30 Day Extended Wear soft contact lenses -- are they really an option?


Contact lens practice has become one of the largest growth areas for
optometrists in the last decade. There are many reasons that this
modality of refractive correction will continue to grow through the next
decade, and though new methods of refractive correction will continue to
be developed, contact lenses have some weighty advantages.

By far, soft contact lenses have been more widely accepted by the
general public than rigid gas permeable (RGP) lenses for many reasons,
including comfort, disposability and marketing. This creates a problem
for optometrists because there is now an expectation in the community
that contact lenses must be so comfortable that you don't feel them. It
makes it rather difficult to persuade patients that RGP lenses are a
better option, although RGP lenses are far superior when you consider
the view point of ocular health.

This drive by consumers for comfort and convenience, while reducing
ocular health risks to acceptable levels, is understandable. It has
driven research in many directions, looking for a semipermanent but
reversible method of vision correction that is cheap and easy. The
idea of a contact lens that can be left on the eye for a month at a time
is very appealing, as opposed to conventional contact lenses which need
to be inserted and removed every day.

A couple of decades ago, when optometry was still in its infancy, and
when contact lenses had just started being a practical method of vision
correction, extended wear was the most popular modality with
optometrists. In extended wear, the contact lenses are being worn while
asleep, as opposed to daily wear, where the lenses are removed before
sleep. Patients found (and still find) that insertion, removal and
cleaning of contact lenses to be annoying and time consuming, especially
when optometrists used to think that extended wear was a good option.

However, optometrists today have echoes of the past to assure them that
extended wear with conventional contact lenses is a big mistake. A
myriad of ocular health risks associated with extended wear lenses,
including blindness resulting from infectious keratitis, caused a big
change in the way we advise patients to wear contact lenses. With the
litigious society that exists today, health professionals are forced to
back their opinions with their bank balances, and this rightly drives us
to a better thought out philosophy on health.

The basis for steering away from extended wear was backed by scientific
studies that revealed many adverse changes in the cornea when subjected
to low levels of oxygen for long periods of time. In addition, soft
contact lenses reduce tear flow on the surface of the cornea, causing
a worsening of these effects. Indeed, any perfect contact lens needs to
have excellent oxygen transmissability through it, and allow good tear
exchange between the cornea and itself. Most conventional soft contact
lenses fail both of these criteria rather dismally.

With wear of conventional soft contact lenses overnight, there is
increased corneal oedema when compared to the 4% swelling found in normal
closed eye conditions.  Mechanical effects, including epithelial breaks
and lens adhesion are also common. Long term changes are similar to
those found in daily wear, except a lot more pronounced. These include
limbal hyperaemia or neovascularisation (signalling a compensatory
mechanism for the low oxygen levels), epithelial microcysts and striae
(indicating dysfunction of the endothelial pumps), and sterile
infiltrative keratitis (indicating an inflammatory response).

In addition, there are lid changes associated with wear of contact
lenses that are increased with more constant wear, of which the most
spectacular is giant papillary conjunctivitis. These changes often signal
a response to chronic trauma, whether it be induced by mechanical,
chemical or other means. Allergic responses are more pronounced with
more constant wear of soft lenses, especially since the chemical
mediators causing the reaction are less likely to be washed out of the
eye by the poor tear flow between the lens and the cornea.

So what's so different about these new lenses?

Basically, the only real difference with the new soft extended wear
lenses is that the oxygen transmissability has been increased to a level
where corneal changes due to hypoxia are reduced to minimal levels.
Mechanical and tear flow effects of the contact lenses are not
significantly changed, and so these lenses are still not perfect for the
extended wear modality. However, they are a big improvement over present
soft contact lenses, and are a step in the right direction.

We are still at the beginning of a long road of clinical trials to
establish the safety of these lenses, and while the early results look
promising, we really cannot make any conclusions. Indeed, it will take
many years to determine whether there is any decrease in the incidence of
infectious keratitis with this modality, and though the incidence is
known to be rather low, every case detected is important, as it may lead
to permanent blindness. A good compromise may be to prescribe these new
lenses with a weekly cleaning schedule, so that the risk of infection is
reduced while patients still retain the ease of extended wear for a week
at a time.

In my opinion, optometrists in Australia should still be wary about
fitting these lenses as 30-day lenses to people who are able and willing
to wear their lenses as daily lenses. However, for people who need a
long term modality, like infants or people with limited manual
dexterity, these are a very good semipermanent solution, especially if
the permanent options of laser or surgical vision correction are less
than welcomed by the patient.


Last edited: 27 May 2000