ANDREW GASSON CONTACT LENSES
A LONDON SPECIALIST CONTACT LENS PRACTICE SINCE 1972
QUESTIONS AND ANSWERS ON CONTACT LENSES
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WHAT IS THE DIFFERENCE BETWEEN SOFT AND HARD LENSES?
Modern contact lenses are all made from some type of plastics. Hard lenses are made from rigid materials, now generally called 'gas-permeable, and are hard to the touch. Soft lenses are manufactured from chemically similar but hydrophilic (water loving) materials which absorb a certain amount of water into their structure. This makes them feel soft and flexible and therefore initially more comfortable than hard lenses.
The latest 'supermeable' materials are called silicone hydrogels. Transmitting five times the oxygen, they allow the eye to breathe much better and frequently dry out less.
WHAT ARE THE ADVANTAGES OF SOFT LENSES COMPARED WITH HARD?
They are more comfortable initially and the wearing time can be built up more rapidly. They are less likely to be dislodged from the eye, especially with sport, and don't have to be worn as regularly as hard lenses. They are also much better in dusty conditions.
WHAT ARE THE ADVANTAGES OF HARD LENSES COMPARED WITH SOFT?
They last longer, often give better vision and are easily made in complex designs such as bifocals. They are easier to look after and there is less chance of allergy to solutions. With some medical cases, hard lenses are the only way to achieve good vision.
WHAT ARE DISPOSABLE LENSES?
Disposable lenses are soft lenses which are discarded and replaced on a frequent basis. This is usually monthly, one or two weekly, or daily.
WHAT ARE THE ADVANTAGES OF DISPOSABLE LENSES?
Experience shows that considerably fewer clinical difficulties arise when lenses are replaced on a regular basis before they reach the troublesome stage. Deposits are avoided and there are reduced risks of discomfort, allergies, infections and red eyes. Simpler 'all in one' solutions can be used - except in cases of allergy
WHAT ARE EXTENDED (PERMANENT OR CONTINUOUS) WEAR LENSES?
Some special types of high grade contact lens allow the eyes to breathe sufficiently well when the lids are closed that they are suitable to use during sleep. This means that they do not have to be removed at night and can be worn for several days or weeks continuously. They are particularly suitable for patients who have difficulty in lens handling. Such lenses are not new or experimental since they have been successfully fitted for more than thirty years. Those made from the latest generation of materials (silicone hydrogels) are hugely more permeable and safer than their earlier counterparts.
COMPARED WITH SPECTACLES, WHAT ARE THE OPTICAL ADVANTAGES OF WEARING CONTACT LENSES?
Contact lenses give a much wider field of view and, because they rest on the eye instead of in front of it, vision appears much more natural. This is especially true for very short-sighted patients who will frequently gain the greatest benefit from contact lenses. With some special eye conditions, a contact lens may be the only way of providing good vision.
CAN YOU CHANGE BETWEEN CONTACT LENSES AND SPECTACLES?
With soft lenses and most gas-permeable hard lenses, you should be able change back to spectacles straight away.
IF YOU HAVE ALREADY FAILED WITH CONTACT LENSES IS IT WORTH TRYING AGAIN?
Modern lenses are frequently much more comfortable and easy to get used to compared with earlier types. Even if you have failed previously, it is almost always worth trying again. This applies to both hard and soft lenses. It is very likely that lenses and designs you may have tried a few years ago now no longer exist.
CAN CHILDREN WEAR CONTACT LENSES?
Children often make extremely good contact lens wearers and there is no actual lower age limit. (In hospital clinics, babies are sometimes fitted when only a few months old). The usual criteria for fitting are that glasses need to be worn all of the time, that both child and parents are keen on the idea and that the child is old enough to understand what is required in handling and taking care of the lenses. It is not necessary to wait for the eyes to stop changing and we still often fit hard lenses as the first choice as these may help to slow down any increase in short sight..
CAN PATIENTS WITH ASTIGMATISM WEAR CONTACT LENSES?
The great majority of patients with astigmatism can be successfully fitted with contact lenses of one sort or another. We still sometimes recommend initially trying hard lenses since these usually give the best possible vision with the simplest and least expensive design of lens. With small degrees of astigmatism, straightforward soft lenses usually also give good vision. Where this is not possible there are now several varieties of soft lens specifically developed to correct even quite large amounts. These are called torics and are available as both conventional and disposable lenses.
CAN PATIENTS WHO NEED READING GLASSES WEAR CONTACT LENSES?
Patients who require reading glasses can be fitted with contact lenses for distance vision in the normal way. There are then three ways of dealing with reading and near vision, either on their own or in combination:
Simple reading glasses to wear on the top of the contact lenses which are worn in the normal way.
