Excimer Laser Surgery for Anisometropic Amblyopia

Inclusion Criteria: 1. Age 3 to \<8 years 2. Best-corrected amblyopic-eye VA using the ATS single-surround HOTV letter protocol (ATS-HOTV) meeting the following criteria: * If age 3 to \<5 years, 20/80 to 20/800 (a re-test is required if the VA is 20/80) * If age 5 to \<8 years, 20/63 to 20/800 (a re-test is required if the VA is 20/63) * Note: For participants who require a re-test (as specified above), the better of the test and re-test acuities must meet the eligibility criteria for the amblyopic eye and will serve as the enrollment VA. 3. Best-corrected fellow-eye VA meeting the following criteria by ATS-HOTV: * If age 3 years, 20/50 or better * If age 4 to 5 years, 20/40 or better * If age 6 to 7 years, 20/32 or better 4. Best-corrected inter-ocular acuity difference ≥ 3 logMAR lines by ATS-HOTV 5. Refractive error meeting the following criteria (based on a cycloplegic refraction that is not more than 4 months old): * Refractive error in the amblyopic eye must be greater than the fellow eye. * If the amblyopic eye is myopic, SE refractive error in the amblyopic eye between -3.00D and -12.00D, inclusive. * If the amblyopic eye is hyperopic, SE refractive error in the amblyopic eye between +3.00D and +6.00D, inclusive, if \<=1.00D of astigmatism in the amblyopic eye; and between +3.00D and +5.00D, inclusive, if \>1.00D of astigmatism in the amblyopic eye. * Astigmatism less than or equal to 3.50D in the amblyopic eye. * SE refractive error in the fellow eye between -4.00D and +3.00D, inclusive, with no astigmatism limits. * For participants 3 to \<5 years of age, at least 5.00D of SE anisometropic difference between the two eyes by cycloplegic refraction; for subjects 5 to \<8 years of age, at least 3.00D SE anisometropic difference * No more than 3.00D of difference in cylinder power between the two eyes * Target postoperative refractive error (if participant becomes eligible for randomization) must be achievable with PRK as defined in Table 3 and must be within 2.00D of the fellow eye. 6. Prior to enrollment into the Patching Run-In Phase, must have had patching and/or optical penalization with atropine or Bangerter filters prescribed for at least 6 months and optical correction of refractive error prescribed for at least 6 months. Prior treatment does not have to be continuous. Compliance with prescribed treatment does not influence eligibility but the best effort at compliance is expected from both the patient and provider. 7. Corneal thickness \>500 microns (\>510 microns within the previous 7 months, or corneal thickness between 500 and 510 microns within the last 2 months). 8. Central corneal thickness must be enough to allow the treatment dose needed while leaving a residual corneal thickness of ≥ 375 microns. 9. IOP ≤ 22 mm Hg within 7 months of enrollment 10. Investigator believes that the participant has achieved maximum improvement in amblyopic-eye VA with conventional treatment. 11. Investigator is willing to prescribe patching, and parent and child are willing to attempt patching for at least 8 weeks for 42 hours per week (averaging 6 hours daily) in the Patching Run-In Phase. 12. No rigid gas permeable lens (including OrthoK) worn in the past 2 months 13. Soft contact lens is currently worn, has been attempted within the past 4 months, or a contact lens fitting exam (paid for by the study) is scheduled or the investigator does the contact lens fitting on the same day as enrollment. 14. Parent understands the protocol and is willing to accept randomization (if child meets eligibility criteria after Patching Run-In Phase). 15. Parent has a phone (or access to phone) and is willing to be contacted by Jaeb Center staff or other study staff during the next 36 months. 16. Relocation outside of area of an active PEDIG site for this study without the next 36 months is not anticipated. Exclusion Criteria: 1. Non-refractive ocular cause for reduced VA in the amblyopic eye (example: cataract, posterior staphyloma, extensive myelinated nerve fiber layer, optic nerve anomaly, macular scar, corneal opacity); or any cause of previous form deprivation. 2. Prior penetrating ocular surgery or injury 3. Prior strabismus surgery within 60 days preceding enrollment 4. Diagnosis of collagen vascular disease, Marfan syndrome, Ehlers-Danlos syndrome or other disorder of collagen synthesis 5. Previous ocular condition that may predispose the eye to be treated for future complications, for example: * Corneal disease (e.g., herpes simplex, herpes zoster keratitis, keratoconus or suspicion of keratoconus based upon family history, slit lamp exam, retinoscopy, or corneal topography (if able), recurrent erosion syndrome, corneal melt, or corneal dystrophy) * Established diagnosis of glaucoma * Any condition that, in the investigator's opinion, would interfere with or prolong corneal epithelial healing * History of significant eye rubbing or dry eye symptoms 6. History of retinopathy of prematurity resulting in macular ectopia 7. Down syndrome (trisomy 21)