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° (SD 2.94°). Comparison with the indirect/protractor method revealed a mean difference of 1.10° (SD 0.99) with a range of 0° to 4° 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° to 16°). Variation between left and right eyes of the same individual was not significant (1.15°, SD 1.39°), and if greater than 4°, probably represents cyclovertical muscle dysfunction or restrictive orbitopathy. The converse, however, may not always be true as individuals with less than 4° difference between eyes may have cyclovertical muscle imbalance