Chapter 68 Refractive surgery in children
Introduction
Excimer laser surgery for high refractive error associated with amblyopia has been performed for over 15 years with good visual acuity and refractive results and minimal complications.1–26 Intraocular refractive procedures have been performed in smaller numbers for higher refractive errors for up to 7 years, also with good visual and refractive outcomes and few complications.
Conventional amblyopia therapy consists of the following:
1. Clearing the ocular media of visual obstructions such as leukoma, cataract, or vitreous hemorrhage.
2. Correcting significant refractive errors either with spectacles or contact lenses.
3. Encouraging use of the amblyopic eye through occlusion or pharmacologic and/or optical penalization of the fellow eye (see Chapter 70).27–29 This conventional therapy is successful in the majority of young amblyopes.
1. Children with bilateral high ametropia (isoametropia) who are spectacle non-compliant or intolerant.
2. Children with severe anisometropia who are non-compliant or intolerant of spectacle and contact lens wear.
3. Children with high ametropia, either anisometropia or isoametropia, who have other special circumstances such as craniofacial anomalies, ear deformities, or neck hypotonia that preclude the proper use of refractive correction.
There are many reasons for poor compliance with spectacles or contact lenses. Spectacles for the treatment of extreme myopia or hyperopia can cause prismatically induced optical aberrations, a narrow visual field, and social ostracism due to unattractive thick lenses. Group 1, above, consists primarily of former premature infants with severe retinopathy of prematurity and high myopia, children with genetic mutations, or with autism spectrum disorder. They are often non-compliant or ill-suited for spectacle wear or contact lenses due to tactile aversion. Their visual impairment may impede their attention and social interaction, exacerbating significant behavioral and social problems and impeding the development of normal skills. In group 2, spectacle-induced aniseikonia and anisovergence impede stereopsis and binocular vision, and may cause asthenopia.30
Types of refractive surgery used in children
1. In PRK, epithelium is removed and Bowman’s membrane and anterior stroma are treated with laser.
2. In LASEK, the epithelium is not removed, but an alcoholic solution is used to loosen the epithelial cells; the surgeon folds the epithelial layer out of the treatment field, performs the laser ablation, and then replaces the epithelial layer.
3. In LASIK, a partial-thickness corneal flap is created using either a mechanical microkeratome or a femtosecond laser microkeratome. A hinge is left at one end of this flap. The flap is folded back and the laser ablation performed on the deeper stroma. The LASIK flap is then repositioned. The flap remains in position by natural adhesion until healing is completed.
Current intraocular refractive procedures change the existing lens power and include phakic intraocular lenses (phIOLs), refractive lens exchange (RLE), and clear lens extraction (CLE). These procedures are used to treat higher refractive errors that fall outside the treatment parameters for the excimer laser, or in cases where the cornea is too thin for the excimer laser. phIOL procedures add or reduce lens power.31 An intraocular lens (IOL) is placed into the anterior or posterior chamber preserving the natural crystalline lens. Anterior or posterior chamber phIOLs can be used to treat severely high myopic refractive errors if the anterior chamber is deep enough to tolerate the lens (minimum 3.2 mm).
Safety of ASA versus LASIK
Box 68.1 outlines the risks of ASA and LASIK. While LASIK has been shown to be effective in children to correct refractive error, ASA holds several advantages. First, no corneal flap is created so there is no risk of flap loss, epithelial in-growth, or flap striae as with LASIK. Second, since ASA is performed on the surface of the cornea, the posterior stroma remains thicker, with less risk of keratectasia. Because most children treated with excimer laser procedures require a large excimer treatment dose, there is significant corneal ablation. There have been no reported cases of keratectasia following ASA in children. The main long-term risk of ASA is corneal haze, but, in our experience, it is uncommon and, typically when the topical steroid (fluorometholone) was discontinued too early. Fluorometholone must be used for 6−12 months following PRK. Corneal haze can be further reduced by limiting ablation treatments to within the Federal Drugs Administration (in the USA) approved parameters and by the child taking vitamin C 250−500 mg daily for a year. The other issue with excimer laser procedures is which causes a reduction in the effect of the procedure or refractive regression. Most of the regression occurs in the first year but it can continue longer; it is more severe with higher excimer treatment doses.
Box 68.1
Risks of ASA versus LASIK
| ASA | LASIK |
ASA = advanced surface ablation; LASIK = laser-assisted in situ keratomileusis.
Phakic intraocular lens safety
Phakic IOL implantation is not subject to refractive regression and may be the preferred surgical correction of pediatric myopia and hyperopia beyond the range of ASA.32 Another major advantage is reversibility. The anterior chamber depth required for an “iris-enclaved” IOL precludes the use of this lens in some children. Children who have high lenticular myopia after retinopathy of prematurity may be unsuitable because of shallow chambers.33 The major concern with a phIOL in a child is the long-term effect on corneal endothelium. Experience indicates however, that endothelial cell loss is low,32,34,42 no greater than in adult implantation. Accurate endothelial cell counts are difficult to obtain in the children who may benefit most from implantation.32 Any refractive surgical procedure, including ASA, LASIK, and RLE/CLE, can cause some reduction of endothelial cell density. We still need to know the comparative loss. Posterior chamber phIOLs have also been implanted in children:38,39,41 Because they lie adjacent to the iris pigment and lens, they risk pigment dispersion and cataract formation. These potential risks are important, but they must be weighed against the certainty of permanent blur-induced visual impairment if the children continue uncorrected. These potential complications may occur many years later.
