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Refractive surgery for unilateral high myopia in children
Refractive Surgery for Unilateral High Myopia in Children Paolo Nucci, MD,a and Arlene V. Drack, MDb Purpose: To evaluate the safety and efficacy of refractive surgery in children. Methods: Pediatric patients with unilateral high myopia who were 9 years of age or older were offered refractive surgery to supplement optical correction. The patients and families were informed that the operation may not improve their best-corrected visual acuity. Photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) was performed on the more myopic eye with the use of topical anesthesia. Cycloplegic refraction, stereopsis, motility, and best-corrected visual acuity were measured before the procedure and at 2 months and 20 months after the procedure. All patients had completed amblyopia therapy before surgery. Results: Fourteen eyes of 14 patients aged 9 to 14 years received refractive surgery. Average age at the time of surgery was 11.9 years (±1,6). Average corrected preoperative visual acuity was 20/147 (±0.065 in decimals). Average preoperative refraction was –7.96 D (±2,16) spherical equivalent. Twenty months after refractive surgery, the uncorrected visual acuity averaged 20/129 (±0.08 in decimals) and bestcorrected vision averaged 20/121 (±0.08 in decimals). Average refraction was –0.46 D (±0,58) at 2 months and –0.67 D (±0,68) D at 20 months. An average myopic shift in refraction of –0.22 D was found in treated eyes during the 20 months of follow-up; this was not statistically significant (P = .69). Three patients had LASIK and 11 patients had PRK. LASIK patients averaged –0.875 D of myopic shift over 20 months of follow-up. Those with PRK averaged –0.025 D. This difference was not statistically significant (P = .10). The vision of 5 of 14 patients improved 1 or 2 lines after refractive surgery. Two patients who had 20/80 vision preoperatively improved to 20/60. No patients lost any lines of vision. Only 4 patients demonstrated stereopsis preoperatively, and all retained stereopsis postoperatively. No patient gained stereopsis. Conclusions: LASIK and PRK can be performed safely and effectively in children who are cooperative enough to undergo the procedures with topical anesthesia. Refractive surgery does not improve vision in densely amblyopic eyes but may give modest improvement in those that are mildly amblyopic. No significant complications were encountered aside from a myopic shift over time. (J AAPOS 2001;5:348-51)
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efractive surgery is becoming a common alternative to spectacles or contact lenses for adults with refractive errors. Although most surgeons require at least 2 years of stable refraction before accepting a candidate for refractive surgery, there is no commonly accepted lower age limit. To date, few patients younger than 18 years have undergone these procedures in the United States; however, in many other countries, children are being offered refractive surgery. A common indication for surgery is anisometropia, both because of its propensity to cause amblyopia in the pediatric age group and because of its relative stability, especially in unilateral high myopia, From the University of Milan, Department of Ophthalmology, San Paolo Hospital, Milan, Italy,a and Emory University, Atlanta, Georgia.b Presented at the 26th Annual Meeting of the American Association for Pediatric Ophthalmology and Strabismus, San Diego, California, April 12-16, 2000. Submitted April 15, 2000. Revision accepted August 1, 2001. Reprint requests: Arlene V. Drack, MD, Emory Eye Center, 4th Floor, Building B, 1365 Clifton Rd, Atlanta, GA 30322. Copyright © 2001 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/2001/$35.00 + 0 75/1/119787 doi:10.1067/mpa.2001.119787
348
December 2001
even in childhood. The current study was undertaken not to analyze the treatment of amblyopia but to systematically evaluate the risks, benefits, and unique problems and concerns associated with refractive surgery in a pediatric population by reviewing the records of a series of children who underwent refractive surgery by Italian surgeons.
