The phoroptor

Contents

CHAPTER | The Evolution of Eye Testing CHAPTER II

The Motor Muscles Joel iex CHAPTER III The Basis of Muscle Testing ;

CHAPTER IV The Phoroptor Be on vak 8 eR CHAPTER V The Maddox Rod Units ores

Preface

H ISTORY is replete with illustrations

of the fact that progress in scientific knowledge and the development of improved apparatus go hand in hand, each being to a ereat extent dependent upon the other. It is therefore not surprising that the constantly increasing realization of the important role played by the motor muscles of the eye in affecting both our vision and health, has been accompanied by marked development in ophthalmologic instruments for making more thorough muscle tests.

If this book contributes in any degree to a clearer understanding of the importance of testing the ocular muscles and of the possibilities of great good to be accomplished through the systematic making of such tests, the object of the work will have been attained.

ieee Ff HOR OP TOR Z

CHAPTER I The Evolution of Eye Testing

LTHOUGH spectacles were invented over six hundred years ago by the Italian d’Armati and have since been worn extensively by every civilized nation, little or no development worthy of mention took place either. in the general construction or the method of application of spectacles until the discovery of astigmatism, by Thomas Young, during the early part of the previous generation.

It is well within the recollection of the writer when it was the custom to purchase spectacles much after the fashion of shoes, from retail stores, by trying them on and taking the pair which seemed to fit the best; no eye examinations of any sort then being made or considered necessary. However, with the discovery of astigmatism and the advent of the cylindrical lens for its correction, the importance of eye examinations became at once apparent and the necessity of examining each eye separately was also recognized. Today no one desiring a correct pair of glasses thinks of purchas-

8 eon} ee E P HOROPTOR ing them in the old way, but consults one trained in the art, who is prepared to systematically test each eye separately and finally both eyes together, and prescribe lenses to meet all requirements, taking into account any imbalances of the motor muscles as well as errors of refraction which may be present.

It has long been recognized that the muscles which move the eyes in their orbits, known as the extrinsic or motor muscles, should be so interrelated or naturally balanced, that the visual axis of one eye will intersect that of the other eye at the point of fixation and the images of the object observed will form on exactly corresponding points in the retinas of the two eyes. In the absence of such natural muscular balance, binocular single vision could only be maintained through constant effort by the weaker muscles; otherwise the stronger and opposing muscle of any pair would rotate the eye toward itself and in so doing prevent intersection of the visual lines at the point of fixation and simultaneously the formation of the images at corresponding points in the two retinas.

As the fundamental law governing binocular single vision is based upon the physiologic fae PueGROFTOR 9 principle of corresponding retinal points, the image of the object in view must of necessity lie in exactly the same relative position upon the retina of each eye. The importance, therefore, of perfect motor muscular balance, otherwise known as orthophoria, is apparent if this fundamental requirement is to obtain without constant nervous and muscular effort.

When the motor muscles are not in balance— a condition known as heterophoria—vision is more or less disturbed and discomfiture frequently experienced, small imbalances often passing unnoticed while the higher degrees may produce double vision, otherwise known as diplopia, or may sometimes produce squint with subsequent amblyopia.

With our present knowledge of the important bearing which the motor muscles have upon comfortable binocular single vision, any tests of the eyes made solely in the interest of correcting errors of the refraction and without regard to the status of the motor muscles, are obviously very incomplete and fall far short of constituting a thorough examination.

Every well-grounded refractionist recognizes the intimate relationship which is known to exist between the intrinsic muscles of accommodation and the extrinsic muscles of convergence; also that stimulation of one gives rise to associate action on the part of the other. In consequence of this co-acting relationship existing between the accommodation and convergence, an otherwise balanced pair of lateral muscles could be thrown completely out of balance by inharmonious ciliary action, while on the other hand, a passive accommodation might, through stimulation of the interni, be induced to become active.

