Contact lenses are thin lenses that are worn directly on the cornea of the eye. These are considered medical devices and can be worn to correct vision or for cosmetic or therapeutic reasons. When compared with spectacles, contact lenses provide better peripheral vision and do not collect moisture from rain, snow, condensation etc. or perspiration. This can make them preferable for sports and other outdoor activities.

Contact lenses are classified in different ways: By their primary function, material, wear schedule (how long a lens can be worn) and replacement schedule (how long before a lens needs to be discarded). They are used to correct the conditions such as Myopia (near sightedness), Hyperopia (farsightedness), Astigmatism (distorted vision), Presbyopia (need for bifocals) same as that spectacles correct. Therapeutic lenses are used to for pain relief or to aid healing whereas cosmetic lenses are used to change the appearance of the eyes.

Contact lenses can also be of daily wear (DW) (for one day), extended wear (EW) (for up to 6 consecutive nights) and continuous wear (CW) (for even longer wear periods of up to 30 consecutive nights).

Soft lenses are made of hydrophilic plastics, a special type of water-absorbing plastic that stays soft and moist as long as it is absorbing lots of water.

Rigid gas permeable lenses (RGP lenses) are also made of plastic which transmits oxygen without absorbing water. Instead, they have microscopic holes in them that allow the oxygen to filter through. Most of them are now made of three main materials: acrylate, silicone and fluorine.

Hybrid contact lenses exist that combine the materials of a RGP lens and a soft contact lens. These lenses have the acrylate, silicone and fluorine combination in the middle of the lens for sharpened central vision and soft contact lens water absorbing hydrogel around the edges for increased comfort.

Contact lenses are typically inserted into the eye by placing them on the index or middle finger with the concave side upward and then using that finger to place the lens on the eye. Rigid lenses should be placed directly on the cornea. Soft lenses may be placed on the sclera (white of the eye) and then slid into place. Another finger of the same hand or a finger of the other hand is used to keep the eye wide open. Alternatively, the user may close their eyes and then look towards their nose, sliding the lens into place over the cornea. Problems may arise if the lens folds, turns inside-out, slides off the finger or adheres more tightly to the finger than the eye surface.

Removing contact lenses incorrectly could result in damage to the lens and injury to the eye so certain precautions must be taken. Extreme care must be exercised when using mechanical tools or fingernails to insert or remove contact lenses. There are small tools specifically for removing lenses usually made of flexible plastic which resemble small tweezers or plungers that suction onto the front of the lens. These tools are used only with rigid lenses. Soft contact lens may be removed by pinching the edge between the thumb and index finger. It is also possible to push or pull a soft lens far enough to the side or bottom of the eyeball to get it to fold then fall out without pinching and damaging it.

Advantages:

• They aren't affected by weather conditions and won't fog up in cold weather like glasses
• They don't get in the way when playing sports and exercising
• They conform to the curvature of your eye, providing a wider field of view and causing less vision distortions and obstructions than spectacles

Disadvantages:

• Some people have trouble applying a contact lens to their eye
• They reduce the amount of oxygen reaching your eye and can cause or increase the severity of dry eye syndrome
• They require proper lens care and lens case cleaning each day, to avoid potentially serious eye infections

Some of the side effects of the contact lenses include blockage of oxygen supply to the eyes, dry eyes, irritation when combined with medication, especially birth control pills, diminished corneal reflex, corneal abrasion, red eye or conjunctivitis, ptosis and corneal ulcer.

Acuvue, Dailies, Air Optix, Biofinity, SofLens are few brands of contact lenses available in the market.

Ravina R. Kajare

T.Y.B.Pharm

Tags: MET Institute of Pharmacy