Decreased cortical activation in response to a motion stimulus in anisometropic amblyopic eyes using functional magnetic resonance imaging.
OBJECTIVE
Motion perception abnormalities and extrastriate abnormalities have been suggested in amblyopia. Functional MRI (fMRI) and motion stimuli were used to study whether interocular differences in activation are detectable in motion-sensitive cortical areas in patients with anisometropic amblyopia.


METHODS
We performed fMRI at 1.5 T 4 control subjects (20/20 OU), 1 with monocular suppression (20/25), and 2 with anisometropic amblyopia (20/60, 20/800). Monocular suppression was thought to be form fruste of amblyopia. The experimental stimulus consisted of expanding and contracting concentric rings, whereas the control condition consisted of stationary concentric rings. Activation was determined by contrasting the 2 conditions for each eye.


RESULTS
Significant fMRI activation and comparable right and left eye activation was found in V3a and V5 in all control subjects (Average z-values in L vs R contrast 0.42, 0.43) and in the subject with monocular suppression (z = 0.19). The anisometropes exhibited decreased extrastriate activation in their amblyopic eyes compared with the fellow eyes (zs = 2.12, 2.76).


CONCLUSIONS
Our data suggest motion-sensitive cortical structures may be less active when anisometropic amblyopic eyes are stimulated with moving rings. These results support the hypothesis that extrastriate cortex is affected in anisometropic amblyopia. Although suggestive of a magnocellular defect, the exact mechanism is unclear.
Bonhomme
Gabrielle R
GR
Children's Hospital of Philadelphia Functional MRI Research Unit and the University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA.
Liu
Grant T
GT
Miki
Atsushi
A
Francis
Ellie
E
Dobre
M-C
MC
Modestino
Edward J
EJ
Aleman
David O
DO
Haselgrove
John C
JC
D000293:Adolescent; D000328:Adult; D000550:Amblyopia / Q000175:diagnosis / Q000503:physiopathology*; D002648:Child; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011379:Prognosis; D012720:Severity of Illness Index; D014793:Visual Cortex / Q000503:physiopathology*