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QuasarPlus
is an innovative aspheric varifocal rigid lens which uses a variety
of aspheric back surface geometries to provide distance, intermediate
and near correction for presbyopic patients. Each lens is designed
on an individual basis, depending on the patientís corneal
topography, the degree of their emmetropia and their reading
addition.
QuasarPlus
is a centre distance lens with increasing positive power towards
the edge of the optic zone. When worn by the specified presbyopic
patient, the aspheric geometry of QuasarPlus will modify the
spherical aberration of the combined optical system of lens,
tears and cornea so as to provide a predictable varifocal effect.
QuasarPlus:
Visual performance
Each lens is designed for a specified patient with the help of
a predictive computer model which uses details of the patientís
cornea and spectacle Rx to simulate an accurate power map of
the QuasarPlus lens on the eye.
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| The central zone provides distance vision |
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| On downgaze, the wearer looks through a zone
of increasingly positive power |
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The power gradients
of the lenses are confirmed by measurement using a Visionix 2001
instrument, a power mapping device which can measure varifocal
contact lenses. No 7 has invested in leading edge manufacturing
and measurement technology so that it can deliver sophisticated
products such as QuasarPlus to its client practitioners.
QuasarPlus:
The lens-cornea relationship
Although the back surface geometry of QuasarPlus will be different
to normal Quasar or spherical lenses, the fitting relationship
between the lens and the cornea is approximately normal as assessed
by means of apical and edge clearance. For each prescription,
the effects of corneal topography and the patientís natural
spectacle correction are included in the calculation of the aspheric
surfaces required.
The pictures above show the fluorescein pattern of a normal tricurve
spherical lens being worn and a computer simulation of the tear
layer in the flatter principal meridian. The apical and edge
clearance are typical with 15 microns apical clearance and
about 95 microns of axial edge clearance.
When the QuasarPlus
lens is designed for this eye, the back surface is adapted to
be aspheric to provide the varifocal optics but the lens cornea
relationship is maintained with apical and edge clearance matching
the spherical lens which the patient was previously wearing.
Best in
Class - the clinical evidence
The on-eye performance of QuasarPlus has been assessed by means
of a clinical investigation conducted by Eurolens Research at
UMIST. In this study, 28 subjects wore the lenses for a
period of three months. The subjects were all presbyopic, ranging
in age from 45 to 68 and having spectacle reading additions in
the range +0.75 to +2.50.
The results
of the study show that the high contrast LogMAR spectacle acuity
at the initial visit had a mean of +0.10 ± 0.12
(which approximates to 6/7.5 ± one Snellen line of acuity)
and that the acuity at the final visit wearing QuasarPlus varifocal
lenses was +0.12 ± 0.10, which also approximates
to 6/7.5 ± one Snellen line of acuity. Clinically and
statistically there was no difference between the high contrast
acuity found at the initial visit for spectacles and that found
for the varifocal contact lenses at the final visit (t = -0.623,
p = 0.5388).
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