Refractive Surgery in Children: Is It Ready for Prime Time?

Transcription

1 The John Pratt-Johnson Annual Lecture Refractive Surgery in Children: Is It Ready for Prime Time? Evelyn A. Paysse, M.D. ABSTRACT Introduction: Potential indications for excimer laser procedures in children include accommodative esotropia, bilateral high ametropia, and severe anisometropia. Treatment of these conditions has traditionally included spectacle or contact lens use. This treatment, however, is often ineffective in children with severe anisometropia or bilateral ametropia, especially those with neuropsychological disorders. Refractive surgery may be a viable treatment option for these conditions. Methods: The visual and refractive results from our studies on photorefractive keratectomy for pediatric anisometropic amblyopia are discussed. Also, I will present a review of the world literature on excimer laser procedures for accommodative esotropia, pediatric high anisometropia, and pediatric bilateral high ametropia. Results: In our study, at 36 months follow-up, 7 of 9 patients who were able to perform psychophysical acuity testing preoperatively had improvement of two or more lines of uncorrected visual acuity and 6 of 9 had improvement of two or more lines of best corrected visual acuity. Fifty percent of the myopic patients and 100% of the hyperopic patients were within 2 D of refractive target at the 36-month follow-up visit. Refractive error stability has been good and corneal haze has been minimal. Conclusions: Refractive surgery in children to reduce amblyopiogenic levels of refractive error is proving to be relatively stable. Best corrected and uncorrected visual acuity has also been shown to improve following the excimer laser procedures. Refractive surgery also appears to be effective for pure accommodative esotropia. Randomized clinical trials are needed to fully establish safety and efficacy. Other refractive procedures, such as clear lens extraction and phakic intraocular lenses, may also prove to be valid treatment options for these conditions in the future. From the Baylor College of Medicine, Houston, Texas. Requests for reprints should be addressed to: Evelyn A. Paysse, M.D., Baylor College of Medicine, Texas Children s Hospital, 6621 Fannin, MC , Houston, TX 77030; epaysse@bcm.edu Presented as the 14 th John Pratt-Johnson Lecture at the annual meeting of the Canadian Orthoptic Society (TCOS), Toronto, Ontario, Canada, June INTRODUCTION Twenty years from now we may be saying, Certain types of amblyopia are surgical diseases. In the future, as alien as it may currently sound, refractive surgery may be the best treatment for severe anisometropia and severe bilateral ametropia. We are standing on a frontier where a rev Board of Regents of the University of Wisconsin System, American Orthoptic Journal, Volume 57, 2007, ISSN X, E-ISSN American Orthoptic Journal 79

2 REFRACTIVE SURGERY olutionary new treatment strategy for amblyopia has the real potential to come to fruition. We may be on the verge of a paradigm shift. Treatments for refractive error have been around for a very long time. Spectacle correction has been in use since the thirteenth century, but most other refractive treatments have come along in the last 150 years. Contact lenses were introduced in Modern surgical treatment for refractive error began with radial keratotomy in the 1970s, followed by epikeratophakia in the 1980s. Both of these procedures have been supplanted by newer and better procedures. Since the early 1990s, excimer laser refractive procedures, including photorefractive keratectomy (PRK) laser in situ keratomileusis (LASIK), and, most recently, laser assisted subepithelial keratectomy (LASEK), have been used extensively in adults to correct refractive error. Conductive keratoplasty is being used to correct hyperopia and presbyopia with mixed results. Ophthalmologists outside of the United States and Canada have been performing clear lens extraction for extremely high refractive errors for the last twenty or more years, but in the United States, lensectomy for this purpose has only recently been used. Phakic intraocular lenses for high refractive error are currently being investigated in adults. Refractive correction, as we all know, greatly improves the quality of life of the affected person. Now that we have effective, predictable, and enduring good results from excimer laser procedures, there is a burgeoning popular interest in using these more permanent solutions for correcting refractive error rather than removable contact lenses or spectacles. Does refractive surgery have a role in the treatment of refractive error in children? When attempting to answer