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 [...]
Addison’s disease (also known as chronic adrenal insufficiency, hypocortisolism or hypocorticism) is a rare endocrine disorder in which the adrenal gland produces insufficient amounts of steroid hormones (glucocorticoids and often mineralocorticoids). It may develop in children as well as adults, and may occur as the result of a large number of underlying causes. The condition is named after Dr Thomas Addison, the British physician who first described the condition in his 1855 publication On the Constitutional and Local Effects of Disease of the Suprarenal Capsules. The adjective “Addisonian” is used for features of the condition, as well as patients with Addison’s disease.
The condition is generally diagnosed with blood tests, medical imaging and additional investigations. Treatment involves replacement of the hormones (oral hydrocortisone and fludrocortisone). If the disease is caused by an underlying problem, it may be possible to address. Regular follow-up and monitoring for other health problems is necessary.
Signs and symptoms of Addison’s disease
The symptoms of Addison’s disease develop insidiously, and it may take some time to be recognized. read more [...]
Ascariasis is a human disease caused by the parasitic roundworm Ascaris lumbricoides. Perhaps as many as one quarter of the world’s people are infected, and ascariasis is particularly prevalent in tropical regions and in areas of poor hygiene. Other species of the genus Ascaris are parasitic and can cause disease in domestic animals.
Infection occurs through ingestion of food contaminated with feces containing Ascaris eggs. The larvae hatch, burrow through the intestine, reach the lungs, and finally migrate up the respiratory tract. From there they are then reswallowed and mature in the intestine, growing up to 30 cm (12 in.) in length and anchoring themselves to the intestinal wall.
Infections are usually asymptomatic, especially if the number of worms is small. They may however be accompanied by inflammation, fever, and diarrhea, and serious problems may develop if the worms migrate to other parts of the body.
Roughly 1.5 billion individuals are infected with this worm, primarily in Africa and Asia. Ascariasis is endemic in the United States including Gulf Coast; in Nigeria and in Southeast Asia. One study indicated that the prevalence of ascariasis in read more [...]
Acromegaly (from Greek akros “extreme” or “extremities” and megalos “large” – extremities enlargement) is a syndrome that results when the pituitary gland produces excess growth hormone (hGH) after epiphyseal plate closure. A number of disorders may be affecting the pituitary to create this circumstance, although most commonly it involves a GH producing tumor derived from a distinct type of cells (somatotrophs) and called pituitary adenoma.
Acromegaly most commonly affects adults in middle age, and can result in severe disfigurement, serious complicating conditions, and premature death if unchecked. Because of its insidious pathogenesis and slow progression, the disease is hard to diagnose in the early stages and is frequently missed for many years, when changes in external features, especially of the face, become noticeable.
Acromegaly is often also associated with gigantism.
Symptoms of Acromegaly
Features that result from high level of hGH or expanding tumor include:
Soft tissue swelling visibly resulting in enlargement of the hands, feet, nose, lips and ears, and a general thickening of the skin
Soft tissue swelling of internal organs, notably read more [...]
Hypothyroidism is the disease state in humans and animals caused by insufficient production of thyroid hormone by the thyroid gland. Cretinism is a form of hypothyroidism found in infants.Causes of Hypothyroidism
About three percent of the general population is hypothyroid. Factors such as iodine deficiency or exposure to Iodine-131 (I-131) can increase that risk. There are a number of causes for overt hypothyroidism. Historically, and still in many developing countries, iodine deficiency is the most common cause of hypothyroidism worldwide. In iodine-replete individuals, hypothyroidism is mostly caused by Hashimoto’s thyroiditis, or by a lack of the thyroid gland or a deficiency of hormones from either the hypothalamus or the pituitary.Hypothyroidism can result from postpartum thyroiditis, a condition that affects about 5% of all women within a year after giving birth. The first phase is typically hyperthyroidism. Then, the thyroid either returns to normal or a woman develops hypothyroidism. Of those women who experience hypothyroidism associated with postpartum thyroiditis, one in five will develop permanent hypothyroidism requiring life-long treatment.Hypothyroidism can read more [...]