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LASIK in Pediatric Eyes
Deepinder K Dhaliwal
At first glance, the concept of pediatric refractive surgery seems quite aggressive and radical. However, when used as a therapeutic modality in children that have no other option to restore vision, pediatric LASIK may have a useful role. Several studies have reported on the use of LASIK in the treatment of anisomyopic amblyopia in children.1–5 It is well known that uncorrected unilateral high myopia results in amblyopia in the pediatric age group.6 Current standard therapy can be successful if there is early detection and compliant treatment with spectacles or contact lens combined with occlusion therapy.7–9 However, some children are not successfully treated using these techniques. Difficulty with compliance is a common cause for failure10 and can be secondary to psychological resistance to patching or heavy and unbalanced myopic glasses that are easily removed.11 In addition, optical problems due to aniseikonia with contact lenses and spectacles12 and induced prism anisophoria with spectacles contribute to dissimilar binocular imagery and may further promote the development of amblyopia and abnormal binocular integration.
In these children that have “failed” conventional amblyopia therapy for anisomyopic amblyopia, LASIK has been shown to be of some benefit in several small studies.1–5 There are many special considerations in performing pediatric LASIK in regards to anesthesia, fixation, microkeratome selection, size of globe, and refractive endpoint that make the surgery different than adult LASIK. These points will be discussed in further detail.
Anesthesia Selection
The choice of anesthesia for pediatric LASIK depends on the maturity and cooperation of the child. General anesthesia has been used safely in small children undergoing LASIK; however, it is critical to minimize the leak of anesthetic gases into the laser environment otherwise the laser will malfunction.13 This occurs because the wavelength of the argon fluoride excimer beam (193 nm) is within the absorption spectrum of anesthetic gases such as nitrous oxide. Therefore, if nitrous oxide escapes into the path of the excimer beam, attenuation of the beam will occur. The laser will attempt to increase voltage to maintain fluence, but if treatment time is prolonged, the laser will stop firing and an error
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message such as “fluence out of range” will appear.13 Laryngeal mask airway is superior to using a face mask when delivering general
Figure 19.1. Pediatric LASIK being performed
anesthesia in pediatric LASIK because gas leak is minimized and unimpeded access to the globe is possible (Fig. 19.1).
Intravenous sedation using ketamine or propofol with topical anesthesia and verbal encouragement has also been successfully used during pediatric refractive surgery.1,14
Fixation/Centration Issues
In sedated children with or without general anesthesia, patient fixation is not possible. During our pediatric LASIK study at the University of Pittsburgh, we found the suction ring to be very helpful in aiding fixation and centration. The Moria microkeratome units (Antony, France) have the feature of a “low vacuum” setting for the suction ring. This enables the surgeon to maintain full control of the globe after the flap is created since suction is switched from high vacuum (used during creation of the corneal flap) to low vacuum, which is maintained until the excimer ablation is completed and the flap is repositioned. The intraocular pressure is raised to only ~40 mmHg so the retinal vasculature is not compromised during low vacuum application to the globe. Preoperative pilocarpine drops are necessary in children under general anesthesia with suction ring globe fixation to avoid excessive pupil dilation, which makes centration by the surgeon difficult. Assessment of angle kappa is made after pilocarpine drops are instilled and the laser ablation is centered closer to this point while staying within the pupil.
Microkeratome Selection
Although there are three studies in which the Automated Corneal Shaper (ACS) (Bausch & Lomb, Claremont, CA) was used,1,3,4 we could not achieve adequate suction on the
globe of our first patient with the suction ring of our ACS unit. Therefore, we switched to the Carriazo-Barraquer microkeratome (Moria) and had no difficulty. Adequate suction was easily achieved on the first attempt and, as mentioned previously; we utilized the low vacuum setting to fixate the globe after flap creation. There is also one report of
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successfully using the Hansatome (Bausch & Lomb Claremont, CA) for pediatric LASIK.5 The only two intraoperative flap complications that occurred in the published studies of pediatric LASIK were free caps, and both occurred with the ACS.1
Size of Globe
The diameter of the cornea and axial length of the eye reach 95 percent of full growth by age 2. Therefore, there is no difficulty encountered in performing LASIK in children in regards to corneal flap diameter or access to the globe through the palpebral fissures.
