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The past 30 years have brought witness to “an explosion in our knowledge of, and ability to diagnose, keratoconus,” said Prof. Charles McGhee, MD, PhD, DSc.
Keratoconus: Treatment paradigms
San Diego-The past 30 years have witnessed “an explosion in our knowledge of, and ability to diagnose, keratoconus,” said Prof. Charles McGhee, MD, PhD, DSc.
The first full keratoconus paper was published in the 1800s, but is “exponentially burgeoning” in this decade, said Dr. McGhee, speaking here during World Cornea Congress.
The long-held belief that keratoconus is non-inflammatory “may or may not be true,” he said.
What is still held true is that the ectactic disorder “leaves scarring and hydrops, and there is no curative treatment,” said Dr. McGhee, who is in private practice in New Zealand.
The etiology of keratoconus is multifactorial, with some suspected environmental elements.
“The incidence ranges form 8.8 to 54.4 per 100,000, depending on the study cited,” Dr. McGhee said. “The variation is due to divergent diagnosis and exposure to cofactors.”
Slit lamp and Placido disc have traditionally been used to diagnose the disorder. Some studies have shown more than 50% of first-degree relatives have astigmatism or abnormal cornea.
“Should we be screening the general population for keratoconus? Probably not, giving the low cost-benefit,” he said. “But there may be some population exceptions, as in the 2.4% of university students in Iran that have keratoconus or suspect keratoconus.”
Genetic disposition does play some role, he said-noting people with Down syndrome are 300 times more likely to develop keratoconus than the general population; similarly, those with Leber congenital auresis are 30% more likely to develop keratoconus.
In cases of known keratoconus, however, “screening family members is useful and will give us the potential ability to prevent disease,” he said.
In the United Kingdom, there is a paradox that atopy is a reverse association-the rate of keratoconus in Indians (who were younger) was 1:4000, but the rate was 1:30,000 for whites.
“So it remains an ongoing debate,” he said.
Eye rubbing is often reported in this group, and “may trigger apoptosis in certain individuals,” he said.
Current treatment paradigms must include early diagnosis, regular monitoring and treatment of environmental factors where possible e.g. treating ocular allergy and minimizing eye rubbing.
Spectacles and rigid gas permeable contact lenses (CL) remain core to the optical management of keratoconus, but although CL “remain a primary long-term intervention, it is well-recognized that CL per se have no beneficial effect on stabilizing the disease,” Dr. McGhee said.
Corneal intra-stromal segments have been employed in the treatment of keratoconus for more than 15 years. These segments have been refined specifically for keratoconus and have demonstrated improvement in: corneal shape, corrected visual acuity, and contact lens wear. However, like CL, segments do not affect the underlying keratoconus progression.
Any contemporary management plan must now include early consideration of treatment to stabilise or slow the disease progression. Corneal collagen cross-linking (CXL) using UVA and riboflavin has emerged from laboratory to clinical application in less than 20 years.
“Indeed, there has been a veritable explosion in its widespread application to ectatic diseases with several hundred related publications since 1997,” he said. “There is significant evidence that CXL will halt or slow progression of keratoconus in the majority of cases. A number of variations, including epithelium-on treatment regimens, have been developed and may have some utility over established protocols. Certainly CXL should be considered in all cases of keratoconus where there is convincing evidence of progression, including early in the second decade.”
Penetrating keratoplasty (PKP) has been practiced successfully for more than 100 years, although before and after the first successful PKP by Zirm, many practitioners explored anterior and posterior lamellar approaches, he said.
However, since the 1960s penetrating keratoplasty has been the preferred technique for advanced keratoconus and the success of the procedure is 90% or more in the hands of experienced surgeons. Risks include endothelial graft rejection and endothelial exhaustion.
Approaches to preserve host Descemets’s and endothelium saw the reemergence of deep anterior lamellar keratoplasty (DALK) as a potential treatment, he said.
The learning curve for DALK is “steep, but the advantage of obviating endothelial rejection is substantial.
Nonetheless, large studies still debate overall superiority of DALK compared to PKP in terms of optical and survival benefits.”
The current treatment algorithm classically moves to penetrating keratoplasty if the disease continues to progress, but Dr. McGhee hopes the work in CXL and DALK may prolong if not obviate the need for PK.
“Movement has been to prevent the progression of the disease,” he said.
“We showed such a decrease in disease progression with CXL in New Zealand this is now a covered procedure,” he said.
A Cochrane Collection review found “evidence is limited due to the lack of properly conducted randomized clinical trials,” although the majority of the world has accepted its ability to improve vision and reduction in the mean K.
Currently, CXL seems to be better in eyes with worse baseline vision. Today, conservative treatment for keratoconus remains CL, with CXL and PRK considered more intermediate approaches.
“We mustn’t forget that the graft survival rate is about 15 years,” he said. PKP works “quite well” in keratoconus eyes, Dr. McGhee said.
Some advanced approaches include phakic IOLS, although those are not used often, and other potential future treatments include epi-K.