2 The procedure
2.1.1 Refractive errors (myopia, hyperopia or astigmatism) can result from non-refractive ophthalmic surgery such as cataract surgery or corneal transplantation.
2.1.2 Refractive errors are usually managed by wearing spectacles or contact lenses. In patients for whom spectacles and contact lenses do not adequately correct the refractive error, other options include corneal relieving incisions, intraocular surgery such as cataract extraction with standard or toric intraocular lenses and laser corrective procedures.
2.2.1 Three types of laser correction are considered in this guidance: photorefractive keratectomy (PRK), laser epithelial keratomileusis (LASEK) and laser in situ keratomileusis (LASIK), all performed with the patient under local anaesthesia. If required, they can be performed on both eyes during the same treatment session.
2.2.2 PRK involves removal of the corneal epithelium by surgical dissection followed by excimer laser ablation of a calculated amount of the stromal bed of the cornea. LASEK is a modification of PRK in which dilute alcohol is used to loosen the corneal epithelium before it is lifted from the treatment zone as a hinged sheet, and then replaced at the end of the procedure. In LASIK, a flap is created with a microkeratome, lifted before laser ablation and then repositioned. Patients may be given pre- or postoperative antibiotics as prophylaxis against infection.
Sections 2.3 and 2.4 describe efficacy and safety outcomes from the published literature that the Committee considered as part of the evidence about this procedure. For more detailed information on the evidence, see the overview.
2.3.1 A case series of 62 patients (87 eyes) who had LASIK after non-refractive ophthalmic surgery or refractive surgery reported that mean spherical equivalent refraction (MSER; a negative reading indicates myopia, a positive reading indicates hyperopia) improved from −5.25 D preoperatively to −0.70 D at 1-year follow-up.
2.3.2 A case series of 59 patients (85 eyes) who had LASIK after multifocal intraocular lens implantation reported that MSER improved from −0.34 D preoperatively to −0.07 D at 6-month follow-up (p = 0.004).
2.3.3 A case series of 48 patients (57 eyes) who had LASIK after penetrating keratoplasty (PK) reported that MSER improved from −3.94 D preoperatively to −0.61 D at 2-year follow-up.
2.3.4 A case series of 38 patients (46 eyes) who had LASIK after PK reported improvement in preoperative mean spherical refraction in myopic eyes (n = 40) and hyperopic eyes (n = 3) from −5.16 D to −0.44 D and 5.75 D to 1.67 D respectively, and improvement in mean preoperative cylindrical refraction in eyes with mixed astigmatism (n = 3) from −5.50 D to −2.42 D at 5-year follow-up. Overall, at 5-year follow-up, 63% (29/46) had a refractive error within 1.00 D of emmetropia.
2.3.5 The case series of 62 patients reported that the proportion of patients' eyes with uncorrected visual acuity of 0.5 or better increased from 5% (4/87) preoperatively to 70% (61/87) at 1-year follow-up.
2.3.6 Case series of 62, 59 and 48 patients who had LASIK after non-refractive ophthalmic surgery reported LASIK re-operation in 22% (19/87), 6% (5/85) and 9% (5/57) of eyes because of residual refractive errors, at follow-ups of 12, 6 and 24 months respectively.
2.3.7 The Specialist Advisers listed key efficacy outcomes as uncorrected visual acuity, reduced refractive error, maintained best‑corrected spectacle vision and improved quality of life.
2.4.1 The case series of 48 patients reported that 15% (8/52) of eyes had lost ≥ 2 Snellen lines of best-corrected visual acuity at 1-year.
2.4.2 A case series of 41 patients (44 eyes) who had PRK after PK reported 3 eyes with grade 2 haze all requiring retreatment.
2.4.3 The case series of 59 patients reported 4 eyes with moderate or marked dry eye developing between 3 and 6 months follow-up. All eyes were treated frequently with lubricant. The case series of 48 patients treated with LASIK after PK reported persistent dry eye in 3 eyes at a mean follow-up of 21 months.
2.4.4 The case series of 48 patients reported: 4 eyes with epithelial ingrowth (requiring removal) between 1 week and 12 months; 2 eyes that required repeat graft for persistent astigmatism between 1 and 3 years; 3 eyes needing repeat graft for oedema between 8 months and 3 years; and 5 eyes with flap dislocation between 1 day and 1 week (2 required sutures, 1 flap was removed and 1 was repositioned without sutures).
2.4.5 A case series of 57 eyes reported: 2% (1/57) of eyes with macular haemorrhages 7 days after LASIK; 7% (4/57) of eyes with epithelial ingrowth; 4% (2/57) of eyes with induced astigmatism; 4% (2/57) of eyes with a free cap; and 25% (14/57) of eyes with night vision problems at a mean follow-up of 9 months.
2.4.6 The case series of 38 patients who had LASIK after PK reported endothelial rejection, which was successfully treated in 1 eye.
2.4.7 The Specialist Advisers considered theoretical adverse events to include ectasia, recurrent epithelial erosion syndrome, epithelial defects, bleeding from the flap edge, interface haemorrhage, interface debris, flap striae, diffuse lamellar keratitis, corneal scarring, glare, infection and pain after treatment.
2.5.1 These procedures can make it more difficult to measure accurately the intraocular pressure used to detect glaucoma, and the intraocular lens power required for cataract surgery. Techniques are available to address these difficulties, provided it is known that photorefractive surgery has previously been done.