title: Occlusion therapy improves phase-alignment of the cortical response in amblyopia.
abstract: The visual evoked potential (VEP) generated by the amblyopic visual system demonstrates reduced amplitude, prolonged latency, and increased variation in response timing (phase-misalignment). This study examined VEPs before and after occlusion therapy (OT) and whether phase-misalignment can account for the amblyopic VEP deficits. VEPs were recorded to 0.5-4cycles/degree gratings in 10 amblyopic children (2-6years age) before and after OT. Phase-misalignment was measured by Fourier analysis across a limited bandwidth. Signal-to-noise ratios (SNRs) were estimated from amplitude and phase synchrony in the Fourier domain. Responses were compared to VEPs corrected for phase-misalignment (individual epochs shifted in time to correct for the misalignment). Before OT, amblyopic eyes (AE) had significantly more phase-misalignment, latency prolongation, and lower SNR relative to the fellow eye. Phase-misalignment contributed significantly to low SNR but less so to latency delay in the AE. After OT, phase-alignment improved, SNR improved and latency shortened in the AE. Raw averaged waveforms from the AE improved after OT, primarily at higher spatial frequencies. Correcting for phase-misalignment in the AE sharpened VEP peak responses primarily at low spatial frequencies, but could not account for VEP waveform improvements in the AE after OT at higher spatial frequencies. In summary, VEP abnormalities from the AE are associated with phase-misalignment and reduced SNR possibly related to desynchronization of neuronal activity. The effect of OT on VEP responses is greater than that accounted for by phase-misalignment and SNR alone.
authors.affiliation: Roger H. Johnson Vision Lab, Seattle Children's Hospital, Division of Ophthalmology, 4800 Sand Point Way NE, Seattle, WA 98105, United States; University of Washington Medical Center, Department of Ophthalmology, Seattle, WA 98105, United States. Electronic address: john.kelly@seattlechildrens.org.
authors.forename: John P
authors.initials: JP
authors.lastname: Kelly
authors.affiliation: Roger H. Johnson Vision Lab, Seattle Children's Hospital, Division of Ophthalmology, 4800 Sand Point Way NE, Seattle, WA 98105, United States; University of Washington Medical Center, Department of Ophthalmology, Seattle, WA 98105, United States.
authors.forename: Kristina
authors.initials: K
authors.lastname: Tarczy-Hornoch
authors.affiliation: Roger H. Johnson Vision Lab, Seattle Children's Hospital, Division of Ophthalmology, 4800 Sand Point Way NE, Seattle, WA 98105, United States; University of Washington Medical Center, Department of Ophthalmology, Seattle, WA 98105, United States.
authors.forename: Erin
authors.initials: E
authors.lastname: Herlihy
authors.affiliation: Roger H. Johnson Vision Lab, Seattle Children's Hospital, Division of Ophthalmology, 4800 Sand Point Way NE, Seattle, WA 98105, United States; University of Washington Medical Center, Department of Ophthalmology, Seattle, WA 98105, United States.
authors.forename: Avery H
authors.initials: AH
authors.lastname: Weiss
mesh_terms: D000550:Amblyopia / Q000503:physiopathology / Q000628:therapy*; D000704:Analysis of Variance; D002648:Child; D002675:Child, Preschool; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology; D011930:Reaction Time; D012683:Sensory Deprivation / Q000502:physiology*; D059629:Signal-To-Noise Ratio; D014792:Visual Acuity / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*
keywords: Amblyopia; Latency; Occlusion therapy; Temporal defect; VEP; Visual evoked potential