POSTERIOR SEGMENT COMPLICATIONS OF LASER IN SITU KERATOMILEUSIS (LASIK)

Abstract

SUMMARY L aser in situ keratomileusis (LASIK), a surgical procedure for correction of refractive errors, has a high level of safety and efficacy. LASIK has become the most frequent refractive surgical procedure worldwide. The range of available correction, the reliability and safety of the results, and the speed of visual recovery after the surgery have made the procedure the most revolutionary breakthrough in ophthalmology in the 1990s. The goal of any refractive surgery is to remodel the eye’s microanatomy in such away that the optical properties will be aligned to the ideal focus. LASIK is a refractive lamellar surgical procedure that alters the anterior curvature of the cornea by removing stroma from within the cornea, leaving Bowman's layer and the epithelium virtually intact. The technique involves creating anterior corneal flap with a microkeratome, ablating the underlying stromal bed with an Excimer laser, and replacing the flap. Rapid development in new laser technology enables the application of ultrashort laser pulses in the femtosecond (fs) regime that marks advancement in conventional standard procedures of refractive surgery by eliminating the use of mechanical knives. With the fs-LASIK procedure, ultrashort laser pulses focus in the near-infrared spectral range and create a laser induced breakdown that disrupts the corneal tissue. However, this procedure may lead to complications. LASIK complications are quite variable and can be classified as anterior segment and posterior segment complications. Posterior segment complications after LASIK are rarely reported such as posterior vitreous detachement, choroidal neovascular membrane, retinal detachement, macular hole, cystoid macular oedema and optic nerve diseases. Although there are potential mechanisms to explain posterior segment complicationsafter LASIK, despite the large number of surgeries performed worldwide, the number of reported events so far is small, and no direct causal relationship has been established. Surgeon recommends an examination of the funds both before and after refractive procedure. Excessive mechanical stress is often suggested as the etiology of vitreoretinal pathology during or after the LASIK procedure. The eye changes shape during the application of the suction ring to fixate the globe during the creation of the corneal flap by the microkeratome. Applying suction causes an increase of intraocular pressure (IOP) to approximately 60 mm Hg. Thus, LASIK can be thought of as a trauma to the eye in the form of increased intraocular pressure (IOP) delivering a ‘‘blow’’ to the retina. LASIK may in rare cases lead to new occurrence of posterior vitreous detachment or extension of a previously existing partial posterior vitreous detachment. With the increase in the number of LASIK procedures performed, there have been reports of rhegmatogenous retinal detachment postoperatively. The suction ring –induced mechanical stretch on the vitreous base may play a role in the occurrence of retinal tears. Thus it might be important to look at the retinal periphery before and after the LASIK procedure. High myopia is associated with the occurrence of macular hemorrhage and choroidal neovascularization (myopic maculopathy). Breaks in Bruch’s membrane, so-called lacquer cracks, and choroidal neovascular membranes may be the source of such macular hemorrhage. Theoretically, such lesions could be induced, or their development accelerated, by mechanical changes of the ocular globe during LASIK. A macular hole may infrequently develop after LASIK for correction of myopia. Incidence of optic nerve diseases extremely rare after LASIK surgery. Improvement of microkeratome designs with shorter suction times and faster cutting is a major factor for an apparent increase in safety. Retinal vascular occlusions after LASIK appear to be an extremely rare complication of LASIK. Although an association cannot be ruled out, The occurrence appears coincidental. Many studies aimed to assess the influence of the transient elevation of IOP during suction in LASIK on the retinal nerve fibre layer (RNFL) thickness both in microkeratome-assisted and FS laser-assisted LASIK. Some studies suggested that excimer laser has no significant effect on RNFL measurements as determined by scanning laser polarimetry. On the other hand, a series of studies suggested that LASIK exert non-significant impact on RNFL as well. Refractive surgery candidates, particularly those with moderate to high myopia, are vulnerable to retinal problems. Myopia itself is a recognized predisposing factor for vitreoretinal complications, regardless of any surgical procedure. It is very important to inform patients that LASIK only corrects the refractive aspect of myopia; the risk of complications related to the myopic eye will persist. A long-term follow-up of these patients is important to confirm our findings. A detailed preoperative dilated fundus examination, with careful attention to the macula, should be done on every patient undergoing LASIK. Patients with pre-existing risk factors should be counseled on the increased possibility of posterior segment complications after LASIK and may also want to consider alternative refractive surgery options Understanding the mechanisms that produce LASIK complications is considered to be the first step in prevention followed by the second step of complication management.