1. What are Flashes and Floaters ?
Most of the interior of the eye is made up of the vitreous jelly. To stop it from sloshing about as the eye moves it is attached by fibrous anchors to the retina. As we get older, the vitreous shrinks and tugs at these attachment points and this can cause bright flashes of light, rather like lightning, at the edges of your vision. Occasionally one of these fibres will break away and will be seen as a floater drifting annoyingly across your vision - always there, but darting out of vision as you turn your eye to try and look at it. Sometimes this tearing of the attachment can leave a hole in the retina through which fluid leaks to cause the more serious condition of a retinal detachment. Professional advise should always be sought if you experience these flashes and/or floaters.
2. What is a cataract?
Inside the eye is a lens, rather like the one in a camera, that focuses light onto the retina. This lens is made up of layers of fibres, arranged rather like the layers that make up an onion. As we get older some of these layers, or individual fibres, can loose some of their transparency and it is this loss of clarity that is the result of a cataract. The effect is to degrade the quality of the image that is projected onto the retina, and to cause flare and dazzle from bright lights such as the headlights of cars.Treatment is simply the removal of this lens and its replacement by a nice new artificial one.
3. WHY is this harder to focus when you are approaching 40?
Many people notice their eyesight getting worse around the ages of 40 . They may notice that they have to strain to read newsprint up close and start holding the print further away to bring it into focus. The smaller print may be impossible to read especially in poor light.These are signs of a natural eye condition that everyone faces sooner or later. The condition is called presbyopia and is caused by a change inside the eye, which prevents the re-focusing of the eye for close distances.Although it is tempting to try hobby glasses, the best solution is to have a full eye examination to make sure the eyes are healthy and determine the exact strength of lens needed to best correct this focusing problem. Simple reading glasses, bifocal glasses or progressive lenses may be required.
4. What are the types of Refractive Surgery?
There are basically 3 main operations performed for correction of refractive errors:
* Radial Keratotomy (RK)
* Photo-Refractive Keratectomy (PRK)
* Laser Assisted Intrastromal Keratomileusis (LASIK)
5. Can I use eye drops with my contact lenses ?
In general eye drops shouldn't be used with contact lenses because the lens can absorb the eye drop and it would result in a concentrated build-up of the solution. There are special, "in-eye" lubricants that many manufacturers/pharmaceutical companies produce for use with contact lenses. Check with your eye care professional if there are any doubts about the solution.
6. How long does it take to adapt to new lenses ?
Soft lenses are generally worn for 2-4 hrs on the first day and the wearing time is increased by about 2 hrs per day, up until 8hrs of daily wear is achieved. The rate at which the wearing time is increased and the maximum number of hours that the lenses can be worn will depend on the recommendations of your eye care practitioner. Rigid lenses are generally worn for 2-4hrs on the first day with an increase of 1-2 hrs each day until 8 hours of daily wear is obtained. Again the rate at which the wearing time is increased and maximum number of hours of wearing time will depend on the person and the recommendations of your eye care practitioner.
7. How do I know when to dispose of my disposable lenses ?
The lenses will not automatically self-destruct at the end of the wearing period . The lenses should be discarded when the lens wearing time has elapsed, as advised by your eyecare professional. This wearing time/period has been chosen to minimise complications with contact lens wear so it should be adhered to !
8. Why is there a limit to the length of wearing time ?
The cornea, the "clear part of the eye", is avascular or without blood supply. It is avascular otherwise it wouldn't transmit light without distortion. As a result of this living tissue being avascular it is necessary to obtain oxygen from the atmosphere. The wearing of a contact lens interrupts the flow of oxygen to the cornea and due to changes in the metabolic pump of the corneal cells the tissue thickens, called oedema. Contact lenses, are manufactured from material that allows maximum oxygen transmission. But this is still not enough. Therefore the lens wearing time must be controlled to reduce oxygen deprivation to the cornea.
9. What is Extended Wear lens?
These lens are manufactured from a high-water content material and/or with a very thin centre thickness to enable maximum oxygen transmission.These lens can be worn overnight, or for a number of days without removal .
10. What is Disposable lens?
Spherical or toric contact lens which are designed to be worn for a certain time period, eg, weekly, two- weekly, monthly.These lens are generally sold in a "blister" combination pack, eg 3 months supply with intention that lens are "disposed" of at the end of the time period.
11. What is Toric ?
It contains both spherical and cylinderical components to correct prescriptions with astigmatism. These lens may be thicker in one meridian or have modified thickness profiles to enable the lens to maintain correct orientation on the eye.
12. What are the difference between soft and hard contact lenses ?
Soft lenses are manufactured from a plastic hydrogel polymer, HydroxyEthylMethacrylate (HEMA) which has a varying water content (38% - 70%). Lens size is between 13.00 and 14.50mm. Centre thickness from 30um.
Hard contact lenses are manufactured from a rigid material, PolyMethylMethacrylate (PMMA). This material can be combined with other plastics to increase the oxygen permeability. Lens size is between 8.0mm and 10.00mm. Centre thickness from 100um.
13. What is Ultra Violet absorption ?
Spectacle lenses, depending on the type of material will absorb varying amounts of ultraviolet light. In order of best absorbing lens the materials are polycarbonate, plastic and finally glass lenses. Different standards define the amount of absorption required, and/or the definition of the categories for spectacle lenses. The amount of UV absorption is also influenced by tinting, dying and lens coatings.
14. How can I reduce the edge thickness of the lens ?
Since edge thickness is a function of lens power, centre thickness and curvature of the front and back curves (all inter-related) the edge thickness is influenced by the following features:
refractive index of the lens material
centre thickness (eg safety lenses have a greater central thickness)
size of the spectacle frame, i.e larger eyesize means a bigger lens.
15. How is Visual Acuity Measured ?
Visual acuity is the measure of the sensitivity of the visual system. It is expressed in Snellen notation, expressed as a fraction, where the numerator indicates the test distance and the denominator denotes the distance at which the letter read by the patient subtends 5 minutes of arc. Normal vision is expressed as 20/20 (or 6/6 in countries where metric measurements are used). An acuity of 20/60 means that the patient was tested at 20feet but could only see letters that a person with normal vision could read at 60feet
16. What is Presbyopia ?
Presbyopia describes the condition whereby the amplitude of accommodation, or ability to focus on objects at near, decreases with increasing age. It is corrected by a different prescription for reading, which is additive to the normal spectacle correction used for distance vision.
17. What is Astigmatism ?
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 [ see section 4.1 ] 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
18. What is Emmetropia ?
Emmetropia is just another name for an eye that has no optical defects and a precise image is formed on the retina.
19. What is Hyperopia ?
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.
20. What is Myopia ?
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.
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