Bifocal contact lenses which can be either hard or soft.
Monovision where we correct one eye for distance and the other for reading.
ARE CONTACT LENSES SUITABLE FOR SPORT?
Contact lenses are suitable for almost all sports, and have considerable advantages over spectacles. Soft lenses, especially, are fitted to be quite stable on the eye, and are most unlikely to fall out.
ARE CONTACT LENSES SUITABLE FOR SWIMMING?
Where possible it is better not to use contact lenses for swimming because of the risk of loss. Hard lenses will almost certainly float off the eye and soft, because they are porous, can absorb chemicals such as chlorine from the water and become quite irritable. There is also a greater risk of eye infection, especially with extended wear. Swimming goggles are recommended as a good compromise.
CAN CONTACT LENSES GET LOST BEHIND THE EYE?
No, but occasionally a lens might slip beneath the top lid and seem to disappear. It will cause no harm on the white of the eye, even if it stays there for a long time. It is anatomically impossible for the lens to get lost behind the eye.
HOW LONG DOES IT TAKE TO BE FITTED WITH LENSES?
Where possible, we carry out the preliminary examination and complete the fitting at your first visit. In this way, we are then in a position either to supply lenses straight away from our extensive stock or to order them to your exact prescription. The laboratory may well have straightforward prescriptions in stock and despatch them the same day. If lenses have to be made specially, depending upon the complexity of the prescription, they may take about seven working days to obtain. With disposable lenses it is frequently possible for them to be collected at your first visit.
HOW LONG DOES IT TAKE TO GET USED TO CONTACT LENSES?
This depends on a number of factors, including each patient's individual sensitivity. On average, however, soft lenses take one or two weeks to get used to and hard lenses about four weeks. The important point is that you should carefully follow the wearing schedule which you are given.
ARE CONTACT LENSES EASY TO HANDLE?
In the majority of cases the handling of both hard and soft lenses is a straightforward procedure which can be learnt in about half an hour. In cases of difficulty we can demonstrate several different techniques for insertion and removal, one of which should allow you to acquire the knack fairly easily. You should regard handling as a minor hurdle to overcome which doesn't really affect the more important issues of vision, comfort and wearing time.
WHAT ARE THE ADVANTAGES OF HAVING A SPARE PAIR?
The main advantage of having a spare pair of lenses is that a replacement is immediately available with no loss of tolerance whilst a new lens is being prepared. This is especially important with high prescriptions where spectacle vision may seem distorted compared with the much more natural sight provided by contact lenses or where complex lenses may take several days to obtain. Patients wearing disposable lenses will generally have their next pair readily available as spares.
WHY DO SOFT LENSES NEED CLEANING AND DISINFECTING?
Soft lenses contain water (saline) and are porous. They are therefore liable to contamination by micro-organisms and sterilisation is essential after lens removal. Whenever soft lenses are worn, they also become coated with deposits from the tears such as mucus and protein. If these are not carefully removed by cleaning each time the lenses have been used, they gradually build up until the lenses become uncomfortable, discoloured and need to be replaced. A stronger cleaning system is recommended for non-disposable lenses. Wearing 'dirty' lenses is also more likely to give sore, red eyes, especially in summer or the hay-fever season.
Daily disposables are the only lenses which do not require looking after. Any lens which is worn more than once MUST be cleaned and sterilised.
CAN DROPS BE USED TO MAKE LENSES MORE COMFORTABLE?
Yes, but they must be specially formulated to use with contact lenses. Generally, when wearing soft lenses you should be very careful about using eye drops. Even quite mild drops or eye-whiteners which can be obtained from a pharmacist should not be used in case they contain the wrong chemicals. There are, however, several solutions specially formulated for use with lenses and these can help with dry eyes. They rewet the lens and can both improve the comfort and extend the wearing time. In cases of doubt ask our advice before using such drops. Some patients find that simple saline solution can also be very helpful.
WHAT HAPPENS IF A SOFT LENS IS ALLOWED TO DRY OUT?
A soft lens is not necessarily spoiled because it has dried out, although in the dry state it is quite brittle and easily broken. It should be immersed in a soft lens soaking solution for about one hour and then carefully examined for any signs of damage. If there is any discomfort it should be discarded.
WHY DO HARD LENSES NEED TO BE KEPT IN SOLUTIONS?
It is very much better for hard lenses also to be kept in solution. It is more hygienic, the comfort is improved, and there is less chance of the lens altering its fitting curvature. Lenses should never be licked before insertion.
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