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The Practical Measurement of Accommodation and Convergence
T H E PRACTICAL M E A S U R E M E N T O F ACCOMMODATION AND CONVERGENCE HILMER G. MARTIN,
M.D.
Milwaukee, Wisconsin The measurement of accommodation near-work distance and convergence need not be time con Amplitude suming nor fatiguing to the patient in the Comparison of accommodation in performance of routine refractions. diopters and convergence in meter angles: To be guided by an accurate deter Maximum mination of the amounts of muscle func Relative, at work distance or any tion in constant use, their maximum func tions, their reserve power, and their re near point lationship to one another is by far more Reserve important than to regulate modification APPARATUS of the refractive correction by considering the position of rest alone. Three parallel rails, calibrated in diop An instrument, partially described in ters and marked in centimeters, are a previous communication,* has been de mounted upon a tiltable-beam unit and vised to facilitate the measurement of are adjustable in all directions. Lens cells the following functions in routine prac and carriers for various indicia are tice: mounted upon and are movable on the Interpupillary distance upper parallel rails. The instrument has Accommodation: expressed in diopters been described and illustrated in the ref and read directly erence. Maximum: monocular and binocular TESTS Amount in use at work distance Interpupillary distance: The lens car Range riers are set before the eyes at the mark Region " O " on the scales. The piano lenses with Relative: positive and negative ele bisecting scratch marks are then inserted ments, at any specified near- into the lens cells. Sighting from the ends work distance of, and along the rail at the eye being Reserve tested (each is done separately), the Comparison of the near add require centers of the lenses are made to coincide ment to accomplish equality in with the center of the pupils by raising or presbyopic subjects lowering the scales and bringing them in Convergence: expressed in meter- or out. The removable plate is then put angle terms and read from chart in place, resting upon the upper surfaces Maximum of the rails with the spirit-level side to Amount required at work distance ward the nose piece, the lens carriers hav Amount required at near point of ing been moved along the scales a very convergence and accommodation short distance to permit placing the plate Amount required at any near point between them on the nose-piece. The lens Reserve at work distance or any carriers are placed in contact with the plate. Sighting through the upper open * Martin, H. G. Amer. Jour. Ophth., 1938, v. grooves, the interpupillary distance is 21, Feb., p. 161. 406
MEASUREMENT OF ACCOMMODATION AND CONVERGENCE read off in millimeters. The plate is then placed at the other end of the scale just in front of, and in contact with, the card car riers, and the scales are brought in or out, raised or lowered, to correspond with the pupillary distance. The plate is then re moved. ACCOMMODATION
Maximum Accommodation Monocular. With one eye occluded, the patient is instructed to fix the gaze upon the test type on the card, which is placed well out along the scale. The examiner then slides the card carrier slowly along the rail toward the eye until the point is reached where the patient can no longer read the test type and the reading on the scale is taken in diopters. The opposite eye is then tested in the same manner. This is, of course, an application of the Prince-rule method. These tests are made without and then with the proposed cor rection in the lens cells. Referring to any of the textbook charts comparison with age normals can be made. Any differ ence between the case reading and that of the age-group normal represents in diopters the spherical strength necessary to bring the patient's maximum accom modation to the normal. To determine the amount of accommo dation required at any specified nearwork distance in centimeters, the card carrier is moved to that point on the scale and the dioptric reading recorded. This reading is expressive of the dioptric spherical-lens strength at the specified distance normally required, or the amount of accommodation in diopters used by the emmetropic eye at this point. The binocu lar function will be considered later on. Range and Region of Accommodation The card carrier is placed at the ex treme end of the scale and is then moved slowly toward the eye until the test type is just readable, and this point is read off
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on the scale. Continuing to move the card carrier toward the eye from this point, the operator notes the point at which clear vision of the test type ceases. The differ ence between the two readings shows the range and also establishes the region of accommodation. In presbyopia and high degrees of hyperopia this is especially important, and that lens is given which permits of the greatest range or which provides the desired region. This test guards against overcorrection in presby opia. Relative Accommodation These tests determine the maximum amount of accommodative effort that the eye can exert, and the maximum ability of accommodative relaxation at any specified distance. The former is spoken of as the positive, and the latter the nega tive element. Positive and negative re lative accommodation can be tested at any specified near point within normal or corrected accommodative range by means of the instrument. Negative Relative Accommodation Each eye is tested separately. The card carrier is placed at the distance from the eye at which the determination of this function is to be made. A known plus spherical lens sufficiently great to blur the test types decidedly is inserted in the lens carrier before the eye to be tested. The examiner then moves the lens carrier along the scale slowly away from the eye and toward the test card to the point where the patient is just able to read the types, where the motion is halted and the dioptric reading taken. The test is re peated with the starting position of the lens well away from the eye and where the type is clearly readable. The lens carrier is then moved toward the eye until the indicia are no longer readable and the dioptric reading again is taken.
