| Product: |
Contact Lenses in general |
| Date: |
05/04/01 (690 review reads) |
| Rating: |
 |
Advantages: superior image quality, low risk of problems, cosmetically excellent
Disadvantages: expensive, cleaning regimens, infections and other complications
Introduction
This wonderful little invention has helped millions improve their visual potential and their use has been widespread, but it is important that people are fully informed of the risks before using them so they can make an informed choice of whether lenses are right for them. Using lenses automatically commits you to looking after them properly or the risk of complications from their use rises dramatically.
Classification
There are three main types of lens, two of which are in common useage today. The latter two are RGP (rigid gas permeable) lenses, which provide a very high oxygen permeability, and soft lenses (which are the most comfortable to wear). The last type which are poorly permeable to oxygen and which are rigid are called hard lenses. These are seldom prescribed for new patients nowadays.
Corneal Physiology
The cornea is the window of the eye, a clear dome of tissue which is curved and acts as part of the focussing system of the eye, like a lens. In order to function properly, the cornea has no blood vessels (so it remains clear and allows light to pass through it).
As there is no blood to supply them, how do the corneal cells obtain the oxygen they need to survive? Oxygen from the air dissolves into the tear film covering the surface of the eye and this bathes the cells directly. In order for fresh oxygen to get to the corneal surface and for waste products to get away, the tear film needs to be replenished frequently. This is done by blinking which removes old tears and spreads new tear fluid over the eye's surface.
Placing a contact lens on the surface of the eye changes all this in two ways:
1 - the surface area available for oxygen transfer to take place is reduced.
2 - tear film turnover is inhibited by the physical presence of the lens.
These profound changes form the basis for the numerous complications which can possibly occur as a result of contact lens use.
Advantages
As an optical "crutch", contact lenses help to smooth out the surface irregularities of the cornea (the clear window at the front of the eye) and thereby improve the quality of image perceived by the eye. They can also overcome a limited amount astigmatism (irregularity of curvature where the cornea is curved more like a rugby ball than a sphere) in the eye.
Cosmetically, lenses can be specially coloured, thereby altering the appearance of the eyes. They also remove the need for glasses and are especially useful for those people who are very short or long sighted where the image of their eyes, as seen through their spectacle lens, is reduced or enlarged (respectively) to the onlooker.
Special lenses can be used as "bandages" in certain eye conditions but these are very specialised are are prescribed by eye doctors in the hospital under careful supervision.
Disadavantages
Daily cleaning regimens are usually the order of the day and strict adherence to these regimens are necessary to reduce the risk of complications. Solutions can be expensive but one should never be tempted to manufacture one's own solutions as it is impossible to produce sterile saline solution at home and one is liable to develop acanthamoeba or bacterial infection which can ruin vision.
Lenses have a limited shelf life and need to be changed periodically. A well made set of lenses is expensive. It is possible to buy disposables nowadays but I suspect that the manufacturing quality is somewhat inferior.
Prolonged use can lead to reduced corneal sensation. This can lead to the inability to recognise corneal abrasions and scratches by the patient. In a contact lens wearer, these need to be rapidly addressed to prevent deterioration to bacterial corneal ulceration.
People with dry eyes or external eye disease should not try contact lenses as these will usually cause worsening of symptoms and irri
table eyes and may predispose them to an increased risk of bacterial ulceration.
Allergies can develop in lens wearers due to the solutions used, as these contain preservatives to increase the shelf life, e.g. thiomersal & benzalkonium chloride. Remember, these work by killing bacteria and if they can do that to bugs, think what they can do to the surface of your eye!
The physical presence of the lens may cause changes to the inside of the eyelid in the form of giant papillary conjunctivitis, as the edges rub against the delicate membrane which lines the lid. This can cause long term mucus discharge, blurred vision and discomfort and may necessitate discontinuation of lens use for a variable period of time.
