Varieties of Heterophoria and Squint
1. Classification According to Direction of Deviating Eye: Heterophoria and squint may be classified according to the direction assumed by the deviating eye. Thus we have the following varieties of heterophoria:
| Heterophoria | |
| Lateral Deviations | |
| Either eye deviates | |
| In, or toward the nose | Esophoria |
| Out, or toward the temple | Exophoria |
| Vertical Deviations | |
| The right eye goes up and the left down | Right Hyperphoria |
| The left eye goes up and the right down | Left Hyperphoria |
In rare cases of vertical heterophoria, each eye has either an upward tendency (anophoria) or a downward tendency (cataphoria). These cases must not be confused with anatropia and catatropia. In anaphoria and cataphoria, there is binocular fixation when both eyes are uncovered, while in anatropia and catatropia one of the eyes squints. This shows the following squint condition:
| Squint |
| Lateral Squint |
| The deviating eye turns in, or toward the nose: |
| Esotropia (Strabismus convergens—Convergent Squint) |
| The deviating eye turns out or toward the temple: |
| Exotropia (Strabismus divergens—Divergent Squint) |
| Vertical Squint |
| The deviating eye turns up: |
| Hypertropia (Strabismus sursumvergens) (Right or left) |
| The deviating eye turns down: |
| Hypotropia (Strabismus deorsumvergens) (Right or left) |
In addition to these lateral and vertical deviations, conditions exist in which the vertical meridian of one eye, instead of maintaining its parallelism with the vertical meridian of the other, either forms (or tends to form) an angle with it (cyclotropia), but is kept in position through muscular effort (cyclophoria.)
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.
Chapter XVI
LAW OF PROJECTION
The movements of the eye are designed primarily to effect fixation—that is, to bring upon the macula the image of the object that we wish to look at. When this has been accomplished, we know as a result of long experience, the direction of the object looked at and also direction of other neighboring objects. This knowledge is doubtless afforded us, in part, by our muscle sense. Thus we know that an object, A, is straight in front of us because we can see it sharply without moving either the head or the eyes from the position of rest or equilibrium; and we know that an object, B, is on the right of us because to see it sharply we have to move either the head or the eyes to the right, thus altering the muscular condition from one of rest to one of tension. But without moving either head or eye, we also know, while still looking at A, that B is to the right, for the image of B is then formed on a portion of the retina situated to the left of the macula. From long experience we also know that an image so situated means an object placed on our right. Moreover, the farther to the left of the macula the image B is, the farther to the right do we judge B itself to be.
Similarly, if B is so placed that its image falls below the macula, we then know B itself is really above A, which forms its image on the macula; and if the image of B is above the macula, we know that B itself is below A.
The [table on page 116] is suggested as a guide in cases of muscular imbalance: