keratoconus

What is keratoconus?

Keratoconus is a progressive eye condition which causes thinning to the cornea (the front surface of the eye), resulting in the cornea protruding forward into an irregular, ‘cone’ like shape, which can lead to significant visual distortion. Keratoconus is diagnosed by corneal tomography which maps out the shape of the cornea.

Early in the course of the condition, visual changes can present as astigmatism. As the condition progresses, so does the irregularity, and patients may experience visual symptoms such as multiple images, streaking of lights, and light sensitivity.

Early cases of keratoconus may not require any management, or may be managed simply with spectacles. As the condition progresses, spectacles may be of little assistance, as the reduction in vision is not due to the prescription of the eye – but rather the ‘shape’ of the eye being distorted. In these cases, rigid gas permeable contact lenses or similar are required, as these provide a more ‘regular’ front surface to the eye.

The prevalence of keratoconus in Australia is approximately 1 in 2000 people. Keratoconus tends to manifest in early adolescence, and can continue to progress, but will tend to stabilise in the mid-late 30s. If there is evidence of progression, a surgical technique known as corneal cross-linking (CXL) can be performed by a corneal specialist. CXL does not fix the condition - the aim is to stabilise the condition and prevent further progression. Whilst we do not perform CXL here, we work closely with local corneal specialists who we can refer on to for CXL.

In cases where the keratoconus is so advanced it cannot be managed with contact lenses, corneal grafting may be required. In this procedure, the diseased cornea is removed and replaced with a healthy, donor cornea. This is reserved for cases where all other options have been exhausted. Fortunately, patients will not go blind from keratoconus.

How is keratoconus diagnosed?

Keratoconus is a multifactorial disease, but is also asymmetrical. Keratoconus results in ‘irregular’ astigmatism, and in the early stages can be misdiagnosed as ‘regular’ astigmatism. The presentation varies from individual to individual, and if one eye is relativey unaffected may go undiagnosed for years. Symptoms include blurry vision, haloes and shadows, particuarly in the evening.

Keratoconus is best detected through instruments that can measure the shape of the cornea. Instruments that are capable of measuring the corneal surface include corneal topography, corneal tomography and anterior-segment optical coherence tomography. These can measure the characteristic changes seen in keratoconus.

At Eyetech Optometrists, we utilise corneal topography, corneal tomography and anterior-segment optical coherence tomography to analyse the cornea and monitor for changes. Corneal topography is a non-invasive technique to measure the the front surface of the cornea. The ‘cooler’ colours (blues to greens) indicate areas that are flatter, whereas the ‘warmer’ colours, (oranges to red) indicate areas that are more curved, or where the ‘cone’ is.

Keratoconus can also be detected via slit lamp biomicroscopy. This is basically a microscope that we direct at the eye to view it in high magnification. Characteristic signs include thinning and forward protrusion of the cornea, more prominent corneal nerves, Fleischer’s iron line around the cone and Vogt’s limbal lines (corneal stress lines from the stretching).

Our Optometrists manage keratoconus and work closely with local corneal specialists should surgery be required. If you have further queries, please do not hesitate to book in for an appointment.

Keratoconus Australia is a support network for patients suffering from keratoconus. You can find more information about keratoconus on their website.

Contact lens options for keratoconus

In early stage of keratoconus, where the degree of irregularity is mild, spectacles may be appropriate. In these cases, soft contact lenses may be an option. As the keratoconus becomes more pronounced and the cornea becomes more distorted, these options may be inadequate for correcting vision.

Once keratoconus reaches this level – rigid gas permeable (RGP) contact lenses or similar are required. Traditionally, keratoconus has been managed with corneal RGP lenses, which are lenses which fit on the cornea, i.e. are smaller than the coloured part of the eye. These lenses not only correct the vision but also afford an excellent health and safety profile, however they can be prone to instability, ejection and foreign particles. They also have an adaptation period which some patients may struggle to get through. However, once patients have passed this adaptation period, they usually have few problems.

For patients that cannot tolerate corneal RGP lenses or for patients who work in windy, dusty environments or are very active, other lens options may be required. These include scleral contact lenses and hybrid contact lenses.

Scleral contact lenses are rigid lenses which extend over the cornea and onto the sclera (the white part of the eye). Hybrid contact lenses are lenses which incorporate a rigid gas permeable centre with a soft outer skirt. Both of these lenses afford greater stability and comfort as compared to corneal RGP lenses, and do not tend to attract foreign particles beneath the lenses. These lenses tend to be comfortable from the beginning and the adaptation period is much faster than with corneal RGP lenses.