Model of Static Accommodative Behavior in Human Amblyopia

When a target is moved from far to near, the normal accommodative system responds by changing the crystalline lens power until the blur of the retinal image is reduced to an acceptable level for clear vision. This feedback mechanism, along with the experimentally derived deadspace operator (representing the depth of field), forward-loop gain, and tonic accommodative bias level have been successfully incorporated into a static model of the normal accommodative system. We extended this model to the investigation of static accommodative responses in amblyopic eyes. The experimentally derived accommodative controller gain of the amblyopic eye was typically smaller than in the fellow dominant eye. In addition, the experimentally derived depth of field was increased in most amblyopic eyes, while the accommodative bias showed no consistent difference between the two eyes. The decrease in accommodative controller gain and increase in depth of field were sufficient to account for the reduction of accommodative responses found in amblyopic eyes. Theoretically, the model provides a conceptual framework for understanding the static accommodative deficits found in amblyopic eyes. Practically, the accommodative controller gain parameter provides a means for uniform assessment of normal and abnormal accommodative function, both experimentally and in the clinic environment.