CONTACT LENSES

Contact Lenses are prescribed in four main types of cases:-

(1) Pathological eyes, e.g. corneal scars
Keratoconus

(2) High refractive errors - high myopes, aphakes: better visual field than
glasses, more natural vision.

(3) Cosmetic - in place of spectacles.

(4) Sport - especially for those involving physical contact or risks.

There are two main types of contact lenses:-
(i) Hard lenses - smaller than the cornea, made of rigid plastic. They
correct moderated amounts of astigmatism as well
as the spherical refractive error.

(ii) Soft lenses - almost the same size as the cornea or larger, made
up of soft plastic sponges containing 40% or more of
water. They correct the spherical errors but can correct
only little astigmatism, unless an astigmatic correction
is incorporated. Soft lenses are subject to infection so
must be sterilized.

Complications:
Corneal abrasions may develop due to ill fitting lenses, or to trauma during
insertion of the lenses. Conjunctivitis and/or Keratitis may occur if the
lens is contaminated. Giant papillary conjunctivitis from soft lenses. The
patient should be instructed to seek attention if undue lacrimation or undue
irritaion persists, or if conjunctival discharge is present. Therapeutic contact
lenses may be used to assist treatment of corneal disease.

Advantages of Contact Lenses:
1. Provide a wider field of view.
2. Move with the eyes so wearer is constantly looking through optical centre
of lens. Most important in higher powered lenses.
3. Eliminate nuisance of spectacle frames which either slip or rub.
4. Well suited to wet weather and steamy conditions where spectacles
become wet or foggy.
5. Can overcome astigmatism as in corneal scarring and conical corneas.
6. Aphakic patients may obtain better vision.
7. Medical conditions eg. scarred eyelids, chemical burns, can be aided
with lenses.

Disadvantages of Contact Lenses:
1. Hazards injury from badly fitting, badly fitted, bad hygiene.
2. TIME FACTOR - finding, fitting, cleansing, sterilizing, adjusting to wearing.