Latent hypermetropia, as is well known, frequently manifests esophoria, when in reality the lateral muscles are in balance; or such a condition of the refraction and consequent action of the accommodation, may likewise conceal true exophoria through the associate stimulation of the interni. On the other hand, these conditions may be reversed and active interni might, as a result of reflex ciliary action, manifest an increase of myopia in a truly myopic eye; myopia in an emmetropic or slightly hyperopic eye; emmetropia in a moderately hyperopic eye or reduced hyperopia in a highly hyperopic eye.

Then again the phorias often cause longitudinal stresses and consequent meridinal

Pate -FPuorR OP TOR 11 corneal depressions and because of such corneal changes, false or pseudo astigmatism will appear. ‘This is particularly true of lateral imbalances of higher degree which materially alter the anatomical rotundity of the cornea along the horizontal meridian of the eye.

Furthermore oblique imbalances may manifest cyclophoria through tortion of the globe and in consequence, no final measurements of the oblique muscles should be made until the status of the recti muscles is definitely determined and any imbalances in them corrected.

In every instance where an imbalance of the motor muscles is found, the error must be corrected if perfect binocular vision is to be had without effort, or diplopia with its train of undesirable consequences is to be avoided.

The importance of testing the muscles as well as the refraction is therefore apparent; also the necessity of suitable equipment for making complete refraction and muscle tests.

12 pa E PHOR OP TOR

CHAPTER II The Motor Muscles

| ieee eye is supplied with six extrinsic or motor muscles, a pair for effecting lateral rotations, a pair for the vertical rotations and still another pair for the prevention of tortion or turning of the eye on its antero-posterior axis. The first two pair are known as the recti and the last pair as the obliques. These muscles are all energized from primary or volitional nerve centers which act only in obedience to the will of the mind. These nerve centers are connected with the muscles in such a manner that the eyes are obliged to move together, it being impossible to voluntarily move one eye without moving the other correspondingly in the same general direction. In looking to the right, (right version) the primary nerve center governing this movement of the eyes, sends down stimulation to the right externus and the left internus; while in looking to the left, (left version) the primary center controlling all such movements of the eyes sends stimulation

Pen eee Oo n.OF TOR 2. lS to the left externus and the right internus. In looking up (super vision), both superior recti are simultaneously energized by the primary center having control of the upward rotation of the eyes; while in looking down (subversion) that center controlling the inferior recti effecting all such movements becomes active. To look in an oblique direction, two or more of these centers act in unison so that the requisite group of muscles necessary in effecting such rotations may be energized simultaneously. When converging, as in reading or looking at any object nearer than infinity, both interni and certain other muscles are stimulated simultaneously by those centers having supervision over the convergence. Hence, all voluntary rotations are binocular.

In addition to the distribution of nerve energy from the primary or volitional centers governing all binocular rotations, the motor muscles receive, when required, a further supply of nerve energy which emanates apparently from secondary or fusion nerve centers. These fusion centers are controlled solely by the fusion faculty of the mind and are wholly outside of any domination by the will of the mind. They function purely in the interest

SP NE OP MRR OPT OR of binocular single vision and have the faculty to move the eyes independently in any direction in order that the visual lines may be constantly co-ordinated to intersect at the point of fixation and the image of the object kept at the macula of each eye. All movements of the eyes therefore which are directed by the fusion faculty are involuntary and are executed solely in the interest of binocular single vision. Were it not for the independent muscular action inspired by the fusion faculty and executed through the agency of the fusion centers, there could be no physiologic compensation for muscular imbalances however great or small.