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This is to check the former reading. The dioptric lens strength is subtracted from this scale reading and the remainder, ex pressed in diopters, is the amount of ac commodative relaxation possible for the eye at this distance. It is, of course, neces sary to correct for the amount of ac commodation normally in use at this same distance. This can be read off on the scale at the point at which the card carrier is placed, and this reading is subtracted from the remainder just de termined and expresses the negative rela tive accommodation at this specified dis tance. Positive Relative Accommodation Replacing the plus lens in the carrier with a minus lens of sufficient strength to blur the type, the test is conducted in the same way, by moving the carrier toward the test indicia until the type be comes readable, when the dioptric read ing is again taken. The dioptric lens strength is subtracted from the scale read ing; the remainder expresses in diopters the greatest amount of accommodative exertion possible for the eye at this dis tance. Correction is again made for the normal amount of accommodation in use at this distance, but this figure is added to the remainder just determined and the result is the positive relative accommoda tion for this specified distance. Example: Let us suppose that the rela tive accommodation is to be determined for a distance of 33 centimeters. Place the card carrier at the 33-centi meter mark on the scale. To test negative relative accommodation, place a 5 -diopter sphere in the lens carrier, and slowly move the carrier away from the eye to a point where the type just becomes read able. Suppose this occurs at 11 centi meters, or 9 diopters on the scale. Sub tract the lens strength, 5 diopters from 9 diopters. Four diopters, then, represents
the greatest amount of accommodative relaxation for 33 centimeters' distance. However, the normal amount of accom modation in use at this distance is found by reading the dioptric scale where the test card has been placed, in this case, 3 diopters. Subtracting this reading of 3 diopters from 4 diopters just determined, leaves 1 diopter, which is the negative relative accommodation. To test positive relative accommoda tion, replace the plus lens with a minus-5diopter sphere, moving it away from the eye until the type is clearly readable. Suppose this point is represented by 6.6 diopters on the scale. The difference be tween the dioptric lens strength, 5 diop ters, and this reading of 6.6 diopters, leaves 1.6 diopters, which represents the greatest amount of accommodative ex ertion at this distance. Since the normal amount of accommodation in use at this distance is 3 diopters, this figure must be added to the remainder just obtained and the resultant, 4.6 diopters, expresses the positive relative accommodation. The amplitude of accommodation is then also apparent for this distance. To insure comfort, the positive must at least equal the negative element at the near-work distance. This test is made first without and then with the proposed refractive cor rection. Indication is given for modifica tion of the correcting lens to insure com fort. The measurement of relaxation or ex ertion of accommodation at a specified near distance as tested by the method offered here, involves really the continu ous exertion or relaxation of accommoda tion to the greatest extent. This effect was found to be more expressive of the actual limitations of these functions, in asmuch as the interchange of lenses of successive strengths, as commonly used, permits of a return to a previous lower
MEASUREMENT OF ACCOMMODATION AND CONVERGENCE
state of activity during these exchanges, often resulting in a fatigue reaction or a stopping-short of the limit of function. Again, if too high a lens strength is used initially, or if the progressive increases are too abrupt, a false end point is often taken as true. For instance, if a patient is able to overcome plus lenses until 4 diopters is reached, it will be found that if an initial lens of 3 diopters is used, the patient fails to overcome this strength even though the limit is actually higher. The method offered here has the advan tage of imposing a constantly increasing load uninterruptedly. The amount of accommodation in con stant use, or the amount required at the patient's working distance, can be deter mined by placing the card carrier at the work distance, and reading this measure ment in diopters from the scale. Having tested the maximum amount of accom modation of which the patient is capable, and comparing that figure with the amount of accommodation in constant use at the work distance, the amount of reserve accommodation is apparent. If the amount of accommodation in constant use approaches too closely to the maxi mum amount of which the patient is capable, the reserve is insufficient and symptoms of discomfort will appear. The existence of accommodative insuffi ciency or excess are brought out by these tests. An important test in presbyopia con sists in determining the far point of ac commodation with the correcting lenses in place, each eye being tested separately. Reference is made, of course, to the farthest point of near-vision range, which should be nearly equal for the two eyes to preserve maximum comfort. An interesting and important phase of accommodative function, 'especially in presbyopic eyes, is the measurement of the
