Second-order spatial summation in amblyopia.
Amblyopes show bilateral loss of sensitivity for second-order (contrast defined) stimuli that can be further suppressed by flanking second-order stimuli (whereas flanks facilitate sensitivity in normal observers). The suppressive flank effect in amblyopes might be explained by abnormal pooling of second-order contrast across visual space. In this study, we investigate whether amblyopes show abnormal second-order spatial summation by measuring contrast detection thresholds for 1c/deg modulations of random noise (stimuli 1-12 cycles) in amblyopic observers, strabismic observers with no visual acuity loss, and normal (control) observers. Non-control observers showed substantial bilateral loss of sensitivity relative to the control observers, as expected. However, all observers showed essentially equal second-order spatial summation: contrast detection threshold decreased with approximately the square root of the number of cycles, and then became independent of size at 6-8 cycles (similar asymptotes). We conclude that the pooling of second-order contrast across visual space is unaffected by amblyopia.
Wong
Erwin H
EH
School of Optometry, University of California, Berkeley, CA 94720, USA. wonge@umsl.edu
Levi
Dennis M
DM
D000293:Adolescent; D000328:Adult; D000550:Amblyopia / Q000503:physiopathology*; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation / Q000379:methods; D012684:Sensory Thresholds / Q000502:physiology; D013028:Space Perception / Q000502:physiology; D013285:Strabismus / Q000503:physiopathology; D015348:Vision, Binocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology