Soft contacts are made from a type of plastic called a hydrogel. They first became available commercially
in the 1970's and were sold by Bausch & Lomb. Hydrogels contain a large percent of water - usually
somewhere between 35% and 80% water. Because of this, they are wet, very pliable and let more oxygen get
to the cornea than hard contacts - which hardly let any oxygen in at all. Because they are soft and pliable
they tend to feel more comfortable on a person's eye - pretty much from the first time they are worn, unlike hard
and RGP contacts which may take a while to get used to. Around 85% of people who wear contacts wear soft ones.
Soft contacts cover the cornea of the eye and part of the sclera. The contact kind of floats on top of the eye
and works like any other lens, in that it bends light.
Prescriptions for soft contacts include information like the size and shape of the eye, that aren't necessary
for glasses. Prescriptions are written with the right eye listed as O.D. and the left eye as O.S. If both
eyes are the same it is written like O/U. Prescriptions for contacts also have to include the brand name of the
When you see an eye doctor to get soft contacts they are usually between 3 and 5 different measurements they
will have to take to fit you properly. These include the power, base curve and diameter.
Power: The units of power are called diopters and is abbreviated as 'D'. For the most part soft contacts
are made with powers of increments of .25 D. If your contacts are for being nearsighted they will have a
minus sign next them. If you are farsighted they will have a plus sign in front. For example, my contacts
have a power of -5.00.
Base Curve: The base curve is the curve of the center of the lens. It is important for making sure
the contacts fit on your eye well. The usual range for a base curve is from 8.1 to 8.9. Sometimes more measurements
of curvature are taken at different measurements
from the center of the eye. Some of these are called: secondary curve (SC), intermediate curve (IC) and the
peripheral curve (PC).
Diameter: The diameter of your contacts also needs to be fitted to your eye. It usually the same for both
eyes. The value of the diameter is usually given with one decimal. For example, my contacts have diameter
Common Brands of Soft Contacts
Some of the more popular brands of contacts are Acuvue 2, Acuvue Advance, Focus Monthly, and Softlens 38.
Acuvue 2: Acuvue 2 are made by Johnson and Johnson Vision Products. They are made of 42% polymer (etafilcon A)
and are 58% water. These contacts were made to be worn for two weeks as a daily wear contact - take them
out every night - or for one week to sleep in then throw away. Have UV blocking too! Powers available are
.5 to 8.0 and -.5 to -12, base curves are 8.30 and 8.70 and diameter, 14.0.
Acuvue Advance: Acuvue Advance is also made by Johnson and Johnson. These however are made from
a different material. They are made from 53% polymer (galyfilcon A), which has been trademarked as HYDRACLEAR.
At the time of writing this these have not been approved for over night wear and are 1-2 week daily wear
disposable contacts. Powers available are .50 to 8.00 and -.50 to -12.00, base curves are 8.30
and 8.70 and diameter, 14.0.
Focus Monthly: Focus Monthly are made by CIBA Vision Corp. These are daily wear contacts that you take
out every night and clean, and put back in the next day. And then throw them away and replace them after
a month. They are made of 45% polymer (vifilcon A) and 55% water. Powers range from
.25 - 6.00 and from -.25 to -15. Base curves are 8.60 and 8.90 and diamter is 14.0.
Softlens 38: Softlens 38 is made by Bausch & Lomb and was formally known as Optima FW (they changed the name).
They are 38% water and are made of 62% polymer (polymacon). They are 1-2 week disposable soft contacts.
They come in powers of between .25 to 4.00 and -.25 to -9.00. Base curves available are 8.40, 8.70 and 9.00.
The diameter is 14.00.
Other articles in this series are:
Contacts - An Introduction Part I: Eyes and Vision,
Contacts - An Introduction Part II: Contact Types and History,
Rigid gas permeable (RGP) Contacts,
Daily Wear Contacts,
Extended Wear Contacts and
Some related web sites are
Bausch & Lomb: Soft Contact Lenses and
Soft Contact Lenses.