| Manuscript review by Kathy Dumbleton.
Although required by a relatively small proportion of wearers,
contact lenses for therapeutic purposes are a very important
indication for contact lens wear. Historically high water or
thin, mid water content hydrogel contact lenses were used for
these applications 1 since therapeutic lenses are generally worn
for prolonged periods and overnight. Unfortunately these lenses
were not able to supply sufficient oxygen to prevent overnight
corneal swelling and the combined effects of anoxia and already
compromised eyes often resulted in complications including infection
and inflammation 2,3 . Silicone elastomer lenses were also occasionally
used for some conditions, however these lenses, although capable
of providing sufficient oxygen to prevent overnight corneal swelling,
unfortunately often resulted in lens adhesion and poor wetting
4 .
The introduction of silicone hydrogel lenses has provided clinicians
with a viable alternative for their therapeutic cases since the
high oxygen transmissibility of these lenses has been shown to
result little additional overnight corneal
swelling when compared to that measured following sleep with
no lens in place. Both CIBA Vision's Focus Night & DayT and
Bausch & Lomb's PureVision T lenses, in addition to being
currently approved for continuous wear, have also received FDA
and CE Mark approval for therapeutic use throughout the U.S.,
Canada and the European Union.
Since therapeutic treatment with contact lenses is relatively
uncommon and varied in nature, it is somewhat difficult to evaluate
the efficacy of specific lens types for these patients in clinical
practice. In order to investigate this application for silicone
hydrogel lenses, a group of clinicians and researchers from the
Singapore National Eye Centre conducted a prospective clinical
trial to evaluate the efficacy of PureVision T contact lenses
in a continuous wear modality for therapeutic indications 5 .
Lim and co-authors report on 54 cases in which PureVision T lenses
were prescribed for pain relief, enhancement of corneal wound
healing, corneal protection, improvement of vision and corneal
sealing. The efficacy of the treatment was then rated at the
conclusion of the treatment process. Patients rated the amount
of pain relief as being: complete, considerable, fair, slight
or none. Wound healing was rated by the clinicians as being:
completely healed, partially healed, remaining the same or getting
worse. In cases of corneal protection, clinicians rated the protection
given by the lenses as being: effective, partially effective
or not effective. For visual improvement and corneal sealing
cases the results were simply reported to be either effective
or not effective. In many cases therapeutic lenses were indicated
for more than one reason.
Ninety six percent of the 28 patients requiring therapeutic
lenses for pain relief reported complete or considerable relief
with the PureVision T lenses. 83% of 40 patients requiring lenses
for wound healing demonstrated complete healing and 13% demonstrated
partial healing. One patient showed no change (2.5%) and one
patient's condition became worse, but in this case the lens had
been removed prematurely. One hundred percent of
the lenses (21 patients) prescribed for corneal protection achieved
this goal effectively. Wound sealing was effectively achieved
in 4 of the 5 patients requiring this treatment. The unsuccessful
patient had a large perforation which required a penetrating
keratoplasty. The two bullous keratopathy patients requiring
therapeutic lenses for visual improvement both achieved effective
results.
There were only two complications reported during the study,
one case of sterile peripheral infiltrates and one mechanical
disturbance of an epithelial defect as a result of the lens fit
being too lose. Both resolved without further sequelae.
The authors concluded that the PureVision T lenses were highly
efficacious in bandage lens functions and since conducting the
study these lenses have become the authors' primary bandage lens
of choice in corneal, external disease and refractive surgery.
A comparison with conventional bandage lenses was not made since
there was no control group in this study. Consequently historical
controls have to be considered when comparing the efficacy of
silicone hydrogel therapeutic lenses for the treatment of corneal
disturbances. Unfortunately this is problematical since a number
of different measures of success have been used in reporting
these data and patients' subjective perceptions also vary considerably.
In addition, the inclusion and exclusion criteria employed in
clinical trials of this nature can have a marked impact on the
success of the treatment. In the study conducted with conventional
therapeutic lenses by Jackson et al 1 , an overall success
rate of 78% for all cases was reported, measured by partial
or full goal achievement. Other studies have reported
success rates from 60% 2 to 92% 6 .
To date, this is the only study of its kind investigating silicone
hydrogel lenses in therapeutic applications. Other studies with
both the Focus Night & Day T lenses and PureVision T lenses
are sure to follow but in the meantime practitioners can apparently
be confident in prescribing these lens types for their patients
requiring therapeutic contact lenses.
References
1. Jackson AJ, Sinton JE, Frazer DG and Morrison E. Therapeutic
contact lenses and their use in the management of anterior segment
pathology. J Br Contact Lens Assoc . 1996; 19(1):11-19.
2. Dohlman CH. Complications in therapeutic soft contact lens
wear. Trans Am Acad Ophthalmol Otol . 1974; 78:399-405.
3. Kent HD, Cohen EJ, Laibson PR and Arentsen JJ. Microbial
keratitis and corneal ulceration associated with therapeutic
contact lenses. CLAO J .1990; 16(1):49-52.
4. Rae S and Huff J. Studies on the initiation of silicone elastomer
lens adnesion in vitro: binding before the indentation ring. CLAO
J . 1991; 17(3): 181-186.
5. Lim L, Tan DTH, and Chan WK. Therapeutic use of Bausch & Lomb
PureVision T contact lenses. CLAO J . 2001: 27(4):179-185.
6. Smiddy WE, Hamburg TR, Kracher GP, Gottsch JD and Stark WJ.
Therapeutic contact lenses. Ophthalmology . 1990; 97(3):291-295.
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Feature Review | 
Kathryn
Dumbleton - BSc (Hons), Uni of Wales1984
MCOptom 1985, MSc Uni of Waterloo 1988