SUBJECTS AND METHODS Medical records of 14 patients aged 14 years or younger at the time of refractive surgery were obtained from the practice of one of the authors (P.N.), a pediatric ophthalmologist who performs this surgery. Data collected included age at surgery, motility, amblyopia status, and preoperative and postoperative measurements of refractive error (measured by using cyclopentolate cycloplegia), visual acuities (both with and without correction), and stereopsis. Type of procedure performed (laser in situ keratomileusis [LASIK] versus photorefractive keratectomy [PRK]), preoperative and postoperative management, and complications were reviewed. Parents were asked before the procedure to sign a standard informed consent for refractive surgery, in which the experimental nature of the procedure and the Journal of AAPOS
Journal of AAPOS Volume 5 Number 6 December 2001
Nucci and Drack
349
TABLE 1. Clinical data for refractive surgery patients before the operation Patient No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Sex
Age at treatment, y
Preop cycloplegic refraction
Preop bestcorrected VA
Amblyopia treatment history
Preop strabismus status
Preop stereopsis
M M F F F M F M F M F M M F
11 13 12 14 13 11 14 14 10 11 11 13 11 9
–8.00 = –1.75 90° –12.00 = –1.75 130° –7.00 = –3.75 90° –9.00 = –0.75 30° –8.00 = –0.50 90° –5.00 = –2.75 10° –5.50 = –0.75 5° –9.00 –7.25 = –1.00 90° –6.00 = –1.75 80° –5.00 = –1.25 90° –8.75 = –2.75 160° –5.00 = –2.25 90° –4.00 = –2.75 180°
20/200 20/400 20/100 20/100 20/100 20/200 20/80 20/100 20/200 20/100 20/100 20/200 20/100 20/80
Y/PFT Y/PFT Y/PFT Y/PFT Y/PFT Y/PFT None Y/PFT None Y/PFT Y/PFT Y/PPT Y/PFT Y/PPT
ET MicroEt X(T) None MicroEt MicroEt X(T) None MicroEt MicroEt None XT MicroEt None
A A P P A A P A A A A A A P
Type of Age at correction first used correction, y Glasses None Glasses CL CL Glasses CL CL CL CL Glasses CL Glasses Glasses
4 2 2 3 6 9 1 3 2 3 3 5 3 3
A, Absent; CL, contact lenses; ET, esotropia; MicroET, microesotropia; P, present; PFT, patching full time; PPT, patching part time; XT, exotropia; X(T), intermittent exotropia; Xf, exophoria; Y, positive history of amblyopia treatment.
limited possibility of obtaining visual improvement were clearly stated. Published papers on the topic1-5 were translated and given to the parents in order to discuss with the family doctor the risk and benefits of the procedure from a scientifically sound point of view.
RESULTS Fourteen eyes of 14 patients aged 9 to 14 years underwent refractive surgery. All procedures were performed with the use of topical anesthesia containing ossibuprocaine or lidocaine 2%. Surgery was performed by using the Chiron Technolas 217 laser (Chiron, Claremont, Calif). LASIK was performed by using the Hansatome keratome (Chiron). The instruments and laser parameters are identical to those used for adult patients. Three patients had LASIK and 11 had PRK. The postoperative regimen for PRK included wearing a soft contact lens for 4 days after the procedure and applying tobramycin twice a day for 5 days. Fluorometholon eye drops were used for up to 4 months, with the dosage titrated to severity of signs and symptoms. Artificial tears were prescribed for use 3 to 4 times a day for 2 months. Ibuprofen was prescribed for symptomatic relief of pain, which reached its peak on day 2 after the procedure. The regimen for LASIK included applying tobramycin twice a day for 5 days and fluorometholon for up to 3 weeks. Artificial tears were prescribed for use 3 to 4 times a day for 2 months. Neither microphthalmia nor microcornea was present in any of the eyes. All patients had already completed amblyopia therapy, and no patient restarted amblyopia therapy after refractive surgery. Data are shown in Tables 1 and 2. The average age at the time of surgery was 11.9 years (±1,6). Average best-corrected preoperative visual acuity was 20/147 (±0.065 in decimals) with an average
correction of –7.96 D (±2,16) D spherical equivalent. All patients had at least 20 months of follow-up. Twenty months after refractive surgery, the average uncorrected visual acuity was 20/129 (±0.08 in decimals), and average best-corrected vision was 20/121 (±0.08 in decimals). The average refraction was –0.46 D (±0,58) at 2 months after surgery and –0.67 D (±0,68) at 20 months after surgery; the decrease was not statistically significant (P < .69). LASIK patients averaged –0.875 D myopic shift over this period, whereas PRK patients averaged –0.025 D. Vision in 5 of 14 patients improved 1 or 2 lines after refractive surgery. Two patients who had 20/80 vision preoperatively improved to 20/60. No patients lost any lines of vision. Only 4 patients demonstrated stereopsis preoperatively. All 4 retained it at the same level. No patients gained stereopsis.
CONCLUSION Pediatric eyes are different from adult eyes in many ways other than size alone. Normal ocular growth can continue into the mid teens, and axial elongation can continue into the 20s and beyond in eyes with myopia. The sclera and cornea are less rigid than in adult eyes, and the cortical visual system is still actively developing. Potential benefits of refractive surgery in the pediatric age group are many. Compliance with unilateral contact lens or high-power spectacle correction is notoriously poor, and amblyopia is a frequent cause of legal blindness in cases of anisometropia. Unilateral high myopia has been reported to be the most refractory type of anisometropic amblyopia to treatment,1 both because of compliance issues and because of the underlying structural abnormalities of the eye, which limit best-corrected vision. Given the underlying organic abnormalities, many parents are reluctant to force a child to wear a contact lens when it is
350
Journal of AAPOS Volume 5 Number 6 December 2001
Nucci and Drack
TABLE 2. Clinical data for refractive surgery patients after the operation Patient No.