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Binocular Near Point of Accommodation The card carriers are removed from the upper scales and, with both eyes un covered, the patient is directed to fixate the test indicia on the card carrier on the lower and middle rail. This card is slowly advanced from a far position toward the eyes by means of turning the thumb screw on the side of the tubular unit. When the point is reached where the type is no longer readable, the dioptric reading is taken from the upper scale. In young patients the monocular and binocular near points of accommodation are very nearly the same, but in presby opic subjects, tested with the near refrac tive correction in place, the binocular near point of accommodation is definitely and consistently greater than the monoc ular. The monocular test is made with the visual axes parallel, but the binocular test involves convergence, so we may con clude that the convergence stimulus might account for the greater binocular nearaccommodative power. The suggestion is offered that if the binocular near point of accommodation is greater (nearer) than the near point of convergence, there is alternate fixation, which may be too rapid to be observed grossly. The monoc ular near point is influenced by the state of pupillary contraction, of course, as evidenced by the increased near point when the pin-hole disc is used. For prac tical purposes, however, the state of the pupil as it obtains in the case under test and at the distance tested is really the guide for the establishment of functional power. It has been noted in young patients that if the binocular is greater than the monocular near point of accommodation, the condition simulates that of presby opia, and the positive relative accommo dation is generally found to be low. An increase of .50 diopter sphere or more addition, for near, results in a
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greater monocular near point of accom modation ; but the binocular is not neces sarily increased, although the near point of convergence may be. In many cases, therefore, the binocular near point, with correction, is more important than the monocular reading in consideration of the convergence factor. In cases of a degree of convergence in sufficiency, the near addition which pro vides a seemingly insufficient monocular near point of accommodation will gener ally be found to give an adequate binoc ular near point of accommodation with complete comfort to the patient. Regional Accommodative Amplitude Since the term "relative accommoda tion" is considered by some to mean the relationship between accommodation and convergence for specific distances, the term "regional accommodative ampli tude" is perhaps more descriptive, and comments refer to what has been called "relative accommodation" in this paper. Binocular Relative Accommodation (or binocular regional accommodative am plitude) With both eyes uncovered, the patient is directed to fixate the indicia on the middle scale card, which is placed at the same mark on the scale at which the monocular tests were made. Then plus and minus lenses of low denomination are placed before the eyes, gradually in creasing the strength of the lenses until the indicia are no longer readable. These limits are recorded, and correction for distance made as in the monocular tests. It has been noted repeatedly that the monocular and binocular end points are not necessarily identical, even in cases in which the monocular regional accommo dative amplitude is equal in the two eyes. In many instances the binocular positive element is only half that of the monoc
ular, while the negative element is the same for both monocular and binocular tests. No cases have been observed in which the binocular positive element ex ceeded the monocular. In cases in which the binocular was appreciably less than the monocular positive element, the con vergence maximum was insufficient. How ever, some patients with a definite con vergence insufficiency manifested equal or nearly equal readings of the positive ele ment, both on monocular and binocular tests. They generally manifested good ac commodative function or even an excess. It is perhaps too elementary to point out that the spherical addition for near vision in presbyopia requires more con sideration than merely increasing the cor rection over the distance determination by some convenient rule of a definite amount of sphere for each year after average presbyopic onset. The indiscrimi nate addition of equal amounts to each eye routinely, is likewise only an estimate and not a measure of correction. The near correction should satisfy equality regard ing the near point of accommodation, the far point, and the range and region in each eye as nearly as possible. CONVERGENCE
The patient's position is maintained and both eyes are now tested simul taneously, the small card carriers being moved to the far end of the scale or re moved entirely. The middle scale is adjusted so that the first marking on the scale, which is 5, is 5 centimeters from the anterior sur face of the cornea. Maximum Convergence This phase of the subject has been cov ered in the earlier paper referred to at the beginning. In it a chart is published which simplifies the use of the instrument.
MEASUREMENT OF ACCOMMODATION AND CONVERGENCE
Reserve Convergence Noting the amount of maximum con vergence and the amount of convergence in use at the patient's usual work dis tance, the amount of reserve convergence is represented by the difference between the two readings. If the amount of con vergence in constant use approaches too closely the maximum convergence, there will necessarily be a low reserve, and CHART 1 CONVERSION
OF PRISM-DUCTION POWER METER-ANGLE VALUES
INTO
A
M.A.
