EyeWorld India December 2013 Issue

41 EWAP CORNEA December 2013 Views from Asia-Pacific Sri GANESH, MD Chairman, Nethradhama Hospitals Pvt. Ltd. 256/14 Kanakapura Main Road, 7th Block Jayanagar, Bangalore – 560082 Tel. no. +91-80-26088000 Fax no. +91-80-26633770 chairman@nethradhama.org C orneal ectasia following LASIK surgery is the most dreaded complication. This has led to a shift towards surface ablations. There are two aspects to this condition: (1) Undiagnosed preoperative keratoconus or forme fruste keratoconus which is stable and nonprogressive and gets precipitated following LASIK surgery, and (2) a perfectly normal cornea which becomes ectatic following LASIK surgery. These two conditions are separate entities with different pathologies and mechanisms of ectasia. In the first scenario, proper screening with advanced diagnostic tools preoperatively can identify forme fruste keratoconus. It is not surprising that most early keratoconus patients are diagnosed in refractive surgery clinics as these patients have problems in quality of vision with their glasses and are looking to refractive surgery for a solution. Assessing the anterior curvature maps, posterior elevation maps, asymmetry indices, irregularity and regional differences, and progression of corneal thickness and comparison with the fellow eye can help in identifying this condition. Such cases can be offered alternative methods of treatment such as phakic IOLs or surface ablation with corneal collagen crosslinking. In the second scenario, various risk factors such as age, family history, extent of refractive correction, preoperative central corneal thickness, flap thickness and residual corneal bed thickness come into play. Other environmental conditions such as dryness, excessive rubbing of the cornea and pregnancy may play a role in the development of post-LASIK ectasia. If the risk factors are high for ectasia on the Randleman’s risk score system, it is best to avoid LASIK or offer safer alternative methods of correction. An alternative school of thought is to routinely crosslink all cases of LASIK if the ectasia risk is borderline, i.e. LASIK Extra. This can be done for younger patients, thinner corneas, and higher refractive errors. There is a shift to making thinner flaps, i.e., sub-Bowman’s keratomelieusis (SBK), either with the femtolaser or with microkeratomes which would improve the stability of the cornea. The emergence of newer technologies for corneal refractive surgery like ReLEx Smile have better biomechanical stability and hence lower risk of postoperative ectasia. They have the safety of surface ablation and the comfort and wow factor of LASIK. Meticulous preoperative screening with advanced diagnostics and thorough assessment of risk factors would be the mainstay in the prevention of post-LASIK ectasia. Editors’ note: Dr. Ganesh has no financial interests related to his comments. WANG Zheng, MD Professor of Ophthalmology, Zhongshan Ophthalmic Center 54 Xianlie South Road, Guangzhou 510060, China Tel. no. +86-13903002594 gzstwang@gmail.com C orneal ectasia is one of the most devastating complications after corneal refractive surgery. It is controversial whether postop ectasia is really caused by the weakening of the cornea by the surgery. Personally, I incline to the thought that the majority of these cases are actually undiagnosed genetic keratoconus, which may be aggravated by the surgery. Only a small portion of cases are real iatrogenic ones. Some subclinical keratoconus patients have not shown clinical signs by the time of surgery, but would develop keratoconus eventually, surgery or not. This is particularly true in China, because the average patient age is younger here. Some practitioners may recommend surface ablation instead of LASIK when the preop assessment shows risk of ectasia, assuming surface procedures are safer because of more residual stroma. In fact, there is no evidence from large studies to support this assumption. Ectasia after surface procedures have been reported. I have seen a case of corneal ectasia 1 week after – 1 D LASEK whose preop topography was normal. So the prevention of ectasia largely relies on preop screening for signs of early keratoconic changes. Placido-based topography is the gold standard in practice, but it has sensitivity and specificity issues. Modern topography and tomography technologies measure the elevation and curvature of both surfaces of the cornea, and the thickness of the entire cornea as well. The diagnostic tools based on these measurements have increased the chance of detecting early cases of keratoconus. Posterior elevation and pachymetry changes are found to be more sensitive and reliable in this regard. However, almost all these methods are based on detection of the morphological changes of the cornea. Are there any keratoconic signs that can be found prior to these? Corneal biomechanics is a possibility. Studies have shown abnormal biomechanical changes in keratoconus. For example, the Corvis-ST (OCULUS Optikgeräte, GmbH, Wetzlar, Germany) uses Scheimpflug imaging technology and a high-speed camera to measure the corneal biomechanical properties. More sophisticated metrics derived from the static and dynamic measurements might help surgeons find potential keratoconus cases before any topographical changes occur. Genetics also holds promise in detecting keratoconus prior to topographical changes. Several genes have been found to be related. Some doctors believe that prophylactic crosslinking may be beneficial for patients with higher risk of developing postop corneal ectasia. Of course, this requires more clinical trials to prove. Editors’ note: Prof. Wang has no financial interests related to his comments.