EDITORIAL
Surgical Correction and Outcome of Exotropia Emilio Campos, MD he issue of surgical correction of exodeviations is still an open one. The article by Raiyawa et al1 entitled ‘‘Outcomes of 3 or 4 Horizontal Muscles Surgery in Large-Angle Exotropia’’ provides an opportunity for a discussion on this topic. When and how much surgery is needed for exotropia is still up to the decision of individual surgeons. Guidelines on these aspects, and the majority of existing clinical aspects of strabismology, are essentially not followed. Exodeviations are a continuum, generally originating at birth, for which the natural mechanisms of balance between converging and diverging forces are not as effective as they should be.2 As a result, the eyes tend to diverge, initially only occasionally and eventually more and more often. Here, anatomical causes for divergence such as orbital anomalies are not considered. If the periods of deviation per day are limited, no sensory adaptations develop. This means that patients experience diplopia. This condition is identified as exophoria. Suppression with no diplopia is found in those patients in whom, already before age 2, moments of deviation are prolonged and repeated during the day: this is defined as intermittent exotropia. The situation may evolve from exophoria, through intermittent exotropia to constant exotropia. Monocular eye closure, in bright light, is a distinctive element that characterizes exodeviations. The origin of this phenomenon is still debated, although it seems to be connected with the increased strain to motor fusion caused by high levels of illumination. The aim of exotropia surgery is to maintain normal binocular vision, which is at risk when periods of deviation prevail over those of control. Patients with intermittent exotropia are more at risk, as compared with those with exophoria, in the absence of subjective symptoms. No orthoptic treatment has been proven to be effective for exodeviations. In selected cases, surgery can be delayed by minus lenses, which favor convergence, because more accommodation is required. A surgical decision should be made when periods of deviation prevail over those of control, ideally not earlier than age 6 or 7, as exodeviations tend to increase spontaneously until age 14 or 15 because of the reduction in accommodative range and widening of the orbits. Overcorrection often aimed for in children can interrupt normal binocular vision permanently. Therefore, it should be avoided, particularly in patients with limited fusional amplitudes. On one hand, retention of normal binocular vision is guaranteed more in exodeviation (because of its tendency to slow deterioration) than in esotropia. On the other hand, a cure for exotropia cannot be achieved even with successful surgery. In fact, a relapse is common, particularly around the onset of presbiopia. Moreover, subjective symptoms, such as asthenopia, are present in exodeviation, because of the prolonged effort to keep the eye aligned, particularly for near vision. Surgery for exotropia in patients with no normal binocular vision offers limited functional advantages. Certainly, a small-angle deviation provides better distance judgments than a large-angle strabismus. Yet, several elements are responsible for the reduced stability of postsurgical results, such as lack of free alternation of fixation, amblyopia of the deviated eye, and previous surgery for esotropia (secondary exotropia). A comparison of surgical results of patients with normal binocular vision with those of patients who lack this function, as done in the article by Raiyawa et al, can be misleading. Only motor control is present in this second instance, and motor fusion does not contribute to maintaining a parallel status of the eyes. Moreover, adjustable sutures should not be used in exotropic patients with normal binocular vision because postoperative adjustment tends to cause an undercorrection for the uncontrolled role of motor fusion. Large-angle exotropia should ideally be corrected by operating on no more than 3 horizontal muscles, leaving the fourth untouched for a second procedure. It is preferable, however, for deviations not exceeding 50 prism diopters to limit surgery to 1 eye (operating on the eye less often used for fixation). Duplication (or tuck) of the medial rectus muscle is preferable as compared with resection: the results are the same, but the risks of inducing a vertical misplacement of the muscle and
T
From the University of Bologna, Bologna, Italy. Received for publication May 24, 2015; accepted May 25, 2015. The author has no funding or conflicts of interest to declare. Reprints: Emilio Campos, MD, Ophthalmology Unit, University of Bologna, S. Orsola-Malpighi Teaching Hospital, Via Palagi, 9, 40138 Bologna, Italy. E-mail: [email protected]. Copyright * 2015 by Asia Pacific Academy of Ophthalmology ISSN: 2162-0989
Asia-Pacific Journal of Ophthalmology
&
Volume 4, Number 4, July/August 2015
www.apjo.org
Copyright © 2015 Asia Pacific Academy of Ophthalmology. Unauthorized reproduction of this article is prohibited.
