After the introduction of the corneal hard lens, the contact lens wearers were introduced to the “Holy Grail” of contact lenses: the RGP lenses. It was supposed to be a hard lenses made from a “breathable” plastic. However the amount of oxygen transmission was not very high and it soon became obvious that lenses with high powers and therefore thicker lenses did not benefit greatly from this new material.

In matter of fact the RGP lenses tended to attract protein deposits in the form of crystal molecules. So after wearing them for a few weeks the lenses became more and more irritating. In the beginning not many practitioners knew the source of the problem. Very often this thin layer of protein deposits from the tear film was not visible to the naked eye. On top of all this the rate of protein depositing depended on the individuals’ eyes. Some contact lens wearers did not experience any depositing while others would start to get irritated eyes within a week of wearing these new lenses.

A lot of time was then wasted by trying to refit the eye with a new RGP lens with different parameters. Slowly the optometrists started to realize that the RGP lenses needed a strict cleaning regime with special protein removing agents and wet overnight storage in contact lens containers to keep the lenses comfortable. For many previous PMMA lens wearers this was an extra burden and in many cases this strict cleaning was not adhered to. A result was that RGP contact lens wearers had to re-visit the optometrists frequently and the end result was frustration and in many cases a refit to PMMA contact lenses. 

I have seen many cases of successful PMMA wearers being converted to RGP with less than satisfactory results. I even know of optometrists who thought that because of this so-called breathable  lens material they now could increase the diameter of the contact lenses as to obtain better vision under low light conditions. The poor contact lens wearer now started to get problems because to remove the lenses from the cornea became harder. Because of the a-spherical nature of the corneal surface the contact lens would now fit much tighter on the eye with the larger diameter lens. Corneal oedema will result and the optical correction of the eye will alter.

A new replacement lens had to be made and more and more problems would result. A lot of confusion among the contact lenses practitioners existed during the years of the late seventies and early eighties. As a result a lot of  spectacle wearers were put off to switch to contact lenses. And even up to now there is still the concept that contact lenses might be difficult to get used to or might be irritating to the eyes.

Technorati Tags: contact lens, contact lenses, eye vision

Toric contact lenses are contact lenses designed to correct astigmatism. These kind lenses are getting more and more popular and are an excellent alternative to spectacles or corrective eye surgery like Lasik.

The next logical development in contact lens would be a multifocal contact lens in the toric design. Especially nowadays with a considerable of contact lens wearers over 50years of age such a new concept would be very advantageous to the optical industry.

At present the only option for presbyopic toric contact lens wearers is the mono-vision adaptation where one of the contact lenses are fitted with a near prescription while the other eye is corrected with a contact lens for distance. It is a compromise situation as the trade-off is a reduced binocular stereoscopic perception.

This might cause problems judging distances which reduces for example the ability of estimating the speed of oncoming traffic. People wearing contact lenses in this fashion should be alert when overtaking on the motorway. Misjudging of distance or speed could have serious implications. However thousands of contact lens wearers have been fitted successfully contact lenses in this mono-vision way. A large percentage would have been suitable for multi focal lenses but a number of optometrists are applying the easiest fitting option.

Multi focal contact lenses are harder to fit and therefore time consuming. This is one of the reasons that the contact lens manufacturers are reluctant to introduce this toric multi focal contact lens concept because without adequate support from optometrists it will not be a profitable product. A disadvantage of Lasik surgery is that mono vision is the only way to correct presbyopia and there is the advantage for the contact lens industry to make sure it keeps its market share over corrective surgery .

Of course there are some contact lens manufacturers like Bausch & Lomb who are safeguarding their future by having an interest in both fields.Certainly that corrective eye surgery is also looking towards correcting presbyopia, but it might take some years in the future because altering the contours of a cornea is riskier and far more complex than producing a special contact lens.

With the onset of nano technology all these breakthroughs will eventually become reality. For now we are waiting for the first toric multifocal contact lens to enter the market and hopefully it will be produced as a cost effective disposable contact  lens.

Technorati Tags: contact lens, contact lenses, eye vision

Contact lenses became popular after the Second World War with the introduction of Perspex. This material called PMMA by the contact lenses industry became the first choice for producing contact lenses.

At first the lenses were made quite large in diameter, but soon contact lens practitioners realized that this caused the cornea to be starved of oxygen. The result was a corneal oedema which usually caused increased myopia. Also many patients started to complain about a halo effect around lights. Some of the halos consisted of a rainbow colors.

