SILICONE HYDROGEL FINDING
A Conjunctival Response to Silicone Hydrogel Lens Wear
new finding reveals how silicone hydrogel lenses may affect the conjunctival epithelium.
By Tom Løfstrøm, OD, MScOptom
& Allan Kruse, OD
introduction of silicone hydrogel lenses has certainly made great strides in improving
the physiological response to contact lens wear. Silicone hydrogels also allow wearers
the benefit of wearing their lenses for longer periods of time without compromising
their eye health.
practitioners see the advantages of lenses that provide higher oxygen transmissibility.
Clinically, we find a significant decrease in limbal and bulbar conjunctival redness
and ghost vessels as well as minimal signs of corneal edema.
However, in spite of their positive
qualities, silicone hydrogels are associated with some complications. Researchers
have to date focused much attention on the adverse event rate, corneal response
and lid response with silicone hydrogels, giving little attention to the conjunctival
tissue response. Although it's common to observe conjunctival staining with any
type of lens wear, practitioners often aren't too concerned about it because of
its minimal clinical significance.
Conjunctival epithelial flap.
A conjunctival flap that extends across the entire
Conjunctival flaps vary in width among subjects.
silicone hydrogel materials have different properties than do hydrogel lenses and
thus may affect the eye differently, we examined silicone hydrogel lens wearers.
Upon close observation of the
conjunctival tissue of silicone hydrogel wearers, we noted a new clinical observation
that no research has previously reported. We call this new finding a conjunctival
Discovering a New Finding
We examined 16 subjects who had successfully worn
either balafilcon A or lotrafilcon A contact lenses for 30-day continuous wear for
a period of at least six months. Of the 16 subjects (32 eyes), seven subjects (14
eyes) wore balafilcon A lenses and nine subjects (18 eyes) wore lotrafilcon A lenses.
We used high magnification, fluorescein dye,
a yellow filter and cobalt blue light to observe the conjunctival epithelial flaps.
We're surprised that we, and other clinicians, haven't observed the flaps before,
but they're difficult to see using white light alone. Slit lamp examination revealed
conjunctival flaps in 34 percent of eyes (11/32).
We noted a significant difference in
the prevalence of conjunctival flaps between the two lens types (Table 1.) Prevalence
with lotrafilcon A was significantly higher compared to balafilcon A (56 percent
vs. eight percent, Fisher's test p=0.01).
Figure 1 shows a conjunctival flap located about
1mm beyond the limbus, in the area adjacent to the lens edge. The flap has an uneven
margin. Using the eyelid margin, we were able to manipulate the flap and move it
around. In this picture, the left part of the flap is facing down whereas the right
part of the flap is facing up.
Figure 2 shows a conjunctival flap that spans
the entire inferior quadrant. Conjunctival flap appearance can vary significantly
between subjects in both the extent (length of the conjunctival flap area) and the
width (Figure 3) of the flap tissue.
We observed conjunctival flaps only
in the superior, inferior or in both quadrants at the same time, and none in the
nasal or temporal areas. The flap may be present by itself or in combination with
conjunctival staining and indentation (which may be the early development stage
of the flap). We typically observe the flap originating from a slightly raised ridge
of what we believe is hyperplastic conjunctival epithelium. We saw no evidence of
fluorescein penetration into the conjunctival flap or into the underlying tissue.
However, we did observe pooling corresponding to the shape of a pre-detached flap.
Possible Contributing Factors
We have observed the flaps almost exclusively
in overnight wear of silicone hydrogels, but we've also seen a few small flaps in
daily wear of these lenses.
Clinicians commonly observe contact lens-induced
conjunctival staining (CLICS) outside of the limbus, following the lens outline
(near the lens edge). This indicates greater lens-tissue interaction and thus may
be a factor in flap development.
Certain lens edge shapes (Figure 4)
may cause more CLICS than others regardless of the lens material. Contact lenses
that have a knife-point edge, for example, are known to cause more CLICS than do
lenses that have rounded edges.
Silicone hydrogel lens materials have
a higher modulus than traditional hydrogel lenses, and non-rounded edge shapes in
these lenses may have greater influence in inducing CLICS, indentation and, therefore,
conjunctival epithelial flaps. The two silicone hydrogel contact lenses that we
studied had similar modulus but different lens edge shapes, and we found that they
produced different conjunctival response, particularly in conjunctival flap prevalence.
Based on this pilot study, we conclude
that the chisel-shape lens edge design of the lotrafilcon A lens worn on a continuous
wear basis resulted in a higher prevalence of conjunctival flaps compared to the
round-edge design of the balafilcon A lenses.
A lenses are available in two base curves, and Table 1 shows our findings for each.
Because of the small sample size for the steep base curve, it's difficult to determine
the effect of base curves on conjunctival flap development, although it appears
that the steeper base curve may result in a slightly higher prevalence.
To date, the presence of conjunctival flaps doesn't
appear to have a direct impact on lens wearing satisfaction or on subjective comfort.
Subjects wearing balafilcon A lenses tended to have less bulbar conjunctival hyperemia
compared to those wearing lotrafilcon A lenses.
We are currently considering a few hypotheses
for what causes the epithelial flaps. As we discussed previously, most are related
to the shape of the lens edge and how it interacts with the conjunctival tissue
and how this relates to overnight wear. In particular:
The lens edge shape configuration
may be carving into the superficial conjunctival tissue, facilitated by lens binding
during eye closure and subsequent movement upon eye opening. However, the absence
of fluorescein penetration and the presence of occasional pooling around this area
may indicate that the conjunctival epithelium is splitting or delaminating.
The lens edge constantly irritates
the conjunctival epithelial tissue and consequently increases the conjunctival epithelial
cell production or redistributes the epithelial cells. We typically observe what
we believe is a raised ridge of hyperplastic conjunctival epithelial tissue. However,
we often see flaps (Figure 5, red arrow) outside of the areas with CLICS (yellow
arrow). Some lens decentration during eye closure may explain this.
Conjunctival tissue irritation
results in conjunctival chemosis/swelling. When you place a higher-modulus contact
lens that has a non-rounded edge on a swollen tissue and a certain pressure is applied
(blinking), then the lens edge becomes superficially embedded in the soft swollen
conjunctival tissue area and a heaping of cells results. Overnight lens wear under
closed-eye conditions and no lens movement may encourage some cells to grow over
this area. Upon waking, the lens starts to move with the blink and shreds the emerging
Figure 5. A
conjunctival epithelial flap (red arrow) located outside
of the area with CLICS (yellow arrow).
this observation is new and hasn't been previously reported, further investigation
is needed. We believe that manufacturers need to recognize that because of the nature
of silicone hydrogel materials, lens fitting, edge shape and parameters are important
factors that ultimately determine their clinical performance. Therefore, we believe
manufacturers should further consider these factors when designing new silicone
We would like to advise our colleagues
to look for the presence of conjunctival epithelial flaps, or "Lens-Induced Flap
Excess of conjunctiva" (LIFE), with silicone hydrogel lens wear and to help us understand
their etiology and clinical significance.
Dr. Løfstrøm is the clinical research
operations manager and manager of the Synoptik Contact Lens R & D Clinic in
Copenhagen, Denmark. A contact lens specialist, he has also served as a clinical
investigator for several international companies and holds several teaching positions.
||Dr. Kruse is a research optometrist in Synoptik Research Clinic,
Contact Lens Spectrum, Issue: September 2005