Contact Lenses (Types and Care)

See related article Contact Lens Problems.

There are 1.65 million contact lens (CL) wearers in the UK.¹ Contact lenses have a range of uses but are most commonly worn as an alternative to spectacles in the correction of refractive errors. They are often chosen for cosmetic reasons but may also have very practical advantages in certain sporting or occupational situations where spectacles can get broken, spattered or prevent the use of protective eye wear. They do, however, need meticulous care if complications are to be avoided, particularly as some of these can be sight threatening. Lenses should normally not be worn more than a specified number of hours each day (this depends on the individual lens) and should not be kept in overnight unless specified by the CL practitioner. Furthermore, patients should immediately stop wearing them on developing a red eye.

• These principally correct myopia and hypermetropia but CLs have now been developed to correct astigmatism and presbyopia.
• Although the great majority are used for cosmetic reasons, certain corneal conditions warrant contact lens wear in preference to spectacle wear to achieve optimal visual acuity. These include irregular astigmatism (such as is found in keratoconus, where the cornea is cone shaped), the presence of superficial corneal irregularities and anisometropia (inequality in refractive power between the two eyes).³
• Hard (rigid) CL – polymethylmethacrylate (PMMA): least hydrophilic and has the greatest deleterious effect on corneal function, restricting oxygen availability and depleting glycogen stores.⁴ These can give rise to a number of problems such as corneal oedema in 6% of patients after six hours wear.⁵ However, they give a good refractive result, they are easy to manipulate and last a long time. They are now seldom used.
• Soft (hydrogel) CL – polymers of HEMA, silicone and other similar materials: hydrophilic (composed of up to 80% water) and oxygen permeable.⁶ These popular lenses are the most comfortable to wear but they may not give the best refractive result. Some have been approved for extended (30 day) wear.
• Gas-permeable rigid lens – these combine the best properties of hard and soft CLs, having a high gas-transfer and reduced toxicity. They are easier to handle than soft lenses, they offer excellent visual acuity and they are more suited than soft CLs to astigmatic patients.⁵ Some types are approved for overnight or extended wear.

• Goniolenses are a group of lenses that are used in clinic and in theatre to look at the iridocorneal angle, principally in the assessment of glaucoma. Some of these are equipped with additional mirrors enabling visualisation of the fundus. These lenses remain on the cornea only during the period of examination.
• Electroretinography lens – this is used in specialist centres to make certain diagnoses: these lenses look at electrical function in the eye much in the same fashion as an electroencephalogram.
• Soft bandage CLs may be used to promote epithelial healing where there are persistent corneal epithelial defects and erosions. They also have a role in pain relief in patients suffering from bullous keratopathy (where exposed corneal nerve endings are subject to the shearing force of the lids during blinking) and in wet filamentary keratitis, seen in patients with brainstem strokes or following chemical exposure.²
• Drug delivery systems – work is being done to develop lenses that provide a controlled release of topical ocular drugs: these are not currently in widespread use.⁴
• A combination of bandage CLs and drug delivery systems can be found in the form of collagen shields² - a special type of biodegradable lens that can last for a maximum of 72h and which can be impregnated with antibiotics. They biodegrade in situ and therefore do not have to be removed.

• Painted CLs – may be worn to improve cosmesis in an unsightly blind eye or to provide an artificial iris in aniridia. These lenses are also sold commercially and can be manufactured to concurrently correct refractive errors.

• Patients will have been taught this by their CL provider.
• It depends on whether the lens is a daily disposable, re-usable or an extended wear lens.
• Daily disposable lenses are thrown away at the end of the day: there are no care solutions for these and patients will have been told that one cannot use lens cleaning solutions to try and prolong their life.
• Repeated use lenses need to be disinfected (solution ± rubbing or rinsing the lens): fresh solution needs to be used every time and there must not be a mixing of different types of solution. They also need to be kept hydrated when not in use. There are various commercially available solutions to carry out one or both of these functions. The storage case needs to be rinsed daily and allowed to dry after use. It will need replacing on a monthly basis.
• Tap water and saliva should not touch the lens.
• The contact lens case needs to be cleaned ± replaced regularly as it can be a source of contaminants.

Using eye preparations

• As a rule of thumb, it is best not to wear CLs when topical eye treatment is necessary: this becomes an absolute rule when treating a red eye (which may be a CL-related microbial keratitis).
• Ointment use is incompatible with any CL wear.
• Rigid lenses can be worn with drops: these can be applied over the lens.
• Soft CLs can only be worn if preservative-free drops are used (look for the presence of benzalkonium chloride in the ingredients). Preservatives accumulate in hydrogel lenses and may induce toxic reactions.

Systemic drugs

These can interact with lenses in a number of ways. Examples are provided below but if you are uncertain, it is wise to check the individual drug's interactions and side effects.