An astigmatic eye generally has two different meridians, at 90degrees to each other, which cause images to focus in different planes for each meridian. The meridians can each be either myopic, hyperopic or emmetropic. The correction for astigmatism is a lens power at a particular direction of orientation. Astigmatism causes images to be out of focus no matter what the distance. It is possible for an astigmatic eye to minimise the blur by accommodating, or focusing to bring the “circle of least confusion” onto the retina.
Hyperopia is often referred to as “long-sightedness” or “far-sighted”. An eye is hyperopic when the far point is at a virtual point behind the eye. Generally the hyperopic eye is too short with respect to the refractive state of the standard eye (ie an emmetropic eye or eye requiring no optical correction) or because the optical power of the eye is too low relative to the length of the standard eye. The focus is correctly adjusted using a “plus” lens power or convex lens.
Myopia is often referred to as “short-sightedness” or “near-sighted”. An eye is myopic when the “far point”; a point at which light from an object is focussed on the retina, is located at a finite distance in front of the eye. Myopia can be due to either an eye which is too long relative to the optical power of the eye (axial myopia), or because the optical power of the eye is too high relative to the length of the standard eye (refractive myopia). The focus is correctly adjusted with a “minus” power lens, or concave lens.
Emmetropia is just another name for an eye that has no optical defects and a precise image is formed on the retina.
Single Vision lenses
Can be spherical or with astigmatism correction depending on your prescription. Made in plastic or glass.
Consider one pair for distance and one pair for reading.
Main distance prescription in the top with an additional segment in the bottom portion of the lens for reading.
Main distance prescription in the top with TWO additional segments in the bottom portion of the lens. One for near (reading) and one for intermediate distances (computer).
Main distance prescription in the top which gradually changes to the near prescription in the bottom. Allows for clarity at many distance between 20ft and 16 inches.
Darken when exposed to short wavelength radiation (300nm – 400nm) or ultra-violet light.
Lenses will not become as dark when driving due to UV absorption by the car windscreen.
Eliminate glare. While sunglasses reduce brightness, the only way to eliminate glare is polarization. Available in glass, plastic and hi-index plastic.
Great for sports, driving and water activities.
Spectacle lenses may often be treated with a surface coating (vacuum coating) to reduce unwanted reflections.
Reduces reflections visible by an observer from the front, internal reflections of the lens itself, reflections from behind the lens (overhead lighting) and reflections from the corneal surface.
Great for night driving and working under florescent lighting.
Hi Index Lenses
A higher refractive index material that enables the lens thickness to be reduced while still maintaining good optics.
Heat or chemical treated to increase impact strength
Used in industrial applications for added safety and protection.
High power plus lenses that were previously used for cataract patients that have no implant.
Made with aspheric surfaces to minimize aberrations due to shape of the lens
No. There are a number of micro-organisms, which like feeding on corneal tissue. Storing lenses in water also defeats the purpose of using a disinfecting solution as there is no disinfection occurring. If anything you are exposing your lenses to more potentially dangerous microorganisms.
In general all contact lenses, whether soft of rigid type, will require a cleaning, disinfecting and rinsing solution. Enzymatic agents (protein remover) may also be required to reduce build up of protein on the lens surface.
Spherical – Single prescription power 360 degrees around the lens.
Disposable – Spherical or toric contact lenses which are designed to be worn for a certain time period, eg, weekly, two- weekly, monthly. Lenses are generally sold in a “blister” combination pack, eg 3 months supply with intention that lenses are “disposed” of at the end of the time period.
Extended Wear – Lens manufactured from a high-water content material and/or with a very thin centre thickness to enable maximum oxygen transmission. Lenses can be worn overnight, or for a number of days without removal (see comments on complications for further information).
Bifocal Lenses – There are a variety of designs in bifocals, essentially all trying to provide a transition or reading zone for use at near. The different designs include; + aspheric multifocal – + simultaneous vision concentric – has either a central near or distance zone with surrounding zone of opposite type to centre (eg, centre near,distance surround) + diffraction/holographic – based on diffraction grating principles