The development of Silicone Hydrogel Contact Lenses (SHCL) marks
the birth of a whole new category of contact lens technology.
Just as RGP materials sounded the death knell for PMMA, SHCL
have the potential to render conventional HEMA materials obsolete.
The introduction of SHCL has however, been surrounded by confusion,
controversy and practitioner resistance. This resistance is primarily
due to the launch of SHCL as extended wear lenses resurrecting
the extended wear debate that was fueled by the 1980's HEMA experience.
Linking SHCL's to extended wear has blinded many practitioners
to the real issue at hand, which is the superiority of SHCL materials
over HEMA for virtually ALL wearing modalities. SHCL are NOT
JUST extended wear lenses!! In order to appreciate the full significance
of this technology, it has to be viewed apart from the EW modality.
The fact that SHCL can be safely used on an overnight basis on
properly fitted patients is simply a bonus that flows naturally
out of the superior material properties.
Limitations of HEMA for both daily wear and extended wear have
been well documented. SHCL's have eliminated some of these limitations
and thus our premise that this is indeed a NEW category.
- Holden and Mertz* and later Fonn et al* demonstrated
quite compellingly that a contact lens placed on the eye
requires a dK/t or between 87 and 125 to avoid overnight corneal
swelling. HEMA by its nature could not deliver much more than
a dK/t or about 30 which is barely enough to avoid daytime
corneal edema. All SCHL's meet or exceed the requirements for
overnight wear and far surpass the corneas daily wear needs.
- HEMA needs a higher water content to deliver
the oxygen required to avoid corneal hypoxia even during daily
wear applications. This leads to dehydration, and chemical
absorption, which further limits a contact lens wearer's comfort
and wearing time. SCHL do not depend on water to deliver oxygen
and because of a lower water content will not dehydrate as
much leading to better all day comfort, less surface deposition
and less chemical absorption.
- SHCL's allow the corneal epithelium to remain
intact and resistant to disease. Dwight Kavanagh has shown
there is a decreased affinity for pseudomonas spc .to
adhere to the corneal epithelium. * with SHCL's whether worn
daily or overnight.
It is true that many patients can wear SHCL's safely overnight. - it
is equally true that MOST patients do very well with these lenses
on a DAILY basis. SHCLs should not be considered for just a select
few patients but for EVERYONE!
In our practice we now have over 1400 patients wearing these
lenses. Most patients started SHCL's on an overnight wear basis
and interestingly about 30% of these patients have developed
a preference for flexible wear. They continue to purchase the
lenses IN SPITE of the increased cost because of the enhanced
comfort, decreased dehydration and decreased limbal injection
when compared to their HEMA lenses.
Our clinical experience, combined with published research data,
has lead us to the conclusion that these lenses are superior
to HEMA in most situations. They are a NEW category of contact
lens that we now reach for FIRST in most fittings.
While it is often the goal of the practitioner and the patients
to sleep with contact lenses in, we have used SHCL's for many
other reasons including;
- Dry eyed patients - Patients exhibiting decreased
tolerance to HEMA products have done very well using SHCL's
for daily wear. Our preference with these patients is to use
a hydrogen peroxide based disinfecting system, but they also
do well with multipurpose solutions.
- Non specific redness - the slight limbal injection
we see with HEMA based products is almost always reduced when
patients are switched to SHCL's with both daily and overnight
wear.
- Resolving hypoxic complications - neovascularization
has been shown to decrease with SHCLs on a daily or continuous
wear basis in patients with moderate levels of vascularization
from HEMA lens wear. Very often only ghost vessels remain.
|
| Neovascularization - click to enlarge |
- Pediatric fittings - We use SHCL's in children
with significant hyperopia, anisometropia, and/or amblyopia.
Children who tolerate spectacles poorly do extremely well with
these lenses. The increased oxygen makes the lens wearable
for either daily or overnight wear.
- High myopes and hyperopes - HEMA lenses do not
supply sufficient oxygen on even a daily wear basis for hyperopes
and high myopes. These patients can be fitted with SHCLs to
prevent the hypoxic complications which would otherwise occur.
These patients also tend to wear their lenses for longer because
of the significant benefits in vision and therefore require
the superior oxygen transmission offered by SHCLs regardless
of the additional cost.
- Sensitivity to solutions - SHCL's reduce the
adverse effects of the chemical systems that we use with all
HEMA products.
|
| Piggyback - click to enlarge |
- SHCL's can also be used for a number of therapeutic
and bandage applications with great success in the following
situations:
- Corneal abrasions
- Bullous keratopathy
- Bells Palsy
- Recurrent corneal erosions
- Corneal perforations and lacerations
- Neurotrophic ulcers
- Post surgical cases (refractive surgery and
keratoplasty)
- Piggyback - We fit keratonconics and corneal
graft patients with a SHCL lens under a high dK RGP
to improve comfort and vision.
- We use SHCL's in high myopic astigmats who have
lost their tolerance to RGP's i.e -10.00 SHCL lens
with remaining Rx in spectacles to create a significant
improvement in function and cosmesis.
All this AND you may be able to sleep with them!!!
Whether your goal is overnight wear, daily wear, or flex wear
SHCL's are clearly the superior choice. A new category of lenses
has arrived. We feel we have an obligation to our patients to
provide them with SHCL's - the very best we have to offer.
|
Tell
a friend
In
The Practice | 
Dr
Kenton Fredlund is an optometrist with particular
interest in contact lenses, refractive surgery, and children's
vision. He received a Bachelor of Science in human anatomy
from the University of Saskatchewan, before studying Optometry
at Pacific University. After graduating from Optometry, he
worked at Pacific Cataract and Laser Institute in Oregon and
Southern Washington. He is on the board of directors for Doctors
Eyecare Network and is involved in coordinating Continuing
Education for Saskatchewan optometrists. 
Dr D James Kerr is a member of the Atrium Optometric
Group in Saskatchewan, Canada. He graduated from Optometry in
Waterloo in 1976. He was elected to the Council of the Saskatchewan
Association of Optometrists in 1979 and served on council for
10 years. During that time he held every office available including
President in 1985/86. In 1990 he was appointed to council of
the Canadian Association of Optometrists. He held most offices
in that association including President in 1995/96. He was a
driving force behind the creation of the Eye Health Council of
Canada, which aims to promote eye health awareness to Canadians.
Dr Kerr has been on many advisory boards and is currently involved
in clinical research in contact lenses. He was one of the founders
of the Horizon Laser Vision Center and continues to sit on its
board of directors.
Dr Michael York attended the Saskatchewan
Technical Institute, receiving a diploma in business administration
in 1982 which led to a 5 year career in the banking industry.
In 1987 he returned to university in pursuit of a career in Optometry
and received his degree from the University of Waterloo in 1992.
Following graduation he was involved in private practice in Brampton,
Ontario, as well as holding a position as clinical supervisor
at the University of Waterloo Optometry Clinic. In 1994 he joined
the Atrium Optometric Group in Saskatchewan, Canada. His practice
has been built primarily on general family vision care and contact
lenses, and he has also developed a special interest in children's
vision and contact lens practice. 
