composed of a main lens and two reading ssegments; one for near and one for intermediate distances (about arm lengths) high power plus lenses used for cataract patients. - made with aspheric surfaces to minimise aberrations due to shape of the lens darken when exposed to short wavelength radiation (300nm - 400nm) or ultra-violet light - rate of darkening and final transmission of the lens (saturation transmission) depends on the ambient temperature.

There are several materials of which spectacle lenses can be made. There is glass, plastic, polycarbonate and high-index materials. Glass is the material that has the truest optical properties and is least likely to scratch. However, glass is easily shattered, heavy and thick, so for these reasons it is usually not the material of choice. Plastic is lighter and thinner than glass, and is more shatter-resistant, but scratches more easily.

This depends on your prescription, the type of lenses you choose, and your frame. The higher the prescription the thicker the lenses, but this can be minimized with high index lenses. In the lower prescription ranges, the type of lens does not matter as much. Ultra-thin Hi index plastics are now available which make plastic lenses much more feasible in more moderate prescriptions. As a general rule, the smaller the frame the thinner the edges of a lens for short-sighted individuals.

Certainly not! Today's spectacle lenses are available in a variety of materials, most of which are designed to reduce thickness and weight. Thickness, of course, is relative to the strength of your prescription. An eye care professional will help you choose the most advantageous lens material. At Look Optical we offer all the latest in state of the art lens materials, one of which is just right for you.

These are lenses which have one fixed focus and can be for distance vision, near vision or intermediate vision. For example driving glasses, reading glasses or computer glasses.

Avesis covers standard single vision, bifocal and trifocal lenses (plastic or glass). If you choose specialty lenses (e.g., progressive or, hi-index), you will receive a discounted retail price and an allowance to use toward that discounted price.

Lenses are offered in different tints and coatings for a variety of reasons, such as vision enhancement, glare reduction and simply cosmetic appeal. Examples: Glare reduction, works just like a sun glass. Approximately 80% of the visible light is filtered out. Mirror coating is mostly a cosmetic aspect. However some mirror lenses filters out more light than a standard gray lens. This lens type is sometimes called a light mirror coating.

With so many lenses available, it is difficult to find ones that will protect your eyes if you don't know what each one will do. Blue-blockers block blue light and usually have amber lenses. Researchers are still unsure whether or not blue light is harmful, but these are popular among skiers, hunters, boaters, and pilots. Both polarized lenses and anti-reflective coating cut reflected glare. Polarized lenses in particular are popular with those who play water and snow sports.

The most widely cited place appears to be photodo, which is sadly out of date. photozone also has lens reviews. A note about lens reviews: There is often significant variation between samples of lenses. Reviews typically consider just a single sample, so you may not get the full picture from reading just a single review.

Having thinner, lighter prescription lenses with a higher index of refraction is the ideal lens for any prescription which requires 4 or more diopters of correction. High index spectacle lenses can accomplish this for a more stylish look and comfortable feel of your new pair of spectacles. Please note that if you need contact lenses for your Keratoconus to correct your vision adequately, spectacles will not give you the same.

Comedo (whiteheads or blackheads) or papules. The comedo is the basic acne lesion, which is a plugged pore. If the plugged pore stays under the skin, it's called a closed comedo and forms a white bump or whitehead. Blackheads are comedos that open up and appear blackish on the surface of the skin. This black color is not due to dirt, but because the air reacts with the excess oil. Nodules. These are more serious acne lesions. They lodge deeper in the skin, are painful, and can cause scarring.

Stress incontinence occurs when you sneeze, cough, laugh, jog, or do other activities that put pressure on your bladder . It is the most common type of urinary incontinence in women. Urge incontinence, also called overactive bladder, occurs when the sensation to urinate is so strong that you cannot reach the toilet in time, even when your bladder contains only a small amount of urine.

Soft, large - these are associated with age, and may enlarge, and may predispose to macular degeneration.