this question, one must consider many issues. One must remember that the pediatric eye is growing and therefore may need more than one refractive procedure. We know that excimer refractive surgery in adults can cause corneal haze and keratectasia. What we still do not know in children is if the long-term corneal response to refractive surgery is different from that of the adult. Could multiple procedures that may be required in children cause more of the complications that have been reported in adults, like corneal haze and keratectasia? The good news from medium-term (3 4 years) results in children who have undergone PRK, LASIK, or LASEK is that corneal haze has been minimal and the refractive correction following these procedures has been relatively stable. We do not know, however, what will happen ten, twenty, or fifty years from now. Regarding growth of the eye, a remarkable amount of refractive power change occurs in the first two years of life where roughly 90% of the growth of the eye occurs. The eye at birth has a mean corneal power of approximately 50 D, a mean lens power of 34 D, and a mean axial length of 17 mm. By two years of age, the eye loses approximately 20 D of its dioptric power through lens growth and corneal flattening, and it loses more from axial elongation. Approximately 90% of the growth of the eye has occurred by 2 years of age. Therefore, if one were to consider refractive surgical intervention as an option for certain conditions in childhood, two years of age would probably be the earliest reasonable age at which to consider it. There are several potential areas for consideration of refractive surgery in children, which include accommodative esotropia, bilateral high refractive error (bilateral ametropia), and anisometropia with or without amblyopia. Possible refractive procedures to consider include: PRK, LASIK, LASEK, clear lens extraction, phakic intraocular lenses, and intrastromal corneal rings. Very little research has yet been published on clear lens extraction, 80 Volume 57, 2007

3 PAYSSE phakic intraocular lenses, and intrastromal corneal rings in children, so most of my discussion will focus on excimer laser procedures and my own personal experience with PRK for severe anisometropia in children. REFRACTIVE SURGERY FOR ACCOMMODATIVE ESOTROPIA A strong theoretical basis exists for considering refractive surgery as a potential treatment for accommodative esotropia. Accommodative esotropia is esotropia with a refractive etiology. As accommodation occurs in a patient with hyperopia and accommodative esotropia, there is an overabundant convergence response that results in esotropia. If the hyperopia could be reduced through a refractive procedure, then there should be a corresponding decrease in accommodation and a secondary decrease in accommodative convergence. In theory, it should work perfectly. Accommodative esotropia, however, occurs in many forms (pure refractive accommodative esotropia, partially accommodative esotropia, high accommodative convergence/ accommodation ratio esotropia), which understandably appears to affect the outcome following refractive surgery. There have been a handful of studies published thus far that deal with excimer refractive surgery for accommodative esotropia. 1 6 All of these studies have only included adults and teenagers. Patients with lower levels of hyperopia (i.e., 5 D or less) and pure refractive accommodative esotropia experienced much better results with regards to ocular alignment following an excimer laser procedure (Table 1). The potential issues/limitations of refractive surgery for accommodative esotropia include the following: 1. Hyperopia decreases with age. Therefore, the age at time of intervention might have to be in the late teens for maximum success. 2. Excimer refractive surgery at this point is not reliable for hyperopia of more than 5 D. 3. There is more postoperative corneal haze with high hyperopic refractive treatments than myopic refractive treatments, which could lead to a decrease in best-corrected visual acuity. 4. Normalizing the refractive error in this patient population could lessen the magnitude of the esotropia to a microtropia and create monofixation syndrome. Because the child looks aligned to his parents, the parents could stop following up, and then the child could develop secondary amblyopia and lose stereopsis. TABLE 1 SUMMARY OF PUBLISHED STUDIES ON EXCIMER LASER PROCEDURES FOR ACCOMMODATIVE ESOTROPIA Number of Mean Preop Study Procedure Age patients SE (D) % Success F/u (months) Hoyos LASIK Adults Nemet LASIK Adults Nucci PRK Adults Stidham LASIK Adults Sabetti LASIK Adults Hittner LASIK Adoles/adults % with 1 procedure 16 Adoles = adolescents, F/u = follow up, LASIK = laser in situ keratomileusis, PRK = photorefractive keratectomy American Orthoptic Journal 81

