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Elevation most effective measure for early detection of keratoconus
Index of high decentration and index of vertical asymmetry were most effective at detecting early stages of keratoconus, while D-index was better suited as the disease progressed, according to a study.
The early stages of keratoconus may be asymptomatic and, therefore, difficult to diagnose. However, it is extremely important to detect corneas at risk of developing the disease when patients are considering refractive surgery, researchers said.
A study carried out at the Goethe University in Frankfurt screened and followed over time the non-ectatic fellow eye of 27 patients with unilateral keratoconus and an equal number of age-matched healthy eyes. The Pentacam Oculus system with integrated Belin/Ambrosio Enhanced Ectasia Software was used. Consecutive examinations were performed until the first signs of keratoconus were visible.
Index of high decentration (IHD) with an area under the curve (AUC) of 0.788 + 0.054 turned out to be the most useful index to identify differentiation of keratoconic from healthy eyes, followed by index of vertical asymmetry (IVA).
“Our results suggest examining IVA and IHD and carefully evaluating these before a patient undergoes refractive surgery,” the authors wrote.
As the disease progressed, D-index acquired a more important role, followed by IHD and IVA.
These results seem to indicate that elevation might be better suited than keratometry and pachymetry to screen for keratoconus in the early stages of the disease.
Another interesting finding was that astigmatism only marginally progressed in the early stages.
“A reason for this could be that the biochemical alteration of the cornea occurs significantly earlier than visible changes to its shape, which might only be secondary,” the authors wrote.
“There are two key points in our study that are relevant to clinical practice,” author Mehdi Shajari, MD, told Primary Care Optometry News. “The first comes from the consideration that corneal refractive surgery should not be performed in eyes being prone to ectatic diseases like keratoconus. In our study we found that asymmetry in corneal power and elevation in corneal back surface are the first two changes in eyes with keratoconus. Refractive surgeons should consequently pay attention to these two points when deciding whether to perform surgery or not. “Second,” Shajari continued, “when evaluating progression of keratoconus in the very early stages, the corneal elevation maps should be examined, as differences in elevation are the main change in the beginning.” – by Michela Cimberle
Disclosure: Shajari receives payment from Oculus. Please see the study for the other authors’ financial disclosures.