Summary
Torsion is an under-recognized component of strabismus. Measurement of torsion is integral to accurate diagnosis of strabismus, and torsional correction is critical to optimize postoperative fusion. Unlike vertical and horizontal diplopia, which can often be ameliorated with prism, torsional diplopia is debilitating, and only correctable with surgery. In children it can cause behavioral problems. Objective torsion is the actual torsion of the eye as measured by the examiner with indirect ophthalmoscopy or fundus photography/imaging. Subjective torsion is the torsion perceived by the patient, as measured with single Maddox rod testing, the double Maddox rod test, Bagolini lenses, and other tests. Sensory adaptations often cause subjective torsion to be lower than objective torsion. Surgical correction can be achieved with oblique muscle surgery, rectus muscle transpositions, and pulley surgeries.
11 Torsion
11.1 Introduction
When either eye is excessively rotated around the visual axis, torsional complaints can occur. Excyclotorsion occurs when the 12 o’clock position of either eye is rotated temporally: counterclockwise in the right and clockwise in the left. Incyclotorsion occurs when the 12 o’clock position of the eye is rotated nasally: clockwise in the right and counterclockwise in the left.
Objective torsion refers to the actual torsional position of the horizontal meridian of the retina, which is measured by observing the position of the macula in relationship to the optic nerve. In a photograph, the normal position of the macula is located on a horizontal line between one-sixth and one-third the distance from the lower edge of the optic nerve. In the office, when viewing with an indirect ophthalmoscope, the retina appears inverted, so the normal macula position is on a horizontal line one-sixth to one-third the distance from the upper edge of the optic nerve (Fig. 11‑1).
Although we compare the position of the macula to that of the optic nerve, in reality the macula receives visual images, and therefore, it is the rest of the eye and the optic nerve that is rotating around the macula.
It is not uncommon for patients to have moderate to large torsion, with less subjective than objective torsion. Subjective torsion is a measure of the patient’s awareness of torsion, and may be influenced by central adaptive mechanisms such as torsional anomalous retinal correspondence. Many of these patients have asthenopic complaints including headaches, eye discomfort, and reading difficulties.
We have underestimated the discomfort caused by moderate to large amounts of torsion. These patients may have elevation or depression of the eye in nasal gaze, but many only have torsion with no other strabismus. The amount of torsion that is needed to cause asthenopia varies among patients. For an equal amount of torsion, incyclotorsion causes more asthenopia than excyclotorsion.
This author has noted that subjective incyclotorsion greater than 4 degrees and excyclotorsion greater than 6 degrees is usually associated with asthenopia. If objective torsion is significantly greater than subjective torsion, the patient is using torsional fusional reserves or sensory adaptations to decrease their awareness of torsion. It is this author’s opinion that torsion is a common cause of headaches, with incyclotorsion causing more severe headache than an equal amount of excyclotorsion.
Hunter states that normal adults can fuse 8 degrees cyclodisparity using cylovergence and another 8 degrees using sensory fusion. 1 These tests were performed for a few seconds on a synoptophore and don’t completely correlate to the demands of a half hour of reading.
Horizontal and vertical strabismus that requires surgical correction offers an excellent opportunity to also correct torsion at the same time. In other cases torsion surgery may be performed alone. Surgical correction of torsion can relieve significant asthenopia, headaches, and reading discomfort.
11.2 History
Children should be questioned about reading difficulties, specifically about eye discomfort, fatigue, and headaches while reading. They may also describe loss of concentration, and difficulty keeping their place on the line of text. Some patients experience peritrochlear superior oblique (SO) discomfort. Behavioral issues such as hyperactivity are common in young children with large excyclotorsion. 2 Clumsiness, with frequent falling or multiple accidents, occurs in association with large amounts of torsion in children.
11.3 Examination
A complete sensorimotor exam is performed with particular attention to the oblique muscles (Chapter 2, Chapter 8, Chapter 9). V pattern with excessive elevation in adduction is often associated with excyclotorsion, and A pattern with excessive depression in adduction is often associated with incyclotorsion.
