Ocular torsion-direct measurement with indirect ophthalmoscope and protractor

Objective measurement of the optic nerve head (ONH)-foveal angle, representing the torsional status of 40 eyes in 20 normal patients, was performed by fundus photography and compared to a method utilizing an indirect ophthalmoscope and protractor described herein. Photography established a mean ONH-foveal angle of 7.03 degrees (SD 2.94 degrees). Comparison with the indirect/protractor method revealed a mean difference of 1.10 degrees (SD 0.99) with a range of 0 degrees to 4 degrees between methods. The indirect/protractor method seems to provide a rapid, inexpensive, and accurate method of determining the degree of ocular torsion when compared to the fundus photograph method which requires greater patient cooperation and investment in time and equipment. The ONH-foveal angle varies widely among normal individuals (0 degrees to 16 degrees). Variation between left and right eyes of the same individual was not significant (1.15 degrees, SD 1.39 degrees), and if greater than 4 degrees, probably represents cyclovertical muscle dysfunction or restrictive orbitopathy. The converse, however, may not always be true as individuals with less than 4 degrees difference between eyes may have cyclovertical muscle imbalance.