Postop cycloplegic refraction*
Postop cycloplegic refraction at 20 mo
Postop uncorrected VA*
Postop uncorrected VA at 20 mo
Postop stereopsis
Postop strabismus status
Procedure
1 2 3 4 5 6 7 8 9 10 11 12 13 14
–1.00 –1.25 = –0.50 100° –0.75 90° –0.25 –0.25 30° +0.75 = –0.75 30° +0.50 –0.25 180° –0.50 180° –1.00 –0.00 = –0.25 90° –1.25 –0.75 = –0.75 90° +0.75
–1.50 –2.00 = –0.75 100° –0.75 90° –1.00 –0.25 30° +0.50 = –0.75 30° 0.00 –0.25 180° –0.50 180° –1.75 –0.50 = –0.25 90° –1.50 –0.50 = –1.25 90° +0.25
20/200 20/200 20/100 20/100 20/100 20/200 20/60 20/100 20/200 20/100 20/80 20/200 20/100 20/60
20/200 20/200 20/100 20/100 20/100 20/100 20/60 20/100 20/200 20/100 20/80 20/200 20/100 20/60
A A P P A A P A A A A A A P
ET MicroEt X(T) None MicroEt MicroEt Xf None MicroEt MicroEt None XT MicroEt None
PRK Lasik PRK Lasik PRK PRK PRK PRK PRK PRK PRK Lasik PRK PRK
A, Absent; CL, contact lenses; ET, esotropia; Lasik, laser in situ keratomileusis; MicroET, microesotropia; P, present; PFT, patching full time; PPT, patching part time; PRK, photorefractive keratectomy; XT, exotropia; X(T), intermittent exotropia; Xf, exophoria; Y, positive history of amblyopia treatment.
uncertain whether they will receive much benefit. Unilateral contact lenses are also very frequently lost, causing lapses in amblyopia therapy as well as being prohibitively expensive. Anisometropic spectacles are easier to handle than contact lenses, but they are no better accepted by most children and have the additional shortfall of inducing anisokonia and prismatic effects, which may degrade stereopsis. All of these issues could be solved by doing a refractive procedure on the ametropic eye. After surgery, only patching or penalization would have to be instituted, removing at least one significant barrier to compliance. Recently, there have been reports of visual improvements in amblyopic eyes after refractive surgery, and in some cases, this occurred without concomitant patching or penalization.2-5 Potential problems one might anticipate in doing refractive surgery in children include poor cooperation with topical anesthesia, which would lead to the increased risk and decreased optical centration inherent in doing the procedure with general anesthesia; variable results as a result of the microkeratome or laser functioning differently on a more malleable eye; large refractive shifts over time due to progressive ectasia of the operated cornea; large myopic shifts caused by eye growth, by unpredictable changes in growth, or by physiology of the developing eye due to the intervention of the laser; unmasking of phorias, especially in cases of partial correction of hyperopia or overcorrection of myopia in esophoria; complications in healing, such as recurrent uveitis or severe corneal haze due to the exaggerated inflammatory response often seen in pediatric eyes after surgery; and intraoperative or postoperative complications including poor cooperation, rubbing the eye, poor compliance with eye drops, etc. We will discuss which of these concerns are at least partially
addressed by the current study and which await further investigation. In this series, no difficulties were encountered when using topical anesthesia with the same instrumentation and algorithms used for adult refractive surgery. We obtained a significant reduction in myopia, best uncorrected vision was markedly improved, and although no patient had a miraculous reversal of amblyopia, those with mild amblyopia (20/80 preoperative) had some functional improvement to 20/60. Vision of 20/60 is considered to be out of the visually handicapped range and is good enough to pass the driver’s license test in some states. This improvement may represent enhanced acuity due to relative magnification and relief from spherical aberrations rather than recovery from amblyopia. No serious complications such as lost flaps, persistent haze, or diminishing vision occurred. No patient developed a new strabismus or diplopia; no patient with preoperative strabismus became orthophoric. Most of the epithelial defects in PRK patients healed within 24 to 48 hours, faster than in most adults. Excessive inflammation was not encountered. Thus, in a short-term study, most of the potential problems that seem more likely to occur in pediatric eyes did not occur. Long-term follow-up under rigorous study protocol conditions will be needed to determine whether refractive surgery is safe for pediatric eyes over a lifetime. Any procedure may have untoward effects on growing eyes that are simply impossible to predict. Lessons learned from other ophthalmologic procedures should serve as guideposts. For example, in the early days of pediatric corneal transplant, the apparently logical decision was made to use donor tissue from pediatric eyes. It soon became apparent that the very malleable transplanted pediatric corneal buttons rapidly became ectatic, bowing forward and inducing significant
Journal of AAPOS Volume 5 Number 6 December 2001
