An asymmetrical optimal viewing position (OVP) effect in isolated word recognition has been well documented, such that recognition speed and accuracy are highest when the point of fixation within the word is slightly to the left of center. However, there remains disagreement as to the source of the asymmetry in the OVP effect. Accounts based on perceptual acuity and on lexical constraint have been difficult to tease apart. Here we take a novel approach, constructing an ideal-observer model of isolated word recognition which takes into account word frequency information and thus intrinsically accounts for the role of lexical constraint. Within this model, the perceptual acuity curve is governed by free parameters that can be estimated from purely behavioral response data from word recognition experiments. Fitting our model to the experimental data, our model results support the position that the perceptual acuity curve in isolated word recognition is indeed asymmetric.