4 REFRACTIVE SURGERY Many questions still remain regarding the possibility of treating accommodative esotropia with excimer refractive surgery: 1. How long should the refractive error be stable prior to undergoing a refractive procedure? 2. What is the maximum amount of hyperopia one should treat? 3. Is the preoperative sensory status important to success? 4. What is the youngest age at which these procedures should be considered for this problem? The ideal patient with accommodative esotropia to consider for refractive surgery would be 13 years of age or older, have less than 5 D of hyperopia and good stereopsis, and have a stable refractive error. This ideal patient, however, is usually well controlled with glasses or contact lenses. Should we then intervene in this situation with a procedure that has the potential of causing corneal haze and a decrease in best-corrected visual acuity when the child is well treated with conventional therapy? REFRACTIVE SURGERY FOR BILATERAL AMETROPIA Another potential disorder that could be considered for treatment with refractive surgery is bilateral high ametropia. There have been several excimer laser pediatric refractive surgery studies that included children with high bilateral ametropia and developmental delay, cerebral palsy, or mental retardation who refused to wear refractive correction. These studies demonstrated a stable reduction in refractive error and no serious complications. 7, 8 In these studies, the authors also mentioned that there was an observable improvement in quality of life in these patients; however, this improvement was not formally evaluated. At our institution, we have performed refractive surgery on several such patients, who also had an excellent reduction in the refractive error and improvement in activities of daily living and social interaction. The condition of high bilateral refractive error in developmentally challenged patients is an area in which refractive surgery could hold great potential promise. These children are frequently tactilely averse and subsequently often refuse to wear their glasses (and contact lenses are impractical). Additionally, because of their behavioral and/or cognitive deficits, they are very difficult to manage and follow. Bilateral high ametropia is becoming a relatively common problem as more and more former extremely premature infants with a history of severe retinopathy of prematurity are surviving with the sequelae of extreme myopia and developmental delay or cerebral palsy/mental retardation. This area deserves further investigation. REFRACTIVE SURGERY FOR ANISOMETROPIC AMBLYOPIA The conventional treatment for anisometropic amblyopia includes refractive correction with spectacles or contact lenses and forced use of the amblyopic eye using either occlusion therapy or pharmacologic and/or optical penalization. The success rate for this seemingly simple strategy overall ranges between 25 90% depending on the level of anisometropia and the definition of success, with most falling around 60% It is also known that the success rate of standard therapy decreases with increasing anisometropia and that the severity of the amblyopia increases with increasing anisometropia. 13 There are several significant problems with conventional therapy for anisometropic amblyopia. Spectacles can cause aniseikonia or diplopia and are often cosmetically unacceptable. Contact lenses are difficult to insert, loss can be frequent, cost can be an issue, and there is an increased 82 Volume 57, 2007

5 PAYSSE risk theoretically of microbial keratitis in children who can be less hygienic than adults. With occlusion therapy and optical penalization, compliance is the most important difficulty, and atropine side effects including photophobia and other anticholinergic side effects can be problematic when using pharmacologic penalization. One must also not forget about the known long-term negative psychosocial effects of all of these interventions Most of the published research to date on refractive surgery in children has dealt with anisometropia. Thus far, the results of excimer refractive surgery in approximately 220 children have been published in the literature. All children have shown good refractive error response, mild to excellent visual acuity improvement, and minimal or no complications How much anisometropia should a child have before considering refractive surgical intervention? This is an important question. We know that amblyogenic levels of anisometropia are 2 D anisomyopia, 1 D anisohyperopia, and 1.5 D anisoastigmatism; 31 however, most patients with this entry level of anisometropia do well with spectacles alone. From Kivlin s data, anisometropia of 3 D or less was associated with good visual outcome with standard therapy. 