Corneal complications caused by contact lenses are particularly common among wearers of soft hydrogel contact lenses, especially the extended-wear variety, which is "thoroughly inadvisable". The only exception would be for cases in which there is no other option, such as elderly people who live alone or those who have particular difficulty in handling contact lenses. This was one of the main conclusions of the Contact Lens and Ocular Surface Conference that last weekend in Barcelona brought together a hundred or so opticians and optometrists from around Spain and was organised by IMO’s Contact Lens Unit.
According to experts, some studies have shown that users of extended-wear lenses are five times more likely to develop eye problems than those who use daily disposable lenses. "As they can cause bacterial infection of the eye surface and result in loss of visual acuity, patients have to stop wearing the lenses immediately, receive treatment for the infection and allow enough recovery time for the cornea to regenerate," explained Laura González, an IMO optometrist and the coordinator of the conference.
Because of this, optometrists generally discourage the use of extended-wear lenses in favour of the daily disposable variety, which, as a result of recent developments, can now be used by people with astigmatism and those with more than 10 dioptres. Previously, the manufacturing range was much more limited (maximum 6 dioptres).
The main complications that can result from misuse or poor maintenance of lenses include giant papillary conjunctivitis (a non-infectious inflammatory process) and dry eye, as well as other more serious conditions, such as hypoxia (lack of oxygen), which causes corneal cell death, and acanthamoeba infections resulting from, for example, bathing at the beach, which can cause perforation of the cornea in less than 24 hours and require transplantation. As a result, in addition to discouraging the use of extended-wear lenses, optometrists also stress the importance of proper use and maintenance to avoid complications. In particular, they recommend that lenses should not be worn for excessive periods, during sleep or at the beach and that products which are specifically designed for hygiene and maintenance should only be used.
These include products that are currently available on the market, such as artificial tears and solutions that moisturise the surface of the contact lens to ensure more comfort when worn. As the conference coordinator explained, "users should be careful to ensure good hygiene and avoid using water or saliva in an emergency, if the lens, for example, falls on the floor."
The experts also recommended that all users should visit their contact lens specialist twice a year and their ophthalmologist at least once a year. The specialists did, however, agree that rigid gas-permeable (RPG) contact lenses were, generally, more advisable than soft lenses, because there is less risk of intolerance and complication, as they are manufactured with more permeable materials to enable oxygen to be transmitted to the cornea. Consequently, the recommendation was to limit the use of soft lenses to specific activities, such as sport, and to choose lenses made from silicone hydrogel to facilitate corneal oxygenation.
This advice means going against the preferences of most users, who tend to prefer soft contact lenses, because RPGs can feel more uncomfortable in the eye, require greater effort in terms of adaptation and are more difficult to handle.
It is estimated that there are more than 125 million contact lenses users in the world and that over 20% eventually stop using them. While most of those who stop cite comfort problems, as the cornea is one of the most sensitive parts of the body, some users claim that glasses provide them with better vision. As Laura González pointed out, "this is often the case with badly prescribed or cheap lenses, which don’t correct astigmatism. Toric lenses, which do correct astigmatism, generally cost twice as much as the normal ones." To correct astigmatism, as well as other factors related to quality of vision (aberrations, contrast sensitivity, etc.), RPG contact lenses are particularly suitable. "The problem of astigmatism is typically caused by a deformation of the cornea. If a soft lens is inserted, it takes on the shape of the cornea, and the problem persists. By contrast, RPG lenses do not change shape and enable the space between the lens and cornea to fill up with lacrimal fluid and function as a lens, creating a new spherical "cornea" without astigmatism," explained Laura González.
Recent advances have helped many users overcome their contact lens intolerance
Specialists have analysed the main advances in contact lens technology, which are predominantly aimed at solving intolerance issues. These include scleral lenses for users with irregular corneas that cannot support traditional lenses or patients with dry eye, who are unable to use lenses due to corneal irritation.
The main innovation with these lenses is that their bulge design keeps them separated from the cornea and moves the support point to the lens perimeter, which rests on the less sensitive sclera (the white part of the eye, adjacent to the cornea). The space between the cornea and the lens is filled with artificial tears to provide constant lubrication to the surface of the eye.
According to Laura González, "scleral lenses correct refractive errors, but also prevent mechanical trauma by protecting the surface, functioning as therapeutic lenses by improving dry eye and possibly delaying the need for keratoconus transplantation" (thinning of the central area of the cornea, which produces irregular astigmatism and is the leading cause of corneal transplantation in younger patients). Another topic addressed at the conference was that of multifocal lenses, which provide the user with good far and near vision and are becoming an increasingly popular choice for many people over the age of 40, when presbyopia (old eyes) usually starts to appear. The optometrists did, however, acknowledge that almost 80% of patients with presbyopia are still unaware that this option exists.
Finally, the specialists emphasised the role of new eye examination techniques, such as anterior OCT (optical coherence tomography), which produces microscopic 3D images of the cornea by means of an infrared laser beam. As Laura González explained, "OCT enables us to design made-to-measure lenses by showing us in an objective manner how they would fit the different points of the cornea."