It is now quite evident that the primary or volitional nerve centers cannot cause movement of one eye without bringing the other eye into similar action and therefore are unable to correct or alter any existing muscular imbalances. It is also evident that the secondary or fusion centers can and do cause movements of one eye without moving the other and thus correct, or tend to correct, existing muscular imbalances.

oe Teororror 1

CHAPTER LI The Basis of Muscle Testing

Bl return to the fundamental law governing binocular single vision and its fixed physiologic principle of corresponding retinal points, the importance of a state of balance of the motor muscles becomes at once apparent if binocular single vision is to obtain without constant muscular action. As the macula is the posterior pole of the eye, it dominates all ocular rotations and is the region on which the image of the object must fall in each eye coincidently if binocular single vision is to follow. Any deviation of the visual axis of either eye from the point of fixation will, of necessity, displace the image from the macula of the deviating eye and thus destroy binocular single vision, unless sufficient stimulation is given by the fusion centers to the proper muscle or muscles, as the case may be, to bring the visual lines into proper coordination and thereby cause them to intersect at the point of fixation.

In orthophoria, where all motor muscles are

16. TNE POR Sr eee in balance, the visual lines will intersect at the distant point of fixation and the image of the object will lie at the central macular region of each eye without any action whatever on the part of either the primary or secondary centers, since the law of corresponding retinal points governing binocular single vision is not then infringed. However, should one of the motor muscles in any pair be weaker than its fellow, the eye would be turned to the side of the stronger muscle and in consequence, the image formed by that eye would no longer fall upon the macular region of that retina. The turning of the eye would produce diplopia and were it not for the constant readiness of the fusion sense to give increased stimulation to the weaker muscle and thereby cause it to pull equally with the stronger or opposing muscle of the pair, binocular single vision would not be restored.

Therefore, as the fusion sense alone dominates every independent action of the extrinsic muscles, a displacement of the image from the macular region would bring about immediate reaction of that muscle or those muscles attached to the opposite side of the globe in an effort to prevent visual disturbance, otherwise

THE PHOROPTOR | ky 3 known as diplopia. Should the image be displaced to the temporal side of the macula in an exactly horizontal direction, only the internal rectus muscle of that eye would be stimulated to action and the resultant rotation of the cornea inwardly and the macula outwardly would be equal to the outward displacement of the image. Such individual reaction is common with any of the recti muscles so long as the amount of the displacement of the image does not exceed the limitations of the fusion field or of the independent contractile power of the muscle concerned. In other words, so long as the amount of such displacement does not exceed the ability of that particular muscle acting independently to rotate the eye sufficiently to relocate the macula beneath the displaced image and thereby re-establish binocular single vision. However, should the image be displaced beyond the limitations of the fusion field, no muscular reaction would take place and the diplopia thus caused would be insuperable or permanent.

Lying within the visual field of the eye there is a fairly well defined area which is presided over by the fusion faculty and which in consequence is known as the fusion field. It is more

18 THE Peo orto or less pear-like in shape with the large end pointing toward the nasal side. Its dimensions are approximately 6 prism diopters displacement in width by about 35 to 40 in length, with the macular region located at the center of its vertical dimension and within about eight prism diopters displacement of the nasalend. Images falling within this field at other than the macular region, cause the eye to rotate in the interest of fusion, while those located outside its confines, have little or no effect upon the fusion sense and in consequence cause no movements of the eye. Hence, should the image be displaced either above or below the macula in a vertical direction to the extent of 5 or 6 prism diopters, or nasalward to the extent of about 10 prism diopters, insuperable diplopia would result, for the image in each instance would then be located beyond the confines of the fusion field and the fusion centers would remain dormant.

Since any of the motor muscles may be individually energized, as already explained, through the agency of the fusion sense, their reactional values may be readily ascertained by placing prisms of known quantity systematically before the eye; for diplopia will not be tHe. PA OR-OP TOR 19 tolerated unless the degree of displacement of the image by the prism is in excess of the reactional range or independent contractile power of the muscle whose duty it is to correct it, or unless the displacement exceeds the limitation of the fusion field. By harnessing the fusion sense in this fashion, it can be made to reveal the comparative reactional value of each extrinsic muscle; all of which is fully explained in the chapters dealing with the duction tests of these muscles.

