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 order to determine which people may need special assistance because of their visual disabilities, various governmental jurisdictions have formulated more complex definitions referred to as legal blindness. In North America and most of Europe, legal blindness is defined as visual acuity (vision) of 20/200 (6/60) or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet (6.1 m) from an object to see it—with vision correction—with the same degree of read more [...]
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) of the eyelid near the roots of the eyelashes. The causes are seborrheic dermatitis (similar to dandruff) and, more rarely, infection by Staphylococcus bacteria.
Posterior blepharitis affects the posterior margin (back) of the eyelids, the part that makes contact with the eyes. This is caused by the oil glands present in this region. It is by far the most common type of blepharitis.
Seborrheic blepharitis, the most common type of blepharitis, is usually one part of the spectrum of seborrheic read more [...]
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
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 when the optical system is perfectly symmetrical. This is often referred to as a “monochromatic aberration”, because it occurs even for light of a single wavelength. This terminology may be misleading, however, as the amount of aberration can vary strongly with wavelength in an optical system.
The second form of astigmatism occurs when the optical system is not symmetric about the optical axis. This may be by design (as in the case of a cylindrical lens), or due to manufacturing error in the surfaces of the components or misalignment of the read more [...]
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 usually alleviates the problem.
On a computer, a CRT with a low refresh rate (less than 70 Hz) can cause similar problems because of the flickering image. Aging CRTs also often go slightly out of focus, and this can also cause eye strain. LCDs do not go out of focus and are less susceptable to visible flicker.
Causes of Asthenopia
Sometimes, asthenopia (aesthenopia) can be due to specific visual problems, such as uncorrected refraction errors or binocular vision problems like accommodative insufficiency or heterophoria.
Homeopathy Treatment for read more [...]
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 visual image. Detecting the condition in early childhood increases the chance of successful treatment.
While the colloquialism “lazy eye” is frequently used to refer to amblyopia, the term is inaccurate because there is no “laziness” of either the eye or the amblyope involved in the condition.
Amblyopia is a developmental problem in the brain, not an organic problem in the eye (although organic problems can induce amblyopia which persist after the organic problem has resolved). The part of the brain corresponding to the visual system from the affected eye is not read more [...]
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 retina. Another cause is the presence of emboli located in the ipsilateral (same side) internal carotid artery. It is a type of transient ischaemic attack (TIA). Those experiencing Amaurosis usually experience complete symptom abeyance within a few minutes. In a small minority of those who experience Amaurosis, stroke or vision loss has resulted. Diabetes, hypertension and smoking are factors known to increase the risks of suffering this condition. It also can be the result of surgical repair to the mitral valve, when very small emboli may break away from the site read more [...]