13 Success rates plummeted with more anisometropia to 25% with 6 D or more of anisometropia. There is no consensus yet with regards to how much anisometropia is acceptable before considering refractive surgery, but probably 4 D of anisometropia would be reasonable, based on data from Kivlin 13 and the Amblyopia 9, 10, 12 Treatment Studies. To summarize briefly the results of all published studies to date on this subject, approximately 220 children have undergone excimer refractive surgical procedures for anisometropic amblyopia. The follow-up has ranged between 12 and 48 months. The age of the patients at time of treatment ranged between 2 and 19 years. All studies have shown a reliable refractive response to the laser procedure, mild to excellent improvement in visual acuity ranging between 2 and 7 lines of acuity improvement, and minimal complications (Table 2) (Figure 1). TABLE 2 SUMMARY OF ALL PUBLISHED STUDIES ON EXCIMER LASER PROCEDURES FOR ANISOMETROPIC MYOPIA Age Number of Mean Mean Mean Pre Mean Post Mean F/U Procedure (years) patients Pre SE Post SE BCVA BCVA (months) Haze Complications Paysse PRK /316 20/ Min None Astle PRK /70 20/40 12 Mild None Alio PRK /114 20/ sev None Singh PRK /82 20/ sev None Nucci Both /125 20/ NR None Nano PRK /400 20/72 12 Mild None Agarwal LASIK /37 20/ mod 2 flaps Rashad LASIK /50 20/25 12 None None Tychsen PRK/L /87 20/47 29 Min None O Keefe LASIK /142 20/63 24 None None Nassaralla LASIK NR NR 12 None None Autrata PRK/L /95 20/26 24 Min None Rybintseva LASIK NR NR NR 18 None None Hittner LASIK /30 20/30 18 None None BCVA = best corrected visual acuity, F/u = follow-up, LASIK = laser in situ keratomileusis, Post = postoperative, PRK = photorefractive keratectomy, Pre = preoperative, SE = spherical equivalent American Orthoptic Journal 83

6 REFRACTIVE SURGERY FIGURE 1: Summary of all pediatric keratorefractive surgery studies to date, demonstrating the mean decrease in myopic or hyperopic refractive error in diopters and the mean best-corrected visual acuity improvement by lines improvement. PRK IN CHILDREN WITH ANISOMETROPIC AMBLYOPIA PROJECT AT BAYLOR COLLEGE OF MEDICINE/TEXAS CHILDREN S HOSPITAL At Baylor College of Medicine we have approached the idea of treating children with photorefractive keratectomy for anisometropic amblyopia very conservatively. Above all we wanted to not do harm. Therefore, we decided to conduct some preliminary studies. We first performed a retrospective study to determine risk factors in patients with anisometropic amblyopia that could predict failure with conventional therapy. We also performed a prospective study of corneal thickness in normal children to determine if the pediatric cornea was thick enough to undergo excimer refractive procedures, as there were no previously published normative data for children except for in infants Then, we enrolled 11 patients in a prospective longterm interventional case series. These children had severe anisometropia with amblyopia and were noncompliant with conventional therapy. We followed them for corneal status, visual acuity, refractive error correction, treatment stability, and stereopsis. We now have follow-up for over four years on this group. The results from the three-year follow-up have been published and will be discussed here. 29 The results have not changed at the four-year follow-up. From the preliminary studies, we found that the significant risk factors for failure with conventional therapy for anisometropic amblyopia included anisoastigmatism of 1.5 D, age > 6 years at the initiation of amblyopia therapy, poor compliance with amblyopia therapy, and initial visual acuity of less than 20/ Regarding pediatric corneal thickness, pachymetry measurements reached adult levels by 2 4 years of age, and at no age was the cornea too thin to perform any excimer laser procedure currently in use. 36 In our prospective interventional case series, all myopic patients had an anisometropia of at least 6 D and all hyperopic patients had at least 4 D of anisohyperopia. They also had at least three lines of bestcorrected visual acuity difference between the two eyes, and no significant abnormality of the macula, optic nerve, lens or cornea. The mean age at time of treatment was 6.1 years (2 11 years), the maximum refractive treatment for myopia was 11.5 D and for hyperopia was 5.25 D, even though some of the myopic children had preoperative refractive errors that were much higher (mean spherical equivalent in the myopic group of and in the hyperopic group of D). Nine children required general anesthesia because of cooperation issues. The protocol for general anesthesia has been published previously. 37 Corneal haze three years after the laser procedure was negligible with a mean corneal haze measurement of 0.3+ on a scale of 0 to 4+ where 0 meant the corneal was crystal clear and 4+ meant the cornea was totally opaque with no view of the iris detail. Refractive error response was good. Fifty percent of the myopic patients and 100% of the hyperopic patients were within 2 D of target. The reason the percentile was 84 Volume 57, 2007

