Anisometropia is a common cause of amblyopia and is traditionally treated with refractive correction combined with occlusion therapy or penalization. However, traditional therapy for severe anisometropia with or without associated amblyopia is frequently unsuccessful, and a direct relationship between the degree of anisometropia and the severity of amblyopia has been documented. Given the poor success rate of conventional therapy in treating severe anisometropia, researchers are investigating new options. Because photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), and laser epithelial keratomileusis (LASEK) are effective in reducing refractive errors in adult patients, these procedures have recently been used on a limited basis in children with severe anisometropia who were poorly compliant or noncompliant with traditional therapy.3-14 To date, refractive results have been good, and mild to moderate visual improvement has been achieved. If these procedures are demonstrated to be safe and effective in children in the long-term, it may be possible to essentially eliminate severe pediatric anisometropia, thereby greatly reducing vision loss associated with this condition.
Problems with Conventional Therapy
Anisometropia of more than 4 diopters (D) has been associated with a poor visual outcome using traditional therapy. In addition, some studies report that up to 100% of hyperopes with 4.0 D of uncorrected anisometropia and myopes with 6.0 D of uncorrected anisometropia will develop amblyopia. Meanwhile, a meta-analysis of 23 studies on therapy of amblyopia demonstrated an overall success rate of only 67% for anisometropic amblyopia patients treated traditionally (Trans Am Ophthalmol Soc. 1998;96:431-450). Other risk factors that portend failure with traditional therapy include astigmatism = 1.50 D, poor compliance with treatment, patient age greater than 6 years at start of treatment, and an initial best corrected visual acuity (BCVA) of 20/200 or worse (J Aapos. 2004;8:429-434).
The Promise of Refractive Surgery
Approximately 165 children who have undergone an excimer laser refractive procedure for anisometropic amblyopia have been reported in published studies. All of these studies have had small sample sizes, and most of the treated children were older than 6-7 years and, thus, suffered deeply ingrained amblyopia; 2 studies included control groups (J Cataract Refract Surg. 2004;30:74-84 & Ophthalmology. 2006;113:169-176). Table 1 shows results from the first of these control group studies (J Cataract Refract Surg. 2004;30:1909-1916). The children in the studies typically had severe anisometropia (mean anisometropia of approximately 10 D or more for myopia and 5 to 6 D for hyperopia). Most researchers in this field agree that if children with these conditions were treated earlier in life, visual results would improve and certainly be better than those typical of the noncompliant patient.
For example, a child treated at age 2 years with -13.75 D of anisometropia and who was noncompliant with traditional amblyopia therapy was recently reported. Although the patient remained noncompliant with both spectacle use and other amblyopia measures following PRK, the child nevertheless achieved a stable BCVA of 20/40 at 12, 24, and 36 months postoperative (Am J Ophthalmol. 2004;138:70-78 & Ophthalmology. 2006;113:169-176). In contrast, patients with similar levels of anisometropia who were reviewed retrospectively as noncompliant controls fared much more poorly with a visual acuity of 20/200 or worse in all cases.
Table 1. Summary of published results of refractive surgery for pediatric anisometropic amblyopia
An Encouraging Outlook
Laser refractive surgery has advanced to the point that reliable reduction or elimination of anisometropia is reasonably possible, and laser refractive surgery has been demonstrated to be safe in the adult population. Existing pilot data support careful consideration of broadening the use of refractive surgery to younger children who are more likely to receive greater benefit compared with that already demonstrated in older children. A multicenter, randomized clinical trial with a larger patient population is recommended to optimally compare this treatment approach with traditional therapy.
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The author states that she has no financial relationship with the manufacturer or provider of any product or service discussed in this article or with the manufacturer or provider of any competing product or service.