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This article outlines the advantages and disadvantages of using contact lenses, and looks at the differences between soft and hard lenses.

contact lenses


Contact lenses are an alternative for people who require glasses. In addition to improving the appearance, contact lenses have special advantages in certain conditions.

Large focussing 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.


In this common condition the front surface of the eye (the cornea) is not spherical but is irregularly curved. Contact lenses may give better vision than glasses in patients with regular astigmatism and after corneal injury, scarring or surgery.



Lenses must usually be inserted and removed daily with scrupulous cleaning and disinfection between each wearing requiring several different sterile solutions and containers.


On-going costs of solutions and regular replacement of lenses make lens wear more expensive than spectacle wear.

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 lens wear unsuitable.

Types of contact lenses

There are two main classes of contact lenses.

1. Soft lenses

Are made of flexible polymers with significant water content. They are larger than the cornea (12-14mm) and mould to the front of the eye with a lens life of 12 to 18 months. Disposable lenses, thrown away and replaced on a monthly basis are also available.


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


They cause more eye infections and allergic reactions and vision may be less clear than with glasses or hard lenses. Soft lenses are easier to damage and more difficult to handle. They are unable to correct much astigmatism.

2. Hard 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 (8-10mm).


The good oxygen transmission maintains corneal health and there is a lower incidence of eye infections and allergic reactions than with soft contact lenses. Hard lenses are able to fully correct astigmatism.


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. Complications 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 practitioners without delay.

Who to contact for more information

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 optician or optometrist for this service.

Note: We advise against the use of extended wear (i.e. overnight) contact lenses except in exceptional circumstances.

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