EyeWorld Asia-Pacific March 2016 Issue

3 EWAP March 2016 Letter from the Editor Dear Friends A stigmatism is widespread among the normal population and there is a progressive drift toward an against-the-rule pattern with age. We have several techniques, including laser correction and toric intraocular lenses, which are extremely effective in dealing with correcting this refractive error in patients undergoing refractive or cataract surgery. The majority of patients have regular astigmatism where the axes are orthogonal and the distribution of the corneal power symmetrical but this is not always the case. We have discussed the management of regular astigmatism previously but of particular interest in this issue is the focus on irregular astigmatism. Wavefront-guided treatment for irregular astigmatism has not proved to be as reliable as hoped for but there are now several laser platforms that are capable of topography-guided laser ablation. This modality is a more logical approach to addressing an irregular corneal surface with astigmatism as evidenced by the increasing number of reports with successful outcomes using this approach in the literature. One of the most interesting applications for topography-guided corrections are patients with early forme fruste keratoconus. Traditionally, laser correction of patients with any evidence of ectasia has been a definite contraindication. The availability of crosslinking to stabilize corneas in patients with forme fruste or early keratoconus, however, has opened up new prospects. The combination of crosslinking with topographic laser-guided ablation has proven to be effective in improving patients’ best corrected acuity, although it is still somewhat uncertain as to the best way to combine these two modalities. Some surgeons suggest simultaneous crosslinking and laser ablation while others recommend initial crosslinking followed by laser ablation at a later date. One of the limiting factors is the need to limit the ablation to approximately 50 microns. It soon becomes evident when contemplating a case of mild keratoconus that this limit is often insufficient to correct irregular astigmatism, aberrations, as well as the underlying manifest refractive error. Designing a treatment plan in these circumstances is complex and the refractive outcomes have not achieved the same level of predictability as we are accustomed to when treating patients with regular astigmatism. Similarly, lens selection for patients undergoing cataract surgery who have keratoconus is more complex. This includes both the prediction of spherical as well as astigmatic outcomes. The corneas are relatively steep and the standard prediction formulae are not as accurate in these circumstances. The measured keratometry may not coincide with the visual axis and the relationship of the posterior cornea may differ in eyes with ectasia. Generally, the refractive outcome tends to be more hyperopic than expected due to an overestimation of the actual keratometry. This tendency is more likely with advanced keratoconus with Ks greater than 55 diopters. It can be helpful to look at the topography of the central 3 mm as the central steepening can be quite localized and the more peripheral K readings often provide a useful indication that a lower K value may be more appropriate. Targeting a moderate level of myopia is advisable in these cases. Equally challenging is the decision whether to use a toric lens in patients with keratoconus. Although one has to be cautious, I generally tend to select a toric lens as long as the axis is identifiable and there is reasonable correspondence between the keratometry and the topography. Looking at the patient’s spectacle correction prior to cataract surgery can also provide guidance, both to the axis and magnitude of astigmatic correction required. Patients who have had previous corneal transplants for keratoconus are an interesting subset. If the graft is clear, the astigmatism relatively regular and the graft likely to be viable for many years, then a toric lens is an excellent option to optically rehabilitate these patients. If the graft is irregular, the function borderline and the patient has always required an RGP for reasonable acuity, then a toric lens may not be appropriate. We are fortunate to have the contribution of many surgeons who have shared their own thoughts and expertise in managing these complex situations with topographic ablations as well as use of toric implants. Although challenging, with careful thought and planning, the refractive outcome of these patients can be greatly improved. I hope the discussions in this issue are helpful in your own practice. Warmest regards Graham Barrett Chief Medical Editor EyeWorld Asia-Pacific EYEWORLD ASIA-PACIFIC EDITORIAL BOARD C HIEF MEDICAL EDITOR Graham BARRETT, Australia MEMBERS Abhay VASAVADA, India ANG Chong Lye, Singapore CHAN Wing Kwong, Singapore CHEE Soon Phaik, Singapore Choun-Ki JOO, Korea Hiroko BISSEN-MIYAJIMA, Japan ASIA-PACIFIC CHINA EDITION Editors-in-Chief ZHAO Jialiang ZHAO Kan Xing Deputy Editor HE Shouzhi Assistant Editor ZHOU Qi ASIA-PACIFIC INDIA EDITION Regional Managing Editor S. NATARAJAN ASIA-PACIFIC KOREA EDITION Regional Editor-in-Chief Hungwon TCHAH Regional Managing Editor Chul Young CHOI Hungwon TCHAH, Korea John CHANG, Hong Kong Johan HUTAURUK, Indonesia Kimiya SHIMIZU, Japan Pannet PANGPUTHIPONG, Thailand Ronald YEOH, Singapore S. NATARAJAN, India Sri GANESH, India YAO Ke, China Y.C. LEE, Malaysia