Introduction

Since the introduction of corneal refractive surgery (CRS), surgeon’s and patient’s expectations have increased in parallel with the improvement of both the equipment and surgical techniques. Currently, a good surgical outcome implies not only emmetropia but also high safety standards and excellent quality of vision. This chapter gives an overview of the most important complications of excimer laser CRS.

Preoperative assessment

Preoperative assessment should evaluate both ocular and medical conditions that may influence the outcome of CRS. The patient should be given a detailed informed consent including expectations and potential complications.

To protect the integrity of the corneal epithelium and postoperative wound healing, dry eye syndrome or uncontrolled blepharitis should be preoperatively treated. In patients with background of herpes keratitis, LASIK should only be performed after 1 year of inactivity without treatment and in absence of stromal disease. Consider oral antiviral prophylaxis1. Moreover, LASIK is contraindicated in anterior basement membrane dystrophy (ABMD), but photorefractive–phototherapeutic keratectomy (PRK-PTK) is an excellent option in myopic patients presenting recurrent epithelial erosions.

In patients with glaucoma, the intraoperative increase in intraocular pressure during suction may cause additional damage to the optic nerve. Moreover, falsely low intraocular pressure (IOP) measurements are obtained by applanation tonometry in thinned corneas or in those rare situations where there is accumulation of fluid at the interface. Dilated fundus examination is mandatory. Peripheral retinal degenerations predisposing to retinal tears should be treated.

Scotopic and photopic pupil size should also be measured. Patients with larger pupils should be warned of the increased risk for postoperative night vision disturbances.

Additionally, presbyopic patients should be informed about the different available options and their limitations. Despite a presbyopic compensation approach being used, near-vision correction with spectacles might still be required in some cases.

In-depth evaluation of corneal topography is a ‘must’ prior to refractive surgery to identify patients with risk of postoperative corneal ectasia. Corneal topographic warning signs include curvature abnormalities, thin central pachymetry, and/or asymmetry in peripheral pachymetry. Ablational corneal refractive procedures are contraindicated in such cases, except in particular situations. Due to the increased risk of visual disturbances and decreased quality of vision, the cornea should not be flattened to less than 36 D or steepened to more than 48 D2.

Finally, connective tissue or autoimmune diseases and systemic immunosuppression are relative contraindications of LASIK. Absolute contraindications are uncontrolled diseases, uncontrolled ocular allergy, and pregnant or nursing women.

Intraoperative complications

The most frequent intraoperative complications are related to the creation of the lamellar corneal flap with the microkeratome. The incidence of intraoperative flap complications ranges from 0.3% to 5.7%, being most frequent at the beginning of the learning curve. Poor quality flaps include incomplete flaps, buttonholes, thin or irregular flaps, and free caps3.

Test all equipment before surgery to avoid complications. Flap diameter may be adjusted in relation to preoperative keratometric power. Flatter corneas have an increased risk of free caps or incomplete flaps, whereas steeper corneas are more prone to epithelial abrasions, buttonholes, and thin or irregular flaps4.

Check proper suction and centration before starting the lamellar keratotomy. Wet the ocular surface during the microkeratome pass to avoid epithelial defects. Evaluate the flap before laser ablation to ensure consistent thickness, intact hinge, good centration, and diameter. If any flap-related complication occurs, abort the procedure and reposition the distorted flap. After complete healing (at least 3 months), another flap may be attempted. When using femtosecond laser microkeratomes, this period might be shorter and complications slightly different.

Postoperative complications

Flap distortions: microstriae, macrostriae, and flap dislocation

Macrostriae are broad, parallel lines that reflect flap wrinkling. Pooling of fluorescein is seen over the base of the folds. Macrostriae may cause decreased best-spectacle corrected visual acuity (BSCVA) and visual disturbances, and constitute an emergency.

Only if detected and treated within the first 24 h of occurrence, it is possible to solve them. Lift the flap, clean the epithelium the gutter, float the flap with balanced salt solution (BSS), and smooth it back into position. If undetected or left untreated for 1 or more days, the folds become fixed due to epithelial remodeling over the folds and stromal collagen fibers contraction. De-epithelialization and swelling of the flap with sterile distilled water is essential to release fixed folds. Place a bandage contact lens (BCL) to stabilize the flap and reduce the risk of epithelial ingrowth. Prescribe topical antibiotics and steroids. If macrostriae persist despite hydration, traction and suturing of the flap are required. However, suturing itself may create new striae or induce regular or irregular astigmatism. In severe cases, amputating the flap or PTK may be effective5.

Microstriae are fine wrinkles in Bowman’s layer. Compared with macrostriae, microstriae are smaller, have a more random pattern, and exhibit negative fluorescein staining. Treatment of visually significant microstriae is the same as the one applied for macrostriae.

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