Blindness is the condition of lacking visual perception due to physiological or neurological factors. Various scales have been developed to describe the extent of vision loss and define “blindness.” Total blindness is the complete lack of form and visual light perception and is clinically recorded as “NLP,” an abbreviation for “no light perception.” Blindness is frequently used to describe severe visual impairment with residual vision. Those described as having only “light perception” have no more sight than the ability to tell light from dark. A person with only “light projection” can tell the general direction of a light source. In [...]
Blepharitis (pronounced /bl?f?r?a?t?s/) is an ocular disease characterized by inflammation of the eyelid margins. Blepharitis may cause redness of the eyes, itching and irritation of the eyelids in one or both eyes. Its appearance is often confused with conjunctivitis and due to its recurring nature it is the most common cause of “recurrent conjunctivitis” in older people. It is also often mistaken for “dry eye” by patients due to the gritty sensation that may occur, however lubricating drops do little to improve the condition. Classification of Blepharitis There are two types of blepharitis: Anterior blepharitis affects the anterior margin (front) [...]
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- (a-) meaning “without” and στ?γμα (stigma), “a mark, spot, puncture”. Forms of astigmatism Astigmatism There are two distinct forms of astigmatism. The first is a third-order aberration, which occurs for objects (or parts of objects) away from the optical axis. This form of aberration occurs even [...]
Asthenopia (aesthenopia) or eye strain is an ophthalmological condition that manifests itself through nonspecific symptoms such as fatigue, red eyes, eye strain, pain in or around the eyes, blurred vision, headache and occasional double vision. Symptoms often occur after reading, computer work, or other activities that involve tedious visual tasks. When concentrating on a visually intense task, such as continuously focusing on a book or computer monitor, the inner eye muscles may tighten, which can cause the eyes to get irritated, dry, and uncomfortable. Giving the eyes a chance to focus on a distant object at least once an hour [...]
Amblyopia, otherwise known as lazy eye, is a disorder of the visual system that is characterized by poor or indistinct vision in an eye that is otherwise physically normal, or out of proportion to associated structural abnormalities. It has been estimated to affect 1–5% of the population. The problem is caused by either no transmission or poor transmission of the visual image to the brain for a sustained period of dysfunction or during early childhood. Amblyopia normally only affects one eye, but it is possible to be amblyopic in both eyes if both are similarly deprived of a good, clear [...]
Amaurosis (Greek meaning darkening, dark, or obscure) is vision loss or weakness that occurs without an apparent lesion affecting the eye . It may result from either a medical condition or from excess acceleration, as in flight. The term is the same as the Latin gutta serena.Types of Amaurosis Leber’s congenital amaurosis is an inherited disease resulting in optic atrophy and secondary severe vision loss or blindness. It was first described by Theodore Leber in the 19th century.Amaurosis fugax (Latin: fugax meaning fugitive) is a temporary loss of vision in one eye caused by decreased blood flow (ischemia) to the [...]
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