Refractive Endpoint
Unlike adult LASIK where emmetropia is generally the goal, the refractive endpoint when performing pediatric LASIK for anisomyopic amblyopia should be balance with the fellow eye. The basic concept is that with an equalization of refractive errors and elimination of anisometropia, amblyopia should be more amenable to treatment with adequate occlusion therapy.
Results of Pediatric LASIK
In reviewing the literature, the cumulative results of pediatric LASIK for anisomyopic amblyopia are overall encouraging. There was a reduction of anisometropia in all cases and an improvement in amblyopia in some cases.1–4Out of a total of 44 eyes in 4 studies, there was a gain of best spectacle corrected visual acuity (BSCVA) in 23 eyes (52%), no change in BSCVA in 19 eyes (43%), and a loss of BSCVA in 2 eyes (5%). The etiology of the loss of BSCVA (which was only one line in both cases) was diffuse interface haze with flap striae in one eye with a free cap that was sutured, and grade 2 interface haze in a patient with preoperative myopia of −23.00 diopters.1
Of note, there is no report of postoperative flap dislocation in the pediatric LASIK literature. This is often the feared complication due to the possibility that a child would rub his eye in the immediate post-operative period. In our series, one child was caught rubbing her eye within the first 24 hours after LASIK; however, there was no evidence of flap striae or dislocation. Perhaps corneal flaps in the pediatric population are more stable due to a stronger endothelial pump mechanism in the cornea.
In summary, pediatric LASIK seems to have a role in the treatment of anisomyopic amblyopia in selected cases. Special adjustments need to be made when performing LASIK in this population, and a multi-disciplinary approach including a refractive surgeon, pediatric ophthalmologist, and pediatric anesthesiologist is needed. Worldwide experience is somewhat limited. Larger series with long-term follow-up are necessary to more thoroughly evaluate this therapeutic modality.
REFERENCES
1.Agarwal A, Agarwal A, Agarwal T et al. Results of pediatric laser in situ keratomileusis. J Cataract Refract Surg 2000; 26(5):684–89.
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2.Dhaliwal DK, Davis JS, Cook DR, Davis PJ, Kira D. Treatment of pediatric Anisometropic myopia with laser in situ keratomileusis (LASIK): A Pilot Study (in press).
3.Nassaralla B, Nassaralla J. Laser in situ keratomileusis in children 8 to 15 years old. J Refrac Surg 2001; 17(5):519–24.
4.Rashad KM. Laser in situ keratomileusis (LASIK) for myopic anisometropia in children. J Cataract Refract Surg 1999; 15:429–35.
5.Rybintseva L, Sheludchenko. Effectiveness of laser in situ keratomileusis with the Nidek EC5000 excimer laser for pediatric correction of spherical anisometropia. J Refract Surg 2001; 17(2):S224–28.
6.Townshend AM, Holmes JM, Evans LS. Depth of Anisometropic amblyopia and difference in refraction. Am J Ophthalmol 1993; 116:431–36.
7.Kutschke PJ, Scott WE, Keech RV. Anisometropic amblyopia. Ophthalmol 1991; 98:258–63.
8.Lithander J, Siostrand J. Anisometropic and strabismic amblyopia in the age group 2 years and above: A prospective study of the results of treatment. Br J Ophthalmol 1991; 75:111–16.
9.Sen DK. Results of treatment in amblyopia associated with unilateral high myopia without strabismus. Br J Ophthalmol 1984; 68:681–85.
10.Oliver M, Newmann R, Chaimovitch Y, et al. Compliance and results of treatment for amblyopia in children more than 8 years old. Am J Ophthalmol 1986; 102(3):340–45.
11.Mets M, Price RL. Contact lenses in the management of myopic Anisometropic amblyopia. Am J Ophthalmol 1981;91:484–89.
12.Romano PE, van Noorden GK. Knapp’s law and unilateral axial high myopia. Binocular Vision and Strabismus Quarterly 1999; 14(3):215–22.
13.Cook DR, Dhaliwal DK, Davis PJ, Davis J. Anesthetic interference with laser function during excimer laser procedures in children. Anesth Analg 2001; 92:1444–45.
14.Alio JL, Artola A, Claramont P et al. Photorefractive keratectomy for pediatric myopic anisometropia. J Cataract Refract Surg 1998; 24:327–30.