myopization. Studies have shown that cataract surgery with intraocular lens implantation may drastically alter the future growth of the eyes in baby monkeys.6 The same is true of peripheral retinal laser ablation.7 Human infants also show altered ocular growth after these treatments.8,9 Our results suggest that in the short term (20 months), refractive surgery is safe and effective. But longer followup is needed. Eyes that were treated with LASIK had a significantly greater amount of correction than eyes with PRK (P = .0038), but this could be due to the larger amount of preoperative myopia in these patients. Many eyes with unilateral high myopia do not have progressive myopic change in childhood. Yet most eyes had a myopic shift postoperatively, with eyes that received LASIK changing more than those that had PRK. This difference was not statistically significant (P = .10); however, the small sample size makes analysis suboptimal. The myopic shift observed in our pediatric patients could represent a similar phenomenon or a change due to corneal ectasia, with unpredictable curvature changes in the more pliable pediatric cornea. Corneal topography and keratometry readings before and after the operation, as well as axial length measurements of both the treated and fellow eyes, would be needed to determine the etiology of this pervasive myopic shift. It has been shown that corneal endothelial cell density decreases after pediatric cataract surgery.10 Although adult corneal endothelial cells have been shown to tolerate refractive surgery well,11 no data exist for children. The endothelium in children may be more vulnerable because it is undergoing a rapid decrease in density over the first 10 years of life as it spreads over the enlarging corneal diameter.12 This study demonstrates no evidence that stereopsis improves after refractive surgery for anisometropia with amblyopia when performed at or after the age of 9 years. This correlates with our knowledge of the critical period for development of stereopsis in the first 2 years of life. Nor is refractive surgery at this age a cure for manifest strabismus according to our data. Clinically, there is some evidence that amblyopic eyes have less exotropic drift if correction is worn; therefore, for patients who are contactlens intolerant and in danger of drifting toward exotropia, refractive surgery might theoretically be helpful (Prof. J. Lang, oral personal communication, June 1999). Far more information is needed before refractive surgery is deemed safe and effective for long-term use in children. But patients with unilateral high myopia would seem to be the ideal first candidates for this procedure.
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Their prognosis with our current treatment is dismal in most cases, especially once contact lens failure or noncompliance has been demonstrated. Of all the pediatric refractive errors, these eyes are the most stable. Such patients could be offered refractive surgery, preferably as part of a study protocol. In the small clinical studies performed to date, information on the response of the eye to the procedure, such as changes in axial length, corneal endothelial cell densities, and corneal topography, is lacking. As pediatric ophthalmologists, we must stress that amblyopia is not and should not be considered a valid indication for refractive surgery, and also we must proceed slowly and with caution as has been done with pediatric intraocular lenses. In this way, we can offer the best treatment with the least chance of morbidity for eyes that will have many decades to live with the surgery we perform now. We thank Drs Brancato, Cantera, Carones, Genisi, and Vinciguerra for sharing their experience with us. References 1. Kutschke PJ, Scott WE, Keech RV. Anisometropic amblyopia. Opthalmology 1991;98:258-63. 2. Chynn EW. Lasik: an option when amblyopia treatment fails. Ophthalmol Times [serial online] August 15, 1999. 3. Rashad KM. Laser in situ keratomileusis for myopic anisometropia in children. J Refract Surg 1999;15:429-35. 4. Alio JL, Artol A, Claramonte P, Ayala MJ, Chipont E. Photorefractive keratectomy for pediatric myopic anisometropia. J Cataract Refract Surg 1998;24:327-30. 5. Nano HD Jr, Muzzin S, Irigaray F. Excimer laser photorefractive keratectomy in pediatric patients. J Cataract Refract Surg 1997; 23:736-9. 6. Sorkin JA, Lambert SR. Longitudinal changes in axial length in pseudophakic children. J Cataract Refract Surg 1997;23:624-8. 7. Drack AV, Hutcheson KA, Fernandes A, Lambert SA, Sorkin JA, Tigges M. Association of TGF beta with decreased axial elongation following diode laser photocoagulation in infant monkey eyes. Invest Ophthalmol Vis Sci 1997;39:S760. 8. Lambert SR, Fernandes A, Drews-Botsch C, Tigges M. Pseudophakia retards axial elongation in neonatal monkey eyes. Invest Ophthalmol Vis Sci 1996;37:451-8. 9. Sorkin JA, Lambert SR. Longitudinal changes in axial length in pseudophakic children. J Cataract Refract Surg 1997;23:624-8. 10. Drack A, Edelhauser H, Awosika A. Endothelial cell counts in pediatric eyes with anterior segment abnormalities. Paper presented at: Annual Meeting of American Association of Pediatric Ophthalmology and Strabismus; April 17, 1999; Toronto, Ontario, Canada. Manuscript in preparation for publication. 11. Jones SS, Azar RG, Cristol SM, Geroski DH, Waring GO III, Stulting RD, et al. Effects of laser in situ keratomileusis (LASIK) on the corneal endothelium. Am J Ophthalmol 1998;125:465-71. 12. Nucci P, Brancato R, Mets MB, Shevell SK. Normal endothelial cell density range in childhood. Arch Ophthalmol 1990;108:247-8.