185
Asia-Pacific Journal of Ophthalmology
Editorial
perforation are eliminated. The final cosmetic appearance of eyes with duplicated versus resected muscles is the same: for a few weeks postoperatively, there is a bulky appearance of the conjunctiva, which flattens rapidly. Finally, the amount of recession and duplication in large-angle exotropia should range from 6 to 8 mm. Smaller amounts are ineffective and require operating on more muscles. Recess/resect or recess (duplication) on 1 eye has been proven to be much more effective than bilateral lateral rectus recession for exotropia. In extreme largeangle deviations, the third muscle operated on should be the contralateral medial rectus (with a duplication) in order to leave the lateral rectus muscle free for possible future modulation. Possible lateral incomitance induced by using too much surgery is a negligible concern in my clinical experience. A residual exodeviation in the presence of efficient motor fusion is usually an acceptable end result. Aiming toward slight overcorrection in surgery for large-angle exotropia is commonly suggested. In principle, this can be acceptable if divergent fusional amplitudes are well developed. Otherwise, patients can be left with persistent postoperative esotropia. This may need further surgery if diplopia cannot be eliminated (adults) or there is a risk of loss of binocular vision (children). A final comment pertains to the relationship between refractive errors and exodeviation. Any surgical decision for exotropia has to be made only after the total optical correction
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Volume 4, Number 4, July/August 2015
of coexisting hyperopia. Very often, surgery can be avoided in these cases. Real problems are due to the coexistence of hyperopia and exotropia. Erroneously, hyperopia is often undercorrected, thus causing asthenopia complaints, particularly after age 20. A correct approach is the total optical correction of hyperopia followed by surgery. In conclusion, some suggestions for the proper handling of exotropia have been offered here. It is hoped that in the future, perspective studies will substitute for retrospective evaluations of results in this and other areas of strabismology. Moreover, patient grouping should be obtained on the basis of surgery performed in childhood versus adulthood, and postoperative follow-up needs to be extended to at least 10 years of observation. REFERENCES 1. Raiyawa T, Jariyakosol S, Praneeprachachon P, et al. Outcomes of 3 or 4 horizontal muscles surgery in large-angle exotropia. Asia Pac J Ophthalmol. 2015;4:208Y211. 2. von Noorden GK, Campos EC. Binocular Vision and Ocular Motility Theory and Management of Strabismus. 6th Edition, CV Mosby, St. Louis, 2002. Available at: http://www.cybersight.org/bins/ content_page.asp?cid=1-2193. Accessed June 5, 2015.
Keep your eyes on the stars, and your feet on the ground. V Theodore Roosevelt
186
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* 2015 Asia Pacific Academy of Ophthalmology
Copyright © 2015 Asia Pacific Academy of Ophthalmology. Unauthorized reproduction of this article is prohibited.
Surgical Correction and Outcome of Exotropia Emilio Campos, MD he issue of surgical correction of exodeviations is still an open one. The article by Raiyawa et al1 entitled ‘‘Outcomes of 3 or 4 Horizontal Muscles Surgery in Large-Angle Exotropia’’ provides an opportunity for a discussion on this topic. When and how much surgery is needed for exotropia is still up to the decision of individual surgeons. Guidelines on these aspects, and the majority of existing clinical aspects of strabismology, are essentially not followed. Exodeviations are a continuum, generally originating at birth, for which the natural mechanisms of balance between converging and diverging forces are not as effective as they should be.2 As a result, the eyes tend to diverge, initially only occasionally and eventually more and more often. Here, anatomical causes for divergence such as orbital anomalies are not considered. If the periods of deviation per day are limited, no sensory adaptations develop. This means that patients experience diplopia. This condition is identified as exophoria. Suppression with no diplopia is found in those patients in whom, already before age 2, moments of deviation are prolonged and repeated during the day: this is defined as intermittent exotropia. The situation may evolve from exophoria, through intermittent exotropia to constant exotropia. Monocular eye closure, in bright light, is a distinctive element that characterizes exodeviations. The origin of this phenomenon is still debated, although it seems to be connected with the increased strain to motor fusion caused by high levels of illumination. The aim of exotropia surgery is to maintain normal binocular vision, which is at risk when periods of deviation prevail over those of control. Patients with intermittent exotropia are more at risk, as compared with those with exophoria, in the absence of subjective symptoms. No orthoptic treatment has been proven to be effective for exodeviations. In selected cases, surgery can be delayed by minus lenses, which favor convergence, because more accommodation is required. A surgical decision should be made when periods of deviation prevail over those of control, ideally not earlier than age 6 or 7, as exodeviations tend to increase spontaneously until age 14 or 15 because of the reduction in accommodative range and widening of the orbits. Overcorrection often aimed for in children can interrupt normal binocular vision permanently. Therefore, it should be avoided, particularly in patients with