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An Hypothesis Concerning the Etiology of Nonparalytic Strabismus*
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WILLIAM H. HAVENER
produce an adequate pupil, it is best to post" pone further attempts. Often the burn, though insufficient to explode a pupil, will cause enough damage so the treated portion of iris will atrophy away during the next few weeks. Mydriatics will help to form or maintain the new pupil. Destruction of unwanted tissue in the posterior portion of the eye calls for varying intensities of treatment. In general, retinoblastomas, angiomas, and melanomas may respond to photocoagulation. In order to treat a malignant tumor, its entire circum ference must be visible. While a small growth may actually be burned up through repeated coagulations, a more effective mech anism of destruction is the coagulation of the tumor blood supply. This is achieved by encircling a peripheral neoplasm with a solid ring of heavy photocoagulation which cuts off both retinal and choroidal vascularization of the encircled area. Obviously this is not effective against growths in the posterior pole where short posterior ciliary arteries enter directly. Large vessels leading to a tumor should not be hit with such heavy coag ulation, or severe hemorrhage develops. The large feeder vessels of a retinal angioma are said to shrink following treatment of the angioma itself. In addition to encircling tu mors, the photocoagulator beam should be directed against the substance of the lesion, with a high intensity light. The surface layers can be destroyed in this fashion, but deeper
tissue is not killed by one treatment. Experience in tumor therapy with the photocoagulator is insufficient to permit spe cific recommendations at this time. However, a trial of photocoagulation of small and ac cessible chorioretinal tumors seems reason able and is advised. Rather dramatic cases of several years of "cure" of retinoblastoma and melanoma exist. Treatment of focal chorioretinitis and perivasculitis is in the experimental stage. It is possible that the course of such inflam mations may be appreciably shortened by photocoagulation. SUMMARY
The clinical indications for photocoagula tion are: 1. Creation of chorioretinal adhesions: (a) sealing of retinal holes before detach ment; (b) supplement to surgery—combined photocoagulation and surgery, reinforcement of diathermy reaction, and walling off lim ited detachments; (c) sealing of holes in the uncommon detachments which settle com pletely with bedrest. 2. Formation of new pupil: (a) updrawn pupil and (b) pigmented secondary mem branes. 3. Destruction of unwanted tissue: (a) neoplasm and (b) inflammation. Photocoagulator use and the "minimum intensity technique" are described. 410 West 10th Avenue (10).
REFERENCE
Meyer-Schwickerath: Further progress in the field of light coagulation. Tr. Ophth. Soc. U. Kingdom, 77 :421-440, 1957.
AN H Y P O T H E S I S CONCERNING T H E ETIOLOGY O F NONPARALYTIC STRABISMUS* SAMUEL C. MCLAUGHLIN, JR.,
M.S.
Ann Arbor, Michigan
In summarizing the evidence regarding the etiology of comitant strabismus, Adler states, "a large number of patients with strabismus can be proved to have neither a
sensory or motor obstacle to fusion . . . this group of patients are sometimes said to have * F r o m t h e Department of Ophthalmology, University of Michigan Medical School.