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efractive surgery is becoming a common alternative to spectacles or contact lenses for adults with refractive errors. Although most surgeons require at least 2 years of stable refraction before accepting a candidate for refractive surgery, there is no commonly accepted lower age limit. To date, few patients younger than 18 years have undergone these procedures in the United States; however, in many other countries, children are being offered refractive surgery. A common indication for surgery is anisometropia, both because of its propensity to cause amblyopia in the pediatric age group and because of its relative stability, especially in unilateral high myopia, From the University of Milan, Department of Ophthalmology, San Paolo Hospital, Milan, Italy,a and Emory University, Atlanta, Georgia.b Presented at the 26th Annual Meeting of the American Association for Pediatric Ophthalmology and Strabismus, San Diego, California, April 12-16, 2000. Submitted April 15, 2000. Revision accepted August 1, 2001. Reprint requests: Arlene V. Drack, MD, Emory Eye Center, 4th Floor, Building B, 1365 Clifton Rd, Atlanta, GA 30322. Copyright © 2001 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/2001/$35.00 + 0 75/1/119787 doi:10.1067/mpa.2001.119787
348
December 2001
even in childhood. The current study was undertaken not to analyze the treatment of amblyopia but to systematically evaluate the risks, benefits, and unique problems and concerns associated with refractive surgery in a pediatric population by reviewing the records of a series of children who underwent refractive surgery by Italian surgeons.
SUBJECTS AND METHODS Medical records of 14 patients aged 14 years or younger at the time of refractive surgery were obtained from the practice of one of the authors (P.N.), a pediatric ophthalmologist who performs this surgery. Data collected included age at surgery, motility, amblyopia status, and preoperative and postoperative measurements of refractive error (measured by using cyclopentolate cycloplegia), visual acuities (both with and without correction), and stereopsis. Type of procedure performed (laser in situ keratomileusis [LASIK] versus photorefractive keratectomy [PRK]), preoperative and postoperative management, and complications were reviewed. Parents were asked before the procedure to sign a standard informed consent for refractive surgery, in which the experimental nature of the procedure and the Journal of AAPOS
Journal of AAPOS Volume 5 Number 6 December 2001
Nucci and Drack
349
TABLE 1. Clinical data for refractive surgery patients before the operation Patient No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Sex
Age at treatment, y
Preop cycloplegic refraction
Preop bestcorrected VA
Amblyopia treatment history
Preop strabismus status
Preop stereopsis
M M F F F M F M F M F M M F
11 13 12 14 13 11 14 14 10 11 11 13 11 9
–8.00 = –1.75 90° –12.00 = –1.75 130° –7.00 = –3.75 90° –9.00 = –0.75 30° –8.00 = –0.50 90° –5.00 = –2.75 10° –5.50 = –0.75 5° –9.00 –7.25 = –1.00 90° –6.00 = –1.75 80° –5.00 = –1.25 90° –8.75 = –2.75 160° –5.00 = –2.25 90° –4.00 = –2.75 180°
20/200 20/400 20/100 20/100 20/100 20/200 20/80 20/100 20/200 20/100 20/100 20/200 20/100 20/80
Y/PFT Y/PFT Y/PFT Y/PFT Y/PFT Y/PFT None Y/PFT None Y/PFT Y/PFT Y/PPT Y/PFT Y/PPT
ET MicroEt X(T) None MicroEt MicroEt X(T) None MicroEt MicroEt None XT MicroEt None
A A P P A A P A A A A A A P
Type of Age at correction first used correction, y Glasses None Glasses CL CL Glasses CL CL CL CL Glasses CL Glasses Glasses
4 2 2 3 6 9 1 3 2 3 3 5 3 3
A, Absent; CL, contact lenses; ET, esotropia; MicroET, microesotropia; P, present; PFT, patching full time; PPT, patching part time; XT, exotropia; X(T), intermittent exotropia; Xf, exophoria; Y, positive history of amblyopia treatment.