By ignoring these symptoms contact lens wearers would develop cell damage to the corneal surface and this made the eyes easy target for viral and bacterial infections. So the logical step was reducing the average diameter of the contact lenses to around 8 mm. Any smaller size was not practical because under low light conditions the pupils would become larger than the contact lenses and the lenses edge reflections started to interfere with the vision.

Another problem usually would be that the smaller contact lenses are more sensitive to the eyelids. This resulted in producing thinner and therefore lighter contact lenses.However these small contact lenses would shift more easily from the cornea to the sclera which is the white part of the eye. Because the sclera has a flatter curve the contact lenses tended difficult to be pushed back on the cornea. In some instances the contact lens wearers thought they had lost their lens only to be located deep under the eyelids by the optometrist.

In order to make it easier to locate the contact lenses the manufacturers started to produce tinted contact lenses. Through using dyes to make the tear flow under the contact lens more visible the optometrist got a better understanding of how the cornea received its oxygen. Because corneas do not possess blood vessels all the oxygen enters through the tear film into the cornea membrane.

Soon it became clear that a good movement of tear flow between the lenses and the corneas were essential to keep the cornea in good condition. A contact lenses fitted too tight would feel comfortable for the eyelids but would have an adverse effect on the health of the cornea. At the other hand a contact lens fitted too loose would move around too much and could easily fall out or constantly shift onto the sclera. So a fine balance was needed to obtain a perfect fitting contact lens. In this stage of contact lens development the fitting of lenses were more art than science and it took years of experience to fine tune these skills.

Technorati Tags: contact lens, contact lenses, eye vision

The generation born just after World War 2 was able to switch from wearing glasses to contact lenses when turning into teenagers. Especially in the USA the contact lenses became very popular after Bausch & Lomb (Optical lenses manufacturer) introduced the spincasted Soflens B-serie . This particular lens was a step forward from the hard contact lens designs by removing the barrier of feeling a definite foreign object introduced onto the eye. Bausch & Lomb initially brought out the Soflens with the idea that one curvature design should fit most wearers. It turned out that this was not the case because problems started to occur after wearing these lenses for a few months or longer. The cornea in many cases started to struggle with oxygen starvation after a period of time. Initially it was unknown why this happened. In theory the contact lens material seems to breathe oxygen to the eye and also there was the “pump effect” underneath the contact lens when the wearer blinked.

What was not taken in account that this might be the case in certain diopter corrections (lens powers) but not all lens powers were behaving the same way? On top of that the cornea topography was not fully understood by the manufacturers. The surface curvature of the corneas was only measured from the apex with a maximum area of approx 3mm across by the existing keratometers. The rest of the 13mm a-spherical area was ignored. This resulted in quite a few cases where the sclera around the cornea became squeezed by the edge peripheral of the contact lens which resulted in a limited blood supply to the edge of the cornea.

In some cases a ring of indentation was visible after the removal of the contact lens.

However there were more issues regarding the wearing of soft contact lenses. The breathable contact lens materials tended to attract a build-up of proteins crystals which were produced by eyelid glands. The result was that after a few months the contact lenses became very scratchy and in the end it would cause irritation, allergies and even damage to the corneal surface. The percentage of protein excretion varied considerable among contact lens wearers.

This meant that some people got away with a minimum of lens cleaning and others could simply not keep the lenses protein free. Up to the 1990’s a contact lens replacement meant considerable cost to the wearers and the result was that contact lenses were worn till they became intolerable before replacing. In many cases the optometrist were consulted after the symptoms became very obvious and the poor optometrist had to refer quite a few cases to the ophthalmologists. Although he patient was usually to blame for not adhering to the optometrists’ wearing regime, the poor optometrist was the one who had to deal with the patient’s frustrations.

Technorati Tags: contact lens, contact lenses, eye vision

Nowadays there are many types of contact lenses on the market. Most of them are being fitted in order to improve the visual aspects, like correcting basic near and long sightedness. However, because many people are in need of a correction for astigmatism, the lens manufacturers are now producing soft contact lenses which cater for this large segment of contact lens wearers. (The term astigmatism stands an eye condition that normally happen when the front surface of the eye, the cornea, has an irregular curvature and as a result the eye can't focus a point object into a sharp focused image on the retina).

Originally the development of “toric” contact lens (lenses which are correcting astigmatism) was very slow to due to the fact that rigid or hard contact lenses usually compensates for astigmatism because of the layer of tear film between the contact lens and the irregular shaped astigmatic cornea. With the introduction of the soft contact lenses the issue of compensating astigmatism became more prominent and in order to further improve market share the manufacturers of soft contact lenses started to invest a lot of capital in the development of toric lenses.

