Evaluation of Compensatory Torsion by Blind Spot Mapping

Elaine Cornell DOBA DipAppSc MA
Jodie Flanagan BappSc (Syd) OD
Robert Heard PhD

Blind spot mapping is a non-contact and relatively simple method to evaluate rotation of the eye in response to head tilt. Any displacement of the blind spot during head tilt indicates the concurrent rotation of the eye, i.e. that which has not been compensated by a torsional movement.
This method was used to evaluate the extent of intorsion and extorsion induced by head rotation from 0° to 30° in 22 normal subjects. Results confirm previous studies that full compensation to head tilt does not occur, even at small degrees of head tilt. The mean responses of compensatory intorsion ranged from 32% to 41% and those of compensatory extorsion from 20% to 25%. This difference between intorsion and extorsion (i.e., a more effective intorsion response) was statistically significant (p<0.0001) at each position of the head tilt. This unequal response must be accompanied by a sensory and /or motor cyclofusion to prevent torsional diplopia from occurring. Although these results do not directly contradict the theoretical basis of the Head Tilt Test, they do suggest that a negative or inconclusive result may be due to poor cyclotorsion.