limited possibility of obtaining visual improvement were clearly stated. Published papers on the topic1-5 were translated and given to the parents in order to discuss with the family doctor the risk and benefits of the procedure from a scientifically sound point of view.
RESULTS Fourteen eyes of 14 patients aged 9 to 14 years underwent refractive surgery. All procedures were performed with the use of topical anesthesia containing ossibuprocaine or lidocaine 2%. Surgery was performed by using the Chiron Technolas 217 laser (Chiron, Claremont, Calif). LASIK was performed by using the Hansatome keratome (Chiron). The instruments and laser parameters are identical to those used for adult patients. Three patients had LASIK and 11 had PRK. The postoperative regimen for PRK included wearing a soft contact lens for 4 days after the procedure and applying tobramycin twice a day for 5 days. Fluorometholon eye drops were used for up to 4 months, with the dosage titrated to severity of signs and symptoms. Artificial tears were prescribed for use 3 to 4 times a day for 2 months. Ibuprofen was prescribed for symptomatic relief of pain, which reached its peak on day 2 after the procedure. The regimen for LASIK included applying tobramycin twice a day for 5 days and fluorometholon for up to 3 weeks. Artificial tears were prescribed for use 3 to 4 times a day for 2 months. Neither microphthalmia nor microcornea was present in any of the eyes. All patients had already completed amblyopia therapy, and no patient restarted amblyopia therapy after refractive surgery. Data are shown in Tables 1 and 2. The average age at the time of surgery was 11.9 years (±1,6). Average best-corrected preoperative visual acuity was 20/147 (±0.065 in decimals) with an average
correction of –7.96 D (±2,16) D spherical equivalent. All patients had at least 20 months of follow-up. Twenty months after refractive surgery, the average uncorrected visual acuity was 20/129 (±0.08 in decimals), and average best-corrected vision was 20/121 (±0.08 in decimals). The average refraction was –0.46 D (±0,58) at 2 months after surgery and –0.67 D (±0,68) at 20 months after surgery; the decrease was not statistically significant (P < .69). LASIK patients averaged –0.875 D myopic shift over this period, whereas PRK patients averaged –0.025 D. Vision in 5 of 14 patients improved 1 or 2 lines after refractive surgery. Two patients who had 20/80 vision preoperatively improved to 20/60. No patients lost any lines of vision. Only 4 patients demonstrated stereopsis preoperatively. All 4 retained it at the same level. No patients gained stereopsis.
CONCLUSION Pediatric eyes are different from adult eyes in many ways other than size alone. Normal ocular growth can continue into the mid teens, and axial elongation can continue into the 20s and beyond in eyes with myopia. The sclera and cornea are less rigid than in adult eyes, and the cortical visual system is still actively developing. Potential benefits of refractive surgery in the pediatric age group are many. Compliance with unilateral contact lens or high-power spectacle correction is notoriously poor, and amblyopia is a frequent cause of legal blindness in cases of anisometropia. Unilateral high myopia has been reported to be the most refractory type of anisometropic amblyopia to treatment,1 both because of compliance issues and because of the underlying structural abnormalities of the eye, which limit best-corrected vision. Given the underlying organic abnormalities, many parents are reluctant to force a child to wear a contact lens when it is
350
Journal of AAPOS Volume 5 Number 6 December 2001
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TABLE 2. Clinical data for refractive surgery patients after the operation Patient No.
