Keratoconus

Keratoconus represents a progressive, non-inflammatory thinning and protrusion of the central cornea (the front surface of the eye) usually manifesting itself in youth or adolescence, although the age of onset can be anywhere between 7 and 50. It is nearly always bilateral, although it is often asymmetrical. Considerable visual impairment can result due to the development of a high degree of irregularity associated with this front surface ("window") of the eye. Due to this marked distortion and irregularity the improvement in vision obtained with spectacles may be minimal. There is usually a marked improvement in vision if rigid contact lenses (or similar) are fitted and they are often the only adequate means of correction for patients suffering this condition. Keratoconus does not cause blindness.

Keratoconus is a genetic condition that occurs in about one in 2,000 people, occurring with equal frequency in males and females. The hereditary nature of the condition is actually quite weak, so only about 10% of people with keratoconus will have an affected relative. Keratoconus is sometimes associated with other conditions such as allergies, asthma, eczema and double jointedness. Excessive eye rubbing has also been strongly implicated as a possible causative factor.

Signs and symptoms of keratoconus include a blurring and distortion of vision that cannot be totally alleviated by spectacle correction; frequent changes in the spectacle prescription over a relatively short period of time; reduced night vision with ghosting and haloes noticed around lights; multiple images observed with the one eye; and eye strain and headaches.

Progression with keratoconus is quite variable, however the condition does tend to progress more rapidly the earlier the age of onset. As stated earlier, keratoconus is basically a bilateral condition, however the degree of progression for the two eyes is often unequal and it is quite common for the keratoconus to be far more advanced in one eye. In about 85% of cases of keratoconus, the condition usually stabilizes anytime between 5 to 15 years after onset. For the remaining 15%, the keratoconus progresses to the point where contact lens fitting is no longer possible and so the only treatment option is then a corneal transplant.

Corneal collagen cross-linking treatment (CXL) of keratoconus is a non-invasive procedure which is aimed at halting the progression of the keratoconus. The procedure works by increasing collagen cross-linking, which helps to prevent the cornea from becoming more conical and irregular, as it would normally with progression of the keratoconic condition. This technique was first developed in Germany about 9 years ago. During the treatment, riboflavin eyedrops are applied to the cornea and then activated by UVA radiation. This process has been shown in laboratory and clinical studies to increase the amount of collagen cross-linking in the cornea, thereby resulting in a stronger cornea. At this stage, the treatment is still classed as an experimental procedure and a CXL treatment trial is currently taking place in Melbourne. The real benefit from CXL treatment is that it has the potential to greatly reduce the number of keratoconic patients who will go on to require a corneal transplant.

In the earliest stages of keratoconus, a spectacle correction may be used to correct the myopia and astigmatism associated with this condition. Soft contact lenses can often also be prescribed during this time for general, recreational or sporting use. As keratoconus progresses, the additional corneal thinning results in the shape of the cornea becoming more irregular to the point that it is not possible to obtain adequate vision with spectacles. At this stage, rigid contact lenses are then required to provide optimal vision. Soft contact lenses cannot be used as they will mould themselves to the shape of the irregular cornea. The contact lenses essentially provide a new, regular front surface for the eye, eliminating the distortions caused by the keratoconus. It should be emphasized that, while contact lenses will generally provide a significant improvement in vision, wearing them is not a cure for keratoconus.

The majority of individuals with keratoconus comfortably wear rigid contact lenses throughout the day, enjoying significant visual improvement. About 10% of keratoconic patients are unable to tolerate wearing rigid contact lenses due to extreme ocular sensitivity. For this group there are other contact lens options available, most notably a hybrid (piggyback) lens design which consists of a rigid central portion attached to a peripheral soft skirt. This hybrid lens design is also a good option for keratoconics who play contact sports such as football, as rigid lenses may be easily dislodged during these types of activities.

Keratoconus is a progressive condition, hence it is important that people with keratoconus have regular examinations to monitor the status of their condition and ensure that their contact lenses are still an optimal fit. Poorly-fitting contact lenses will generally have a radius of curvature much flatter (greater) than that of the cornea and this situation can arise either from a practitioner prescribing an inappropriate contact lens curvature or the patient continuing to wear an older contact lens prescription when their has been a significant progression in their keratoconus. Flat-fitting lenses can lead to corneal abrasions and subsequent corneal scarring; the corneal scarring may then result in a significant reduction in vision.

Only in about 10% of cases of keratoconus does a corneal transplant (graft) become necessary. A corneal graft (or keratoplasty) is an operation in which the affected (thinned) area of the cornea is removed and replaced by normal tissue transplanted from a donor cornea. Corneal grafting is required when either a satisfactory fit or normal visual acuity cannot be achieved with contact lenses, or the patient has extreme ocular sensitivity and so is unable to tolerate wearing any form of contact lens (this type of scenario is quite uncommon in clinical practice). The success rate for corneal grafts for keratoconus is very high (between 95-100%), although about 60% of people will be required to wear spectacles after a graft and approximately 30% of people will need to wear contact lenses to achieve normal vision subsequent to having a graft. Keratoconus does not generally reoccur after a corneal graft. There have been a few isolated examples in the past 30 years where this has happened, however it is generally thought in these cases that this was due to the inadvertent use of a donor cornea from a decedent who had keratoconus.