No7 Contact Lenses: Student Support website
Only by using state-of-the-art lathing technology and computer modelling were No7’s design team able to produce a lens with differing aspheric geometries in the two principal meridians. The result is a lens with an edge clearance and alignment identical to those of a Quasar lens on an eye with no astigmatism.
– Quasar Toric
The Quasar Toric has been designed using the well-established and highly successful Quasar multi-aspheric geometry. Only by using leading-edge lathing and computer modelling were we able to create a lens with varying aspheric geometries in the two principal meridians. This ensures that the edge clearance and alignment of the Quasar Toric are exactly the same as with those achieved with Quasar lens on patients with no astigmatism.
The need to introduce multi-aspheric geometry to toric lenses arises from the fact that the flatter meridian of an astigmatic eye flattens less rapidly than the steeper meridian. A lens with the same relative flattening in the two principal meridians will therefore be too tight in the steeper meridian compared to the flatter.
The resultant ideal fit for Quasar Toric is perfect alignment in the flattest meridian with precisely calculated flattening towards the periphery in the steep meridian to allow excellent movement, optics and corneal health.
In Quasar lenses, the lathe-generated edge form is well-rounded and has a centrally positioned apex 0.12mm thick. All are lenticulated and the form of the front surface is custom designed to maintain the consistent edge and junctional thicknesses needed for maximum comfort and oxygen flow. Where there is a cylinder applied on the front surface the lenticular design is modified to optimise the thickness and thereby the comfort.
– Quasar Toric
No7 recommends the Optimum rage of materials. Other materials available on request.
|Radii||Flattest meridian 7.00 to 9.00 in 0.05mm steps|
|Max Difference Flat/Steep||2.0mm|
|Total Diameters||+8.80, 9.20, 9.60, 10.00mm|
|B.V. Power Range||+25.00 to – 25.00 in 0.25D steps|
|Central Thickness||Minimum 0.12mm|
– Quasar Toric
The Quasar Toric is always fitted empirically. The laboratory should be provided with the keratometry readings, the spectacle refraction, back vertex power and the total diameter of the lens required. A custom designed lens will be produced for that particular patient which then serves as a trial lens. In the vast majority of cases that lens will be dispensed as the patient’s final lens.
Figure 1 – Ideal Fit
As with Quasar lenses, if the practitioner decides that a larger or smaller lens is ultimately required, no change is made to the radii unless they do not align perfectly with the cornea.
Figure 2 – Quasar Toric Fit
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