Types of Refractive Surgery

An ever-increasing range of surgical procedures is available to treat refractive errors. The refractive status of the eye can be modified by changing the corneal shape using a diamond blade (radial keratotomy), an excimer laser (photorefractive keratectomy and laser assisted in-situ keratomileusis) or a perspex implant (intra-stromal rings). Alternatively, additional lenses can be inserted into the eye or the crystalline lens can be removed and replaced with an implant, as is the case in cataract surgery and clear lens extraction.

Views as to the most suitable technique for the correction of a particular refractive error vary between surgeons but a guide from the council of the British Society for Refractive Surgery is given in figure 6. Each of the surgical techniques will be considered in turn, along with a few that are less well established or have become obsolete. The outcome of a particular refractive surgery procedure is traditionally stated in terms of the percentage of eyes that achieve 6/6 (20/20) or better unaided, and 6/12 (20/40) or better unaided. To give an idea of the practical relevance of these results, an individual achieving 6/6 vision will manage without spectacles and those achieving 6/12 are probably legal to drive without correction of any residual refractive error. The safety of a procedure is indicated to some degree by the percentage of eyes that lose two or more lines of visual acuity when ay residual refractive error is corrected (best corrected

Figure 6: Surgical options for treating a range of refractive errors

PRK: photorefractive keratectomy

LASIK: Laser assisted in-situ keratomileusis

LASEK: Laser epithelial keratomileusis

ICRS: Intra-corneal ring segments

Lens exchange: following removal of a cataractous or clear lens

Phakic IOL (intraocular lens placed in the eye in addition to the crystalline lens

LTK: Holmium laser thermokeratoplasty

DTK: Diode thermokeratoplasty

© British Society for Refractive Surgery and Catharine Chisholm