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Tear Break-up Time
Tear break-up time (TBUT) also known as tear film break-up time (TFBUT) is the time taken for the first dry spot to appear on the cornea after a complete blink. TFBUT measurement is an easy and fast method used to assess the stability of tear film. It is a standard diagnostic procedure in the dry eye clinics. The volume of tear in the eye depends on two factors, drainage through the lacrimal passages and evaporation. Factors like decreased tear production, increased evaporation rate, tearfilm instability, tear hyperosmolarity, inflammations, ocular surface damages etc. can cause dryness to the eyes. TBUT test was first described by Norn MS, and then revised by Lemp and Holly. The conventional and most common TBUT measurement method is using slit lamp and sodium fluorescein. Noninvasive instruments (Oculus Keratograph 5M, Germany; K5) are used for automatic non-invasive tear breakup time (NIBUT) measurements. In non-invasive procedure, a grid or concentric ring pattern is project ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cornea
The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea Refraction, 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. The cornea can be reshaped by surgical procedures such as LASIK. While the cornea contributes most of the eye's focusing power, its Focus (optics), focus is fixed. Accommodation (eye), Accommodation (the refocusing of light to better view near objects) is accomplished by changing the geometry of the lens. Medical terms related to the cornea often start with the prefix "''wikt:kerat-, kerat-''" from the Ancient Greek, Greek word κέρας, ''horn''. Structure The cornea has myelinated, unmyelinated nerve endings sensitive to touch, temperature and chemicals; a to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contact Lens
Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic or therapeutic reasons. In 2010, the worldwide market for contact lenses was estimated at $6.1 billion, while the US soft lens market was estimated at $2.1 billion.Nichols, Jason J., et a"ANNUAL REPORT: Contact Lenses 2010" January 2011. Multiple analysts estimated that the global market for contact lenses would reach $11.7 billion by 2015. the average age of contact lens wearers globally was 31 years old, and two-thirds of wearers were female.Morgan, Philip B., et al"International Contact Lens Prescribing in 2010" ''Contact Lens Spectrum''. October 2011. People choose to wear contact lenses for many reasons. Aesthetics and cosmetics are main motivating factors for people who want to avoid wearing glasses or to change the appearance or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schirmer's Test
Schirmer's test determines whether the human eye, eye produces enough tears to keep it moist. This test is used when a person experiences very dry eyes or excessive watering of the eyes. It can cause damage to the cornea. A negative (more than 10 mm of moisture on the filter paper in 5 minutes) test result is normal. Both eyes normally secrete the same amount of tears. It is named for Otto Schirmer. Test procedure The test works by the principle of capillary action, which allows the water in tears to travel along the length of a paper test strip in an identical fashion as a horizontal capillary tube. The rate of travel along the test strip is proportional to the rate of tear production. The patient is instructed to look upward, and the patient’s eyelid is pulled down. The bent end of the test strip is placed in the eye such that it rests between the palpebral conjunctiva of the lower eyelid and the bulbar conjunctiva of the eye. Schirmer's test uses paper strips inserted i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benzalkonium Chloride
Benzalkonium chloride (BZK, BKC, BAK, BAC), also known as alkyldimethylbenzylammonium chloride (ADBAC) is a type of cationic surfactant. It is an organic salt classified as a quaternary ammonium compound. ADBACs have three main categories of use: as a biocide, a cationic surfactant, and a phase transfer agent. ADBACs are a mixture of alkylbenzyldimethylammonium chlorides, in which the alkyl group has various even-numbered alkyl chain lengths. Solubility and physical properties Depending on purity, benzalkonium chloride ranges from colourless to a pale yellow (impure). Benzalkonium chloride is readily soluble in ethanol and acetone. Dissolution in water is ready, upon agitation. Aqueous solutions should be neutral to slightly alkaline. Solutions foam when shaken. Concentrated solutions have a bitter taste and a faint almond-like odour. Standard concentrates are manufactured as 50% and 80% w/w solutions, and sold under trade names such as BC50, BC80, BAC50, BAC80, etc. The 50 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnification
Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a size ratio called optical magnification. When this number is less than one, it refers to a reduction in size, sometimes called ''de-magnification''. Typically, magnification is related to scaling up visuals or images to be able to see more detail, increasing resolution, using microscope, printing techniques, or digital processing. In all cases, the magnification of the image does not change the perspective of the image. Examples of magnification Some optical instruments provide visual aid by magnifying small or distant subjects. * A magnifying glass, which uses a positive (convex) lens to make things look bigger by allowing the user to hold them closer to their eye. * A telescope, which uses its large objective lens or primary mirror to create an image of a distant object and then allows the user to examine the image closely with a smaller ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vitamin A Deficiency
Vitamin A deficiency (VAD) or hypovitaminosis A is a lack of vitamin A in blood and tissues. It is common in poorer countries, especially among children and women of reproductive age, but is rarely seen in more developed countries. Vitamin A plays a major role in phototransduction, so this deficiency impairs vision, often presenting with nyctalopia (night blindness). In more severe VAD cases, it can progress to xerophthalmia, keratomalacia, and complete blindness. Vitamin A deficiency is the leading cause of preventable childhood blindness worldwide and is a major cause of childhood mortality. Each year, approximately 250,000 to 500,000 malnourished children in the developing world go blind from a VAD, with about half of whom dying within a year of losing their sight. Addressing VAD has been a critical focus of global health initiatives, including Sustainable Development Goal 2: to end hunger, achieve food security and improved nutrition and promote sustainable agriculture. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diuretics
