Daniel Woolf

“ Squint is also called strabismus, or heterotropia. In other words, in orthophoria there is binocular fixation all the time and under all conditions; in heterophoria it is present only when the two eyes are uncovered, so that both see the object looked at; while in squint it is not present at all.
Or, in still plainer terms, in orthophoria both eyes are straight all the time; in heterophoria both are straight, but only so long as both are uncovered; and in squint only one eye is straight, no matter whether both eyes are uncovered or not. ”

“ Where a patient is unable to call each day for this muscular treatment or exercise, the work will be greatly facilitated by employing a specially designed set of square prisms ranging in strength from 1⁄2 to 20 degrees for home treatment. As in the case previously cited, it is necessary to carefully instruct the patient that the interni muscles must be developed, hence prism base out with apex in must be employed. Attention should then be directed to a candle light, serving as a muscle testing spot of light and stationed in a semi-dark room at an approximate distance of twenty feet. ”

“ Exophoria If a case is one of exophoria of six degrees, where the second method of treatment or muscular exercise is in line of routine, it is essential to first determine through a duction test and the preparation of the diagram exactly which one of the four muscles are faulty (Fig. 24) .
Having determined, with the aid of the diagram, first, the existence of 6 degrees of exophoria; second, 18 degrees of adduction; third, a weak left internus—the next procedure is to determine what degree of prism will enable the patient to obtain single binocular vision, with both eyes looking “straight.” ”

“ Where the Ski-optometer is correctly fitted to the face, the patient invariably remains in a comfortable position (Fig. 11) . The instrument [Pg 31] is shaped to fit the face like a mask, so that even with a pupillary distance of but 50 m/m (that of a child) there still remains, without pinching, ample room for the widest nose of an adult.
Before making an examination, the correct pupillary distance should always be obtained by drawing an imaginary vertical line downward through the center of each eye from the 90° point on the Ski-optometer axis scale. ”

“ Likewise, in cases of esophoria, hyperphoria, or cataphoria, the making of definite muscle measurements independently through the prescribed method would show through the merest glance at a similar diagram which muscle or muscles were relatively out of balance. Heterphoria of almost any type, or tendencies other than normal, may be fully investigated by making a thorough and separate test of each muscle.
Where an imbalance exists, a rapid test may be employed to distinguish a pseudo or false condition from a true condition. ”

“ For example, where the phorometer indicates esophoria it is usually associated with hyperopia, whereas exophoria is usually associated with myopia, thus serving as a clue for the optical correction.
Assuming for example that the binocular muscle test shows six degrees of esophoria without the optical correction, and with it but four degrees, it is readily seen that the imbalance has been benefited by the optical correction. Under such conditions it is safe to believe that the optical correction will continue to benefit as the patient advances in years, tending to overcome muscular defect. ”

“ THIRD METHOD OF TREATMENT—PRISM LENSES When and How Employed As stated in the preceding chapter, on ascertaining the failure of the second muscular treatment or method, prisms are employed for constant wear. When prism lenses are used, whether the case is exophoria or esophoria, or right or left hyperphoria, it is always safe to prescribe one-quarter degree prism for each degree of prism imbalance for each eye. For example, in a case of 6 degrees of esophoria, a prism of 11⁄2 degree base out should be prescribed for each eye ”

“ The muscles forming any one pair are called associates. Any two associates acting together will move their respective eyes in precisely the same direction and to the same extent. Thus the right superior rectus moves the eye up to the left and rotates its vertical meridian to the left; and its associate, the left inferior oblique, moves its eye up to the left and rotates its vertical meridian to the left. ”

“ To fully appreciate the effect of this muscular treatment, the reader need only hold his head in a stationary position, casting his eyes several times from the extreme right to the extreme left, not failing to note the apparent muscular strain. On the other hand, with the aid of the Ski-optometer’s rotating prisms, the refractionist not only has complete control of the patient’s muscles at all times, but scientifically accomplishes muscular exercise without any tiresome strain, overcoming all possible exertion. ”

“ In many cases, if the visual acuity in each eye be made normal, the fusion impulse alone will be sufficient to restore compensation.
Many cases of esophoria result from overstimulation of the centers for convergence and accommodation, made necessary by hyperopia and astigmatism, entirely disappearing when glasses abolish the need of accommodation. Cases of exophoria are sometimes due to the abnormal relaxation of accommodation and convergence which secures the best distant vision in myopia. ”

“ The patient whose attention is directed to the usual muscle-testing spot of light, will see two spots.
Aside from the instrument itself, and in further explanation of the phorometer’s principle and construction, when two five-degree prisms are placed together so that their bases are directly opposite, they naturally neutralize; when their bases are together, their strength is doubled. Thus while the prisms of the phorometer are rotating, they give prism values from plano to ten degrees, the same being indicated by the pointer on the phorometer’s scale of measurements. ”

“ If astigmatism exists, vision will usually show signs of improvement at some point, indicating the approximate axis. Once the latter is ascertained, the refractionist may readily turn the Ski-optometer’s cylinder reel and obtain the correct cylinder [Pg 26] lens strength, after which the axis indicator should be moved in either direction in order to obtain the best possible vision for the patient.
The refractionist should always aim to obtain normal (or 20/20) vision with the weakest concave cylinder, combined with the strongest plus sphere, or weakest minus sphere. ”

“ It must always be remembered before the refractionist is ready to employ the muscular exercise or second method, that the degree of prism required to give the patient single binocular vision must be determined with the optical correction in place. The exercise must be practised daily in routine, a daily record being essential. ”

“ INTRODUCTORY While in a measure the conventional trial-case still serves its purpose, so much of the refractionist’s time is consumed through the mechanical process of individually transferring the trial-case spheres and cylinder lenses, that far too little thought is given to muscular imbalance, notwithstanding its importance in all refraction cases. ”

