Photorefractive Keratectomy for Severe Anisometropia and Isoametropia Associated With Amblyopia

Study Overview
=================
Brief Summary
-----------------
Photorefractive keratectomy (PRK) with excimer laser has been used successfully to treat myopia, hyperopia, and astigmatism in adults for over 35 years. Children with high refractive errors that go untreated will develop severe amblyopia. PRK can normalize high refractive errors and potentially improve the visual acuity in affected children. The purpose of this study is to investigate whether children with high anisometropia or isoametropia with amblyopia that are nonresponsive to standard therapy and receive PRK develop better longterm visual acuity.

Detailed Description
-----------------
Anisometropia is a condition in which one eye has a significantly different refractive error from the other and commonly leads to the development of refractive amblyopia in the affected eye. High isoametropia is the condition in which both eyes have high refractive error and commonly leads to bilateral refractive amblyopia if untreated. Amblyopia is the condition in which vision does not develop fully in the brain due to disuse or misuse of one or both eyes. Typically, in high anisometropia, a contact lens in the eye with the stronger refractive error and/or glasses must be used to correct the refractive error. Commonly, infants and children with this condition refuse to wear the contact lens or glasses because the other eye sees normally. There are other problems in treating high anisometropia with glasses. One is aniseikonia, the condition of image size disparity between the two eyes. This causes difficulty for the brain of the affected person to fuse the images from the two eyes because the image from one eye is much larger than that from the other eye. This results in asthenopia (eye fatigue) and sometimes even diplopia. If the anisometropia is severe, significant amblyopia will result in the eye with the stronger refractive error and, if not treated at an early age, permanent and potentially severe vision loss will result. In high isoametropia, contact lenses or glasses must likewise be used in order for normal vision to develop. Most children with isoametropia will wear glasses well because they cannot see well without them. By contrast, children with developmental delays, chromosomal abnormalities, autism, or attention deficit hyperactivity disorder and high isoametropia very commonly will not wear the needed refractive correction due to strong tactile aversion to anything touching their face or head. If the refractive error is high, significant bilateral (isoametropic) amblyopia will result and, if not treated at an early age, permanent and potentially severe vision loss will result. PRK can normalize high refractive errors and potentially reduce or eliminate the amblyopia in affected children. The purpose of this study is to investigate whether children with high anisometropia or isoametropia with amblyopia that are nonresponsive to standard therapy and receive PRK develop better longterm visual acuity. Secondary outcomes are stability of refractive correction, and corneal health.

Official Title
-----------------
Photorefractive Keratectomy for Anisometropic and Isoametropic Amblyopia in Children Refractory to Conventional Treatment

Conditions
-----------------
Anisometropia, Hyperopia, High Myopia, Amblyopia Isometropic, Amblyopia Bilateral, High Astigmatism

Intervention / Treatment
-----------------
* Procedure: Photorefractive keratectomy


Participation Criteria
=================
Eligibility Criteria
-----------------
Inclusion Criteria:. Children aged 2 to 17 with significant anisometropia or isoametropia and amblyopia that have failed traditional treatment for at least 6 months. Anisometropic group: The anisometropia must be at least 3.00 diopters. The amblyopic eye best corrected visual acuity must be at least 2 lines worse than the fellow eye in verbal children Isoametropic group Myopia must be at least -4.00 diopters in both eyes Hyperopia must be at least +4.00 diopters in both eyes Astigmatism must be at least +2.50 diopters in both eyes. Exclusion Criteria: History of significant corneal abnormality that, in the investigator's opinion, may limit visual rehabilitation. History of known collagen disorder History of known corneal ectasia History of previous herpes simplex keratitis Corneal thickness of less than 450u

Ages Eligible for Study
-----------------
Minimum Age: 2 Years
Maximum Age: 17 Years

Sexes Eligible for Study
-----------------
All

Accepts Healthy Volunteers
-----------------
No

Study Plan
=================
How is the study designed?
-----------------

Design Details

Primary Purpose: Treatment
Intervention Model: Single Group Assignment
Interventional Model Description: Photorefractive Keratectomy
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Other: Photorefractive keratectomy<br>The children will undergo PRK in the affected eye(s) using previously derived formulas for PRK. | Procedure: Photorefractive keratectomy<br> <br> |

What is the study measuring?
-----------------
Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Visual acuity | Snellen equivalent | 10 years | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Refractive error | cycloplegic refraction | 10 years | 
| Corneal clarity | slit lamp exam | 10 years |