7 PAYSSE lower for the myopic group was that the extremely high myopic children had a larger response than expected from the treatment dose. This larger than expected treatment response was actually beneficial as these patients eyes had 17 D and 22 D of spherical equivalent refractive error preoperatively (Figure 2). Refractive error stability has also been quite good over the three-year follow up period. In the myopic group, there was a mean regression of 2.50 D over the first 12 months, but thereafter it was stable up to the 36-month follow-up. The hyperopic group demonstrated regression over a longer period of time with a 1.10 D regression in the first 12 months and then 0.60 D more over the next two years. Visual acuity improved in almost all patients. At the 36-month follow-up examination, 7 of the 9 patients who were able to perform psychophysical acuity testing preoperatively had an improvement of two or more lines in uncorrected visual acuity, and 6 of 9 had improvement of two or more lines of best corrected visual acuity (Figure 3). Our youngest participant was 2 years of age at treatment and had the most remarkable response. Preoperatively, he had anisomyopia of D and a preoperative FIGURE 3A: Comparison of preoperative, 12-month, and 36-month postoperative uncorrected visual acuities. Seven (77%) of 9 children able to perform psychophysical visual acuity testing pre- and postoperatively had at least two lines of improved uncorrected visual acuity. Points below the line represent improved postoperative visual acuity and points above the line represent reduced postoperative acuity. FIGURE 3B: Comparison of preoperative, 12-month, and 36-month postoperative best spectacle-corrected visual acuities. Six (67%) of 9 children able to perform psychophysical visual acuity testing pre- and postoperatively had at least two lines of improved best spectacle-corrected visual acuity. Points below the line represent improved postoperative visual acuity and points above the line represent reduced postoperative acuity. FIGURE 2: Percentage of treated patients at last follow-up (mean 31 months) who were within 1 or 2 D of the target refraction. In the myopic group, the extremely myopic children ( 17 and 22 D) had larger than expected responses to the laser treatment, which actually helped them get closer to emmetropia. vision in the affected eye of fix and follow. He was never compliant with spectacle wear or occlusion therapy before or after the PRK, and at his three-year postoperative follow-up, his refractive error was 0.75 D in the treated eye, his uncorrected visual acuity was 20/40 and his best corrected visual acuity was 20/30. When compared to a noncompliant control group with similar levels of anisometropia, our PRK group demonstrated statistically significant best-corrected visual acuity improvement at a level of P = Fifty-six percent of the orthotropic American Orthoptic Journal 85

8 REFRACTIVE SURGERY group experienced a marked improvement in stereopsis as well. We are continuing to follow this group and beginning to treat others that qualify. OTHER POTENTIAL REFRACTIVE TREATMENTS FOR CHILDREN There are several other refractive surgical procedures that may become useful in children in the future. These include clear lens extraction, phakic intraocular lenses, and intrastromal corneal rings. Intrastromal corneal rings are not presently practical for children because they do not correct enough refractive error. Clear lens extraction has been used for years in Latin America for adults with extremely high refractive error with good results Ali et al. recently reported excellent refractive and visual outcomes in children with high anisometropic myopia following refractive lensectomy. 43 An important potential risk of clear lens extraction in children with high axial myopia is the increased risk of retinal detachment. Highly myopic patients often have axial myopia and are at increased risk of retinal detachment already. The lensectomy just increases this risk. Phakic intraocular lenses (IOLs) have been successfully used in adults with high refractive error, and there have been a few case reports of good visual results using phakic IOLs in children The potential serious risk(s) with phakic IOLs are corneal endothelial cell loss with subsequent corneal decompensation and cataract development. 