Contact lens side effects | Contact lens how to use | Contact lens | Type of contact lenses | Scleral contact lens | Contact lens materials | Spectacle and contact lenses | Complication of contact lenses | Advantages of contact lenses | Contact lens calculation | How to wear contact lens.
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Contact Lenses
An attractive alternative to spectacles for correcting refractive errors, contact lens are also used for various therapeutic, pharmacological and cosmetic procedures.
A contact lens is an optical device that is placed directly over the corneal and scleral surfaces of the eye. Modern contact lenses are polymers that are relatively safe, on-toxic and on-allergic.
Since the cornea derives its oxygen requirement mainly from the atmosphere, placing a lens on the corneal surface can impede the oxygen supply to the cornea. Newer types of lenses, however, allow oxygen to pass through them to the cornea.
Types of Contact Lenses
There are three types of contact lenses: soft, semi-soft and hard.
• Soft contact lenses: These are very flexible lenses made of a polymer called hydroxyl ethyl metha acrylate (HEMA). They are very comfortable to wear and permit oxygen to reach the cornea.
• Semi-soft lenses or rigid gas permeable lenses: These lenses are made from special materials like cellulose or silicon acrylate. They are less flexible than soft contact lens but allow some oxygen to pass through to the cornea. Thought less comfortable than soft lenses, they can be used to correct steep corneas and high stigmatism.
• Hard contact lens: Made of a polymer called poly methyl metha acrylate (PMMA), hard lens are the least flexible of all lenses and permit almost no oxygen to pass through to the cornea. However, the advantage of a hard contact lens is its durability.
Advantages of Contact Lenses
• Contact lenses provide a larger field of vision than spectacles and a better range of mobility. Hence, they are ideally suited for sportspersons and people engaged in outdoor physical activities.
• In people with uniocular refractive error (power difference of more than 3 dioptres between the eyes), spectacles will produce double vision due to the discrepancy in the size of the image. Contact lens can be used in such cases.
• Cosmetically, they offer an advantage over spectacles.
• Apart from correcting refractive errors, contact lens are also used to deliver drugs to the eyes and treat corneal diseases
• Nowadays, contact lenses are available in various colors and can even be used by people with normal vision for cosmetic purposes.
Precautions
With all these advantages, there are also some precautions to be taken before opting for contact lenses:
• An ophthalmologist should examine the eyes to rule out infections and other disorders of the eye
• Only a qualified contact lens specialist should fit the lens. The tests
include measuring the corneal curvature and diameter and issuing a suitable pair of contact lens. After wearing them, the specialist examines the eyes to check for a good, comfortable fit.
• Hand-washing with soap before inserting and removing the contact lens from the eye is mandatory.
• Proper maintenance of the contact lens by cleansing it with the appropriate lens fluid is necessary.
• If the eyes are red or there is a white discharge from the eyes, the contact lens should not be used and the eye care professional should be contacted for further instructions.
• One should not sleep overnight with the contact lenses on. The oxygen supply to the cornea is totally cut off by the contact lenses during sleep. The oxygen deprived cornea becomes vulnerable to damage and ulceration.
• The eyes should be periodically examined by an eye care professional to check for an infections or corneal damage due to contact lens wear.
The latest innovation in the field is extended wear contact lenses which can be used over a longer period of time. These lenses allow the free passage of oxygen to the cornea, but even they must be used with care.
Contact lenses offer a lot of advantages but they can also cause serious complications if not handled properly.
A little care and attention will go a long way in enabling a person to enjoy the benefits and avoid the problems.
OPTOMETRY-SHARP VISION
Optometrist