A diuretic () is any substance that promotes diuresis, the increased production of urine. This includes forced diuresis. A diuretic tablet is sometimes colloquially called a water tablet. There are several categories of diuretics. All diuretics increase the excretion of water from the body, through the kidneys. There exist several classes of diuretic, and each works in a distinct way. Alternatively, an antidiuretic, such as vasopressin (antidiuretic hormone), is an agent or drug which reduces the excretion of water in urine. Medical uses In medicine, diuretics are used to treat heart failure, liver cirrhosis, hypertension, influenza, water poisoning, and certain kidney diseases. Some diuretics, such as acetazolamide, help to make the urine more alkaline, and are helpful in increasing excretion of substances such as aspirin in cases of overdose or poisoning. Diuretics are sometimes abused by people with an eating disorder, especially people with bulimia nervosa, with the goal of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antispasmodics
An antispasmodic (synonym: spasmolytic) is a pharmaceutical drug or other agent that suppresses muscle spasms. Smooth muscle spasm One type of antispasmodics is used for smooth muscle relaxation, especially in tubular organs of the gastrointestinal tract. The effect is to prevent spasms of the stomach, intestine or urinary bladder. Both dicyclomine and hyoscyamine are antispasmodic due to their anticholinergic action. Both of these drugs have side effects common to anticholinergics and can worsen gastroesophageal reflux disease (GERD). Papaverine is an opium alkaloid used to treat visceral spasms, particularly those of the intestines. Mebeverine is a papaverine analog and spasmolytic with a strong and selective action on the smooth muscles of the gastrointestinal tract, particularly of the colon. Despite being anticholinergic, it does not have the systemic anticholinergic side effects seen in other such drugs. Peppermint oil has been traditionally used as an antispasmodic, an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beta Blockers
Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms (arrhythmia), and to protect the heart from a second heart attack after a first heart attack (secondary prevention). They are also widely used to treat high blood pressure, although they are no longer the first choice for initial treatment of most people. Beta blockers are competitive antagonists that block the receptor sites for the endogenous catecholamines epinephrine (adrenaline) and norepinephrine (noradrenaline) on adrenergic beta receptors, of the sympathetic nervous system, which mediates the fight-or-flight response. Beta-adrenergic receptors are found on cells of the heart muscles, smooth muscles, airways, arteries, kidneys, and other tissues that are part of the sympathetic nervous system and lead to stress responses, especially when they are stimulated by epinephrine (adrenaline). Beta blockers interfere with the binding to the receptor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antihistamines
Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provides relief from nasal congestion, sneezing, or hives caused by pollen, dust mites, or animal allergy with few side effects. Antihistamines are usually for short-term treatment. Chronic allergies increase the risk of health problems which antihistamines might not treat, including asthma, sinusitis, and lower respiratory tract infection. Consultation of a medical professional is recommended for those who intend to take antihistamines for longer-term use. Although the general public typically uses the word "antihistamine" to describe drugs for treating allergies, physicians and scientists use the term to describe a class of drug that opposes the activity of histamine receptors in the body. In this sense of the word, antihistamines are subclas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Vision Syndrome
Computer vision syndrome (CVS) is a condition resulting from focusing the eyes An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ... on a computer or other display device for protracted, uninterrupted periods of time and the ciliary body, eye's muscles being unable to recover from the constant tension required to maintain focus on a close object. Symptoms Some symptoms of CVS include headaches, Blurry vision, blurred vision, neck pain, fatigue (physical), fatigue, eye strain, dry eyes, irritated eyes, double vision, vertigo/dizziness, polyopia, and difficulty refocusing the eyes. These symptoms can be further aggravated by improper lighting conditions (i.e. glare, strong blue-spectrum backlights, or bright overhead lighting) or air moving past the eyes (e.g. overhead vents, or direct ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blinking
Blinking is a bodily function; it is a semi-autonomic rapid closing of the eyelid. A single blink is determined by the forceful closing of the eyelid or inactivation of the levator palpebrae superioris and the activation of the palpebral portion of the orbicularis oculi, not the full open and close. It is an essential function of the eye that helps spread tears across and remove irritants from the surface of the cornea and conjunctiva. Blinking may have other functions since it occurs more often than necessary just to keep the eye lubricated. Researchers think blinking may help with disengagement of attention; following blink onset, cortical activity decreases in the dorsal network and increases in the default-mode network, associated with internal processing. Blink speed can be affected by elements such as fatigue, eye injury, medication, and disease. The blinking rate is determined by the "blinking center", but it can also be affected by external stimulus. Some animals, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