A
M.A.
A
M.A.
4 S 6 7 8 9 10 11 12 13 14 15
1.24 1.54 1.87 2.18 2.46 2.79 3.12 3.42 3.70 4.05 4.36 4.66
16 17 18 19 20 21 22 23 24 25 26 27
4.97 5.06
28 29 30
8.72 9.03 9.33
5.6
5.89 6.21 6.54 6.85 7.15 7.46 7.78 8.07 8.58
consequent symptoms of discomfort, or limited ability to perform close work with comfort. At least 6 meter angles of re serve should obtain. Amplitude of Convergence A chart is appended, in which prismduction power, determined in the usual way, is converted into meter-angle values. In this way the maximum amount of relaxation of convergence added to the divergence in meter angles, expresses the patient's amplitude of convergence. Indication is given as to the proper correction which will provide a sufficient reserve and insure comfort to the patient at the work distance. By these tests the presence of con vergent insufficiency or excess is evident. These tests are performed without the correction to determine the patient's mus cular ability, and then with correction to
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determine satisfaction of the patient's re quirements. Alternate fixation or suppression is also brought out in the performance of these tests. COMPARISON OF THE ACCOMMODATIVE AND THE CONVERGENT FUNCTIONS
With the various phases of accommoda tion expressed in diopters, and conver gence expressed in meter-angle terms, the following comparisons can be made: (a) Comparison of maximum accom modation and convergence (b) Comparison of accommodation and convergence at any near point or usual work distance (c) Comparison of reserve accommo dation and convergence, maximal ly, at usual work distance, or any specified near point, which will assist in defining accommodative convergence insufficiency or ex cess. In these tests the convergence is kept constant while the accommodation is be ing determined, and the accommodation is a known quantity while the unknown convergence is being determined. In other words, all other conditions are maintained at a constant while one single function is being determined. COMMENT
In routine refractions the measurement of phoria and duction is commonly done, although the status of accommodation and convergence, maximal, relative and associated, for near-work distance is for the most part, neglected. The latter func tions cannot be surmised from the phoria and duction determinations. Without an adaptable means such as this instrument affords, these tests are necessarily time consuming, fatiguing, and not correlated. It is a simple matter to include the usual prism appliances for near-duction
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as well as for phoria examinations. Much has been written of the change occurring in the phoria status when the direction of gaze is directed elsewhere than directly ahead with visual axes par allel. Nothing has been recorded in the literature of the effect of accommodation and convergence under these conditions. This instrument is adaptable for such measurements by tilting the beam verti cally, by rotating the chin rest laterally, and readjusting the rails in relation to the changed position of the head. In cases of accommodative convergence insufficiency the latent period of accom modative action is definitely slowed down, as is seen when testing the positive rela tive accommodation for near. In alternating-suppression cases the relative accommodation is generally greater for the fixating eye. Symptomology is not always propor tionate to the existing error. The matter of the reserves offers the best solution. Patients with a high exophoria, but with a good near point of convergence, tolerate plus corrections well, since the position of rest only is faulty, and normal convergence power is present, although it may be latent. These may be designated as cases of functional accommodative convergence insufficiency. In duction insufficiency there is gen erally an accommodative spasm. In convergence insufficiency there is usually a remote near point of accom modation. In general, the greater the esophoria,
the greater is the positive relative ac commodation; which explains why some patients tolerate a definite imbalance with few symptoms. They usually have a suffi cient reserve of accommodation to satisfy overconvergence. In general, the greater the exophoria, the less is the positive relative accom modation. As a definitely high exophoria for near becomes less, the convergence near point becomes nearer in young patients. Spasm of accommodation is often due to the excess convergence impulse neces sary to overcome the exophoria. Accommodative spasm in hyperopic subjects is usually an accommodative convergence excess. The counterpart is observed in patients with so-called rela tive hyperopia, who acquire strong con vergence tendencies when they try to correct the hyperopia by strong accommotion. CONCLUSION
Inasmuch as a large number of cases of heterophoria are cured or greatly irhproved by correcting the refraction alone, greater precision in prescribing refractive corrections should be observed, not only in consideration of the positions of rest and ductions, but also with due regard to accommodation and convergence in their various phases, and their respective balance relationships; especially if a defi nite disproportion of accommodation and convergence exists. 231 West Wisconsin Avenue.