The main issue was not how to produce a toric power in the contact lens but how to stabilize the contact lens on the eye so it would not rotate or swivel. Astigmatism needs to be correct under a certain angle (also known as “axis”) any “off axis” placement of the lens will result in blurry vision. The compensation of  astigmatism meant that the contact lens was not allow to rotate more than a few degrees after blinking and then it should return quickly to the original position. A lot of experimenting went on and with this the development of “corneal mapping’ equipment was developed.

The first mainstream toric soft lenses were tailor-made lenses and as a result the cost of this type of lens was very high. Most of them needed replacement after 12 months and to replicate them accurately was not always successful. The contact lens wearers often complained about the difference in comfort or vision in case when the previous pair was produced more accurately to the manufacturers’ standards. In a lot of cases it was a matter of the human element (technician’s skills) rater than quality of manufacturers tooling. After a few years with the introduction of computer guided lathes and polishing machinery the consistency in quality improved and as the manufacturing cost per contact lens went down the availability and affordability made the toric soft contact lens a mainstream lens.  

Technorati Tags: contact lens, contact lenses, eye vision

Originally, when the hard (pmma) contact lens was developed, the correction of astigmatism was not much of an issue due to the fact that this lens material was rigid and therefore did not follow the contour of the irregularities of the cornea and so the tear film between the lens and the cornea of the eye would function as an extra lens which would compensate the irregularities and also most of the astigmatism caused by the cornea.

With the onset of soft contact lenses, the problem of correcting astigmatism suddenly re-emerged because this type of lens material (as the name already suggests) does follow the contour of the cornea and therefore does not compensate for astigmatism. The end result was that the popularity of soft contact lens was slowed down since most hard contact lenses wearers who use refitted with soft contact lens suddenly realize that their vision was not quite as clear with the newly fitted soft lens. So the main reason for the refit from hard to soft lenses was the advantage of comfort or the fact that the soft lens did not spontaneous fell out during contact sports. Other reason for contact lens wearers to stay with the rigid hard lens was the low maintenance cost. The pmma lens was made out of Perspex and therefore needed very little care. Most users would just keep the lenses dry during the night and use a few drops of saline to help to insert the lenses in the morning. Some people even used saliva to clean or wet the lens before putting it in their eyes.

The next development was the gas permeable (hard) rigid lens which was to replace the pmma hard lens. This lens was as uncomfortable as the pmma lens and also needed a long adaptation period for the wearer to get used to. The advantage of this type of lens was that the oxygen transmission to the cornea improved and therefore could be worn for longer periods without complications such as oxygen deprivation which could lead to cornea oedema and other symptoms. The correction of astigmatism was again not much of an issue.

The main drawback of this type of lens was the depositing of protein molecules on the lens surface especially when the lens wearer did not adhere to a strict cleaning regime. The lenses users had to spend additional money for the lenses maintenance and the average lenses replacement time went down from ten plus years for the pmma lens to four years for the gas permeable lens. Most optometrists were able to convince their patients of the benefits of this new development although a considerable number of successful pmma lens wearers were not very happy with the increased spending and protein depositing of these new lenses.

Technorati Tags: contact lens, contact lenses, eye vision

Over the years contact lenses have improved tremendously. From the beginning of hard Perspex lens to the daily disposable lenses and nowday also the “permanent wear” lenses.

Unfortunately the difficult wearing adaptation of the hard lens have cast a long shadow and not until the 1990’s potential contact lens wearers started to realize that wearing of the modern advanced contact lenses is comfortable and hassle-free.   The experience of feeling a foreign object placed on your eye when trying contact lenses is over. Nowadays a large numbers of people especially in the entertainment industry are wearing colour enhanced lenses in order to look better rather than seeing better. Even a darker hazel coloured iris can be changed to for example blue. Some Asian ladies always wanted to have “blue eyes” and this has now become easy and cheap.

With the introduction of the daily disposable lens the try of making your contact lens 100% clean and sterile is not required. No more bottles of contact lens solutions to be carried around when travelling. After wearing this lens during the day it can be thrown out before going to sleep – next morning a new lens can be pulled out off a blister pack of lenses. All very easy and convenient.

For those people who are working irregular hours or have to get ready for work unexpectantly in case of emergency (like firemen or medical staff) there are the “continuous wear” contact lenses. One of the well known brands is “Night & Day” by CibaVision. This type of lens can be worn without removing it from the eye for up to a week at a time. After a good clean this procedure can be repeated once a week. After one month the lens need to be disposed and replaced with a new and fresh replacement lens.  Thanks to the high oxygen transmission this lens can be safely worn although regular check-ups by an optometrist are recommended.

Technorati Tags: contact lens, contact lenses, eye vision