ETIOLOGY OF NONPARALYTIC STRABISMUS strabismus on the basis of undetermined eti ology."1 The purpose of the present paper is to state an hypothesis concerning the etiol ogy of strabismus in patients of this type. According to Gesell2 and Piaget,3 it is not until the age of about four months that hu man infants start to learn that their visual images represent things which can be touched and manipulated. Consider an infant, who at this age, has a temporary or remediable ob stacle to fusion, such as delayed myelinization of the oculomotor fibers. Then, during this period of sensory-motor development, the in fant will see two different images of every object, and the two will appear to be in different places. If the child's perceptual development is to continue, one of the images must be chosen as representing the object. The remaining image will then be perceived as unreal, in the sense that it will appear to be devoid of tactile-kinesthetic properties. It will look like a mere image, a thing that cannot be touched. There is no difficulty in assuming that the child can learn to do this, for during this stage of growth he learns that there are many visual stimuli which can be seen but not touched: mirror images, cigarette smoke, sunbeams, and so forth. As an aid in differentiating between real objects and their unreal images, the strabismic child adopts the technique of perceiving all images associated with one eye as real, and all images associated with the other eye as unreal. It is this perceptual pattern which underlies the distinction between fixating eye and nonfixating eye in strabismus. Let us assume that the original obstacle to fusion persists only until the child is one year old. My hypothesis is that the real-unreal distinction, between images associated with the fixating eye and images associated with the nonfixating eye, now constitutes an ob stacle to fusion and accounts for the per sistence of the strabismic condition in the absence of any physiologic causative factor. The ages and time intervals specified in the foregoing accounts are purely illustra tive. The same sequence of events—tem
1219/133
porary obstacle to fusion, perceptual adapta tion, disappearance of the original defect, and persistence of the strabismic condition— may occur even in an adult patient. The process may require several years in an adult who has an injured external rectus; whereas the same process—learning to in terpret one image as unreal—may require only a few hours during the period of in fancy when sensory-motor maturation is the chief business of living. This real-unreal distinction can be ob served in any patient with a well-established strabismic condition who is aware of diplopia for an object. It has escaped observa tion by previous investigators because of the widespread practice of examining pa tients on a troposcope or similar instrument, particularly for research purposes. On the troposcope, all images are unreal; but if a strabismus patient can be made aware of diplopia for a real object, he will readily agree that the image associated with the fixating eye is "the real one," whereas the image associated with the non-fixating eye is "unreal" or "fake" or "make believe." In carrying out this examination, no prism should be placed before either eye. The reason for this is that the distortion in ap parent position caused by the prism may be sufficient to cause one of the two images to ap pear unreal, thus invalidating the observation. A normal binocular individual who is aware of diplopia for an object may also perceive one image as real and the other image as unreal. But he does not make this distinction as easily or as accurately as the strabismus patient does. The true strabis mus patient does not have to make a con scious judgment in choosing between the two images. As soon as he sees them, he in voluntarily sees one as real and the other as unreal, as if these properties of reality and unreality resided in the stimuli themselves. To understand why the real-unreal dis tinction is an obstacle to fusion, consider the mechanism of normal binocular fusion. When a normal individual fuses two images,
1220/134
S A M U E L c. M C L A U G H L I N ,
he does so because he interprets both of them as representing the same object. We would hardly credit him with normal binocular vision if he were to fuse the images of two different objects in the field of view. The two images having been interpreted as repre senting the same object, the appropriate optomotor reflexes are called upon to po sition the eyes in such a way as to combine the two images, and the two are seen as one. In strabismus, on the other hand, the two images of a single object are not interpreted as representing the same thing. One repre sents a real, solid object, whereas the other represents nothing, only itself—a mere im age. As a result, the optomotor reflexes appropriate to bifoveal fixation are not called into play, and an abnormal pattern of bin ocular vision results. The real-unreal distinction also constitutes the mechanism of suppression in strabis mus. A simple analogy will serve to illus trate this part of the hypothesis. Consider a patient who has a disturbance of the ocular media which causes him to see a stone wall directly in front of him at all times. The patient can see other things through the stone wall and even in the same place as the stone wall. He cannot touch or approach the stone wall, because this is a strictly ocular disorder. Given an early onset of this condition, the patient will gradually become unaware of the stone wall. He will not see it except under special conditions of viewing or with the aid of a course of training in stone wall awareness. A less hypothetic analogy is to be found in the entoptic images associated with cellu lar debris and other opacities in the re fractive media of the human eye. One can easily learn to be aware of these phenomena under ordinary conditions of viewing, and they are evidently present as visual stimuli at all times. When seen, they are perceived as unreal, and the observer makes no effort to approach or touch them. The analogy is quite direct: the strabismus patient is not ordinarily aware of his squinting eye images
JR.
