The widespread use of contact lenses means that the general practitioner and the ophthal- mic casualty department find themselves con- fronted with more and more patients who have run into wearing problems of one kind or another. For this reason, some of the likely emergency requirements are considered here.
Types of Contact Lens
As long ago as 1912, a glass contact lens was being produced, but because of the manufactur- ing difficulties and wearing problems, the wide- spread use of this type of optical aid was delayed until the introduction of plastic scleral lenses in 1937. The obvious advantage of placing a lens directly on the cornea over the wearing of spec- tacles is the cosmetic one, but the system also has optical advantages. Because the lens moves with the eye, there are none of the problems associated with looking through the edge of the lens experienced by the wearer of spectacles. In addition, a more subtle effect is the more accu- rate representation of image size on the retina in subjects with high degrees of refractive error.
Although the original type of moulded scleral contact lenses are still occasionally used, they have been largely replaced by the modern rigid and soft lenses, which are much smaller and thinner and hence cause less interference with corneal physiology. Rigid lenses are made from gas-permeable plastics and have generally replaced the early “hard” lenses, which were impermeable to oxygen. In 1960, the hydrophilic
soft contact lens was introduced. This had the great advantage of being soft and malleable and hence more comfortable to wear, but optically it has never been quite as good as the rigid lens, especially when the patient has high degrees of astigmatism. Several different materials have now been used in the production of soft lenses, although the basic material used is hydroxy- ethylmethacrylate. The different types of soft lenses differ in their ability to take up water and transmit oxygen.Lenses are now being made that can be worn for long periods without needing to be removed and cleaned. Similarly, disposable and “planned-replacement” contact lenses are now widely available. Care should be taken that such lenses are used under professional care.
Soft contact lenses tend to absorb and adsorb material from the tear film. It is particularly important to ensure that a patient is not wearing a soft lens before fluorescein dye is instilled into the eye.
Side Effects
In general, soft contact lenses have more side effects than rigid lenses in the long term. The commonest complication of wearing modern contact lenses is losing them. Patients are well advised to have a pair of glasses at hand in case they have contact-lens-wearing problems or a lens is lost. More serious trouble can result from clumsy handling of the lens or leaving a rigid lens in the eye for too long a period. Such patients quite often present with severe pain in
10
Contact Lenses
77
the eye, and examination reveals a partially healed corneal abrasion. This must be treated in the usual manner and the patient advised against wearing the lens again for several weeks, depending on the extent of the abrasion. The contact lenses themselves should also be exam- ined by the patient’s fitter to make sure that they are not faulty. Bearing in mind the troubles that can ensue when an abrasion becomes recurrent, the indications for wearing the lenses in the first place should be reconsidered.
The risk of infection by lens contamination or secondary to corneal abrasions is increased.
Recently, Acanthamoeba keratitis has been described. This disease occurs more often in contact lens wearers.
Another sequel to wearing contact lenses, either rigid or soft, is the appearance of chronic inflammatory changes in the conjunctiva, often characterised by a papillary conjunctivitis. The resulting irritation and redness of the eyes can persist for some weeks after the wearing of the contact lenses ceases. Unfortunately, these symptoms can appear after wearing lenses suc- cessfully for some years and they tend to recur in spite of renewing or modifying the lenses.
Some patients who tolerate contact lenses well can develop corneal changes after some years.
Peripheral vascularisation can become evident and in neglected cases, there could be band degeneration of the cornea. Some contact-lens wearers complain of recurrent blurring of their vision and this could be due to an ill-fitting lens producing corneal epithelial oedema or simply to the excessive accumulation of mucus on the lens (Figure 10.1).
Indications
These can be considered as either cosmetic or therapeutic.
Cosmetic
There are obvious cosmetic advantages for the wearer of contact lenses, especially the teenager.
However, the potential wearer should realise the possible difficulties involved: the need to clean and sterilise the lenses and the need for some degree of finger dexterity when they are inserted and removed. There are numerous and varied cleaning and disinfection systems on the market. Contact lenses might be required for certain pursuits, such as golf or athletics, where the spectacle wearer is handicapped by misting up of the glasses in wet weather. Patients over the age of 45 or 50 will find that they require reading glasses as well and these, of course, must be worn over the contact lenses, thereby some- what reducing the cosmetic value of the latter.
Multifocal contact lenses are available but have limited success. Some patients tolerate being corrected in one eye for distance vision and in the other for reading with contact lenses. Care should be taken in this situation when assessing the visual acuity because the eye corrected for near vision will be blurred for distance.
Therapeutic
There are instances when the contact lens can result in much better vision than spectacles, for example in patients with high degrees of corneal astigmatism that are not fully cor- rectable with glasses. This accounts for the benefit of contact lenses in patients with kera- toconus. Soft contact lenses are sometimes used as “bandage lenses” to protect the cornea after corneal burns or in patients with bullous kera- topathy. The contact lens has a special impor- tance in the correction of unilateral aphakia (see Chapter 11) by reducing the image size on the retina to such an extent that the two eyes can once again be used together. If eye drops are being regularly instilled into the eyes, soft contact lenses can absorb the drug being used or the preservative in the drops. In fact, attempts have been made to use soft contact lenses as a slow-release system by impregnating them with the drug before fitting.
78 Common Eye Diseases and their Management
Figure 10.1. Hard contact lens with lipid deposits (with acknowledgement to Professor M. Rubinstein).
