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Arcuate keratotomies and limbal anti-astigmatic incisions attain stability after 12 months and they remain stable over time, according to a study presented at the UKISCRS 2003 conference. Researchers at Worcestershire Royal Hospital began the study, called 'Kill the Cyl', in 1999. In earlier studies they had compared post-phaco astigmatism between a control group of 40 patients who underwent clear corneal temporal phaco and a treatment group of 40 patients who underwent planned anti-astigmatic treatment in the form of arcuate keratotomies or limbal relaxing incisions.
The four-year follow-up revealed that the prevalence of post-phacoemulsification astigmatism of greater than one dioptre was 47% in the control group compared with just 17% in the treatment group. The researchers reported that stability was achieved at 15 months (Phase II) with only 22% showing greater than one dioptre of astigmatism. Vector analysis demonstrated an overall 0.45 D change in that time. The current four-year follow-up showed that the stability was maintained in the long term. "There are two questions which must be given serious consideration before attempting to treat astigmatism. Firstly, there is considerable skepticism as to whether the reduction in astigmatism is maintained, as it is thought that the astigmatism will drift back to its pre-treatment magnitude and axis. Secondly, if treatment is indeed effective - when is it stable? This is particularly pertinent when considering retreatment," Amir Hamid BMedSci, BM BS told the conference. All patients were recalled for corneal topography, and each patient underwent a minimum of three examinations performed by a single operator, with reproducibility assessed by an independent observer. Vector analysis was performed on the data using surgically induced refractive change, using the mathematics of obliquely crossed cylinders. The topography analysis indicated that half of the patients had less than 0.10 D of increase in corneal steepening, and 80% had less than 0.25 D. Dr Hamid believes that the larger amounts of corneal steepening seen in some eyes were due to tear film instability rather than a real significant change in corneal astigmatism. This was evidenced by the fact that in these patients there was considerable difficulty in obtaining consistent corneal topography. "We have demonstrated that after an initial 0.45 D of regression in the first year, there is very little change in corneal astigmatism during the subsequent four years. The cornea appears to completely stabilise at 12 months and there is virtually no drift back to its pretreatment astigmatism. We have managed to use this data to make minor modifications to our nomograms for against the rule astigmatism," Dr. Hamid told the conference. "The results of modern cataract surgery are already so good that further improvements are aimed at reducing or eliminating pre-existing factors such as astigmatism," said Dr. David Allen, consultant ophthalmologist with Sunderland Eye Infirmary and president of the United Kingdom and Ireland Society of Cataract and Refractive Surgeons (UKISCRS). "Many question whether the relatively benign procedures of limbal relaxing incisions have any long-term stability. This study goes some way to demonstrating that they do," he added. The team is continuing research in this area. They are planning to study the effect, if any, of the posterior corneal curvature and astigmatism on postoperative manifest refraction and therefore its impact on the anti-astigmatic treatment. This will be facilitated by the use of scanning slit topography which would enable both anterior and posterior corneal topography to be assessed in greater detail.David Allen FRCS mir Hamid BMedSci BM BS |
