The Future: Contact Lenses in Silicone Hydrogel

The concept of lenses made from siliconethan their conventional counterparts, due to the
hydrogel was first proposed over 20 years ago.presence of silicone. This increased rigidity does
The potential benefits were clear but thepossess some advantages, making the lenses
technological challenge was as difficult as needingmarkedly easier to handle and thus the ideal
to combine oil and water to produce an opticallychoice for wearers with a less delicate touch.
clear product. Researcher organizations have toThere is a downside to this however in that the
date invested considerable academic and financialrigidity makes the lenses less prone to adopting
resources to achieve the high performance softthe shape of the eye so readily, resulting in the
lenses of today. They have done this quite simplypossibility for some of reduced comfort.
because they see this material as the wayREDUCED DEPOSITIONS
forward and the ultimate standard of the future.Historically, the deposition of proteins and lipids has
At the time of writing, silicone hydrogel lenses arebeen a problem with contact lenses. The amount
available in the USA from four manufacturers:of depositions is essentially linked to the duration
"Night & Day" and "O2OPTIX" from CIBAof wear, the lens material and the tear
Vision, "Pure Vision" from Bausch & Lomb, composition of each individual wearer. With
and "Acuvue OASYS" and "Advance" fromtraditional lenses, a frequent replacement schedule
J&J Vision Care.greatly reduces the buildup of harmful  deposits.
OXYGEN TRANSPORTSilicone hydrogel contact lenses have been proven
So what's so special about silicone hydrogel as ato offer major benefits in the reduction of protein
lens material? Essentially, the great benefit of thisand lysozyme deposition. Indeed, combined with
material is it's ability to transport oxygen to thethe correct replacement schedule and appropriate
eye and thus maintain proper eye health. Moderncare system, problems associated with protein
contact lens technology is all to do with oxygendeposition have become almost a thing of the
permability, which is measured using the "Dk"past.
index. And for optimal oxygen transmission, thisDRY EYES
must be as high as possible.A problem frequently encountered by wearers of
The Dk of traditional, non-silicone based hydrogeltraditional soft contact lenses is one of a feeling
lenses is directly related to the amount of waterof discomfort and "grittiness" in the eyes towards
that the material can hold, since oxygen dissolvesthe end of the day. It has been reported that
into the water-component of the material andafter one week wearing silicone hydrogel lenses,
thus diffuses through the lens. The Dk in factthe quantity of regular soft lens wearers in a
increases logarithmically with increasing waterparticular study group who previously suffered
content. Water itself has a Dk of only 80, thussignificantly from end-of-day dryness, was
placing a ceiling on the Dk of convential materials,reduced dramatically to only 13% of the sample.
and the original soft contact lens material,LIFESTYLE BENEFITS
polyHEMA, possesses a Dk of only around 10Silicone hydrogel contact lenses also provide some
(with a water content of about 38%).benefits that conventional lenses don't. Continuous
However, in silicone hydrogels, the relationshipwear contact lenses can be particularly beneficial
between Dk and water content is  the opposite.for use by members of certain professions, such
Here higher water content implies lower Dk. Withas medical workers, police, the armed forces and
these lenses Dk increases significantly as thefirefighters who frequently work unpredictable and
silicone content - not water content - of the lenslong hours.
increases. The Dk values of silicone hydrogelFurthermore, an increasing numbers of contact
contact lenses are much higher than those oflens wearers can now enjoy active outdoor
older soft lens materials.lifestyles, enjoying pursuits such as camping and
SLEEPING IN CONTACT LENSEShiking where it is often difficult to handle and
According to market data from CIBA Vision,disinfect the lenses with the appropriate level of
84% of soft contact lens wearers occasionallyhygiene.
sleep with their lenses in, and one-third admit toTHE FUTURE FOR CONTACT LENSES
doing this regularly. 25% of wearers of one toThere is much evidence to suggest that, owing to
two-week disposable lenses with low oxygentheir significant benefits over conventional soft
transmissibility occasionally or routinely sleep inlenses, silicone hydrogel lenses will ultimately, and
their lenses overnight. And 72% of soft contactsooner rather than later, displace other types of
lens wearers said they would prefer to be allowedcontact lens as the prefferred choice for both
to wear their lenses overnight provided it wasdaily and overnight wear for the majority of
safe.contact lens wearers. Silicone hydrogel lenses
Thus the demand for lenses with the capablitiesprovide a much improved physical performance,
of silicone hydrogels is evidently very high withexcellent handling properties and greater comfort.
almost three-quarters of soft lens wearersThey might be considered as the ideal lens for
wanting to be able to sleep in their lenses.general purpose use that exists today and are
LENS HANDLINGlikely to become the new everyday standard.
Silicone hydrogel lenses are significantly more rigid