| Purpose:
|
| Tear microspheres
(TMSs) also referred to as pre-corneal deposits, "lipid
plugs" or "mucin balls", have been observed
in low numbers with soft and RGP contact lens wear. We compared
the incidence of TMSs between low DK (group IV) and high DK
(group I) hydrogel lenses during extended wear. |
| Method: |
| 153 subjects were randomly
assigned either the low DK 6N EW (n = 77) or the high DK 30N
CW (n = 76) lenses bilaterally. TMSs were observed using a
biomicroscope (16x) as small (10-50 m) spheres showing reversed
illumination and trapped between the lens and the cornea.
They were seen to be adherent to the cornea until soon after
lens removal leaving small, fluorescein filled indentations.
The number of TMSs was counted at baseline, one week, 1,3,6,9
and 12-month visits. |
| Results: |
| A significantly higher number
of TMSs (p < 0.05) were found in the high DK lens wear
group (mean for all visits, 14 26) compared to low DK (5 4)
lenses at all visits except 12 month EW visit (p<0.05).
No relationship could be found between TMSs and any adverse
events. |
| Conclusions: |
| High DK lenses produced
a higher incidence and number of TMSs, than the low DK lenses.
We are investigating the hypothesis that they are lipid
encapsulated mucin and proteinaceous material resulting
from a "shearing" interaction between the lens,
tear film and ocular surface which especially occurs with
high DK lenses. This could be related to the higher lens
modulus of elasticity or surface properties of the high
DK materials. TMSs do not apparently cause any clinical
adverse effects.
This research was supported in part by the Australian government
via the Cooperative Research Centres program and CIBA Vision. |
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