Timothy C. Hain, MD Page last modified: March 30, 2017
The eyes can move horizontally, vertically, as well as around their front-back axis. The latter movement is called "torsion", and it involves a "twisting" of the eyes.
Diplopia is "double vision". It means that the eyes are not registering the same image, in a spatial sense. For horizontal diplopia, the eyes are either "converged" or "diverged" from each other. For vertical diplopia, one eye's position is above the other (this is called a hyper).
For torsion, the center of the one eye may be aligned with the other, but the periphery is displaced because the eyes are "twisted" with respect to each other. This also called "cyclodeviation".
It is also possible for the both eyes to be conjugately twisted with respect to the head.
According to Miller (2015), the most common cause of torsional diplopia is superior oblique palsy, which accounts for about 67% of all cases. Most of these are congenital.
Thyroid orbitopathy is another source of torsional diplopia.
It can also occur following orbital decompression (Garrity et al, 1992; Serafino et al, 2010), and after strabismus surgery.
It has been reported after macular translocation surgery (Sterker et al, 2002).
It can follow retinal surgery such as placement of a scleral buckle.
Of course, brainstem strokes can cause ocular muscle weakness, and therefore can sometimes cause torsional diplopia as well.
While detection of horizontal and vertical misalignment is relatively simple, assessment of torsional misalignment is more complex.
The double Maddox rod is a bedside method where each eye views a line, generated by an outside light. The angle of the lines can be adjusted by the patient, and then the angle read off.
The Lancaster test can be adapted for torsional diplopia, and is an excellent method for doing this.
Other methods include the "synoptophore" (Flodin et al, 2016)
The OCT test can measure torsion, but commercial devices only measure one eye at a time, allowing for a different head position between each measurement.
Torsional diplopia can be treated with "occlusion", meaning patching of one eye. This is similar to "if your right arm offends you, strike it off". Or, "throwing the baby out with the bathwater". Sure it works, but when you do this, you lose an eye.
In general, diplopia can sometimes be treated through activities that increase vergence. There is no literature published on exercise treatment for torsional diplopia, although there is such a thing as cyclovergence (e.g. Crone, 1975). It seems theoretically possible to adjust for torsional diplopia using virtual reality, as well as perhaps to treat torsional diplopia this way. However, there is no literature about this approach as yet. One would expect that torsional amplitudes might be increased through partial correction, and then "teasing" the fusional amplitudes to become larger.
Prism treatment is not helpful for torsional diplopia (Miller, 2015), presumably because there are no reasonable methods of tilting the optical image of one eye vs. the other.
Surgical treatment can sometimes be helpful, for example, the Harada-Ito procedure has been reported to sometimes be helpful. (Bradfield et al, 2012)