Postop cycloplegic refraction*
Postop cycloplegic refraction at 20 mo
Postop uncorrected VA*
Postop uncorrected VA at 20 mo
Postop stereopsis
Postop strabismus status
Procedure
1 2 3 4 5 6 7 8 9 10 11 12 13 14
–1.00 –1.25 = –0.50 100° –0.75 90° –0.25 –0.25 30° +0.75 = –0.75 30° +0.50 –0.25 180° –0.50 180° –1.00 –0.00 = –0.25 90° –1.25 –0.75 = –0.75 90° +0.75
–1.50 –2.00 = –0.75 100° –0.75 90° –1.00 –0.25 30° +0.50 = –0.75 30° 0.00 –0.25 180° –0.50 180° –1.75 –0.50 = –0.25 90° –1.50 –0.50 = –1.25 90° +0.25
20/200 20/200 20/100 20/100 20/100 20/200 20/60 20/100 20/200 20/100 20/80 20/200 20/100 20/60
20/200 20/200 20/100 20/100 20/100 20/100 20/60 20/100 20/200 20/100 20/80 20/200 20/100 20/60
A A P P A A P A A A A A A P
ET MicroEt X(T) None MicroEt MicroEt Xf None MicroEt MicroEt None XT MicroEt None
PRK Lasik PRK Lasik PRK PRK PRK PRK PRK PRK PRK Lasik PRK PRK
A, Absent; CL, contact lenses; ET, esotropia; Lasik, laser in situ keratomileusis; MicroET, microesotropia; P, present; PFT, patching full time; PPT, patching part time; PRK, photorefractive keratectomy; XT, exotropia; X(T), intermittent exotropia; Xf, exophoria; Y, positive history of amblyopia treatment.
uncertain whether they will receive much benefit. Unilateral contact lenses are also very frequently lost, causing lapses in amblyopia therapy as well as being prohibitively expensive. Anisometropic spectacles are easier to handle than contact lenses, but they are no better accepted by most children and have the additional shortfall of inducing anisokonia and prismatic effects, which may degrade stereopsis. All of these issues could be solved by doing a refractive procedure on the ametropic eye. After surgery, only patching or penalization would have to be instituted, removing at least one significant barrier to compliance. Recently, there have been reports of visual improvements in amblyopic eyes after refractive surgery, and in some cases, this occurred without concomitant patching or penalization.2-5 Potential problems one might anticipate in doing refractive surgery in children include poor cooperation with topical anesthesia, which would lead to the increased risk and decreased optical centration inherent in doing the procedure with general anesthesia; variable results as a result of the microkeratome or laser functioning differently on a more malleable eye; large refractive shifts over time due to progressive ectasia of the operated cornea; large myopic shifts caused by eye growth, by unpredictable changes in growth, or by physiology of the developing eye due to the intervention of the laser; unmasking of phorias, especially in cases of partial correction of hyperopia or overcorrection of myopia in esophoria; complications in healing, such as recurrent uveitis or severe corneal haze due to the exaggerated inflammatory response often seen in pediatric eyes after surgery; and intraoperative or postoperative complications including poor cooperation, rubbing the eye, poor compliance with eye drops, etc. We will discuss which of these concerns are at least partially
addressed by the current study and which await further investigation. In this series, no difficulties were encountered when using topical anesthesia with the same instrumentation and algorithms used for adult refractive surgery. We obtained a significant reduction in myopia, best uncorrected vision was markedly improved, and although no patient had a miraculous reversal of amblyopia, those with mild amblyopia (20/80 preoperative) had some functional improvement to 20/60. Vision of 20/60 is considered to be out of the visually handicapped range and is good enough to pass the driver’s license test in some states. This improvement may represent enhanced acuity due to relative magnification and relief from spherical aberrations rather than recovery from amblyopia. No serious complications such as lost flaps, persistent haze, or diminishing vision occurred. No patient developed a new strabismus or diplopia; no patient with preoperative strabismus became orthophoric. Most of the epithelial defects in PRK patients healed within 24 to 48 hours, faster than in most adults. Excessive inflammation was not encountered. Thus, in a short-term study, most of the potential problems that seem more likely to occur in pediatric eyes did not occur. Long-term follow-up under rigorous study protocol conditions will be needed to determine whether refractive surgery is safe for pediatric eyes over a lifetime. Any procedure may have untoward effects on growing eyes that are simply impossible to predict. Lessons learned from other ophthalmologic procedures should serve as guideposts. For example, in the early days of pediatric corneal transplant, the apparently logical decision was made to use donor tissue from pediatric eyes. It soon became apparent that the very malleable transplanted pediatric corneal buttons rapidly became ectatic, bowing forward and inducing significant
