Contact lenses

Contact lenses are an alternative to wearing spectacles for people who have a focusing error. In addition to improved appearance, they may have particular advantages in certain conditions. Contact lenses may also have particular disadvantages under certain conditions.

Advantages of contact lenses

Large focusing errors
In short-sightedness (myopia) lenses give increased magnification and an improved field of side vision. People who have had a cataract extraction, without insertion of an intraocular lens implant benefit from reduced distortion, improved field of side vision and better cosmetic appearance when lenses replace thick spectacles.

Astigmatism
In this common condition the front surface of the eye, the cornea, is not spherical but has a variable curvature in different areas. This may be present in an otherwise normal eye, be part of a corneal disease such as keratoconus, or be caused by corneal scarring from injury, infection or surgery. Contact lenses may give better vision than glasses in most cases of astigmatism.

Occupations
Some recreational or occupational activities may be better suited to contact lenses than to glasses. They are a good option where appearance is important, where a wide field of view is useful, or where glasses may be dislodged, damaged or obscured such as in water or contact sports.

Disadvantages of contact lenses

Inconvenience

Lenses must usually be inserted and removed daily with scrupulous cleaning and disinfection between each wearing requiring several different sterile solutions and containers. Even disposable contact lenses must be removed and cleaned on a daily basis.

Expense
Ongoing costs of solutions and regular replacement of lenses make them more expensive than wearing spectacles.

Eye protection
Lenses do not protect against eye trauma nor against dust and dirt. Protective eyewear must still be worn in sporting or industrial activities. Dusty or dirty environments may make wearing lenses unsuitable.

Types of contact lenses

There are two main classes of contact lenses.

Soft contact lenses
These are made of flexible polymers and have significant water content. They are larger than the cornea and mould to the shape of the front of the eye. They have a lens life of about 12 to 18 months. Disposable lenses, thrown away and replaced on a monthly, weekly or even daily basis, are also available.

Advantages
They are comfortable even on first fitting and stable on the eye for sporting activities. Intermittent wear is possible.

Disadvantages
Soft lenses are easier to damage and more difficult to handle. They may be unable to correct astigmatism fully (especially high amounts of astigmatism and irregular astigmatism from keratoconus, surgery or scarring) and so vision may be less clear than with glasses or hard lenses. The oxygen permeability is not as high as with hard lenses and in some conditions this may lead to corneal disease. Eye infections and allergic reactions are more common than with hard lenses.

Hard lenses (rigid gas permeable)
Lenses are made of polymers that do not absorb water but have a high permeability to oxygen. They are smaller in diameter than the cornea (8.0 - 10.0mm).

Advantages
The good oxygen transmission maintains corneal health. There is a lower incidence of corneal infections and allergic reactions than with soft lenses. Hard lenses are better able to correct astigmatism. Patients with keratoconus may require a hard contact lens to achieve reasonable vision. Your ophthalmologist may be able to apply for a government subsidy to help with the costs of contact lens wear in this condition.

Disadvantages
Although less comfortable when first inserted, a good level of comfort is achieved after a period of adaptation. This makes them less suitable for part-time wear alternating with glasses. They are more easily dislodged from the eye and less suitable for dusty conditions.

Complications of contact lens wear

Hard or soft lens wear can lead to complications related to the lens itself, the solutions used, or to underlying eye conditions made worse by lens wear. These include infectious, allergic or toxic conjunctivitis, and corneal damage such as abrasion, infection, swelling and development of abnormal blood vessels.

Symptoms include discomfort or pain, redness, discharge or deteriorating vision. If any of these symptoms develop during contact lens wear you should see your contact lens practitioner without delay.

Overnight wear (including the recently developed extended wear soft contact lenses with very high oxygen permeability) has a much higher rate of corneal infection than daily wear. We advise against extended wear except under close supervision in exceptional circumstances.

Further information and support

Your ophthalmologist is able to examine your eyes, advise on suitability for contact lens wear and discuss which type of lens would be best for you. In addition some ophthalmologists fit and dispense contact lenses. Others may choose to refer you to an optometrist for this service.

Original material provided by Auckland Eye, and reviewed May 2005. Edited by everybody.