to measure Fixation Disparity or Accommodative Lag, yields clinically accurate estimates - testing is quick and extensive use has shown the results to be reliable over time - The Wesson Fixation Disparity Card© can be used to measure Fixation Disparity or Accommodative Lag. The Card yields clinically accurate estimates of several key parameters involved in measurements of these functions. Testing is quick and extensive use has shown the results to be reliable over time. Fixation disparity is a compensatory mechanism between fusional or disparity vergence and its relationship with the underlying phoric posture. Fixational disparity is sometimes called Retinal Slip and is measured in minutes of arc. The associated phoria is measured in prism diopters. Fixational disparity is not necessarily in the same direction as the phoric posture and therefore should be measured independently of the dissociated phoria. Fixation disparity cannot be measured using a prism to neutralize the misalignment noted in an AO vectographic target or a Mallet unit. This neutral point represents the associated phoria not the fixation disparity. The Wesson Fixation Disparity Card© is used to measure both horizontal and vertical disparity. With a set of loose prisms, the Card can also be used to measure a forced vergence fixation disparity curve. Further, the Card can be used for adults and pre-reader children to in the measurement of Accommodative Lag using either the MEM method, the Nott method or the DOG method. The reverse side provides a Gaussians waveform required for the DOG method. Kit includes polarized glasses. Hole are punched for phoropter mounting. For use at 40 or 25 CM