51 These potential complications, though they have not been reported in children, could be devastating. If these procedures are found to be effective in children, we must carefully weigh the risks and benefits of these procedures against the definite result of permanent visual impairment from amblyopia in the noncompliant child with high uncorrected refractive error. CONCLUSION So, getting back to the title question of my lecture, Is refractive surgery in children ready for prime time?, I would have to say that at this point the answer is No. Even though the results have been good, all studies to date have had small sample sizes, and only two studies have included a control group. 26, 29 Excimer laser procedures appear to be safe and effective at the medium-term follow-up; however, longer follow-up is needed to ensure that there are no serious late complications, such as keratectasia that have been reported with LASIK in adults. Surgical intervention at a younger age when there is more plasticity in the visual cortex may also yield better visual outcomes. Randomized clinical trials with larger patient numbers are needed where children are randomized to conventional therapy or an excimer laser refractive procedure with continuing attempt at occlusion or penalization therapy. This would determine with statistical proof whether these new treatments truly improve final visual outcome more than traditional therapy. Research in this exciting area of ophthalmology is ongoing, and other procedures may also become viable and possibly even better options in the future. REFERENCES 1. Hoyos JE, Cigales M, Hoyos-Chacon J, et al.: Hyperopic laser in situ keratomileusis for refractive accommodative esotropia. J Cataract Refract Surg 2002;28: Nemet P, Levenger S, Nemet A: Refractive surgery for refractive errors which cause strabismus. A report of 8 cases. Binocul Vis Strabismus Q 2002;17: ; discussion Nucci P, Serafino M, Hutchinson AK: Photorefractive keratectomy for the treatment of purely refractive accommodative esotropia. J Cataract Refract Surg 2003;29: Stidham DB, Borissova O, Borissov V, Prager TC: Effect of hyperopic laser in situ keratomileusis on ocular alignment and stereopsis in patients with 86 Volume 57, 2007

9 PAYSSE accommodative esotropia. Ophthalmology 2002; 109: Sabetti L, Spadea L, D Alessandri L, Balestrazzi E: Photorefractive keratectomy and laser in situ keratomileusis in refractive accommodative esotropia. J Cataract Refract Surg 2005;31: Phillips CB, Prager TC, McClellan G, Mintz- Hittner HA: Laser in situ keratomileusis for treated anisometropic amblyopia in awake, autofixating pediatric and adolescent patients. J Cataract Refract Surg 2004;30: Astle WF, Papp A, Huang PT, Ingram A: Refractive laser surgery in children with coexisting medical and ocular pathology. J Cataract Refract Surg 2006;32: Tychsen L, Hoekel J: Refractive surgery for high bilateral myopia in children with neurobehavioral disorders: 2. Laser-assisted subepithelial keratectomy (LASEK). J AAPOS 2006;10: Holmes JM, Kraker RT, Beck RW, et al.: A randomized trial of prescribed patching regimens for treatment of severe amblyopia in children. Ophthalmology 2003;110: Repka MX, Beck RW, Holmes JM, et al.: A randomized trial of patching regimens for treatment of moderate amblyopia in children. Arch Ophthalmol 2003;121: Flynn JT, Schiffman J, Feuer W, Corona A: The therapy of amblyopia: An analysis of the results of amblyopia therapy utilizing the pooled data of published studies. Trans Am Ophthalmol Soc 1998;96: ; discussion Pediatric Eye Disease Investigator Group: A randomized trial of atropine vs. patching for treatment of moderate amblyopia in children. Arch Ophthalmol 2002;120: Kivlin JD, Flynn JT: Therapy of anisometropic amblyopia. J Pediatr Ophthalmol Strabismus 1981;18: Holmes JM, Beck RW, Kraker RT, et al.: Impact of patching and atropine treatment on the child and family in the amblyopia treatment study. Arch Ophthalmol 2003;121: Koklanis K, Abel LA, Aroni R: Psychosocial impact of amblyopia and its treatment: A multidisciplinary study. Clin Experiment Ophthalmol 2006;34: Packwood EA, Cruz OA, Rychwalski PJ, Keech RV: The psychosocial effects of amblyopia study. J AAPOS 1999;3: Rashad KM: Laser in situ keratomileusis for myopic anisometropia in children. J Refract Surg 1999;15: Agarwal A, Agarwal T, Siraj AA, et al.: Results of pediatric laser in situ keratomileusis. J Cataract Refract Surg 