While at the cinema recently I cringed when I saw an advertisement for monthly disposables which are left in for the whole month and changed on a monthly basis. I suspect these are hydrogel type lenses with a high water content and higher permeability to oxygen. However, they are still foreign bodies, and their presence in the eye still prevents adequate tear film replenishment and turnover and also must increase the risk of infection enormously by keeping a filthy bio-film mixture of old tears and bacteria against the surface of the eye. Note, that this also occurs with lenses worn normally and so the risk of infection is increased in normal contact lens wearers.
Finally, I mentioned earlier that the normal healthy cornea has no blood vessels, but a sign of prolonged or over-use of contact lenses is the growth of small blood vessels into the peripheral cornea. This is because the contact lens reduces the surface area of cornea available to allow exchange of oxygen to take place and in so doing stimulates the body to take reparative measures. In order to remedy the situation, the eye grows new blood vessels to bring fresh oxygen to the oxygen-starved cornea. One can easily appreciate that this is a flawed process and in very ad
vanced cases can cause obscuration of the central cornea with reduced vision. If this does occur, and a corneal graft (for whatever reason) is required in the future, the risk of surgical failure is very high.
Conclusions
Contact lenses are a wonderful tool, ideal for sports people (but not swimmers in whom serious infections can occur) and for occasional use, but the risks when they are abused should be considered by anyone planning on wearing them. The image quality obtained is usually superior to that obtained with a spectacle correction and they are cosmetically superb. But be careful because they can bite back.
WARNING: If you are a contact lens wearer and you develop a red eye whilst wearing your lenses, remove them immediately and seek the attention of your optometrist who may well refer you to your local Hospital Eye Service.
Summary:
|
Last comments:
 |
- 13/08/06 I wish my optician had given me an ounce of the information you have written when I first started wearing contact lenses. Of course, anything I voluntarily put into my eye is my own responsibility. Certainly, as a health professional myself, I have a responsibility to provide my patients with risks as well as benefits.
I initially had daily disposable contact lenses, which, like you said, lead to overgrowth of corneal blood vessels. In order to give my eye better oxygenation, I was warmly recommended the 30 day leave/sleep in contact lenses.
For 18 months I have had no major dramas with them, and found the ease of use great. I was careful with hygiene when changing them.
However, I am now recovering from pseudomonas corneal ulceraton caused by my contact lenses, a condition I was not even aware existed. I very nearly lost the vision in my eye, and was very lucky to get rapid treatment which was successful, but needed very aggressive attention in hospital. I will always have a corneal scar, which luckily is just outside my field of vision.
I do not think the optician has to list every condition linked with contact lenses, however, I believe minimal attention was paid to outlining the differences with the old and new lenses in terms of care and things to look out for, and that seeking opthalmic assessment with red eye, pain and irritation is extremely important in continous wear lense users. I was given the hard sell on these lenses and bought it lock stock and barrel.
Although I was essentially very happy with the lenses, it is not worth the damage that I sustained. Bacterial ulceration of the cornea sets in very quicly, is extremely aggressive and can cause great damage and even blindness within 24-48 hrs.
Just to warn...! |
 |
- 04/04/03 Ive just started wearing contacts. My first weekactually. I thought your opinion was very very informative |
 |
- 05/01/03 Very useful, and I now feel better about the fact that I rarely bother with my lenses (probably about one evening a week). You've got me slightly worried about the bandage lenses my mother has to wear as a result of having Recurrent Epithelial Erosion Syndrome and very dry eyes, but she's under the care of Moorfields who are said to be the top, I imagine they know what they're doing. One of the best things she did was learn to put them in and take them out herself, but since she only replaces her lenses every fortnight (usually they'd be monthly, but not with her eye condition), she keeps forgetting, plus she's understandly quite phobic about the whole thing, so it's taking her a while to learn. Having been wearing lenses for the last fourteen years, I don't even think while I'm inserting or removing them any more!
Now I wish I could find more info about the visual problems I have as a result of having M.E. The hassle I have over strip lighting at uni is unbelievable. |
View all
15
comments
|
Deutschland 
España 
Italia 
France - 