Observe head tilts. Head tilt to the right suggests incyclotorsion in the right eye or excyclotorsion in the left eye; however, vertical deviation without torsion may also cause head tilt. Significant subjective and objective torsion may exist in the absence of manifest strabismic deviation or A or V pattern. Pulley heterotopy can simulate oblique dysfunction and cause substantial torsion (Chapter 4, Chapter 19).
This author has recently started requesting that school-aged children with subjective torsion read an age-appropriate paragraph, and then read the same words listed one word at a time in vertical order. These patients usually read the vertical material 10 to 20% more quickly than the paragraph. This difference is not observed in patients without torsion.
11.3.1 Subjective Torsion
The single Maddox rod test is not widely utilized, but it is the preferred subjective test of torsion for this author. With room lights at very minimal illumination, aim a penlight at the right eye from 4 feet. Patch the left eye. Hold a single red Maddox rod attached to a stick, with the lines arranged initially 15 degrees to the temporal side of the vertical, and slowly rotate the Maddox lines toward the 90-degree position. The patient is instructed to say “stop” when the red line appears horizontal. Patients with excyclotorsion will usually report more torsion if the Maddox lines are begun from the temporal position as opposed to beginning nasally.
To test for incyclotorsion on the right eye, start with the vertical red Maddox lines about 15 degrees on the nasal side of the vertical meridian, and slowly rotate the Maddox rods temporally toward the vertical 90-degree position. When the line appears horizontal the patient again is instructed to say “stop.” Estimate the amount of torsion in each eye, and repeat each measurement for confirmation (Video 11.1). The compass setting on a cell phone can be used to help approximate torsion angles. I usually take a photo of the torted Maddox rod in each eye for documentation and to show the patient. Obtain single Maddox rod torsion numbers on at least two separate visits before surgery, since subjective torsion numbers vary.
Most physicians and orthoptists prefer the double Maddox rod test, which usually measures slightly less torsion in each eye than the single Maddox method. The best technique for double Maddox rod testing is not uniformly accepted. Guyton prefers to always begin with the right eye (personal communication, 2017), but others prefer the dominant eye. Should the lines be arranged vertically in both eyes, or vertically in one and horizontally in the other? Should one use one red and one white Maddox lens?
This author prefers to start with the dominant eye. To measure eye dominance, the patient holds the handle of a stick with the round Maddox rod removed. With arms held outstretched, the patient identifies the plane from the Allen pictures projected at distance. The right eye is covered and the patient is asked whether the picture disappears. This is then repeated with covering of the left eye. The eye that does not experience the image loss is dominant (Fig. 11‑2).
If the double Maddox rod is performed with one red and one white lens, 83% of patients will orient more torsion to the eye with the red Maddox. 3 Two red Maddox rods arranged vertically in a trial frame eliminates that problem. Patch the nondominant eye. The patient first adjusts one Maddox rod to have the red line appear horizontal. The patch is then removed, and a 6 diopter base down prism is held in front of the nondominant eye. The patient is instructed to align the second Maddox rod red line parallel to the one in the dominant eye. Torsion measurements can be variable, so it is best to perform them on at least two separate exams.
Loose Bagolini lenses can also be used to measure torsion, with the advantage of less disruption of patient fusion. Some patients with significant double Maddox rod torsion have decreased or absent torsion when tested with Bagolini lenses, suggesting significant sensory adaptation. The Lancaster red-green test is another method to measure subjective torsion.
Patients who have had excyclotorsion for long periods of time usually have less subjective excyclotorsion than objective excyclotorsion, due to central sensory adaptations. Patients with recent head injuries usually have similar subjective and objective torsion.
11.3.2 Objective Torsion
Objective torsion is the term used to describe the degrees of fundus torsion as noted by the examiner with an indirect ophthalmoscope or photograph. Sit squarely in front of the patient, with eyes level to those of the patient. Record individually the objective torsion observed in each eye. Do not add the amount of torsion in each eye together for a total amount of torsion. One may estimate torsion as Guyton does, as +1 to +4 excyclotorsion or incyclotorsion, with marks 3.5 degrees apart. 2 I prefer to estimate torsion, rather than use a +1 to +4 designation. It is helpful to draw objective torsion on a schematic fundus view, using a circle to represent the optic nerve and a dot for the macula. I draw the position of the macula as it would appear in a photograph, but one may choose to represent the indirect ophthalmoscopic, inverted view, exactly as seen by the examiner in the office or operating room (OR).
