Bifocal lens Health Dictionary

Contact lenses are lenses worn in contact with the EYE, behind the eyelids and in front of the cornea. They may be worn for cosmetic, optical or therapeutic reasons. The commonest reason for wear is cosmetic, many short-sighted people preferring to wear contact lenses instead of glasses. Optical reasons for contact-lens wear include cataract surgery (usually unilateral extraction) and the considerable improvement in overall standard of vision experienced by very short-sighted people when wearing contact lenses instead of glasses. Therapeutic lenses are those used in the treatment of eye disease: ‘bandage lenses’ are used in certain corneal diseases; contact lenses can be soaked in a particular drug and then put on the eye so that the drug slowly leaks out on to the eye. Contact lenses may be hard, soft or gas permeable. Hard lenses are more optically accurate (because they are rigid), cheaper and more durable than soft. The main advantage of soft lenses is that they are more comfortable to wear. Gas-permeable lenses are so-called because they are more permeable to oxygen than other lenses, thus allowing more oxygen to reach the cornea.

Disposable lenses are soft lenses designed to be thrown away after a short period of continuous use; their popularity rests on the fact that they need not be cleaned. The instructions on use should be followed carefully because the risk of complications, such as corneal infection, are higher than with other types of contact lenses.

Contraindications to the use of contact lenses include a history of ATOPY, ‘dry eyes’, previous GLAUCOMA surgery and a person’s inability to cope with the management of lenses. The best way to determine whether contact lenses are suitable, however, may be to try them out. Good hygiene is essential for wearers so as to minimise the risk of infection, which may lead to a corneal abscess – a serious complication. Corneal abrasions are fairly common and, if a contact-lens wearer develops a red eye, the lens should be removed and the eye tested with ?uorescein dye to identify any abrasions. Appropriate treatment should be given and the lens not worn again until the abrasion or infection has cleared up.... contact lenses

The internal optical component of the eye responsible for focusing; also called the crystalline lens. It is situated behind the iris and is suspended on delicate fibres from the ciliary body. The lens is elastic, transparent, and slightly less convex on the front surface than on the back. Changing its curvature alters

the focus so that near or distant objects can be seen sharply (see accommodation). Opacification of the lens is called cataract. (See also lens dislocation.)... lens

A plastic prosthesis used to replace the removed opaque lens in cataract surgery.... lens implant

Medic.

Family: Vitaceae.

Habitat: Forests of tropical and subtropical India, from Himalayas as far west as Kumaon, and southwards to the Peninsula.

Ayurvedic: Chhatri, Karkatajihvaa, Kukurjihvaa.

Siddha/Tamil: Nalava, Nyekki, Ottanali.

Folk: Karkani (Maharashtra).

Synonym: L. esculenta Moench.

Family: Papilionaceae; Fabaceae.

Habitat: Native to South West Asia; cultivated as a pulse crop mainly in North India, Madhya Pradesh and some parts of Maharashtra.

English: Lentil.

Ayurvedic: Masura, Masurikaa, Mangalyaa, Mangalyak, Adaasa.

Unani: Masoor.

Siddha: Misurpurpu.

Action: Seeds—mostly used as a pulse. Contain as much as 30% proteins (similar to those of peas and beans). Soup is used in gastric troubles and constipation. Paste or poultice is applied to foul and indolent ulcers.

Dosage: Dried seed—10-20 g. (API, Vol. III.) oil, extracted from the seeds, is similar to olive oil. The seeds possess feeble antimalarial activity. The seed extract showed 100% toxicity against Alternaria alternata and marked toxicity against Aspergillus niger.

Dosage: Root—5-10 g powder. (API, Vol. IV.)... lens culinaris

See EYE.... lens of the eye

Irritation, soreness, friction, inflammation. “People who use extended- wear soft contact lenses are more likely to develop serious microbial keratitis infection than users of other lenses.” (Research team, Moorfields Eye Hospital, London) Risk of keratitis was seen to increase when soft lenses were worn for more than six days.

Alternatives:– Douche. Simple teas: Fennel or German Chamomile; half a teaspoon dried herb or teabag to cup boiling water. Infuse 15 minutes. Half-fill eye-bath and use as douche, tepid. OR: quarter of a teaspoon distilled extract Witch Hazel in eye-bath; half-fill with water. Natural lubricant for contact lens is Evening Primrose oil (contents of a capsule). See: EYES, INFECTION.

Supplements. Daily. Vitamin A 7500iu, Vitamin B2 10mg, Vitamin C 400mg, Vitamin E 400iu, Beta carotene. Zinc 15mg. ... contact lens fatigue

A spectacle lens with 2 different focal lengths. Glasses with bifocal lenses make corrections for both close and distant vision.... bifocal

Displacement of the crystalline lens from its normal position in the eye. Lens dislocation is almost always caused by an injury that ruptures the fibres connecting the lens to the ciliary body. In Marfan’s syndrome, these fibres are particularly weak and lens dislocation is common.A dislocated lens may produce severe visual distortion or double vision, and sometimes causes a form of glaucoma if drainage of fluid from the front of the eye is affected. If glaucoma is severe, the lens may need to be removed. (See also aphakia.)... lens dislocation

lenses that are specially designed to give clear images, eliminating the coloured fringes that are produced with ordinary lenses (caused by splitting of the light into different wavelengths and hence its component colours). Such lenses are useful in scientific instruments, such as the eyepieces of microscopes.... achromatic lenses

a lens with fine parallel lines (almost invisible striations) across its width, used in various vision tests; for example, to test suppression and abnormal retinal correspondence. [B. Bagolini (20th century), Italian ophthalmologist]... bagolini lens

a soft contact lens that can be useful in managing certain external eye disorders, including tiny perforations.... bandage lens

n. a surgical procedure in which the crystalline lens of the eye is removed.... lensectomy

n. an instrument used to measure the refractive properties of an artificial lens, such as a spectacle lens.... lensmeter

lenses containing more than one segment made to different prescriptions for visual correction. See bifocal lens; trifocal lenses.... multifocal lenses

see varifocal lenses.... progressive lenses

lenses in which there are three segments. The upper provides a clear image of distant objects; the lower is used for reading and close work; and the middle one for the intermediate distance. Musicians sometimes find the middle segment useful for reading the score during performance.... trifocal lenses

(progressive lenses) lenses in which the power (see dioptre) gradually changes from one prescription to the other and there is no dividing line on the lens between the different segments (compare multifocal lenses). The wearer can see clearly at any distance by raising or lowering the eyes.... varifocal lenses