Corneal ectasia following LASIK

Abstract

The cornea is a perplexing and enigmatic ocular structure. Its invigorating functions consist of conflicting demands. The cornea has to protect the eye, contain the intraocular pressure, and provide a smooth optical surface. These functions can be affected by a variety of diseases including immunologic, infectious, metabolic, genetic, and traumatic disorders. These disorders may compromise the ocular surface leading to ocular morbidity and visual loss. Careful management of corneal disorders may lead to prevention of visual loss and rehabilitation of vision. Recent advances in immunology and molecular biology have contributed to our understanding of the basic pathogenesis of corneal diseases, greatly augmented our management of ocular disorders, and improved the visual outcome and rehabilitation of vision. Furthermore, our conceptual breakthroughs in refractive corneal surgery were in-large due to the technological advancement and recent technical improvement in laser devices. The cornea is a dynamic structure. It is a biological system under constant remodeling. Several chemical compounds may affect its extracellular matrix homeostasis. We deal with the cornea as a mechanical structure. We stretch it with ring segment, sculpt it with excimer, cut it with femtosecond and blades in order to reshape and correct its refractive power. We have to deal with the cornea not as a stationary stable structure but as a dynamic structure that may show modifications and changes under normal or abnormal conditions. Corneal ectasia is a rare serious complication of refractive surgery. It is progressive steepening and thinning of the cornea. It may occur after excimer corneal refractive surgery because of corneal abnormalities or because of inducing mechanical weakness in the collagen tensile strengths. In rare cases, it may occur due to certain physiochemical modulation of the collagen by hormones such as relaxin which is increased during pregnancy or by inflammatory mediators and upregulation of metalloproteinases following adenoviral keratitis. Many factors have been associated with an increased risk for ectasia including pre-operative topographic abnormality, low pachymetry, high posterior surface, low residual corneal stromal bed, young age, and high myopia. Genetic factors and family history of keratoconus may play a role. In this issue of the Saudi Journal of Ophthalmology, we have focused on corneal disorders and refractive procedures. Laser in situ keratomileusis (LASIK) procedure is safe and effective for the management of many refractive errors (Al-Mezaine et al., 2011). The complications of LASIK occur during surgery or in the immediate post-operative period and in some cases it was related to pre-existing conditions (Al-Mezaine et al., 2011; Al Mahmoud et al., 2011). Said et al. (2011) showed that late onset corneal ectasia may occur due to other factors that were not existing before surgery such as pregnancy, or adenoviral keratoconjunctivitis. The development of corneal ectasia after surgery has grave medical and legal consequences for the patient and the physician. Most cases reported in the literature have been associated with certain preexisting corneal risk factors. New advances in understanding and technology have helped us in detecting predisposed cases and risk factors that may cause ectasia in normal corneas. Certain individuals, however, may develop post-operative corneal ectasia in the absence of known risk factors (Klein et al., 2006; Tuli and Iyer, 2007). The findings by (Al-Mezaine et al. (2011) indicate that we were successful in reducing incidence of post-LASIK corneal ectasia. There are, however, other exogenous factors that may predispose to corneal ectasia such as severe adenoviral keratoconjunctivitis. It appears that pregnancy and adenoviral keratoconjunctivitis may lead to mechanical weakening of the cornea and sometimes may eventuate in late onset corneal ectasia in patients, who had undergone LASIK (Said et al., 2011). All patients undergoing LASIK should be aware of the fact that there may be a small risk of late onset post-LASIK corneal ectasia. We have moved to a new era of technological and medical advances that allow the management of refractive errors of the eye and management of the corneal disorders that lead to visual disability. Such developments have led to improved outcome and prevention of visual loss. The late onset complications of such procedures should be taken into consideration.