M.D.
Milwaukee, Wisconsin The measurement of accommodation near-work distance and convergence need not be time con Amplitude suming nor fatiguing to the patient in the Comparison of accommodation in performance of routine refractions. diopters and convergence in meter angles: To be guided by an accurate deter Maximum mination of the amounts of muscle func Relative, at work distance or any tion in constant use, their maximum func tions, their reserve power, and their re near point lationship to one another is by far more Reserve important than to regulate modification APPARATUS of the refractive correction by considering the position of rest alone. Three parallel rails, calibrated in diop An instrument, partially described in ters and marked in centimeters, are a previous communication,* has been de mounted upon a tiltable-beam unit and vised to facilitate the measurement of are adjustable in all directions. Lens cells the following functions in routine prac and carriers for various indicia are tice: mounted upon and are movable on the Interpupillary distance upper parallel rails. The instrument has Accommodation: expressed in diopters been described and illustrated in the ref and read directly erence. Maximum: monocular and binocular TESTS Amount in use at work distance Interpupillary distance: The lens car Range riers are set before the eyes at the mark Region " O " on the scales. The piano lenses with Relative: positive and negative ele bisecting scratch marks are then inserted ments, at any specified near- into the lens cells. Sighting from the ends work distance of, and along the rail at the eye being Reserve tested (each is done separately), the Comparison of the near add require centers of the lenses are made to coincide ment to accomplish equality in with the center of the pupils by raising or presbyopic subjects lowering the scales and bringing them in Convergence: expressed in meter- or out. The removable plate is then put angle terms and read from chart in place, resting upon the upper surfaces Maximum of the rails with the spirit-level side to Amount required at work distance ward the nose piece, the lens carriers hav Amount required at near point of ing been moved along the scales a very convergence and accommodation short distance to permit placing the plate Amount required at any near point between them on the nose-piece. The lens Reserve at work distance or any carriers are placed in contact with the plate. Sighting through the upper open * Martin, H. G. Amer. Jour. Ophth., 1938, v. grooves, the interpupillary distance is 21, Feb., p. 161. 406
MEASUREMENT OF ACCOMMODATION AND CONVERGENCE read off in millimeters. The plate is then placed at the other end of the scale just in front of, and in contact with, the card car riers, and the scales are brought in or out, raised or lowered, to correspond with the pupillary distance. The plate is then re moved. ACCOMMODATION
Maximum Accommodation Monocular. With one eye occluded, the patient is instructed to fix the gaze upon the test type on the card, which is placed well out along the scale. The examiner then slides the card carrier slowly along the rail toward the eye until the point is reached where the patient can no longer read the test type and the reading on the scale is taken in diopters. The opposite eye is then tested in the same manner. This is, of course, an application of the Prince-rule method. These tests are made without and then with the proposed cor rection in the lens cells. Referring to any of the textbook charts comparison with age normals can be made. Any differ ence between the case reading and that of the age-group normal represents in diopters the spherical strength necessary to bring the patient's maximum accom modation to the normal. To determine the amount of accommo dation required at any specified nearwork distance in centimeters, the card carrier is moved to that point on the scale and the dioptric reading recorded. This reading is expressive of the dioptric spherical-lens strength at the specified distance normally required, or the amount of accommodation in diopters used by the emmetropic eye at this point. The binocu lar function will be considered later on. Range and Region of Accommodation The card carrier is placed at the ex treme end of the scale and is then moved slowly toward the eye until the test type is just readable, and this point is read off
407
on the scale. Continuing to move the card carrier toward the eye from this point, the operator notes the point at which clear vision of the test type ceases. The differ ence between the two readings shows the range and also establishes the region of accommodation. In presbyopia and high degrees of hyperopia this is especially important, and that lens is given which permits of the greatest range or which provides the desired region. This test guards against overcorrection in presby opia. Relative Accommodation These tests determine the maximum amount of accommodative effort that the eye can exert, and the maximum ability of accommodative relaxation at any specified distance. The former is spoken of as the positive, and the latter the nega tive element. Positive and negative re lative accommodation can be tested at any specified near point within normal or corrected accommodative range by means of the instrument. Negative Relative Accommodation Each eye is tested separately. The card carrier is placed at the distance from the eye at which the determination of this function is to be made. A known plus spherical lens sufficiently great to blur the test types decidedly is inserted in the lens carrier before the eye to be tested. The examiner then moves the lens carrier along the scale slowly away from the eye and toward the test card to the point where the patient is just able to read the types, where the motion is halted and the dioptric reading taken. The test is re peated with the starting position of the lens well away from the eye and where the type is clearly readable. The lens carrier is then moved toward the eye until the indicia are no longer readable and the dioptric reading again is taken.
