Feature Products
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| QUASAR PLUS Multifocal RGP |
The Central zone is powered for distance vision
On downgaze, the pupil looks through a zone of progressively postive power
Quasar Plus 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 patients's corneal topography, the degree of their emmetropia and their reading addition.
Quasar Plus 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 Quasar Plus will modify the spherical aberration of the combined optical system of lens, tears and cornea so as to provide a predictable varifocal effect.
Each lens is designed for a specified patient with the help of a predictive computer model which uses details of the patient's cornea and spectacle Rx to simulate an accurate power map of the Quasar Plus lens on the eye. 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.
Posted October 01, 2002
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| RGP Photochrome Lens |
The RSP Lens
Photochromic Colour
Harbour City Contact Lens Services introduces The RSP Gas Permeable Lens with photochromic dye, produced by Progressive Optical Research Ltd. This RGP material is designed by copolymerising oxygen permeable monomers, hardening agent monomers, wetting agents and cross-linking agents. The distinguishing feature of the RSP material is that it employs two wetting agents – one acidic and one basic. These wetting agents are copolymerised into the matrix of the polymer to give a balanced pH surface of the lens while increasing wettability for the desired comfort. The technologically advanced design of the material gives stability to the lens as well as exceptional wettability and comfort.
The introduction of the photochromic dye is infused in the monomeric stage; which is polymerized and the dye is distributed throughout the matrix of the plastic. The lenses photochromic activity is accomplished by UV radiation from the sun (can also be another source); which temporarily breaks a bond in the molecule which then twists and opens into a planar coloured form. The reversion to the non-coloured form (original colour) is accomplished by ambient heat (heat from the patient’s eyes).
There are two selected variations of the colour in the RSP material. The first material in its original state has a colourless to light greenish tint and changes to a beautiful blue tint colour under the sunlight. The second material is a turquoise-greenish colour that changes to a strong blue colour in the sunlight.
When the lenses are exposed to sunlight, the colour transition gradually takes place in 15 – 20 seconds. The reversal from the blue colour to the original colour gradually takes from 20 – 45 seconds to complete the transition to about 60%. To get to it’s original value it takes approximately 3 minutes if the lens is placed on the eyes. When the lens is in the container where there is no heat it will take longer.
Expectancy of the photochromic activity in the lens is about 1 to 2 years; however reheating the lens just under the glass transition temperature of the plastic can extend it; wherein, the photochromic activity may resume again. The benefits of the photochromic contact lens are that it blocks all UV light in the region from 220 nm to about 430 nm. It also removes the glare effect in certain light conditions (i.e. skiing in the bright snow, laying on the beach, night driving, etc).
Posted May 01, 2002
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| Copyright 2001 Harbour City Contact Lens Services. |
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