Australia’s first Corneal Allogenic Intrastromal Ring Segment (CAIRS) surgery has been successfully performed at the Queensland Eye Institute (QEI), paving the way to better sight for many sufferers of keratoconus.
Keratoconus occurs when the cornea thins and its shape changes from round to cone-shaped, thereby causing blurry and/or double vision, short sightedness and light sensitivity. Australia has one of the highest rates of keratoconus in the world, affecting one in every 84 people aged in their twenties. Men and women are equally affected and, left untreated, it can lead to severe visual impairment.
Spectacles and rigid gas permeable (RGP) contact lenses are often used to manage keratoconus in its earlier stages, however these visual aids do not treat the condition itself. The current management approach is to refer patients early for corneal cross-linking, which stabilises the disease but generally does not improve vision. Correction with glasses or RGPs is often still required after treatment. Approximately 20% of patients will need a full corneal graft to regain sight.
Plastic intracorneal ring segments have also been successfully used, particularly in moderate keratoconus, to improve the shape of the cornea without removing tissue. However these rings come with higher rates of complications, including erosion of the implant onto the eye’s surface and corneal melt or infection. Indeed, many implants last only five to ten years before removal.
USING DONOR CORNEAL TISSUE
CAIRS, which uses donor corneal tissue, is the next progression of intracorneal ring segment surgery and it opens up more treatment options for patients with keratoconus.
QEI ophthalmologist Dr David Gunn, who recently performed Australia’s first CAIRS surgery, explained that because the ring segments are biocompatible, CAIRS lowers the risks of infection, and because they are more superficially placed than the plastic alternative, CAIRS can be used in patients with more severe disease.
The procedure begins with harvesting a ring of corneal tissue from a donor graft. Laser is used to form channels in the patient’s cornea, into which the stromal ring segments are threaded.
Dr Gunn said the ring segments thicken the cornea in the periphery, causing the peripheral cornea to steepen and the central cornea to flatten, which in turn changes the shape and power of the cornea. By placing a segment rather than a full ring, the effect is localised, reducing inferior steepening, decentration and astigmatism.
IMPROVING SHAPE AND VISION
Unlike standard cross linking, which has very little effect on the corneal shape, Dr Gunn said the purpose of CAIRS is to improve shape and vision.
“Cross-linking is usually needed at the same time, or later, to stop the disease getting worse. Often topographic corneal laser is used to enhance the result from CAIRS, or an update in glasses”.
CAIRS surgery takes approximately 30 minutes and patients usually notice significant improvements to their vision within a month, with positive change likely to continue and remain permanently. For some patients it can mean the end of reliance on hard contact lenses as they can obtain improved quality of vision in glasses. It may also mean that some patients can avoid a full corneal graft with its invasiveness and higher risks.
Dr Gunn said one significant impediment to widespread uptake of CAIRS in Australia is the limited access to a femtosecond suite in an accredited day hospital.
“Most laser suites are not located in accredited hospitals and so do not meet the rigorous standards required to perform corneal transplant surgery. To perform this surgery outside that environment would raise concerns over potential infection risk and also create issues around funding if there is inability to attract Medicare and private health insurance rebates,” he explained.