for the same reason that I am not ordinarily aware of my muscae volitantes and other entoptic images. Experimental evidence supporting this en tire retionale for the etiology of strabismus has been presented in a different context in two previous papers. The evidence is of course indirect, for it is not feasible to evaluate the subjective visual experience of three-month-old infants. In the first paper of the series,4 it was shown that lessening of the real-unreal distinction has the effect of reducing the intensity of monocular sup pression in strabismus patients, so that the patients tend to become acutely aware of diplopia. The presence of constant diplopia has not been a source of confusion or an noyance to any patient who has participated in this program of research. The second paper of this series5 presented evidence that the real-unreal distinction constitutes an obstacle to fusion. In this experiment, it was shown that lessening of the real-unreal distinction, in patients who were already aware of diplopia, made some of the patients capable of fusion. The pa tients who responded to this treatment ac tually overcame angles of strabismus of as much as 30 prism diopters, indicating the presence of intact optomotor reflexes which had not been brought into play simply be cause of the interpretation of images associ ated with the nonfixating eye as unreal. This method of treatment is by no means a cure-all for comitant strabismus, but the results so far obtained are sufficient to indi cate that the real-unreal distinction, as it exists in strabismus, is a major obstacle to fusion and a prominent etiologic feature of the disorder. If the hypothesis set forth here is a correct statement of the etiology of strabismus, then the following inferences from it · are also correct: First, the condition described by Adler as strabismus of undetermined etiology is an acquired disorder. Therefore it is, in princi ple, remediable.
ETIOLOGY OF NONPARALYTIC STRABISMUS Second, the genetic facts are to be accounted for in terms of the temporary physiologic or anatomic cause of onset, and not in terms of any undetected physiologic condi-
1221/135
tion assumed to be present at the time of examination. 3536 Kresge Building.
REFERENCES
1. Adler, F. H.: Physiology of the Eye: Clinical Application. St. Louis, Mosby, 1959, ed. 3, p. 471. 2. Gesell, A., Ilg, F. L., and Bullis, G. E.: Vision: Its Development in the Infant and Child. New York, Hoeber, 1949, pp. 88-90. 3. Piaget, J., and Inhelder, B.: The Child's Conception of Space. (Translated by F. J. Langdon and J. L. Lunzer.) London, Routledge and Kegan, 1956, p. 6. 4. McLaughlin, S. C.: Increasing the awareness of diplopia in strabismic patients. Am. Orthoptic J., 9:77-88,1959. 5. : The elicitation of fusion in strabismus patients who are aware of diplopia. Am. J. Ophth., 48:148-153 (July pt. II 1959).
H O W VALID IS A SCLERAL T O N O M E T E R ? * RAYMOND E. HOGG, M.D.,
AND MATHEW ALPERN, P H . D .
Ann Arbor, Michigan The diagnosis of glaucoma is at best a most difficult task, tonometry being one of the many adjuncts in the detection of this disease. Any clinical tonometer, regardless of how accurate, must be considered in the light of what it really contributes to the di agnosis and management of glaucoma. The scleral tonometer which was introduced over 10 years ago1 has enjoyed a certain amount of popularity. Its working principles are similar to those of the well known corneal (Schi^tz) tonometer but it does not require conjunctival anesthesia and it can be used with the patients in a semi-reclining posi tion. 2 · 3 Although the scleral tonometer has been used within the past decade studies of its validity are incomplete. Hirsch 4 found that the correlation coefficient between the sec ond and third repetitions of measurements with the scleral tonometer was +0.77 and this gives an indication of how reliable the instrument is. Talcott3 made measurements with both the corneal and scleral tonometer on 23 patients and found a correlation coeffi* From the Department of Ophthalmology, Uni versity of Michigan. Presented at the meeting of the East-Central Section. Ann Arbor. January, 1960.