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This is to check the former reading. The dioptric lens strength is subtracted from this scale reading and the remainder, ex pressed in diopters, is the amount of ac commodative relaxation possible for the eye at this distance. It is, of course, neces sary to correct for the amount of ac commodation normally in use at this same distance. This can be read off on the scale at the point at which the card carrier is placed, and this reading is subtracted from the remainder just de termined and expresses the negative rela tive accommodation at this specified dis tance. Positive Relative Accommodation Replacing the plus lens in the carrier with a minus lens of sufficient strength to blur the type, the test is conducted in the same way, by moving the carrier toward the test indicia until the type be comes readable, when the dioptric read ing is again taken. The dioptric lens strength is subtracted from the scale read ing; the remainder expresses in diopters the greatest amount of accommodative exertion possible for the eye at this dis tance. Correction is again made for the normal amount of accommodation in use at this distance, but this figure is added to the remainder just determined and the result is the positive relative accommoda tion for this specified distance. Example: Let us suppose that the rela tive accommodation is to be determined for a distance of 33 centimeters. Place the card carrier at the 33-centi meter mark on the scale. To test negative relative accommodation, place a 5 -diopter sphere in the lens carrier, and slowly move the carrier away from the eye to a point where the type just becomes read able. Suppose this occurs at 11 centi meters, or 9 diopters on the scale. Sub tract the lens strength, 5 diopters from 9 diopters. Four diopters, then, represents
the greatest amount of accommodative relaxation for 33 centimeters' distance. However, the normal amount of accom modation in use at this distance is found by reading the dioptric scale where the test card has been placed, in this case, 3 diopters. Subtracting this reading of 3 diopters from 4 diopters just determined, leaves 1 diopter, which is the negative relative accommodation. To test positive relative accommoda tion, replace the plus lens with a minus-5diopter sphere, moving it away from the eye until the type is clearly readable. Suppose this point is represented by 6.6 diopters on the scale. The difference be tween the dioptric lens strength, 5 diop ters, and this reading of 6.6 diopters, leaves 1.6 diopters, which represents the greatest amount of accommodative ex ertion at this distance. Since the normal amount of accommodation in use at this distance is 3 diopters, this figure must be added to the remainder just obtained and the resultant, 4.6 diopters, expresses the positive relative accommodation. The amplitude of accommodation is then also apparent for this distance. To insure comfort, the positive must at least equal the negative element at the near-work distance. This test is made first without and then with the proposed refractive cor rection. Indication is given for modifica tion of the correcting lens to insure com fort. The measurement of relaxation or ex ertion of accommodation at a specified near distance as tested by the method offered here, involves really the continu ous exertion or relaxation of accommoda tion to the greatest extent. This effect was found to be more expressive of the actual limitations of these functions, in asmuch as the interchange of lenses of successive strengths, as commonly used, permits of a return to a previous lower
MEASUREMENT OF ACCOMMODATION AND CONVERGENCE
state of activity during these exchanges, often resulting in a fatigue reaction or a stopping-short of the limit of function. Again, if too high a lens strength is used initially, or if the progressive increases are too abrupt, a false end point is often taken as true. For instance, if a patient is able to overcome plus lenses until 4 diopters is reached, it will be found that if an initial lens of 3 diopters is used, the patient fails to overcome this strength even though the limit is actually higher. The method offered here has the advan tage of imposing a constantly increasing load uninterruptedly. The amount of accommodation in con stant use, or the amount required at the patient's working distance, can be deter mined by placing the card carrier at the work distance, and reading this measure ment in diopters from the scale. Having tested the maximum amount of accom modation of which the patient is capable, and comparing that figure with the amount of accommodation in constant use at the work distance, the amount of reserve accommodation is apparent. If the amount of accommodation in constant use approaches too closely to the maxi mum amount of which the patient is capable, the reserve is insufficient and symptoms of discomfort will appear. The existence of accommodative insuffi ciency or excess are brought out by these tests. An important test in presbyopia con sists in determining the far point of ac commodation with the correcting lenses in place, each eye being tested separately. Reference is made, of course, to the farthest point of near-vision range, which should be nearly equal for the two eyes to preserve maximum comfort. An interesting and important phase of accommodative function, 'especially in presbyopic eyes, is the measurement of the
409