2000;26: Nucci P, Drack AV: Refractive surgery for unilateral high myopia in children. J AAPOS 2001;5: Alio JL, Artola A, Claramonte P, et al.: Photorefractive keratectomy for pediatric myopic anisometropia. J Cataract Refract Surg 1998;24: Singh D: Photorefractive keratectomy in pediatric patients. J Cataract Refract Surg 1995;21: Astle WF, Huang PT, Ells AL, et al.: Photorefractive keratectomy in children. J Cataract Refract Surg 2002;28: Astle WF, Huang PT, Ingram AD, Farran RP: Laser-assisted subepithelial keratectomy in children. J Cataract Refract Surg 2004;30: Nano HD, Jr., Muzzin S, Irigaray F: Excimer laser photorefractive keratectomy in pediatric patients. J Cataract Refract Surg 1997;23: Rybintseva LV, Sheludchenko VM: Effectiveness of laser in situ keratomileusis with the Nidek EC-5000 excimer laser for pediatric correction of spherical anisometropia. J Refract Surg 2001; 17(2 Suppl):S Autrata R, Rehurek J: Laser-assisted subepithelial keratectomy and photorefractive keratectomy versus conventional treatment of myopic anisometropic amblyopia in children. J Cataract Refract Surg 2004;30: O Keefe M, Nolan L: LASIK surgery in children. Br J Ophthalmol 2004;88: Paysse EA. Photorefractive keratectomy for anisometropic amblyopia in children. Trans Am Ophthalmol Soc 2004;102: Paysse EA, Coats DK, Hussein MA, et al.: Longterm outcomes of photorefractive keratectomy for anisometropic amblyopia in children. Ophthalmology 2006;113: Tychsen L, Packwood E, Berdy G: Correction of large amblyopiogenic refractive errors in children using the excimer laser. J AAPOS 2005;9: Nassaralla BR, Nassaralla JJ, Jr.: Laser in situ keratomileusis in children 8 to 15 years old. J Refract Surg 2001;17: Remon L, Cristobal JA, Castillo J, et al.: Central and peripheral corneal thickness in full-term newborns by ultrasonic pachymetry. Invest Ophthalmol Vis Sci 1992;33: Autzen T, Bjornstrom L: Central corneal thickness in premature babies. Acta Ophthalmol (Copenh) 1991;69: Portellinha W, Belfort R, Jr.: Central and peripheral corneal thickness in newborns. Acta Ophthalmol (Copenh) 1991;69: Hussein MA, Coats DK, Muthialu A, et al.: Risk American Orthoptic Journal 87

10 REFRACTIVE SURGERY factors for treatment failure of anisometropic amblyopia. J AAPOS 2004;8: Hussein MA, Paysse EA, Bell NP, et al.: Corneal thickness in children. Am J Ophthalmol 2004; 138: Paysse EA, Hussein MA, Koch DD, et al.: Successful implementation of a protocol for photorefractive keratectomy in children requiring anesthesia. J Cataract Refract Surg 2003;29: Ceschi GP, Artaria LG: [Clear lens extraction (CLE) for correction of high grade myopia]. Klin Monatsbl Augenheilkd 1998;212: Fernandez-Vega L, Alfonso JF, Villacampa T: Clear lens extraction for the correction of high myopia. Ophthalmology 2003;110: Kubaloglu A, Yazicioglu T, Tacer S: Small incision clear lens extraction for correction of high myopia. Eur J Ophthalmol 2004;14: Lyle WA, Jin GJ: Clear lens extraction for the correction of high refractive error. J Cataract Refract Surg 1994;20: Pozarowska D, Toczolowski J: [The results of clear lens extraction for anisometropia treatment in patients with high myopia and unilateral cataract]. Klin Oczna 2001;103: Ali A, Packwood E, Lueder G, Tychsen L: Unilateral lens extraction for high anisometropic myopia in children and adolescents. J AAPOS 2007; 11: Moshirfar M, Feilmeier MR, Kang PC: Implantation of verisyse phakic intraocular lens to correct myopic refractive error after penetrating keratoplasty in pseudophakic eyes. Cornea 2006;25: Tahzib NG, Cheng YY, Nuijts RM: Three-year follow-up analysis of Artisan toric lens implantation for correction of postkeratoplasty ametropia in phakic and pseudophakic eyes. Ophthalmology 2006;113: Saxena R, van der Torren K, Veckeneer M, Luyten GP: Iris-fixated phakic IOLs to correct postoperative anisometropia in unilateral cataract patients with bilateral high myopia. J Cataract Refract Surg 2004;30: Lesueur LC, Arne JL: Phakic intraocular lens to correct high myopic amblyopia in children. J Refract Surg 2002;18: Lesueur LC, Arne JL: Phakic posterior chamber lens implantation in children with high myopia. J Cataract Refract Surg 1999;25: BenEzra D, Cohen E, Karshai I: Phakic posterior chamber intraocular lens for the correction of anisometropia and treatment of amblyopia. Am J Ophthalmol 2000;130: Chipont EM, Garcia-Hermosa P, Alio JL: Reversal of myopic anisometropic amblyopia with phakic intraocular lens implantation. J Refract Surg 2001;17: Eleftheriadis H: Potential complications of phakic IOLs. Br J Ophthalmol 2004;88: Key words: refractive surgery, excimer laser procedures, accommodative esotropia, anisometropia, ametropia 88 Volume 57, 2007