cient of +0.85 and concluded that this vali dated the instrument. On the other hand Cockburn5 made a study of the scleral as compared to the Schi^tz tonometer on 22 eyes known to have glaucoma and 22 nonglaucomatous controls. The corneal tonom eter quite accurately differentiated these two groups (with only two false positives and one failure) while the scleral tonometer failed to differentiate the two groups and allowed only poor discrimination. Carter 6 also has made a study of the scleral tonometer with regard to theoretical considerations relating to its use but his measurements do not include any thorough analysis of the validity of the instrument. The present study was undertaken to de termine how accurately the scleral tonometer measures the intraocular pressure with re spect to the standard corneal instrument which has been in use for over 50 years. PROCEDURE
Two separate experiments were carried out: 1. Freshly enucleated adult pig eyes were used in the following manner: Each eye was cannulated through the optic nerve6 where-
WILLIAM H. HAVENER
produce an adequate pupil, it is best to post" pone further attempts. Often the burn, though insufficient to explode a pupil, will cause enough damage so the treated portion of iris will atrophy away during the next few weeks. Mydriatics will help to form or maintain the new pupil. Destruction of unwanted tissue in the posterior portion of the eye calls for varying intensities of treatment. In general, retinoblastomas, angiomas, and melanomas may respond to photocoagulation. In order to treat a malignant tumor, its entire circum ference must be visible. While a small growth may actually be burned up through repeated coagulations, a more effective mech anism of destruction is the coagulation of the tumor blood supply. This is achieved by encircling a peripheral neoplasm with a solid ring of heavy photocoagulation which cuts off both retinal and choroidal vascularization of the encircled area. Obviously this is not effective against growths in the posterior pole where short posterior ciliary arteries enter directly. Large vessels leading to a tumor should not be hit with such heavy coag ulation, or severe hemorrhage develops. The large feeder vessels of a retinal angioma are said to shrink following treatment of the angioma itself. In addition to encircling tu mors, the photocoagulator beam should be directed against the substance of the lesion, with a high intensity light. The surface layers can be destroyed in this fashion, but deeper
tissue is not killed by one treatment. Experience in tumor therapy with the photocoagulator is insufficient to permit spe cific recommendations at this time. However, a trial of photocoagulation of small and ac cessible chorioretinal tumors seems reason able and is advised. Rather dramatic cases of several years of "cure" of retinoblastoma and melanoma exist. Treatment of focal chorioretinitis and perivasculitis is in the experimental stage. It is possible that the course of such inflam mations may be appreciably shortened by photocoagulation. SUMMARY
The clinical indications for photocoagula tion are: 1. Creation of chorioretinal adhesions: (a) sealing of retinal holes before detach ment; (b) supplement to surgery—combined photocoagulation and surgery, reinforcement of diathermy reaction, and walling off lim ited detachments; (c) sealing of holes in the uncommon detachments which settle com pletely with bedrest. 2. Formation of new pupil: (a) updrawn pupil and (b) pigmented secondary mem branes. 3. Destruction of unwanted tissue: (a) neoplasm and (b) inflammation. Photocoagulator use and the "minimum intensity technique" are described. 410 West 10th Avenue (10).
REFERENCE
Meyer-Schwickerath: Further progress in the field of light coagulation. Tr. Ophth. Soc. U. Kingdom, 77 :421-440, 1957.
AN H Y P O T H E S I S CONCERNING T H E ETIOLOGY O F NONPARALYTIC STRABISMUS* SAMUEL C. MCLAUGHLIN, JR.,
M.S.
Ann Arbor, Michigan
In summarizing the evidence regarding the etiology of comitant strabismus, Adler states, "a large number of patients with strabismus can be proved to have neither a
sensory or motor obstacle to fusion . . . this group of patients are sometimes said to have * F r o m t h e Department of Ophthalmology, University of Michigan Medical School.