“ At the end of each three months’ period, the patient should be requested to return, when the binocular and the duction test should again be made, comparing results with the work previously accomplished. An improvement tending to build up the left weak externus will possibly permit of a decrease of the excessive spherical power, so that excessive spherical power is reduced until completely removed, in all probability overcoming the muscular defect. Esophoria is almost invariably a false condition and frequently is outgrown under this treatment as the child advances in years. ”

“ We sometimes take advantage of this tendency when we prescribe for constant use weak prisms with the apex over the weak muscle, which gradually becomes strong from the exercise of overcoming it. This plan is effective only in patients who have a strong fusion impulse, and the prism selected must be weak enough to be easily overcome. We can accomplish the same effect by decentering the patient’s refraction lenses. ”

“ The primary action of the superior rectus is to raise the eye. Because of the way in which the muscles run, obliquely from within outward, its lifting action increases when the eye is abducted and diminishes to little or nothing when the eye is adducted.
The inferior rectus carries the eye down. Owing to the oblique direction of the muscle, its depressing action increases as the eye is abducted and decreases to zero as the eye is adducted. ”

“ Duction chart should show a tendency to reduce exophoria by a gradual building up of adduction, approximately one week is usually sufficient to teach patient to hold streak within the spot (between 38° and 42°) . Exercise [Pg 92] to be continued until both prisms are worked down to zero. Exercise tends to teach patient how to establish same image on each fovea or retina at same time.
5th—If patient is unable to call daily for treatment, employ home treatment. (Read “Home Treatment for Muscular Exercising,” Page 82) . ”

“ However, when these conditions result from other imbalances, they must be treated more carefully. For instance, a patient whose right internus is paralysed or congenitally defective on looking to the left, has a cross diplopia which vanishes to the right; as a result, he soon assumes a habit of carrying his head in this position. Ordinarily, this will cause no discomfort; but if the left internus is so weak that it cannot follow the right externus to its position of greatest ease, the visual lines are evidently different and the case must be treated as an exophoria. ”

“ It is difficult to account for, except on the theory that definite movement of the eyes is rather to the right than to the left in most occupations. The position of the paper in writing at a desk tends toward dextrophoria; in reading, we move our eyes steadily from left to [Pg 133] right and then begin a new line by a single brief movement to the left; the things that a man uses most—whether he be laborer or student—are kept within reach of the right hand, and in referring to them the eyes are constantly turned toward the right. ”

“ THE USE OF THE SKI-OPTOMETER The Ski-optometer is equipped with an adjustable head-rest, permitting its lenses to be brought as close as possible to the eye without touching the patient’s lashes, a matter of importance in every examination. ”

“ The treatment of heterophoria depends on a careful study of each individual case, but it cannot be too strongly emphasized that in the great majority of cases the subjective symptoms disappear after a full correction of the refraction is made. ”

“ To fully realize its labor saving value in obtaining accurate examination results, it is only necessary to recall the tedious method of individually handling and transferring each lens from the trial-case to the trial-frame, watching the stamped number on each lens handle, wiping each lens and in the case of cylindrical lenses setting each one at a designated axis—all being needless steps where the Ski-optometer is employed. ”

“ Esophoria signifies inward tendency. Exophoria signifies outward tendency. Hyperphoria signifies upward tendency. Hypophoria signifies downward tendency. Cyclophoria signifies tendency to torsion. Esotropia signifies inward turning. Exotropia signifies outward turning. Hypertropia signifies upward turning. Hypotropia signifies downward turning. Cyclotropia signifies actual torsion.
Combinations are describable in similar terms. A tendency of the right eye to turn up and inward, is a “right hyperesophoria”; the left eye to turn down and out, a “left hyperexophoria,” etc. ”

“ It is [Pg 109] only when there is marked amblyopia, particularly as the result of a central scotoma (or spot on the cornea in the line of vision) that the squinting eye loses its power to fix at all, and wanders uncertainly about, receiving impressions now on one, now on another portion of the retina.
The term imbalance is often used to denote the two conditions opposed to orthophoria; i.e., to denote collectively heterophoria and squint. ”

“ A comparison of the left eye shows adduction of 18 degrees with an abduction of 8 degrees, proving a lateral insufficiency because the ratio is less than 3 to 1; and the muscles of the left eye are at fault. The power of 2 degrees superduction and 2 degrees subduction, proves that no weakness exists in the vertical muscles. ”

“ As previously stated, the power to converge is normally rated 3 to 1, or 8 to 24, as shown above, while the power of the eye to look upward, is equal to the power to look downward. The diagram accordingly proves that the muscles of the right eye are in perfect balance, having equal muscular energy. ”

“ Likewise the correction of myopia, by increasing the far point, may diminish the amount of convergence necessary for near vision. [Pg 131]
Prisms for constant use are often prescribed, so placed as to help the weak muscles and counteract the strong. For instance, in esophoria we find the prism which, base in, will produce orthophoria for distance and prescribe a quarter of it, base in, before each eye. ”

“ Under normal conditions, when the head is erect and the eye is directed straight forward—that is, when its line of sight is perpendicular to the line joining the centres of rotation of the two eyes in the horizontal plane—the muscles are all balanced. ”

“ The impulse to maintain it grows with exercise, and soon becomes so strong that after the age of infancy binocular fixation is present in the great majority of persons, and in most of them is present all the time. ”

“ In a word, the Ski-optometer’s cylinder lenses set directly next to the patient’s eye, followed by the stronger sphericals, so that the weakest spherical or +.25 (the lens of least importance) sets farthest away. ”