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Refractive Surgery for the Treatment of Amblyopia in Children

By

L. E. Leguire Ph.D., MBA

 and

David Rogers, MD

LASIK (Laser in situ keratomileusis) is often called "Laser surgery" for correcting refractive error - either myopia (nearsightedness), hyperopia (farsightedness) or astigmatism (misshaped cornea).  LASIK is one form of "refractive surgery", along with LASEK (Laser-assisted subepithelial keratectomy)  and PRK (photorefractive keratectomy).  In all three types of refractive surgery, surgery is performed on the front of the eye, the cornea, to change the optical properties of the eye and decrease the need for other types of optical correction such as glasses or contact lenses.  We have all seen the ads for LASIK on TV commercials and billboards.  Usually aimed at adults who wish to decrease their reliance on glasses, refractive surgery is performed on about 1.3 million adults each year.  In the present article, we will refer to "refractive surgery" as any surgery on the cornea that changes the optical powers of the eye, although most of the literature review is in reference to LASIK or LASEK.

Recently, research has been undertaken on the use of refractive surgery in children who are amblyopic and who have anisometropia; a high refractive error in one eye (the amblyopic eye).  The surgery is often seen as a "last resort", after the children failed to have their refractive error corrected by usual means (glasses or contacts).  This article discusses issues surrounding the use of refractive surgery in pediatric patients and, specifically, patients with refractive or anisometropic amblyopia.  It must be emphasized that the FDA has not approved refractive surgery for use in children. This article is purely related to research efforts at better understanding the use of refractive surgery as a last resort in certain amblyopic children.

In LASIK surgery, the patient may be placed under local (eye only) or general (whole body) anesthesia depending on the child's age.  Younger patients, usually under the age of 10 years, require general anesthesia while older children may only require local anesthesia.  A very sharp instrument, a microkeratome, is used to slice the very front of the cornea off except for a small hinge.  Newer instruments use a laser to cut the so-called "corneal flap".  The front of the cornea is pealed back, exposing the inner part of the cornea.  A laser is used to remove a thin amount of cornea tissue and, with the help of the cornea hinge; the cornea is placed back on the front of the eye without the need for stitches although in children a stitch is usually required.

Brief Literature Review

A review of refractive surgery in children was undertaken by Tychsen (2008, Current Opinion Ophthalmology, p342-348).  He notes that the majority of pediatric patients had either PRK or LASEK.  The greatest drawback is that in children with very high refractive errors (greater than 10 diopters of myopia and greater than 4.5 diopters of hyperopia) is "refractive regression", whereby the eye regresses or gets worse again after the surgery.  Also, children who have such high refractive errors also need additional intervention such as the placement of intraocular lens or need to have their natural lens removed and replaced with an intraocular lens of the correct power.  Refractive surgery may be of benefit to special needs children who are basically blind without optical correction and who, for whatever reason(s), will not or cannot tolerate standard optical correction such as glasses or contact lenses.  Tychsen does note that complications are low in refractive surgery for children.

In one of the larger refractive surgery studies in children to date, Astle and colleagues (2008 J Cataract and Refractive Surgery, p411-416) reviewed the records of 39 children who has either LASEK or PRK on one or both eyes.  In addition to assessing the change in refractive error after surgery and visual acuity, these authors also looked at quality of life issues after the refractive surgery.  The average age of the children was 6 1/2 years and the investigators followed the children for a minimum of 3 1/2 years.  After refractive surgery, the children on average still needed glasses or refractive correction but the need for "thick glasses" was greatly reduced.  Importantly, the refractive state of the eyes and the clarity of the cornea were constant over the long term in all the operated eyes.  In patients who had visual acuity measured before and after surgery, visual acuity improved by an average of 1.6 lines.  Importantly, no patient had a loss of visual acuity or loss of binocular fusion (ability to add the images of the two eyes together for single vision) following surgery.  Also important, the authors found that no family complained of negative opinions of the surgery and no family experienced negative social or functional consequences following the surgery.

Levenger and colleagues (2006 Binocular Vision and Strabismus Quarterly, p231-234) performed refractive surgery in 11 children with special needs.  These children were not successfully treated by standard means such as glasses and contact lenses.  They found that the refractive surgery "improved vision and improved the daily function of children with developmental delay".  These authors did not find any complications with the surgery in these children.

