous humour or vitreous humor (US spelling) is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. It is often referred to as the vitreous body or simply "the vitreous" may cause acute visual loss as manifested by blurry vision or reduced visual acuity Visual acuity is acuteness or clearness of vision, especially for vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain. While pupillary reflexes Accommodation and vergence are also known as the "near response", while inhibition of the ciliary muscle is also known as the "far response" may be affected, these conditions generally do not cause a relative afferent pupillary defect.
Causes of media opacity include corneal edema, hyphema Hyphema is blood in the front (anterior) chamber of the eye. It may appear as a reddish tinge, or it may appear as a small pool of blood at the bottom of the iris or in the cornea, cataract A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light. Early in the development of age-related cataract the power of the lens may be increased, causing near-sightedness , and the gradual yellowing and opacification of the and vitreous hemorrhage.
Retinal disease
Retinal diseases may cause sudden visual loss. Because the retina is being affected, there is usually a concomitant relative afferent pupillary defect. Conditions that affect or destroy the retina include retinal detachment Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blindness. It is a medical emergency; macular The macula or macula lutea is an oval-shaped highly pigmented yellow spot near the center of the retina of the human eye. It has a diameter of around 5 mm and is often histologically defined as having two or more layers of ganglion cells. Near its center is the fovea, a small pit that contains the largest concentration of cone cells in the eye and disease (e.g., macular degeneration Age related macular degeneration is a medical condition which usually affects older adults that results in a loss of vision in the center of the visual field because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of visual impairment in older adults (>50 years). Macular degeneration can make it); and retinal vascular occlusions Ocular ischemic syndrome is the constellation of ocular signs and symptoms secondary to severe, chronic arterial hypoperfusion to the eye. Amaurosis fugax is a form of acute vision loss caused by reduced blood flow to the eye that may be a warning sign of an impending stroke. Consequently, those with transient blurring of vision are advised to, the most important of which is central retinal artery occlusion.
Optic nerve disease
Diseases which affect the optic nerve may cause acute visual loss. Signs A medical sign is an objective indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient include an abnormal pupillary reflex, with an afferent pupillary defect when the optic nerve disease is unilateral. It can also be caused by strobe light Strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. It is one of a number of devices that can be used as a stroboscope. The word originated from the Greek strobos, meaning "act of whirling.".
The optic nerve The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during embryonic development. Consequently, the fibres are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system can be affected by many diseases including optic neuritis Optic neuritis is the inflammation of the optic nerve that may cause a complete or partial loss of vision, retrobulbar neuritis Optic neuritis is the inflammation of the optic nerve that may cause a complete or partial loss of vision, papillitis Papillitis is the term for a specific type of optic neuritis. If ocular inflammation is restricted to the optic nerve head the condition is called papillitis , and if it is located in the orbital portion of the nerve it is called retrobulbar optic neuritis (or orbital optic neuritis), papilledema Papilledema is optic disc swelling that is caused by increased intracranial pressure. The swelling is usually bilateral but can be unilateral which is extremely rare and can occur over a period of hours to weeks, glaucoma Glaucoma is a disease in which the optic nerve is damaged, leading to progressive, irreversible loss of vision. It is often, but not always, associated with increased pressure of the fluid in the eye, ischemic optic neuropathy Ischemic optic neuropathy is the loss of structure and function of a portion of the optic nerve due to obstruction of blood flow to the nerve (i.e. ischemia). ION is typically classified as either anterior ischemic optic neuropathy or posterior ischemic optic neuropathy according to the part of the optic nerve that is affected, and giant cell arteritis Giant cell arteritis is an inflammatory disease of blood vessels (most commonly large and medium arteries of the head). It is a form of vasculitis.
