Flexure And Residual Astigmatism Of Opus III Lenses On Toric Corneas.

The study of hard lens flexure and residual
astigmatism began in 1961 with a paper by Neal Bailey.
Since then a number of studies using the new RGP
materials have been conducted (eg. Harris, 1970;
Harris & Rodoya, 1982; Harris, 1982; Herman, 1983;
Kochanny, 1984; Pole). The results of these studies
indicate that rigid contact lenses flex on toric
corneas, thus inducing residual astigmatism. The
amount of flexure and residual astigmatism is
dependent
thickness,
on the degree of
and the effective
corneal toricity, lens
base curve to cornea
fitting relationship. Pole found that lenses fit
steeper than 'k' flexed significantly more than
lenses fit on 'k' and flatter than 'k'. A comparative
study done by Kochanny revealed that the three most
popular RGP materials, Boston, polycon and silcon
flexed approximately 0.250/diopter of corneal
toricity. The present study was designed to measure
the flexure and residual astigmatism of the Opus
III lens material. The Opus III is a new generation
of styrene based gas permeable hard lenses. The
lens is composed of tertiary butyl styrene
copolymerized with four other monomers, including
silicon, to increase 02 permeability. The Dk value
of the new material is 14 x 10-" @ 35°C with a wetting
angle of 46 via the captive bubble technique