Since its launch in August 2001, the silicone hydrogels website
has reflected the growing interest of eyecare practitioners and
researchers in the new products, with more visitors to the site
each month, and increasing numbers of queries and comments to
the Q&A section.
Over the past 18 months we have looked at various aspects of
the clinical performance of the lenses, and of silicone hydrogels
in practice, with the aim of providing useful information and
insights to all those working in the field. The recent redesign
of the site aims to enhance the accessibility of the information,
and we hope that it will continue to be a valuable resource for
all visitors.
Silicone Hydrogels in 2003
The elimination of hypoxia and its associated symptoms with continuous
wear silicone hydrogels is a tremendous achievement. We can now
prescribe continuous wear with confidence – something most
practitioners would not have imagined possible during the horror
stories of the 1980s.
As Brien Holden wrote in the first editorial on this site, “Overnight
edema levels with the new generation materials are similar to
the levels seen with no lens wear and are far lower than those
with commercially available disposable soft lenses [Fonn 1999;
Covey 2001]. A number of other markers of hypoxic stress have
been monitored in clinical studies at Vision Cooperative Research Centre (VisionCRC) and the Centre
for Contact Lens Research (CCLR) at the University of Waterloo,
Canada. For example, contact lens induced corneal striae [Covey
2001], microcysts [Keay 2000] (the classic marker of epithelial
hypoxia) and CL induced endothelial polymegethism are rarely if
ever seen with silicone hydrogel compared with disposable lens
contact lens wear [Covey 2001]. Corneal exhaustion syndrome should
be a problem of the past.”
We are now seeing incredible growth in the use of silicone hydrogels
around the world with the global launch of the two products from
CIBA Vision and Bausch & Lomb. Based on lens sales data, the
number of silicone hydrogel wearers worldwide is estimated at
850 000. The approval of lenses by the FDA for 30 days and nights
of continuous wear has triggered a rapid rise in sales, with many
existing and new lens wearers attracted by the convenience offered
by the modality.
 Vision Cooperative Research Centre (VisionCRC)
patients who have worn silicone hydrogel lenses successfully for
12 months or longer report overwhelming satisfaction with CW,
93% rating the lenses as excellent. The main reason for their
satisfaction with the CW system was its convenience i.e. the elimination
of the need for care and maintenance and lens handling (88 per
cent), being able to see in the morning (7 per cent) and excellent
comfort (5 per cent). Ten per cent of patients reported that they
forgot that they were wearing lenses at all.
A recent assessment of practitioner attitudes to EW found that
the US was the least conservative, with only 15% of clinicians
fitting no EW and 24% of practitioners fitting EW in more than
15% of their patients. Canada was the most conservative, with
42% fitting no EW and only 2% of practitioners fitting >15%
of their patients with EW (Jones 2002). According to Morgan (2002)
extended wear is now prescribed for 16% of soft lens refits in
the US, 13% in Australia, and 11% in the UK, with 95% of EW being
silicone hydrogels.
 Recent
conference activity also demonstrates the interest in the new
lenses. In December the American Academy of Optometry meeting
was held, and close to 20% of papers presented in the cornea and
contact lens section were on silicone hydrogel lenses. The papers
included patient and practitioner attitudes, and clinical perceptions
of silicone hydrogel continuous wear. Previously, a World Summit
Symposium on Continuous Wear Contact Lenses was held in San Diego
on August 15-18, 2002, and attracted a wide range of presenters
from around the world.
In the foreword to the special January CLAO supplement featuring
papers from the summit, H. Dwight Cavanagh writes “This
special ‘World Summit’ symposium of investigators…reports
to the world community the painstaking science behind these unique
new hyper-oxygen transmissible contact lenses materials and their
extraordinary clinical performance on the human cornea, in all
modes of wear.
“This was truly a meeting for a new millennium. The discerning
readers can now examine the compelling evidence for themselves
and afterward, this writer believes, all practitioners will conclude
that, collectively, these new lenses are and will become the future
standard of all contact lens wear for all patients, throughout
the world. It truly appears that real continuous wear is here
at last!”
The latest on Microbial Keratitis
One of the most important issues continues to be the question
of the risk of Microbial Keratitis (MK) with high Dk CW. While
silicone hydrogels appear to have reduced the incidence of certain
complications of wear, and it is theorised that MK is among them,
there is little data yet available on the absolute risk to wearers.
CRCERT has attempted to track all cases of MK worldwide. To date
we are aware of 23 cases of MK reported in silicone hydrogel lenses:
- 10 in Australia
- 3 in the USA
- 4 in the UK
- 2 in Norway
- 1 in France
- 1 in Italy
- 2 in India.
With an estimated 850,000 current silicone hydrogel wearers representing
approximately 640,000 patient years, these 23 cases represent
a rate of incidence of MK of 1 in 28,000 patient years. While
these global numbers may not be complete, we are reasonably certain
that we are aware of all cases that have occurred in Australia.
The Australian figures are 10 cases in an estimated 70,000 silicone
hydrogel wearers, giving us a rate of 1 in 7,000. This is contrasted
with the rate of 1 in 500 patient years found with low Dk EW of
soft contact lenses (Cheng 1999; Poggio 1989), and 1 per 2,500
found with low Dk daily wear (Cheng 1999; Poggio 1989).
Thus it is clear that even if the rate of MK with silicone hydrogels
is considerably higher than our current best estimates, it will
still be lower than with other modalities and lenses. While studies
will continue to keep a close watch with the aim of establishing
the true risk of MK with silicone hydrogels, this is a terrific
achievement.
