Abstract Amblyopia is a commoncause of visual morbidity in children.Anisometropic amblyopia is the second most common cause,it is caused by unequal focus between the two eyes, resulting chronic blur onone retina.
Unlike strabismic amblyopia, the eyes appear normal to the observer.Anisometropic amblyopia can occur with small amounts of astigmatism or asymmetrichyperopia. However, large amounts of anisomyopia are needed for amblyopia todevelop. This literature reviewlooks into whether or not refractive surgery is an effective way of treating anisometropicamblyopia. Introduction In the past hundred years Anisometropicamblyopia management hasn’t changed greatly.
Traditional therapy consists ofcorrecting the refractive error with contact lenses or spectacles, followed by occlusionof the good eye if the amblyopia persists, this forces the brain to use theamblyopic eye hence improving visual acuity. These therapies fail notinfrequently. Recentadvances in refractive surgery suggest that surgical treatment may be a good alternativeto traditional therapy in selected situations. The science of correctingrefractive error has undergone an interesting evolution.
Spectacle correctionhas been around since the 13th century and contact lenses since the1880s. Refractive surgical procedures began in the 1970s with radial keratotomyfollowed by epikeratophakia and now excimer laser procedures. Most recently,clear lens extraction and phakic intraocular lenses have been accepted as treatmentfor selected refractive error problems in the adult population. POTENTIALINDICATIONS FOR SURGICAL INTERVENTION Why should we consider surgicalinterventions for anisometropic amblyopia? There are several reasons: (1) Conventional therapy sometimesfails, leaving patients with no other alternatives(2)Not getting the desired vision even after being successfully treated (3) Residual amblyopia is very commonand could possibly be prevented if the refractive error were normalized at anearlier age(4) With severe anisometropia, correcting the refractive error for severe anisometropia often causesaniseikonia, reduced stereopsis/ binocularity, and image distortion(5) Lastly, it is incumbent upon all physicians to continue to responsiblyexplore potential new treatment options that may offer better outcomes and/orsimplify treatment regimens. We know that the success rateof traditional therapy declines with increasing anisometropia, and the severityof the amblyopia increases with increasing anisometropia so what then are thepotential indications for surgical intervention of anisometropic amblyopia? Anobvious potential indication would be failure with conventional therapy.Another possible indication could be a certain level of severe anisometropia knownto be associated with a poor visual outcome.
Amblyopiogenic levels ofanisometropia are well known. Two dioptres of anisomyopia, 1 D ofanisohyperopia, and 1.5 D of anisoastigmatism are known to lead to amblyopia ifleft uncorrected. Is this entry level of anisometropia, however, enough tooffer refractive surgery? It probably is not, because the success rate for thisentry level of anisometropia is exceedingly high with conventional therapy.
Fromdata, it is probably reasonable to con- sider refractive surgery foranisometropic amblyopia when at least 3 to 4 D of anisomyopia or anisohyperopiais present. POTENTIALREFRACTIVE SURGICAL PROCEDURES FOR ANISOMETROPIA The specific refractive procedures thatmay be applicable for children are photo- refractive keratectomy (PRK), laserin situ keratomileusis (LASIK), laser assisted subepithelial keratectomy(LASEK), clear lens extraction, phakic intraocular lenses, and intrastromalcorneal rings (Intacs). The only refractive procedures that have undergone anysignificant investigation in children are LASEK, LASIK AND PRK. RISKS AND BENEFITS OF VARIOUS REFRACTIVESURGICAL PROCEDURES As with any medical or surgical intervention,there are pros and cons associated with each of these excimer laser procedures.The advantages of PRK include achieving a stable refractive correction with aless invasive procedure than LASIK as it is a surface ablation.
The disadvantagesof PRK when compared to LASIK are the risk of postoperative corneal haze thatmay require four to six months of topical corticosteroid use, longer recoverytime (approximately three days for the epithelium to heal), and morediscomfort. When compared to PRK, LASIK enjoys the same advantages of stablecorrection, but it offers the benefits of faster recovery and limited pain. Thepotential disadvantages/ complicationsof LASIK, however, are significant, potentially vision threatening, and includeflap dislocation, tear (or hole) keratectasia, epithelial ingrowth, and possiblelong-term corneal endothelial cell loss. LASEK essentially has the same riskprofile as PRK, though it may be associated with less discomfort. TABLE SUMMARY OF STUDIES ON EXCIMER REFRACTIVE SURGERY FOR ANISOMETROPIC AMBLYOPIA Study Procedure Age (yrs) No of patients Pre mean SE (D) Mean post SE (D) Uncorrected VA improvement BCVA improvement Mean follow up month Corneal haze Complications Paysse PRK 2-11 8 3 -13.70 +4.
75 -3.55 +1.41 5/7 children – 2 lines 4/7 children – 2 lines 1- 7 lines 31 Min None Dedhia Lasik 3 under 18yrs 21 N/A N/A 2 or more lines for all patients 12yr old gained 4 lines 1 or more lines in 61.9% of eyes 3 Min none 4 Lasik 8-15 9 -7.66 -0.
22 All eyes- at least 5 eyes N/A 3 N/A none 5- LIN Lasik 5-14 24 +7.35 -8.01 +3.30 -1.32 Pre = 0.06 Post= 0.43 Pre-0.26 Post-0.
67 33 3 cases mild none Zhang Lasik 6-16 33 -10.00 -0.60 Pre to post 1.
74 to 0.45 (UDVA) Pre to post 0.98 to 0.41 (CDVA) 8 None none Ghanam Lasik 18 -7.75 -0.50 N/A Pre 0.72 Post 0.47 24 N/A none Yin Lasik 6-14 42 32 N/A N/A N/A Myopia Pre to post 0.
40 to 0.59 (CDVA) Hyperopia Pre to post 0.53 to 0.31 (CDVA) 36 36 N/A none Agarwal Lasik 5-11 16 -14.88 -1.44 N/A Pre 0.53 Post 0.
54 12 eyes regained their BCVA, 2 eyes lost 1 line BCVA, 2 eyes gained 1 line 12 3 eyes grade 2 haze No eyes with induced astigmatism of more than 0.5D, no complications ConclusionAllstudies have shown consistent, predictable refractive correction, mild toexcellent visual acuity improvement, and minimal or no complications. Instudies that evaluated stereopsis, more than 50% of patients tested improvedregardless of age at time of refractive procedure.
Sample size, however, hasbeen small in all studies to date and very few studies have included a controlgroup.Randomized clinical trials are now needed to optimally evaluate these surgicalalternatives for anisometropic amblyopia.