Cyclotropia is usually due to paralysis of one of the ocular muscles, causing the vertical meridian of the affected eye to be tilted out or toward the temple (extorsion) or in toward the nose (intorsion). A tilting of the vertical meridian toward the right is also called dextrotorsion (or positive declination); and to the left, levotorsion or negative declination.
2. Constant, Intermittent and Periodic Deviations: A deviation, whether squint or heterophoria, may be present at all times (constant), or occasionally present and occasionally absent (intermittent). In this case we may have heterophoria alternating with orthophoria, or heterophoria alternating with squint; or squint alternating with orthophoria. We also find variations such as a squint for near and a heterophoria or orthophoria for distance; or a heterophoria for near and orthophoria for distance; or a constant squint for near and an intermittent squint for distance, etc. Again, a deviation may be periodic, in that its amount for distance may greatly exceed that for near, or vice versa.
Opposed to a periodic deviation is one which is present, and in about equal amount, both for distance and near. Such a deviation, whether squint or heterophoria, is called “continuous.”
3. Alternating and Uniocular Squint: An alternating squint is one in which when both eyes are uncovered, so that both have a chance to “fix”; sometimes the right eye will deviate, sometimes the left. In uniocular (less properly monocular) squint, under the same conditions, one eye, either the right or the left, always “fixes” and the other always deviates. A uniocular squint is denoted as right or left, according to whether it is the right or left eye which deviates.
A Typical Refraction Room—
The Woolf Sanitary All-Metal Equipment
Installation comprising: Ophthalmic Chair, complete with Ski-optometer, Test Letter Cabinet, Asceptic Trial-Case Cabinet, Muscle Testing and Skioscopic Lamp, Ophthalmometer, Perimeter, Adjustable Tables, Adjustable Stool.
4. Comitant and Non-Comitant Deviations: In some varieties of heterophoria and squint, the amount of deviation is the same in all directions of the gaze, so that the angle between the visual line of one eye and that of the other remains the same, no matter which way the eyes are turned. Such deviations are called comitant or non-comitant, because one eye accompanies and keeps pace with the other in all its movements. In other cases, the deviation changes as the eyes are moved in different directions, so that the angle between the two visual lines constantly varies. Such deviations are termed concomitant. Usually in a non-comitant squint the angle of deviation increases in a regular way as the eyes are moved in one direction and decreases as they move in the direction opposite.
In cases of long standing, however, the squinting eye, particularly when very amblyopic, wanders in an uncertain way and apparently quite without reference to the movements of the other eye.