The visual outcomes for these 23 patients were:
- 14: No change
- 3: Loss of one line of VA
- 2: Loss of 2 lines (keratoplasty required)
- 4: No data.
Of importance to practitioners and patients is the identification
of risk factors associated with MK. In the 23 cases the main risk
factors appear to be:
- Swimming (>30% of cases)
- History of irritation especially in that eye
- Persistence in wearing lenses after initial symptoms
- Persistence in wearing lenses overnight when sick.
Other factors may be
The issue of swimming is of particular interest. We have, for
example, had two cases of MK in New South Wales, Australia in
people who have swum recently. One was a daily wear patient, the
other, extended wear, each with silicone hydrogel lenses. We have
no idea whether this has any relation to the quality of the water
and the current drought in Australia but we did previously find
that the cycle of bacterial contamination in Sydney water did
correlate with the frequency of bacteria-driven adverse events
(Willcox 1997).
Until we know how to eliminate these problems altogether we suggest
that the following recommendations be strongly delivered to every
contact lens patient:
1. Do not swim in your lenses without swimming goggles - you
could get an infection, which if left untreated could lead to
a scar or, in rare cases, loss of vision.
2. If you remove your lenses and store them for any period of
time, make sure that they are properly cleaned and disinfected
before putting them back in your eyes.
Our preferred methods are:
- Clean and disinfect using a peroxide system with a 4-6 hour
soak prior to wear, or
- Thoroughly rub and rinse the lens with multipurpose solution
followed by a 4-6 hour soak in fresh solution prior to wear
3. Use a new disposable case for storage.
4. Never use ‘old’ lenses, solutions or cases.
5. Do not wear lenses if your eyes become red or sore. Remove
them immediately and call your practitioner without delay. Don’t
wait.
6. Do not wear lenses if you are sick.
7. Have an up-to-date pair of spectacles available for you to
wear if you need to remove your lenses.
This advice has been designed as a card which can be given to
patients. You can download
the patient card free of charge for use in your practice here.
By making sure that every patient:
- is careful when swimming or coming into contact with contaminated
water
- disinfects their lenses properly if they are out of the eye
for any period of time
- understands the warning signs of MK and what to do; and
- gets rapid and proper treatment if a problem arises indicating
MK,
practitioners will significantly reduce the risk of MK. It is
also important that practitioners know how to treat suspected
MK cases properly, as prompt treatment has a crucial effect
on visual outcome.
New MK studies
Establishing the relative risk of MK with silicone hydrogel CW
will enable patients and practitioners to make accurate decisions
about lens wear and to take appropriate measures to prevent infection.
At the American Academy meeting Lyndon Jones concluded that “Practitioners
remain cautious with the concept of CW, and desire more information
and longer-term results before adopting this modality on a larger
scale.”
At CRCERT we are about to commence a population-based study to
establish the incidence of MK amongst all contact lens wearers
using lenses for the correction of low refractive errors. The
number of cases of infection will be determined through active
surveillance of ophthalmologists and optometrists in Australia,
and the number of wearers in the community will be established
using a telephone survey.
Contact lens hygiene, compliance and other risk factor data will
be collected from both cases and controls to enable the effects
of available care systems, lens types and wear modalities to be
evaluated. This information is important to help us understand
the causes of corneal infection, and thus reduce the incidence
of infection and limit its morbidity.
The study also proposes to investigate particular bacteria associated
with contact lens related infections. Pseudomonas aeruginosa is
identified as the causative organism in 70% of lens-related corneal
infections, however pathogenic mechanisms in contact lens-related
infection are not yet well understood. We believe that determining
the phenotypic characteristics and signal molecule profile of
corneal and non-corneal isolates of this organism will elucidate
likely mechanisms, and will have practical implications for the
prevention and management of this disease.
Both CIBA Vision and Bausch & Lomb are conducting studies
which will continue to contribute to our knowledge in this area.
As a condition of FDA approval, each manufacturer was required
to conduct a postapproval study to gather additional data regarding
the risk of MK. The studies are of large cohort design, with each
study involving around 100 monitoring sites. Each prospective,
active monitoring study is designed to provide data on 4,500 to
5,000 patient-years of 30-day wear, with monitoring every 6 months
for 1 year. The studies are designed to provide an early indication
for risks in the real world setting and when completed, this information
will be added to the product labelling (Saviola 2003).
Into the future
Over the next year we will undoubtedly see further growth in the
silicone hydrogel market as more patients hear about the lenses,
and more practitioners become experienced in fitting and managing
silicone hydrogel patients.
Importantly, we may begin to have answers on the rates of MK
and other adverse events with silicone hydrogels, and the risk
factors involved. This will provide valuable information to enable
practitioners and patients to optimise their strategies and preventing
such events.
The task for researchers is to further lower the risk of MK and
other adverse events with the next generation of lenses. This
may be through the incorporation of anti-microbial properties
on or in the lens. Comfort too will continue to be high on the
list of priorities, with developments in the area of material
and surface biocompatibility, and lens design.
Wider ranging research will continue to enhance our understanding
of how the cornea responds to contact lens wear, the long-term
effects of contact lenses on vision, and other issues such as
whether contact lenses can play a role in combatting the myopia
epidemic.
Silicone hydrogels have made a strong start in the field of vision
correction, and will continue to grow as a major sector in this
market. In this website we will continue to present new developments
and findings in the field, and look forward to the comments and
experiences of our visitors. |
Tell
a friend
Editorial
| 
Deborah
Sweeney - BOptom (UNSW) 1980 PhD
(UNSW) 1992
Desmond Fonn