Binocular Near Point of Accommodation The card carriers are removed from the upper scales and, with both eyes un covered, the patient is directed to fixate the test indicia on the card carrier on the lower and middle rail. This card is slowly advanced from a far position toward the eyes by means of turning the thumb screw on the side of the tubular unit. When the point is reached where the type is no longer readable, the dioptric reading is taken from the upper scale. In young patients the monocular and binocular near points of accommodation are very nearly the same, but in presby opic subjects, tested with the near refrac tive correction in place, the binocular near point of accommodation is definitely and consistently greater than the monoc ular. The monocular test is made with the visual axes parallel, but the binocular test involves convergence, so we may con clude that the convergence stimulus might account for the greater binocular nearaccommodative power. The suggestion is offered that if the binocular near point of accommodation is greater (nearer) than the near point of convergence, there is alternate fixation, which may be too rapid to be observed grossly. The monoc ular near point is influenced by the state of pupillary contraction, of course, as evidenced by the increased near point when the pin-hole disc is used. For prac tical purposes, however, the state of the pupil as it obtains in the case under test and at the distance tested is really the guide for the establishment of functional power. It has been noted in young patients that if the binocular is greater than the monocular near point of accommodation, the condition simulates that of presby opia, and the positive relative accommo dation is generally found to be low. An increase of .50 diopter sphere or more addition, for near, results in a
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HILMAR G. MARTIN
greater monocular near point of accom modation ; but the binocular is not neces sarily increased, although the near point of convergence may be. In many cases, therefore, the binocular near point, with correction, is more important than the monocular reading in consideration of the convergence factor. In cases of a degree of convergence in sufficiency, the near addition which pro vides a seemingly insufficient monocular near point of accommodation will gener ally be found to give an adequate binoc ular near point of accommodation with complete comfort to the patient. Regional Accommodative Amplitude Since the term "relative accommoda tion" is considered by some to mean the relationship between accommodation and convergence for specific distances, the term "regional accommodative ampli tude" is perhaps more descriptive, and comments refer to what has been called "relative accommodation" in this paper. Binocular Relative Accommodation (or binocular regional accommodative am plitude) With both eyes uncovered, the patient is directed to fixate the indicia on the middle scale card, which is placed at the same mark on the scale at which the monocular tests were made. Then plus and minus lenses of low denomination are placed before the eyes, gradually in creasing the strength of the lenses until the indicia are no longer readable. These limits are recorded, and correction for distance made as in the monocular tests. It has been noted repeatedly that the monocular and binocular end points are not necessarily identical, even in cases in which the monocular regional accommo dative amplitude is equal in the two eyes. In many instances the binocular positive element is only half that of the monoc
ular, while the negative element is the same for both monocular and binocular tests. No cases have been observed in which the binocular positive element ex ceeded the monocular. In cases in which the binocular was appreciably less than the monocular positive element, the con vergence maximum was insufficient. How ever, some patients with a definite con vergence insufficiency manifested equal or nearly equal readings of the positive ele ment, both on monocular and binocular tests. They generally manifested good ac commodative function or even an excess. It is perhaps too elementary to point out that the spherical addition for near vision in presbyopia requires more con sideration than merely increasing the cor rection over the distance determination by some convenient rule of a definite amount of sphere for each year after average presbyopic onset. The indiscrimi nate addition of equal amounts to each eye routinely, is likewise only an estimate and not a measure of correction. The near correction should satisfy equality regard ing the near point of accommodation, the far point, and the range and region in each eye as nearly as possible. CONVERGENCE
The patient's position is maintained and both eyes are now tested simul taneously, the small card carriers being moved to the far end of the scale or re moved entirely. The middle scale is adjusted so that the first marking on the scale, which is 5, is 5 centimeters from the anterior sur face of the cornea. Maximum Convergence This phase of the subject has been cov ered in the earlier paper referred to at the beginning. In it a chart is published which simplifies the use of the instrument.
MEASUREMENT OF ACCOMMODATION AND CONVERGENCE
Reserve Convergence Noting the amount of maximum con vergence and the amount of convergence in use at the patient's usual work dis tance, the amount of reserve convergence is represented by the difference between the two readings. If the amount of con vergence in constant use approaches too closely the maximum convergence, there will necessarily be a low reserve, and CHART 1 CONVERSION
OF PRISM-DUCTION POWER METER-ANGLE VALUES
INTO
A
M.A.