ETIOLOGY OF NONPARALYTIC STRABISMUS strabismus on the basis of undetermined eti ology."1 The purpose of the present paper is to state an hypothesis concerning the etiol ogy of strabismus in patients of this type. According to Gesell2 and Piaget,3 it is not until the age of about four months that hu man infants start to learn that their visual images represent things which can be touched and manipulated. Consider an infant, who at this age, has a temporary or remediable ob stacle to fusion, such as delayed myelinization of the oculomotor fibers. Then, during this period of sensory-motor development, the in fant will see two different images of every object, and the two will appear to be in different places. If the child's perceptual development is to continue, one of the images must be chosen as representing the object. The remaining image will then be perceived as unreal, in the sense that it will appear to be devoid of tactile-kinesthetic properties. It will look like a mere image, a thing that cannot be touched. There is no difficulty in assuming that the child can learn to do this, for during this stage of growth he learns that there are many visual stimuli which can be seen but not touched: mirror images, cigarette smoke, sunbeams, and so forth. As an aid in differentiating between real objects and their unreal images, the strabismic child adopts the technique of perceiving all images associated with one eye as real, and all images associated with the other eye as unreal. It is this perceptual pattern which underlies the distinction between fixating eye and nonfixating eye in strabismus. Let us assume that the original obstacle to fusion persists only until the child is one year old. My hypothesis is that the real-unreal distinction, between images associated with the fixating eye and images associated with the nonfixating eye, now constitutes an ob stacle to fusion and accounts for the per sistence of the strabismic condition in the absence of any physiologic causative factor. The ages and time intervals specified in the foregoing accounts are purely illustra tive. The same sequence of events—tem
1219/133
porary obstacle to fusion, perceptual adapta tion, disappearance of the original defect, and persistence of the strabismic condition— may occur even in an adult patient. The process may require several years in an adult who has an injured external rectus; whereas the same process—learning to in terpret one image as unreal—may require only a few hours during the period of in fancy when sensory-motor maturation is the chief business of living. This real-unreal distinction can be ob served in any patient with a well-established strabismic condition who is aware of diplopia for an object. It has escaped observa tion by previous investigators because of the widespread practice of examining pa tients on a troposcope or similar instrument, particularly for research purposes. On the troposcope, all images are unreal; but if a strabismus patient can be made aware of diplopia for a real object, he will readily agree that the image associated with the fixating eye is "the real one," whereas the image associated with the non-fixating eye is "unreal" or "fake" or "make believe." In carrying out this examination, no prism should be placed before either eye. The reason for this is that the distortion in ap parent position caused by the prism may be sufficient to cause one of the two images to ap pear unreal, thus invalidating the observation. A normal binocular individual who is aware of diplopia for an object may also perceive one image as real and the other image as unreal. But he does not make this distinction as easily or as accurately as the strabismus patient does. The true strabis mus patient does not have to make a con scious judgment in choosing between the two images. As soon as he sees them, he in voluntarily sees one as real and the other as unreal, as if these properties of reality and unreality resided in the stimuli themselves. To understand why the real-unreal dis tinction is an obstacle to fusion, consider the mechanism of normal binocular fusion. When a normal individual fuses two images,
1220/134
S A M U E L c. M C L A U G H L I N ,
he does so because he interprets both of them as representing the same object. We would hardly credit him with normal binocular vision if he were to fuse the images of two different objects in the field of view. The two images having been interpreted as repre senting the same object, the appropriate optomotor reflexes are called upon to po sition the eyes in such a way as to combine the two images, and the two are seen as one. In strabismus, on the other hand, the two images of a single object are not interpreted as representing the same thing. One repre sents a real, solid object, whereas the other represents nothing, only itself—a mere im age. As a result, the optomotor reflexes appropriate to bifoveal fixation are not called into play, and an abnormal pattern of bin ocular vision results. The real-unreal distinction also constitutes the mechanism of suppression in strabis mus. A simple analogy will serve to illus trate this part of the hypothesis. Consider a patient who has a disturbance of the ocular media which causes him to see a stone wall directly in front of him at all times. The patient can see other things through the stone wall and even in the same place as the stone wall. He cannot touch or approach the stone wall, because this is a strictly ocular disorder. Given an early onset of this condition, the patient will gradually become unaware of the stone wall. He will not see it except under special conditions of viewing or with the aid of a course of training in stone wall awareness. A less hypothetic analogy is to be found in the entoptic images associated with cellu lar debris and other opacities in the re fractive media of the human eye. One can easily learn to be aware of these phenomena under ordinary conditions of viewing, and they are evidently present as visual stimuli at all times. When seen, they are perceived as unreal, and the observer makes no effort to approach or touch them. The analogy is quite direct: the strabismus patient is not ordinarily aware of his squinting eye images
JR.
