1. Purpose  Amblyopia is a developmental disorder of the visual cortex affecting 2-3% of the population  Previous investigations by Ciuffreda, Levi, and Selenow (1991) have determined that amblyopia is characterized by undersampling in the visual cortex  We investigated whether or not amblyopia also causes systematic mismapping in the deficient visual cortex (Bedell, Flom, 1981)  We also investigated whether the development in amblyopes mirrors that of normal observers  Rapid and accurate localization of the position of objects and judging the distance between them is essential for real world operations  Understanding amblyopia helps us to better understand normal visionMethods  Eight amblyopic and nine normal observers were tested on a computer  Three micropatterns (aka Gabor patches) were displayed so that the outer two were vertically aligned, while the middle one vertically bisected them  The middle micropattern was randomly displaced to the left or to the right by a variable amount from an imaginary axis formed by the top and bottom micropatterns  Observers were asked to judge in which direction the displacement was. There were two test conditions: 1) the bars in all three patches were vertical (collinear) 2) the bars in the outside patches were vertical but the middle one was horizontal (orthogonal)  We compared directional bias and accuracy for -Amblyopes: dominant vs. amblyopic eyes -Normals: dominant vs. non-dominant eyes Results Using 3-Way within and between subjects ANOVA analysis, we found that:  Amblyopic eyes are significantly less accurate than normal eyes  Amblyopes are also much less precise in their amblyopic eye than in their dominant eye  There may be a greater effect of orientation on the accuracy of amblyopic eyes, though we do not have enough data to verify this idea  In both normal and amblyopic viewers, orientation does not have a significant effect on accuracy, though it does have a significant effect on precision. Observers were generally less precise in the orthogonal condition  In amblyopic eyes, there’s a strong correlation between the bias in the collinear and orthogonal orientations  Overall, amblyopic eyes had lower accuracy and lower precision than the dominant eyes of amblyopes, and both eyes of normal subjects  However, we found that variation in precision only accounted for about 20% of the variance in the accuracy What is Amblyopia?  Amblyopia is a visual disorder, resulting from abnormal neural development at a young age  It affects roughly 2-3% of the population  The most common causes are misaligned eyes (strabismus), or a large refractive difference between the two eyes (anisometropia)  It is characterized by poor vision in an eye that is otherwise physically healthy and normal  Amblyopia is NOT a problem with the eye, but a developmental problem in the brain  It can also be treated by occlusion therapy at an early age Alignment Bias And Precision In Normal Vision And Amblyopia Kevin Yuen, Ariella Popple & Dennis Levi School of Optometry, University of California, Berkeley, CA 94720 Conclusions  There are no significant differences between the eyes of normal subjects  The visual cortex associated with the amblyopic eye is often characterized by mismapping (bias) in addition to undersampling or blur (threshold).  This mismapping likely occurs at the level of V1 in the visual cortex Acknowledgements  I ’ d like to thank Dr. Ariella Popple and Dr. Dennis Levi for their guidance and support on this research projectReferences  Ciuffreda, K., Levi, D.M., Selenow, A., (1981). “Amblyopia: Basic and Clinical Aspects.” Stoneham, MA: Butterworth-Heinemann, 1991.  Popple, A.V., Levi, D.M. (2002). Response to Keeble and Hess. Vision Research, 42, 1431-1433.  Bedell, H.D., Flom, M.C. (1981). Monocular Spatial Distortion In Strabismus. Investigative Ophthalmology and Visual Science, 2, 263-268