Yin and colleagues (2007, J AAPOS) undertook LASIK surgery for the management of amblyopia in 74 children (42 with high hyperopic anisometropia and 32 with high myopic anisometropia) between the ages of 6 - 14 years.  The children were followed after surgery for about 18 months on average (range from 6 to 36 months).  They found that distance visual acuity improved from about 20/50 before surgery to 20/31 at the end of the follow-up period in the myopic group (i.e., about 2 lines of improvement on a visual acuity chart).  Visual acuity improved from about 20/90 before surgery to 20/39 at the end of the follow-up period in the hyperopic group (about 3 1/2 lines on a visual acuity chart). 

Nucci and Drack (2001, J AAPOS 5(6):348-351) undertook either LASIK or PRK in 14 older amblyopic children who had myopia in the amblyopic eye.  These children had completed amblyopia therapy and the refractive surgery was used to decrease the need for thick glasses.  Visual acuity before the surgery was 20/147 and average refractive error was about -8 diopters (very nearsighted).  After surgery, visual acuity was 20/121 with best correction and 20/129 without correction.  Average refractive error was -0.67 diopters 20 months after surgery.  Five of 14 patients improved 1 to 2 lines of visual acuity.  The authors conclude that LASIK was well tolerated and effective in this small group of children.  However, the change in visual acuity from 20/147 to 20/121 is less than one line on the visual acuity chart, not a statistically significant improvement.

Holland and colleagues (Holland et al, Cataract Refractive Surgery, 2000 Oct; 26 (10): p1555-1557) reported on an amblyopic patient with anisometropia (difference in refractive error between the two eyes) who had LASIK surgery in both eyes.  After LASIK surgery the patient complained of persistent diplopia (double vision).  Unfortunately, the patient could not have eye muscle surgery to correct the double vision because of the lack of fusion in the patient; that is, the patient could not "add together" the images from each eye to form a single image - the patient saw everything as double.  The authors suggest that patients with anisometropic amblyopia be screened for fusion ability before having LASIK surgery.  [Fusion is the ability to combine the images from each eye to a single unified image in the brain.]  This patient suffered from double vision after the LASIK surgery and the double vision could not be corrected.

Lai and colleagues (Lai et al, Chang Gung Med J. 2001, p593-598) reported on an amblyopia adult who had undergone LASIK surgery.  The patient was lost to follow up (patients should be followed closely after surgery to make sure of no complications).  The patient returned over 2 months later because he started to lose his vision.  Examination revealed the growth of white spots in the cornea that blocked vision.  Also, the corneal epithelium (surface of the cornea) grew into the area of the incision (lamellar interface) and caused a corneal irregularity that, in turn, blurred vision.  Surgery was not successful to correct the problem and the patient was reported to suffer from a permanent loss of vision.

Rashad (1999, J. Refract. Surg. 15(4); 429-435) undertook LASIK surgery in 14 children between the ages of 7 - 12 years to help in the management of the amblyopia.  All the children had myopic anisometropic amblyopia (nearsighted in one eye) and all the children had LASIK surgery on the myopic eye.  Before LASIK surgery, the children had a refractive error that ranged from -4.6 diopters to -12.5 diopters.  Visual acuity with glasses ranged from 20/40 to 20/100 with a midpoint of 20/50.  After LASIK surgery, the children had a refractive error that ranged from 0 to 1.5 diopters.  After surgery, visual acuity with glasses, if needed, improved in all cases and ranged from 20/20 to 20/40, with a midpoint of 20/25.  Without glasses, visual acuity after surgery ranged from 20/20 to 20/70, with a midpoint of 20/30.  The author of this study suggests that LASIK was well tolerated and yielded good visual acuity results.  Long-term effects, however, are not known.

Pros and Cons of Refractive Surgery in Amblyopic Children

            Pros

Children with special needs often cannot tolerate glasses and are not good candidates for contact lenses.  As a consequence, it may be difficult to correct a large refractive error in one or both eyes and the children may develop amblyopia in one of both eyes.  In addition, a large refractive error in a special needs child can also lead to further developmental delay, hampering the visual and visual-motor function of the child. In these children, refractive surgery offers some hope at correcting their refractive error and improving their daily lives and even visual-motor skills.  In addition, sometimes just correcting a refractive error may improve vision in amblyopic patients and improve the chance of normal visual function including the use of both eyes together.