A
M.A.
A
M.A.
4 S 6 7 8 9 10 11 12 13 14 15
1.24 1.54 1.87 2.18 2.46 2.79 3.12 3.42 3.70 4.05 4.36 4.66
16 17 18 19 20 21 22 23 24 25 26 27
4.97 5.06
28 29 30
8.72 9.03 9.33
5.6
5.89 6.21 6.54 6.85 7.15 7.46 7.78 8.07 8.58
consequent symptoms of discomfort, or limited ability to perform close work with comfort. At least 6 meter angles of re serve should obtain. Amplitude of Convergence A chart is appended, in which prismduction power, determined in the usual way, is converted into meter-angle values. In this way the maximum amount of relaxation of convergence added to the divergence in meter angles, expresses the patient's amplitude of convergence. Indication is given as to the proper correction which will provide a sufficient reserve and insure comfort to the patient at the work distance. By these tests the presence of con vergent insufficiency or excess is evident. These tests are performed without the correction to determine the patient's mus cular ability, and then with correction to
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determine satisfaction of the patient's re quirements. Alternate fixation or suppression is also brought out in the performance of these tests. COMPARISON OF THE ACCOMMODATIVE AND THE CONVERGENT FUNCTIONS
With the various phases of accommoda tion expressed in diopters, and conver gence expressed in meter-angle terms, the following comparisons can be made: (a) Comparison of maximum accom modation and convergence (b) Comparison of accommodation and convergence at any near point or usual work distance (c) Comparison of reserve accommo dation and convergence, maximal ly, at usual work distance, or any specified near point, which will assist in defining accommodative convergence insufficiency or ex cess. In these tests the convergence is kept constant while the accommodation is be ing determined, and the accommodation is a known quantity while the unknown convergence is being determined. In other words, all other conditions are maintained at a constant while one single function is being determined. COMMENT
In routine refractions the measurement of phoria and duction is commonly done, although the status of accommodation and convergence, maximal, relative and associated, for near-work distance is for the most part, neglected. The latter func tions cannot be surmised from the phoria and duction determinations. Without an adaptable means such as this instrument affords, these tests are necessarily time consuming, fatiguing, and not correlated. It is a simple matter to include the usual prism appliances for near-duction
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as well as for phoria examinations. Much has been written of the change occurring in the phoria status when the direction of gaze is directed elsewhere than directly ahead with visual axes par allel. Nothing has been recorded in the literature of the effect of accommodation and convergence under these conditions. This instrument is adaptable for such measurements by tilting the beam verti cally, by rotating the chin rest laterally, and readjusting the rails in relation to the changed position of the head. In cases of accommodative convergence insufficiency the latent period of accom modative action is definitely slowed down, as is seen when testing the positive rela tive accommodation for near. In alternating-suppression cases the relative accommodation is generally greater for the fixating eye. Symptomology is not always propor tionate to the existing error. The matter of the reserves offers the best solution. Patients with a high exophoria, but with a good near point of convergence, tolerate plus corrections well, since the position of rest only is faulty, and normal convergence power is present, although it may be latent. These may be designated as cases of functional accommodative convergence insufficiency. In duction insufficiency there is gen erally an accommodative spasm. In convergence insufficiency there is usually a remote near point of accom modation. In general, the greater the esophoria,
the greater is the positive relative ac commodation; which explains why some patients tolerate a definite imbalance with few symptoms. They usually have a suffi cient reserve of accommodation to satisfy overconvergence. In general, the greater the exophoria, the less is the positive relative accom modation. As a definitely high exophoria for near becomes less, the convergence near point becomes nearer in young patients. Spasm of accommodation is often due to the excess convergence impulse neces sary to overcome the exophoria. Accommodative spasm in hyperopic subjects is usually an accommodative convergence excess. The counterpart is observed in patients with so-called rela tive hyperopia, who acquire strong con vergence tendencies when they try to correct the hyperopia by strong accommotion. CONCLUSION
Inasmuch as a large number of cases of heterophoria are cured or greatly irhproved by correcting the refraction alone, greater precision in prescribing refractive corrections should be observed, not only in consideration of the positions of rest and ductions, but also with due regard to accommodation and convergence in their various phases, and their respective balance relationships; especially if a defi nite disproportion of accommodation and convergence exists. 231 West Wisconsin Avenue.