Most strokes are caused by a blood clot or a narrowing of a blood vessel (artery) leading to the brain, known as ichemic stroke. Other strokes are caused by a hemorrhage (bleeding) from an artery in the brain itself, known as hemorrhagic stroke.

Atopic eczema is the commonest form of eczema and is closely linked with asthma and hayfever. It can affect both children and adults, usually running in families. One of the most common symptoms of atopic eczema is its itchiness (or pruritis), which can be almost unbearable. Other symptoms include overall dryness of the skin, redness and inflammation. Constant scratching can also cause the skin to split, leaving it prone to infection.

See Special Events for a detailed description. A "regular" orienteering meet is point to point, take the controls in order, fastest person wins. A Score-o leaves the order up to the competitor. Controls have a point value. Most points in shortest time wins. A Night-o is just like regular Orienteering, it's just in the dark, and, yes, you bring a flashlight!

Seizures can be a brief interruption of brain activity (an absence seizure) or more intense and dramatic, including falling or abnormal muscles movements. (Click here to go to the Epilepsy Foundation of American Web site for a description of seizure types.) During a seizure, patient behavior depends on the area of the brain involved by abnormal electrical discharges in nerve cells. Different areas of the brain control different body activities.

Unstable angina. People with coronary artery disease may develop unstable angina, meaning pain and discomfort can happen unpredictably, even during rest. The pain is generally more severe and frequent than that of chronic angina. New or more severe symptoms of unstable angina require medical help right away, since a heart attack may be about to happen. Chronic angina patients may develop unstable angina as their condition progresses. Syndrome X.

Diabetic retinopathy is classified as either nonproliferative (background) or proliferative. Nonproliferative retinopathy is the early stage, where small retinal blood vessels break and leak. In proliferative retinopathy, new blood vessels grow abnormally within the retina. This new growth can cause scarring or retinal detachment, which can lead to vision loss. The new blood vessels may also grow or bleed into the vitreous humor, the transparent gel filling the eyeball in front of the retina.

All types respond differently to natural hormones occurring in different amounts in both men and women. Not all hair is visible on the surface of your skin. Hair growth goes between active and resting stages. On your head, above 90% of your hair is in the active growing stage that can last up to 7 years. The growing cycle of your body hair lasts only for a few months and as much as 30% of your hair is in the resting stage.

The two most prevalent types of migraine headache are migraines with aura and migraine without aura, the latter of the two being more common.

There are many different types of kidney stones. The vast majority of stones are composed of calcium. The most common types of stones are calcium oxalate (70%), calcium phosphate (5-10%), struvite (10%), uric acid (10%) and cystine (1%). It is not uncommon for a single stone to be made of more than one of these types. When this occurs, the stone is commonly referred to as a mixed stone. Less common types of kidney stones include Xanthine, DHA and crixivan stones.

Macular degeneration is classified as either dry or wet. The dry form is more common than the wet (about 90% of patients). It may result from the aging and thinning of macular tissues, depositing of pigment in the macula or a combination of the two. In the wet form, new blood vessels grow beneath the retina and leak blood and fluid. This leakage causes retinal cells to die and creates blind spots in central vision.

There are many different kinds of brain tumors. The first way to divide brain tumors is based on whether they are primary or secondary. Primary tumors are tumors that begin in the brain. Secondary tumors are tumors that started our elsewhere in the body and spread, or metastasized, to the brain. For example, secondary brain tumors could have begun as breast cancer or lung cancer. Primary brain tumors can be further divided based on what type of cell the tumor began as.

There are 5 types that are kept as pets: Syrian, Campbell's, Winter White, Roborovski and Chinese. There are lots more but these types aren't kept as pets.

Strip Shingles -- these asphalt shingles are approximately three times as long as they are wide. Manufactured in both standard and metric dimensions, strip shingles are distinguished by the number of cutouts or tabs that they have. The most common type of strip shingle is the "three-tab" shingle. Different textural and lighting/shadowing effects can be achieved with strip shingles depending on the number, shape and alignment of the cutouts.