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myopization. Studies have shown that cataract surgery with intraocular lens implantation may drastically alter the future growth of the eyes in baby monkeys.6 The same is true of peripheral retinal laser ablation.7 Human infants also show altered ocular growth after these treatments.8,9 Our results suggest that in the short term (20 months), refractive surgery is safe and effective. But longer followup is needed. Eyes that were treated with LASIK had a significantly greater amount of correction than eyes with PRK (P = .0038), but this could be due to the larger amount of preoperative myopia in these patients. Many eyes with unilateral high myopia do not have progressive myopic change in childhood. Yet most eyes had a myopic shift postoperatively, with eyes that received LASIK changing more than those that had PRK. This difference was not statistically significant (P = .10); however, the small sample size makes analysis suboptimal. The myopic shift observed in our pediatric patients could represent a similar phenomenon or a change due to corneal ectasia, with unpredictable curvature changes in the more pliable pediatric cornea. Corneal topography and keratometry readings before and after the operation, as well as axial length measurements of both the treated and fellow eyes, would be needed to determine the etiology of this pervasive myopic shift. It has been shown that corneal endothelial cell density decreases after pediatric cataract surgery.10 Although adult corneal endothelial cells have been shown to tolerate refractive surgery well,11 no data exist for children. The endothelium in children may be more vulnerable because it is undergoing a rapid decrease in density over the first 10 years of life as it spreads over the enlarging corneal diameter.12 This study demonstrates no evidence that stereopsis improves after refractive surgery for anisometropia with amblyopia when performed at or after the age of 9 years. This correlates with our knowledge of the critical period for development of stereopsis in the first 2 years of life. Nor is refractive surgery at this age a cure for manifest strabismus according to our data. Clinically, there is some evidence that amblyopic eyes have less exotropic drift if correction is worn; therefore, for patients who are contactlens intolerant and in danger of drifting toward exotropia, refractive surgery might theoretically be helpful (Prof. J. Lang, oral personal communication, June 1999). Far more information is needed before refractive surgery is deemed safe and effective for long-term use in children. But patients with unilateral high myopia would seem to be the ideal first candidates for this procedure.
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Their prognosis with our current treatment is dismal in most cases, especially once contact lens failure or noncompliance has been demonstrated. Of all the pediatric refractive errors, these eyes are the most stable. Such patients could be offered refractive surgery, preferably as part of a study protocol. In the small clinical studies performed to date, information on the response of the eye to the procedure, such as changes in axial length, corneal endothelial cell densities, and corneal topography, is lacking. As pediatric ophthalmologists, we must stress that amblyopia is not and should not be considered a valid indication for refractive surgery, and also we must proceed slowly and with caution as has been done with pediatric intraocular lenses. In this way, we can offer the best treatment with the least chance of morbidity for eyes that will have many decades to live with the surgery we perform now. We thank Drs Brancato, Cantera, Carones, Genisi, and Vinciguerra for sharing their experience with us. References 1. Kutschke PJ, Scott WE, Keech RV. Anisometropic amblyopia. Opthalmology 1991;98:258-63. 2. Chynn EW. Lasik: an option when amblyopia treatment fails. Ophthalmol Times [serial online] August 15, 1999. 3. Rashad KM. Laser in situ keratomileusis for myopic anisometropia in children. J Refract Surg 1999;15:429-35. 4. Alio JL, Artol A, Claramonte P, Ayala MJ, Chipont E. Photorefractive keratectomy for pediatric myopic anisometropia. J Cataract Refract Surg 1998;24:327-30. 5. Nano HD Jr, Muzzin S, Irigaray F. Excimer laser photorefractive keratectomy in pediatric patients. J Cataract Refract Surg 1997; 23:736-9. 6. Sorkin JA, Lambert SR. Longitudinal changes in axial length in pseudophakic children. J Cataract Refract Surg 1997;23:624-8. 7. Drack AV, Hutcheson KA, Fernandes A, Lambert SA, Sorkin JA, Tigges M. Association of TGF beta with decreased axial elongation following diode laser photocoagulation in infant monkey eyes. Invest Ophthalmol Vis Sci 1997;39:S760. 8. Lambert SR, Fernandes A, Drews-Botsch C, Tigges M. Pseudophakia retards axial elongation in neonatal monkey eyes. Invest Ophthalmol Vis Sci 1996;37:451-8. 9. Sorkin JA, Lambert SR. Longitudinal changes in axial length in pseudophakic children. J Cataract Refract Surg 1997;23:624-8. 10. Drack A, Edelhauser H, Awosika A. Endothelial cell counts in pediatric eyes with anterior segment abnormalities. Paper presented at: Annual Meeting of American Association of Pediatric Ophthalmology and Strabismus; April 17, 1999; Toronto, Ontario, Canada. Manuscript in preparation for publication. 11. Jones SS, Azar RG, Cristol SM, Geroski DH, Waring GO III, Stulting RD, et al. Effects of laser in situ keratomileusis (LASIK) on the corneal endothelium. Am J Ophthalmol 1998;125:465-71. 12. Nucci P, Brancato R, Mets MB, Shevell SK. Normal endothelial cell density range in childhood. Arch Ophthalmol 1990;108:247-8.