Posterior segment complications of refractive surgery

Abstract

Refractive surgery encompasses a range of procedures aimed at changing the refraction of the eye by altering the cornea or the lens, the principal refractive components (Mimura and Azar, 2008). One of those procedures is Laser assisted stromal in situ keratomileusis (LASIK). 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 (Dada et al., 2003). LASIK complications are quite variable and can be classified as anterior segment and posterior segment complications. Although there are potential mechanisms to explain posterior segment complications after 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. Considering the potential sight –threatening nature of vitreoretinal complications, a possible relationship should be discussed with potential LASIK candidates. Surgeon recommends an examination of the funds both before and after refractive procedure (Arevalo, 2008). LASIK may in rare cases lead to new occurrence of posterior Vitreous detachment or extension of a previously existing partial posterior vitreous detachment (Mirshahi and Baatz 2009). summary 41 The giant retinal tears may be coincidental, but the suction ring –induced mechanical stretch on the vitreous base and the shock wave that originates from LASER photorefractive keratectomy may play a role in the occurrence of giant retinal tears. Thus it might be important to look at the retinal periphery before and after the LASIK procedure (Arevalo et al., 2005). Careful pre operative macular evaluation is recommended. Even pre –LASIK fluorescence angiography in high myopia and suspicion cases. A possible mechanism could be that LASIK weakened the structure of the fragile sub macular vessels and predisposed to the occurrence of choroidal neovascular membrane in degenerative myopia. Some authors have commented that shock waves produced by Excimer LASER might contribute to development of some alterations in the fragile sub macular vessels or the retinal pigment epithelium, leading to cystoids macular edema or sub macular hemorrhage. Mechanical force produced by suction and microkeratome might be another cause. Gentle manipulation of the suction ring and microkeratome is obligatory in extremely myopic cases. The possibility of choroidal neovascular membrane and sub retinal hemorrhage are rare (Saeed et al., 2004). A macular hole may infrequently develop after LASIK for correction of myopia (Arevalo et al., 2005). Preexisting macular pathology such as retinal pigment epithelium atrophy could be a new contraindication to LASIK for hypermetropia with possible development of central serous choroido retinopathy, requiring a careful examination of the fundus pre – LASIK (Singhvi et al., 2004). Several types of lenticular refractive procedures are currently being performed today: phakic IOL implantation, refractive lens summary 42 exchange (RLE) and cataract extraction with a monofocal, multifocal or accommodative IOL (Koo et al., 2006). The unique complications of phakic IOLs are primarily mechanical in nature and result from the anatomic relationships between the IOL and its neighboring ocular structures. With the anterior chamber lenses, the main complications arise from: (1) Contact with the endothelium resulting in endothelial cell loss and corneal oedema; (2) contact with the iris leading to pigment dispersion and chronic uveitis; (3) papillary block leading to acute angle closure glaucoma; (4) deformation of the iridocorneo- scleral angle structures by the haptics, resulting in pupil ovalisation, peripheral anterior synechiae, glaucoma and occasionally (5) contact with the natural crystalline lens leading to cataract formation. In addition, IOL decentration, tilt, pupil ovalisation, and the smaller IOL optic required by anterior chamber lenses can all contribute to the symptoms of glare and halos (Koo et al., 2006). Refractive lens extraction (RLE) is an intraocular refractive surgery consisting of the extraction of the natural lens and its substitution by an posterior chamber intraocular lens (IOL) of proper dioptric (D) power. Theoretically, RLE is a surgical procedure with the same risks and complications as cataract extraction surgery. The most common significant complication in high myopic eyes is retinal detachment (RD). In those eyes with high myopia which underwent RLE, the major risk for permanent visual loss is also secondary to RD. The main risk factors include: peripheral retinal degeneration, intra-operative posterior capsular rupture, absence of posterior chamber IOL, and Nd:YAG laser application after surgery. Macular complications are less frequent, but this complications might summaryproduce permanent visual loss. Other less frequent complications following RLE reported include: raised IOP, cystic macular edema (CME), and intra-operative vitreous loss (Koo et al., 2006).