for the same reason that I am not ordinarily aware of my muscae volitantes and other entoptic images. Experimental evidence supporting this en tire retionale for the etiology of strabismus has been presented in a different context in two previous papers. The evidence is of course indirect, for it is not feasible to evaluate the subjective visual experience of three-month-old infants. In the first paper of the series,4 it was shown that lessening of the real-unreal distinction has the effect of reducing the intensity of monocular sup pression in strabismus patients, so that the patients tend to become acutely aware of diplopia. The presence of constant diplopia has not been a source of confusion or an noyance to any patient who has participated in this program of research. The second paper of this series5 presented evidence that the real-unreal distinction constitutes an obstacle to fusion. In this experiment, it was shown that lessening of the real-unreal distinction, in patients who were already aware of diplopia, made some of the patients capable of fusion. The pa tients who responded to this treatment ac tually overcame angles of strabismus of as much as 30 prism diopters, indicating the presence of intact optomotor reflexes which had not been brought into play simply be cause of the interpretation of images associ ated with the nonfixating eye as unreal. This method of treatment is by no means a cure-all for comitant strabismus, but the results so far obtained are sufficient to indi cate that the real-unreal distinction, as it exists in strabismus, is a major obstacle to fusion and a prominent etiologic feature of the disorder. If the hypothesis set forth here is a correct statement of the etiology of strabismus, then the following inferences from it · are also correct: First, the condition described by Adler as strabismus of undetermined etiology is an acquired disorder. Therefore it is, in princi ple, remediable.
ETIOLOGY OF NONPARALYTIC STRABISMUS Second, the genetic facts are to be accounted for in terms of the temporary physiologic or anatomic cause of onset, and not in terms of any undetected physiologic condi-
1221/135
tion assumed to be present at the time of examination. 3536 Kresge Building.
REFERENCES
1. Adler, F. H.: Physiology of the Eye: Clinical Application. St. Louis, Mosby, 1959, ed. 3, p. 471. 2. Gesell, A., Ilg, F. L., and Bullis, G. E.: Vision: Its Development in the Infant and Child. New York, Hoeber, 1949, pp. 88-90. 3. Piaget, J., and Inhelder, B.: The Child's Conception of Space. (Translated by F. J. Langdon and J. L. Lunzer.) London, Routledge and Kegan, 1956, p. 6. 4. McLaughlin, S. C.: Increasing the awareness of diplopia in strabismic patients. Am. Orthoptic J., 9:77-88,1959. 5. : The elicitation of fusion in strabismus patients who are aware of diplopia. Am. J. Ophth., 48:148-153 (July pt. II 1959).
H O W VALID IS A SCLERAL T O N O M E T E R ? * RAYMOND E. HOGG, M.D.,
AND MATHEW ALPERN, P H . D .
Ann Arbor, Michigan The diagnosis of glaucoma is at best a most difficult task, tonometry being one of the many adjuncts in the detection of this disease. Any clinical tonometer, regardless of how accurate, must be considered in the light of what it really contributes to the di agnosis and management of glaucoma. The scleral tonometer which was introduced over 10 years ago1 has enjoyed a certain amount of popularity. Its working principles are similar to those of the well known corneal (Schi^tz) tonometer but it does not require conjunctival anesthesia and it can be used with the patients in a semi-reclining posi tion. 2 · 3 Although the scleral tonometer has been used within the past decade studies of its validity are incomplete. Hirsch 4 found that the correlation coefficient between the sec ond and third repetitions of measurements with the scleral tonometer was +0.77 and this gives an indication of how reliable the instrument is. Talcott3 made measurements with both the corneal and scleral tonometer on 23 patients and found a correlation coeffi* From the Department of Ophthalmology, Uni versity of Michigan. Presented at the meeting of the East-Central Section. Ann Arbor. January, 1960.
cient of +0.85 and concluded that this vali dated the instrument. On the other hand Cockburn5 made a study of the scleral as compared to the Schi^tz tonometer on 22 eyes known to have glaucoma and 22 nonglaucomatous controls. The corneal tonom eter quite accurately differentiated these two groups (with only two false positives and one failure) while the scleral tonometer failed to differentiate the two groups and allowed only poor discrimination. Carter 6 also has made a study of the scleral tonometer with regard to theoretical considerations relating to its use but his measurements do not include any thorough analysis of the validity of the instrument. The present study was undertaken to de termine how accurately the scleral tonometer measures the intraocular pressure with re spect to the standard corneal instrument which has been in use for over 50 years. PROCEDURE
Two separate experiments were carried out: 1. Freshly enucleated adult pig eyes were used in the following manner: Each eye was cannulated through the optic nerve6 where-