Fixation disparity measurement
Reviewed by Fiona Rowe

The authors evaluate different procedures looking at point zero, fixation disparity (FD) and motor fusion amplitude in order to calibrate the measurement of FD with Ogle’s apparatus with the overall goal to create a standardised measurement of the FD curve for clinical use. Twenty-six subjects were evaluated using four procedures. In P1 and 2, prisms were built up in increasing strength starting with base in. In P3 and 4 prisms were built up with attenuating base in and base out. A significant difference was found between P1 and 2 and P3 and 4. P1 and 3 had highest point zero. A significant difference was found for motor fusion amplitude for P1 and 2, P1 and 3 and P2 and 4. P1 had the highest motor fusion amplitude and P4 had the lowest. There was no significant difference for eso disparity but significant disparity was found for exo with the highest in P1 and lowest in P4. Clinically significant differences were mainly caused by differences in line shifting. Most accurate P procedure was using prisms of increasing strength with base in first.

An optimal measurement of fixation disparity using Ogle’s apparatus.
De Meij L, Telleman MAJ, Luijten MRC, et al.
STRABISMUS
2017;25:128-33.