In order to obtain the highest degree of stimulation in estimating the reactional values of the various recti muscles, through displacement of the image by means of prisms, the double rotary prism unit will be found highly advantageous as compared with prisms of fixed values. In using the double rotary prism unit, the image never leaves the macula and diplopia does not occur until the amount of displacement of the image exceeds the maximum rotation of the eye. Advantage of the highest retinal stimulation to the maintenance of binocular single vision is obtained in this way. When prisms of fixed value are employed in these tests, diplopia occurs the moment the prism is interposed between the eye and the object, for the image is never at the macula until fusion has taken place and the effect of the prism has been overcome. Each increase in the strength of fixed prisms employed in this way, displaces the image farther away from the macula when first applied and therefore upon a correspondingly less sensitive portion of the fusion field, with reduced reactional tendency. It is therefore obvious that the same fusion effort cannot be obtained by the employment of prisms of fixed value as by the use of the double rotary prism unit. Measurements made therefore with the fixed prisms will usually be somewhat less than those obtained by the use of the double rotary prism unit.

The cause of visual disturbances traceable to non-coordination of the visual axes of the eyes having now been shown to be due to a lack of balance of the muscular system of one eye or of both, and that one or more pairs of muscles in one or in both systems may be involved, the motor muscles must be tested in pairs, one pair at a time, if the exact location of an imbalance is to be determined.

To test the motor muscles in pairs, the test must be made monocularly and the basis therefore of all muscle testing should be established ree FSB OR OP TOR ay on the same foundation as is the testing of the refraction; namely, that each eye should be tested separately for its individual errors, whether they be of a refractive or muscular character or both. Finally both eyes should be brought into the field, with the correction for each in place in muscle work the same as is done in the final stage of a refraction test and any slight changes then made as may be required or considered desirable for the benefit or comfort of the patient.

In making monocular muscle tests, it should be clearly understood that both eyes are always seeing the same test object and that the eye under test is the one before which the prisms and other testing units, including the Maddox rod, are placed. The other eye is termed the fixing eye, as it never leaves its primary or fixed position with respect to the test object or original point of fixation. In addition to the necessity of having both eyes constantly in the field when making the muscle tests or giving muscle exercises, as explained in subsequent chapters of this book, the visual perception must be sufficient in each eye to enable the patient to discriminate quickly and accurately. The vision therefore

22 THE PHRHOROP TOR should not be less than three-fifths of normal in any instance whether a correction for the refraction is needed or not to bring the vision to this standard.

CHAPTER IV The Phoroptor

HE importance of making thorough tests of the motor muscles and of making them monocularly, has been shown in previous chapters to be fully as essential as the making of monocular tests of the refractive media. To meet this necessity, the writer has devised the Phoroptor, which is here briefly described. The instrument contains all of the essentials for making both of these tests in this way, also for giving muscle exercises.

A complete description of the Phoroptor can best be given in terms of its application, and the succeeding chapters should be closely read if a full comprehension of the construction and functioning of the instrument is to be acquired. The suggestions here offered for making the different tests with the Phoroptor will show that the instrument provides exact and complete means for determining the status of the refraction and of the motor muscles, also for strengthening any one or more of the muscles

24 THE PHORDP TOR when that is necessary and possible, through a system of gymnastics.

The Phoroptor is binocular in construction and carries on each side five fundamental elements with the necessary supplemental equipment including a near point card holder.

The Phoroptor.

Fig. 1.

The five elements are, (1) the graduated Maddox multiple white rod unit; (2) the universal double rotary, or mobile prism unit; (3) the cylindrical lens unit; (4) the fixed displacing prisms, and (5) the spherical lens unit. These five elements are mounted from front to back in the order named and are fully described in subsequent chapters.

The Phoroptor proper is supported in adjustable fashion upon a horizontal arm projecting from a wall bracket, a floor stand or a chair fixture. Each of these fixtures for carrying the Phoroptor has both coarse and fine adjustments for bringing the instrument into proper alignment with both the patient and the test objects.

