Digital measurement of torsional eye movement due to postural change and its effect on reading performance

Purpose. Posture induced torsional eye movements have rarely been investiga ted. The current study made use of digital imaging technology to measure th e cycloduction resulting from postural change. The effect of cycloduction o n reading performance was also investigated. Methods. Thirty subjects were recruited and pictures of the right eye were captured using a digital camera at three postures, i. e. sitting, 90 degree s tilted to the right and 90 degrees tilted to the left. With the identific ation of a conjunctival landmark, torsional eye movement was measured. The subjects were then required to read a custom designed near chart while in t hose three postures, the reading card being rotated 90 degrees clockwise or 90 degrees anti-clockwise, to match with the tilting of the head. The repr oducibility of the torsional eye movement and reading performance measure w as determined in 12 of those 30 subjects. Results. Incycloduction was induced when tilting to the right and excyclodu ction when tilting to the left. This method was found to be reproducible wi th the 95% confidence limits of 0.80 degrees between visits. The mean incyc loduction induced was 6.50 degrees (SD 1.51 degrees) and 6.41 degrees (SD 1 .46 degrees) for excycloduction. No significant difference in amount was de monstrated (paired t-test: t = 0.624, P = 0.538). No significant difference was found in the reading scores at various postures (Repeated measures ANO VA: df = 2, F = 1.881, P = 0.162). Conclusions. The results presented here demonstrate that we have developed an objective and instantaneous method with good precision, which could be a pplied in other studies that require the measurement of torsional eye movem ents. The induced cycloduction did not affect the reading performance.