One main goal of refractive surgery in children with amblyopia is to lessen the impact of compliance with glasses or with contact lenses on the child’s treatment.  If the refractive error is corrected with refractive surgery there may be a better chance that the amblyopia may be cured since issues regarding correcting the refractive error (i.e., glasses or contacts) would be less of a concern. 

Refractive surgery has a very low serious complication rate.  After refractive surgery, the young amblyopic patient may not need thick glasses to correct his/her eye sight.  Further, given that the refractive surgery corrects the refractive error that caused the amblyopia, the patient may improve in visual acuity and may reduce the need or duration of occlusion therapy, depending on the circumstances.  Recent studies with a small number of subjects have shown that refractive surgery is well tolerated in children and may improve vision and perhaps speed the recovery of vision.

            Cons

As with any surgery, refractive surgery can have serious adverse complications including but not limited to infections, halos and glare problems, dry eyes, under and over optical corrections, and possible blindness.  One also has to consider the serious consequences of general anesthesia in children, including brain damage and even death albeit rare.  In amblyopic children, the amblyopia could get worse if the refractive surgery has adverse complications that reduce clarity of vision in the operated eye (e.g., cloudy cornea).  If the patient rubs or hits his or her eyes after LASIK surgery, the cornea flap may become dislodged and cause vision loss.  Further, children are not very hygienic and an infection of the cornea after LASIK surgery could lead to the need for a cornea transplant or cause blindness.  Long-term complications for children who have had refractive surgery are not known. 

A further complication regarding refractive surgery in children is that the eyes continue to grow.  For example, Saw and colleagues (Br J Ophthalmology 2005, p1489 - 1494) showed that in younger children, 7 - 9 years of age, the eyes grow an average of about 0.30mm/year.  From about 11 years of age to about 30 years of age the eyes grow in length by about 0.043mm/year (data extrapolated from Ip et al, 2007 Eye and from Bullimore et al, 2006, Optom and Vis Sci).  Thus, eye length grows a lot faster in younger than older children and adults.  How refractive surgery affects eye growth is not known.  Eye growth relates to the need for glasses; nearsighted patients have longer eyes than farsighted patients.  Refractive surgery may cause the eyes to grow more or less than normal in children and affect the type of glasses the patient may need in the future for clear eyesight.

It has been known for some time that refractive surgery can lead to inaccurate readings of intraocular pressure (IOP) and given artificially low IOP readings (Svedberg and colleagues, 2005 Graefes Arch Exp Ophthalmol, p1218-1220).  This is important in terms of screening as well as management of glaucoma.  An artificially low reading of IOP may give the eye doctor a false sense of security that IOP is normal when, in fact, it may be elevated but artificially low due to refractive surgery.  As a consequence, all patients, regardless of age, should make sure that their eye doctor is aware that they have had refractive surgery so the eye doctor can look for other early signs of glaucoma other than simply relying on IOP measurements.

A concern which needs to be addressed in children with anisometropia, whether or not they have refractive surgery, is that the difference in refractive error between the eyes can also lead to a different sized image in each eye, a condition known as aniseikonia.  Unless the image sizes are similar between the eyes the brain will simply "turn-off" the image coming from one eye and prevent the development of binocular vision or the ability to use both eyes together.  Or, even more seriously, a patient who has large differences in image size between the eyes may develop double vision.  So the presence of anisometropia as well as the treatment of anisometropia with refractive surgery must consider retinal image size in long term treatment strategies.

A drawback of most of the studies that have used refractive surgery on children is the lack of information on the long-term side effects.  Also, there needs to be questions asked of the children regarding their vision - do they notice any change in their vision?  Would they have the surgery done again?  Has their quality of life changed?  What are the long-term consequences and side effects?  These types of important questions are just now starting to be addressed.

Finally, it must be emphasized that refractive surgery in children under the age of 21 has not been approved by the FDA.  Use of refractive surgery has only been authorized in research arenas where special exemption from the FDA was given for compassionate use.

Conclusion

Refractive surgery to correct large refractive errors in one or both eyes of children and, specifically, anisometropia in children has been undertaken in the past few years.  Preliminary research studies on small groups of children have shown that refractive surgery is well tolerated but long-term consequences are not known.  Studies have not adequately addressed the side effects of refractive surgery in children, how it might affect eye growth or if it improves the management of amblyopia or improves long-term outcome in terms of vision and visual function.  Finally, it must be emphasized that refractive surgery has not been approved by the FDA for children and its use is restricted to special circumstances.