The body structure of the instrument consists chiefly of two rearwardly extending arms supported by a pair of adjustable slides, each arm carrying a full complement of the five fundamental elements already mentioned for making complete monocular tests of both the refraction and the motor muscles. A lateral screw adjustment is provided for the slides, also a graduated millimeter scale, and by their use the separation of the two complete aggregations of testing units may be altered to conform with the interpupillary dimensions of the observer. A spirit level is mounted at the center of the instrument for obtaining a true horizontal setting, which is essential in securing an accurate axis for a correcting cylinder,

26 THE PHOROPTOR =: a true base for a correcting prism or an exact axis for a Maddox rod.

Mounted back of the rear shields of the spherical lens batteries are a pair of eye cups, which insure correct positioning of the eyes of the observer with respect to the sight openings in the Phoroptor. These eye cups aid materially in securing accurate results in both the refraction and muscle tests. They also offer some support for the head, thereby reducing the fatigue accompanying eye examinations and the consequent tendency to move the head out of the primary position.

Another auxiliary which is of great utility in muscle testing, is a red color filter which may be placed in operative position before either eye and which furnishes an easy and positive differentiation between the images as viewed by the two eyes.

All of the units embraced in the Phoroptor are adjustably mounted and may therefore be brought into operative alignment individually or in any desired combination. Positive and exact stops are arranged for giving perfect optical alignment to all adjustable elements when placed in operative position before the sight openings.

CHAPTER V The Maddox Rod Units

HE Maddox multiple glass rod, which is the essential part of the graduated Maddox Multiple Rod unit, comprises a lens plano on one side and multi-corrugated on the other. This lens, in effect, is similar to a number of very strong plano convex cylinder lenses placed side by side with their axes parallel. The axis of the Maddox multiple rod is therefore coincident with the direction of its corrugations and light in passing through it is distributed at right angles with its axis. Therefore, if the corrugations or axis were in a vertical position (Fig. 2) a distant spot of light viewed through the rod would be changed in appearance to a horizontal streak of light of the same width as the diameter of the spot, and conversely, if the corrugations or axis were horizontal (Fig. 3), the streak would appear in a vertical position. The corrugated glass dise or rod proper is mounted in a circular plate having a handle and two indicators. This plate is adjustably

28 LHe Paoror tox supported by a holder which has a degree scale on its upper section and by the combined use of this scale and the indicators on the plate, the amount of rotation which may be given to the rod by the handle will be denoted in degrees of arc. The nasal and the temporal

Maddox Multiple Rods with Axes Vertical. Fig. 2.

quadrants of the scale carry the minus and plus characters respectively for the classification of imbalances of the oblique muscles.

If, in looking at a point of light through the rod with axis vertical, the streak of light thus produced should appear other than horizontal, it could be corrected as to position by a ne Fe eR OF TOR 29 partial rotation of the rod in its holder, the amount of such rotation being registered upon the degree scale in the upper section of the holder. For example, should the indicator stand at the 15 degree graduation in the nasal

Maddox Multiple Rods with Axes Horizontal

Fig. 3.

quadrant of the scale, it would indicate fifteen degrees of minus cyclophoria. | Conversely should the indicator show fifteen degrees on the temporal side of zero, a corresponding amount of plus cyclophoria would be indicated, all as fully explained in chapters 16 and 17, dealing with tests of the oblique muscles.

All Maddox multiple rods should be accurately ground on both the plano and the corrugated sides. Ground rods are free from prismatic effects, distortions and other errors which are necessarily present in pressed or blown rods. Researches recently carried out by leading authorities have shown beyond question that blown or pressed Maddox rods are so defective in their function of transforming a point of light into a clearly defined and reliably located streak, that they are wholly unfitted for use in muscle work. Maddox rods which are not ground on both surfaces should therefore never be used in muscle testing instruments, for it is fully as indefensible to use blown or pressed Maddox rods as it would be to use blown or pressed trial case lenses instead of lenses which are perfectly ground. Fortunately for the public, blown or pressed trial case lenses are never used and the increasing realization of the inaccuracies of blown Maddox rods will soon demand the use of nothing but ground rods in eye testing equipment.

