SOME IMPORTANT ASPECTS OF CONTACT LENSES
Wearing the contact lenses verily depends on sufficient tear production by the eyes. Dry eye condition makes difficulty and insufficiency in contact lenses wearing.
Indications
1.Protrusion of or extension of the central part of the cornea beyond the limit. (Cornea-the pupil cap).This condition is known as Keratoconus
2.Absence of eye lens. The condition is known as Aphakia
3.Visual blurring
4. Nearsightedness is known as Myopia
5.Distant sightedness known as Hyperopia
6.Improper focus of light rays known as Astigmatism
7.Improper accommodation and no flexibility of lens known as Presbyopia
8. One eye is having near vision while the other is having a far vision. The condition is known as Monovision.
Contra-Indications
1. Work requires high exposure to dust.
2. Exposure to high winds
3.Exposure to high smoke.
4.Chronic conjunctivitis
5.Chronic blepharitis
6.Recurring infections
Precautions
Caution should be exercised by patients who suffers and possibilities of changes in eye conditions as follows:-
1.Epilepsy
2.High B.P. which may damage retina
3.Cardiac diseases.
4.Diabetes Mellitus which causes outgrowth of vessels in the iris and the eye's anterior chamber.
5. Taking oral contraceptives as regular consumption may alter the optical physiology. These changes are corneal sensitivity elevation, color changes, decreased visual acuity.
Types of Contact Lenses
1. There are some contact lenses made of polymethylmethacrylate(PMMA). These are rigid and water-resistant. These are Hard Glasses commercially known as Lucite or Plexiglas.
These hard lenses are having major advantages are their cost effects when compared with soft lenses and they can be easily marked to identify for the left or right eye.
The disadvantages also like minimum wettability,and limited oxygen permeability. Because of the hardness which does not permit sufficient oxygen and moisture it is difficult for the individual to adapt with it for a longer time.
2. Soft Lenses are made out of glasses that are flexible, and oxygen and water permeable.
These are easy to use,more comfortable to wear, and more difficult to dislocate from the position.
There are disadvantages like they are prone to absorb harmful chemicals,high costs,very easily deteriorate from storage,and altered visual acuity due to hydration of the lens.
Patients wearing soft lenses can use a few drops of rewetting agents. At the same time they should avoid other ophthalmic agents.
3. There are other types of lenses such as Gas Permeable Lenses. These are soft lenses contains PMMA. Hence they permit only oxygen but resist water.
They have the advantages over the hard lenses by their comfortability,and increased visual acuity.
Also they have the advantage over the soft lenses by their impermeability to resist chemicals.
The disadvantage of the gas permeable lenses is the accumulation of proteins and lipid deposits as they are moisture resistant.
Toxic Effects
Corneal edema due to improper oxygenation of the eye.
Medication can affect the eyes and potentiate the problems.
e.g.Oral contraceptives.
Decongestants
Antihistamines
Tricyclic Antidepressants such as amitriptyline,imipramine etc
Diuretics
Lens Care
Hard lenses are cleaned to remove oil,dust, and debris,followed by soaking in a storage solution,wetting to retain its hydrophilic surface,and rewetting.
Soft lenses are cleaned by surface-active or enzymatic cleaners,followed by disinfectants thermally or chemically. Finally rewet them.
Gas permeable lenses are cared for by cleaning,wetting, and soaking. Some are containing more silicone agents, requiring conditioning solutions that are made especially for rewetting purposes.
Solutions Recipe
Cleaning Products generally contain non ionic or amphoteric surfactants,which remove mucus,lipids,and proteins from the lens. Contact lenses should be rinsed following the cleaning steps to prevent eye irritations
Wetting Solutions are applied directly into the lens before inserting the lens into the eyes. Wetting solutions are intended to lubricate,decrease lens surface tension,and change the lens surface from hydrophobic to hydrophilic.
Wetting and Soaking solutions are meant for creating an aseptic environment and to hydrate the lens.
Preservatives
1.Benzalkonium chloride,
2. Thimerosal,this may produce more irritating episodes.
3.Phenylmercuric nitrate,
4.Sorbic acid,
5.Sodium edetate.