Hypoxia
The eye is very sensitive to restriction of its supply of oxygen. A dimming of vision (a brownout or greyout) accompanied by loss of peripheral perception may result from low blood pressure, shock Circulatory shock, commonly known simply as shock, is a serious, life-threatening medical condition characterized by a decrease in tissue perfusion to a point at which it is inadequate to meet cellular metabolic needs. As the blood carries oxygen and nutrients around the body, reduced flow hinders the delivery of these components to the tissues,, g-LOC G-LOC, pronounced 'GEE-lock', is the abbreviation of G-force induced Loss Of Consciousness, a term generally used in aerospace physiology to describe a loss of consciousness occurring from excessive and sustained g-forces draining blood away from the brain causing cerebral hypoxia. The condition is most likely to affect pilots of high performance (an aviation related problem) or simply standing up suddenly, especially if sick or otherwise infirm. Vision usually returns readily once the conditions restricting blood flow are lifted.
Visual pathway disorder
Visual pathway disorders are any problems that may impede the visual pathway The visual system is the part of the central nervous system which enables organisms to see. It interprets the information from visible light to build a representation of the world surrounding the body. The visual system accomplishes a number of complex tasks, including the reception of light and the formation of monocular representations; the. Rarely, acute visual loss is caused by homonymous hemianopia and, more rarely, cortical blindness Cortical blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the visual area in the brain's occipital cortex.
Also traumatic causes can lead to Acute Vision Loss.
Functional disorder
The term functional disorder is now used where hysterical Hysteria, in its colloquial use, describes a state of mind, one of unmanageable fear or emotional excesses. The fear is often caused by multiple events in one's past that involved some sort of severe conflict; the fear can be centered on a body part or most commonly on an imagined problem with that body part. Disease is a common complaint; see and malingering Malingering is a medical term that refers to fabricating or exaggerating the symptoms of mental or physical disorders for a variety of "secondary gain" motives, which may include financial compensation ; avoiding school, work or military service; obtaining drugs; getting lighter criminal sentences; or simply to attract attention or were historically used. This shift recognizes the inherent inability of the physician to identify the subjective experience of a patient (and thus whether that patient can truly see or not).
See also
- Blindness Blindness is the condition of lacking visual perception due to physiological or neurological factors
- Eye examination An eye examination is a battery of tests performed by an ophthalmologist, optometrist, or orthoptist assessing vision and ability to focus on and discern objects, as well as other tests and examinations pertaining to the eyes. All people should have periodic and thorough eye examinations as part of routine primary care, especially since many eye
- Low vision Low vision is a subspecialty within the professions of optometry and ophthalmology dealing with individuals who have reduced vision even when using the best possible spectacle or contact lens correction available. It can be a result of either congenital disease or acquired factors (such as in some forms of optic atrophy)
- Visual acuity Visual acuity is acuteness or clearness of vision, especially for vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain
- Visual impairment Visual impairment is vision loss (of a person) to such a degree as to qualify as an additional support need through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive correction, medication, or surgery. This
- Vitreous Hemorrhage
References
- ^ a b International Council of Ophthalmology. "International Standards: Visual Standards — Aspects and Ranges of Vision Loss with Emphasis on Popular Surveys." April 2002.
- ^ World Health Organization. International Classification of Diseases, 9th Revision (ICD-9), World Health Organization, Geneva, 1977.
External links
- AFB Senior Site Expanding possibilities for people with vision loss
- CDC's "Learn the Signs. Act Early." campaign - Information for parents on early childhood development and developmental disabilities such as vision loss
- Living with Vision Loss - American Foundation for the Blind
- VisionAWARE - Self Help for Vision Loss Independence for adults with low vision
- Living with sight loss (RNIB)
- International Standards: "Visual Standards - Aspects and Ranges of Vision Loss" - International Council of Ophthalmology
- Catalan Association for the Blind and Visually Impaired
- LowVision.com Low Vision online informational resource center and referral hub
- Center for the Partially Sighted Low Vision Information and Resources
Categories: Blindness Categories: Accessibility | Ophthalmology | Communication disorders | Visual system | Disability | Ophthalmology Categories: Medical specialties | Surgical specialties | Eye | Vision
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