CHAPTER VI The Rotary Prism Units

HE universal double rotary, or mobile, prism units described herein, are similar

to the Crete and the Risley prisms and are individually composed of two 71% diopter prisms mounted back to back in separate cells. The cells have gear teeth or annular racks about their outer peripheries and engage a radial pinion which is located between them. When the prism unit is completely assembled within a circular holder forming the prism case and the radial pinion is turned by an extended milled head, the prisms are caused to rotate inversely with respect to each other about a common center. By reason of this inverse rotation, the bases of the prisms may be so interrelated that any desired prism equivalent ranging from zero to the maximum of 15 prism diopters may be obtained. When the bases of the prisms are diametrically opposed, the unit has no prism value and the indicator will then stand at zero. But when the bases of the prisms are at an angle with each other,

32 THE: PHoOoOROPTOR prism value then exists and the base of the resultant prism equivalent will be located midway upon the are of their approach. The position of base of the resultant prism equivalent would therefore always be at the 15 diop-

5 fe % a

2 8 3 26

3 2%

Double Rotary Prisms, Zero Graduations Horizontal.

Fig. 4.

ter graduation of the scale and on that side of zero with which the prism indicator is in register. The more acute the angle between the bases of the prisms becomes, as they approach each other through their inverse rotation when actuated by turning the milled head, the greater the power of the resultant prism equivalent will be, as shown by the position of the movable indicator with respect to the radial prism dioptric scale engraved upon the face of the prism case.

In order that the base of any obtainable prism equivalent may be accurately located in any angular position before the eye, the prism case has an index on either side at the 15 diopter line and is adjustably mounted in a fully graduated support. These indicators on the edge of the case co-acting with the annular degree scale on the mounting, give facility for the universal adaptability of the resultant prism base. With this construction it is evident that any prism equivalent varying in strength from zero to 15 prism diopters may be readily obtained and the base of such equivalent located on any desired meridian.

The prisms function as follows: With zero graduation of the prism scale in horizontal position and the movable indicator set therewith, as shown in Fig. 4, a rotation of the indicator upward to 4 upon the scale would give the equivalent of a 4 diopter prism with base up, while a rotation from zero downward to 4, would give the equivalent of a 4 diopter prism with base down. With zero gradua-

34 TRE: PHOROPTOR tion vertical and indicator set therewith, as shown in Fig. 5, a rotation of the indicator outward to 8 upon the scale would give the equivalent of an 8 diopter prism with base out, while a similar rotation inward from zero, ah ak 780 RSs nm hire ry Xs See

Double Rotary Prisms, Zero Graduations Vertical.

Fig. 5.

would give the equivalent of an 8 diopter prism with base in. Hence, a rotation of the indicator up or down, when the zero graduation is in a horizontal position, would give the indicated prism equivalent with base located up or down respectively. Similarly,

Ce ee PH'O:R0P TOR 35 ee when the zero graduation of the prism scale is vertical, a rotation of the indicator in or out from zero, would give the indicated prism equivalent with base in or out respectively.

The range of the double rotary prism units of the phoroptor is purposely limited to a maximum of 15 prism diopters in order that a more open and readable scale may be had and in consequence, a higher degree of accuracy obtained than would otherwise be possible from the closely graduated scale of prism units having a higher maximum range. This open scale is of especial value where measurements of low degree are required as in making the tests of the vertical muscles.

When prism power greater than 15 diopters is required, as in applying the adduction test, a supplementary fixed prism of 15 diopters may be placed in operative position, base out, in conjunction with the double rotary prism unit. This will extend the prism range of the Phoroptor to a maximum of 30 diopters when base is out. This supplementary 15 diopter fixed prism is carried in one of the shields and is so mounted that its base is always out when it is in operative position before the sight opening.