limited fusional amplitudes. On one hand, retention of normal binocular vision is guaranteed more in exodeviation (because of its tendency to slow deterioration) than in esotropia. On the other hand, a cure for exotropia cannot be achieved even with successful surgery. In fact, a relapse is common, particularly around the onset of presbiopia. Moreover, subjective symptoms, such as asthenopia, are present in exodeviation, because of the prolonged effort to keep the eye aligned, particularly for near vision. Surgery for exotropia in patients with no normal binocular vision offers limited functional advantages. Certainly, a small-angle deviation provides better distance judgments than a large-angle strabismus. Yet, several elements are responsible for the reduced stability of postsurgical results, such as lack of free alternation of fixation, amblyopia of the deviated eye, and previous surgery for esotropia (secondary exotropia). A comparison of surgical results of patients with normal binocular vision with those of patients who lack this function, as done in the article by Raiyawa et al, can be misleading. Only motor control is present in this second instance, and motor fusion does not contribute to maintaining a parallel status of the eyes. Moreover, adjustable sutures should not be used in exotropic patients with normal binocular vision because postoperative adjustment tends to cause an undercorrection for the uncontrolled role of motor fusion. Large-angle exotropia should ideally be corrected by operating on no more than 3 horizontal muscles, leaving the fourth untouched for a second procedure. It is preferable, however, for deviations not exceeding 50 prism diopters to limit surgery to 1 eye (operating on the eye less often used for fixation). Duplication (or tuck) of the medial rectus muscle is preferable as compared with resection: the results are the same, but the risks of inducing a vertical misplacement of the muscle and
T
From the University of Bologna, Bologna, Italy. Received for publication May 24, 2015; accepted May 25, 2015. The author has no funding or conflicts of interest to declare. Reprints: Emilio Campos, MD, Ophthalmology Unit, University of Bologna, S. Orsola-Malpighi Teaching Hospital, Via Palagi, 9, 40138 Bologna, Italy. E-mail: [email protected]. Copyright * 2015 by Asia Pacific Academy of Ophthalmology ISSN: 2162-0989
Asia-Pacific Journal of Ophthalmology
&
Volume 4, Number 4, July/August 2015
www.apjo.org
Copyright © 2015 Asia Pacific Academy of Ophthalmology. Unauthorized reproduction of this article is prohibited.
185
Asia-Pacific Journal of Ophthalmology
Editorial
perforation are eliminated. The final cosmetic appearance of eyes with duplicated versus resected muscles is the same: for a few weeks postoperatively, there is a bulky appearance of the conjunctiva, which flattens rapidly. Finally, the amount of recession and duplication in large-angle exotropia should range from 6 to 8 mm. Smaller amounts are ineffective and require operating on more muscles. Recess/resect or recess (duplication) on 1 eye has been proven to be much more effective than bilateral lateral rectus recession for exotropia. In extreme largeangle deviations, the third muscle operated on should be the contralateral medial rectus (with a duplication) in order to leave the lateral rectus muscle free for possible future modulation. Possible lateral incomitance induced by using too much surgery is a negligible concern in my clinical experience. A residual exodeviation in the presence of efficient motor fusion is usually an acceptable end result. Aiming toward slight overcorrection in surgery for large-angle exotropia is commonly suggested. In principle, this can be acceptable if divergent fusional amplitudes are well developed. Otherwise, patients can be left with persistent postoperative esotropia. This may need further surgery if diplopia cannot be eliminated (adults) or there is a risk of loss of binocular vision (children). A final comment pertains to the relationship between refractive errors and exodeviation. Any surgical decision for exotropia has to be made only after the total optical correction
&
Volume 4, Number 4, July/August 2015
of coexisting hyperopia. Very often, surgery can be avoided in these cases. Real problems are due to the coexistence of hyperopia and exotropia. Erroneously, hyperopia is often undercorrected, thus causing asthenopia complaints, particularly after age 20. A correct approach is the total optical correction of hyperopia followed by surgery. In conclusion, some suggestions for the proper handling of exotropia have been offered here. It is hoped that in the future, perspective studies will substitute for retrospective evaluations of results in this and other areas of strabismology. Moreover, patient grouping should be obtained on the basis of surgery performed in childhood versus adulthood, and postoperative follow-up needs to be extended to at least 10 years of observation. REFERENCES 1. Raiyawa T, Jariyakosol S, Praneeprachachon P, et al. Outcomes of 3 or 4 horizontal muscles surgery in large-angle exotropia. Asia Pac J Ophthalmol. 2015;4:208Y211. 2. von Noorden GK, Campos EC. Binocular Vision and Ocular Motility Theory and Management of Strabismus. 6th Edition, CV Mosby, St. Louis, 2002. Available at: http://www.cybersight.org/bins/ content_page.asp?cid=1-2193. Accessed June 5, 2015.
Keep your eyes on the stars, and your feet on the ground. V Theodore Roosevelt
186
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* 2015 Asia Pacific Academy of Ophthalmology
Copyright © 2015 Asia Pacific Academy of Ophthalmology. Unauthorized reproduction of this article is prohibited.
