Both the study protocol and informed consent forms were approved by the Institutional Review Board of the Illinois College of Optometry. In accordance with the guidelines of the Declaration of Helsinki, written informed consent was obtained from the parent or legal guardian of each child, and each subject gave verbal assent to participate in the study.
A total of 31 children diagnosed with myopic anisometropic amblyopia were recruited at the Illinois Eye Institute, the teaching clinic of the Illinois College of Optometry. The characteristics of the subjects are listed in
Table 1. All subjects underwent a comprehensive eye examination including VA, refraction, dilated fundus examination with indirect ophthalmoscopy, cycloplegic refraction, and A-scan ultrasound biometry. Monocular distance VA was tested at 3 meters (10 feet) using a computer-based electronic VA tester,
22,23 which is commonly used in amblyopia studies.
24,25 For children aged younger than 7 years, HOTV optotypes with surrounding bars were used according to the Amblyopia Treatment Study VA protocol.
26 For children aged 7 years or older, single optotypes of the ETDRS acuity chart with surrounding bars were presented. Cycloplegia was induced with 1% cyclopentolate, 1% tropicamide, and 2.5% phenylephrine (1 drop each). Fixation of subjects was evaluated using visuoscopy. Due to either a blurred image through the ophthalmoscope or lack of foveal reflex, fixation was not able to be evaluated in 10 out of 31 subjects. For the remaining 21, three had eccentric fixation, five subjects had unsteady central fixation, and 13 had central steady fixation. Other than refractive error and amblyopia, all subjects had no concurrent ocular disease. The eligibility criteria are listed as follows:
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Amblyopia associated with myopic anisometropia
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Best-corrected VA in the amblyopic eye 20/40 to 20/400 inclusive
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Best-corrected VA in the fellow normal eye ≥20/40
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Interocular acuity difference ≥3 LogMAR lines
All OCT measurements (Stratus OCT3; Carl Zeiss Meditec, Dublin, CA) were performed after subjects' pupils were dilated to at least 5 mm in diameter. The measurements were done by a single skilled technician who was masked to the diagnoses of the subjects. Scans were performed using the fast macular thickness protocol, in which six 6-mm lines in a radial spoke-like pattern are obtained in a continuous automated sequence. All scans had signal strength of at least 6. In addition, all the macular images were collected using the following protocol to ensure that the foveal depression was in the center of the scan. Alignment mode was used by the technician to ensure each 6-mm line scan was through the center of the fovea. When a scan was observed to be off the center of the fovea even if the subject's fixation was accurate, the procedure of adjusting scan placement was performed to move the scan location to the center of the fovea. The following 10 parameters were measured for each subject: foveal minimum thickness, average foveal thickness, inner nasal, superior, temporal, and inferior macular thickness, outer nasal, superior, temporal, and inferior macular thickness.
Figure 1A demonstrates the locations of fovea, inner macula, and outer macula. The foveal area is defined as the central circle of 1 mm diameter. Inner macula refers to the ring around the foveal area of 3 mm diameter and outer macula refers to the ring around the inner macula of 6 mm diameter.