Young children can be difficult to examine. This examiner has noted 2 to 4 degrees more of excyclotorsion in the left eye. Therefore examine the left fundus first, since one may not be able to examine both. Loba and Simera have calculated that there is 2.24 degrees more excyclotorsion in the left eye as compared to the right using Cyclocheck software. 4
Fundus photography and use of a free software program, Cyclocheck, can be used to determine the exact degrees of torsion (Fig. 11‑3). 5 With this software, torsion is measured as the angle between a horizontal line from the center of the optic nerve and a second line that connects from the center of the optic nerve through the macula. A photo is uploaded to the free software. The macula and the upper and lower edge of the optic nerve are located. The software calculates an immediate torsion number in degrees. Cyclocheck, using photographs, arbitrarily assigns positive numbers to all foveal positions below the center of the optic nerve. All foveal positions above the center of the optic nerve are given negative numbers.
This author has coined the expression “real torsion” to mean the amount of extra incylotorsion or excyclotorsion in degrees from the expected normal position of the fovea. Because there is a range of what is considered the normal position of the fovea, torsion has usually been measured using the center of the optic nerve as a reliable, but inaccurate, starting calculation point.
In a photograph the normal macula is usually about 8 degrees below the center of the optic nerve. If the macula is located just below the optic nerve, this is reported as about 12 degrees in the positive excyclotorted direction. In reality, this reported 12 degrees of excyclotorsion is actually 12 degrees minus the 8 degrees position of the normally located macula. Therefore, what has often been shown as 12 degrees of excyclotorsion in photographs is only about 4 degrees of “real excyclotorsion.” When using the “real” torsional figure, one finds that patients’ subjective and objective torsion measurements agree more closely.
In a photograph, if the macula is noted to be exactly opposite the center of the optic nerve, Cyclocheck will report this number as zero. Because this macula position is actually about 8 degrees intorted from the average normal position of the macula, real torsion is 8 degrees of incyclotorsion. If the macula, in a photo, is halfway between the center of the optic nerve and the normal position of the macula, this is 4 degrees of incyclotorsion. This finding is frequently missed because it is easy to mistake this intorted macula for a normally located macula.
Measurement of objective torsion is usually an estimate when examined with an indirect ophthalmoscope. Indirect ophthalmosocopic views with measured amounts of torsion as we view the patient in the office or the OR are included for reference to help the reader become familiar with estimating amount of torsion (Fig. 11‑4). This is a critical skill to learn, to be able to estimate approximate torsion in the office and OR.
I now write down the full photographic amount of torsion, as calculated by the traditional Cyclocheck method. I also write a second number, which I call “real excyclotorsion” or “real incyclotorsion.” In the second recorded torsion number one must add or subtract 8 (the average excyclotorted position of a normal macula from the center of the optic nerve) from the original way of calculating torsion. A composite of approximate estimated “real torsion” amounts using indirect ophthamoscopy is also included (Fig. 11‑5).
To determine whether torsion during surgery is the same as in the office, almost all patients are dilated just before surgery. Torsion is evaluated by indirect ophthalmoscopy soon after induction with nondepolarizing muscle relaxant anesthesia. Excyclotorsion in degrees is usually similar to office excyclotorsion, but incyclotorsion often increases. Torsion is monitored by indirect ophthalmoscopy several times during surgery and at the completion of surgery, to confirm correction and adjust the surgery if needed. This requires putting on a second set of sterile gloves and changing loupes for an indirect ophthalmoscope. The eye is kept sterile with an extra set of drapes placed around the eyes.
It is this author’s clinical impression that patients with incyclotorsion are more uncomfortable, with more asthenopia, than patients with an equivalent amount of excyclotorsion, for unknown reasons. This author has noted that many patients with larger excyclotorsion in the left eye have mild flattening of the frontal bone on the left side with probable resultant elevation of the superior orbital rim, which may be responsible for the increase in excyclotorsion in the left eye. Asthenopia, headaches, head tilts, balance issues, and reading difficulties are frequent complaints of patients with incyclotorsion. Right eye incyclotorsion usually is greater than intorsion in the left eye, also for unknown reasons.
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