Brief
Course Description

Optical
Principles of Contact Lesnes

There
are many reasons why a contact lens prescription can differ significantly
from a spectacle prescription belonging to the same patient. By studying
the principles
of optics which need to be considered when fitting rigid and soft lenses,
many of these reasons will be explained.

We
start with a review
of the anatomical features of the human eye with a special emphasis
on the tear film and the cornea. This will be followed by proper patient
selection through the use of appropriate pre-fit testing and interviewing
techniques. An attempt will be made to identify those contact lens candidates
with the best prognosis as well as those with a reduced prognosis for
successful fitting.

Following
this is a discussion of vertex distance compensation, a subject which
assumes added importance when fitting contact lenses. A prescription
in excess of ±4.00D at the spectacle plane must be compensated for contact
lenses which are fit at the corneal plane. When a rigid contact lens
is placed on the cornea, a tear layer is formed between the back surface
of the lens and the front surface of the cornea. This liquid or lacrimal
lens can sometimes assume the shape and power of a plus or minus lens.
The added power must then be considered when determining the final power
of the contact lens. Examples and practice exercises are presented to
cover instances of rigid lenses fit on K, steeper than K and flatter
than K