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Early Surgery in Intermittent Exotropia
EARLY SURGERY IN I N T E R M I T T E N T EXOTROPIA J. A.
PRATT-JOHNSON,
F.R.C.S.(C), J. M.
B A R L O W , AND
G.
TILLSON
Vancouver, British Columbia
Intermittent exotropia of the diver gence excess type is characterized by an exodeviation that is greater at a distance of 20 feet or more than at a near distance. In a child with intermittent exotropia, unconscious divergence of one eye is often noted before 18 months of age, par ticularly when the child is tired, day dreaming, or looking into the distance. H e may close and rub one eye in bright sunlight. Suppression associated with in termittent exotropia permits the eye to become divergent without diplopia and usually without the patient's awareness. Vision is suppressed in the deviated eye when the eye diverges, and disappears when the eye is straight or convergent. In contrast, the exophoric patient experienc es diplopia every time his eye diverges. The causes of the initial divergence in intermittent exotropia are not clear, but the suppression makes it impossible for patients to control the deviation. Diver gence fusional amplitudes are character istically absent in intermittent exotropia. Despite excellent articles on the treat ment of intermittent exotropia, the effect of such treatment on the sensory state has been insufficiently emphasized. Suppres sion, in intermittent exotropia, is "switched off" when the eyes are straight or in the esotropie position. Hence, at near, where most patients with intermit tent exotropia control, 40 seconds of arc stereopsis with the Wirth four-dot stereo scopic test can usually be recorded before any treatment has been instituted. Thus, From the Department of Ophthalmology, Univer sity of British Columbia and the Vancouver General Hospital, Vancouver, British Columbia, Canada. Reprint requests to John A. Pratt-Johnson, M.B., Department of Ophthalmology, University of Brit ish Columbia, 2550 Willow St., Vancouver, British Columbia, V5Z 3N9, Canada.
assessment of the sensory state must in volve tests for the presence or absence of suppression while the eyes are divergent. Such tests must include the demonstra tion of the presence or absence of a nor mal divergence fusional amplitude with diplopia on exceeding it. Preoccupation with the final motor position of the eyes and overall appearance has preempted the possibility of converting an intermittent exotropia to a tiny, almost unnoticeable secondary esotropia with a monofixating syndrome 1 (one fovea suppressed with peripheral fusion under binocular condi tions). We designed this study to deter mine whether the suppression associated with intermittent exotropia of the diver gence excess type could be eradicated with surgery, and whether there was a danger of producing a different type of suppression in over-corrected patients. S U B J E C T S AND M E T H O D S
All 100 cases included in this study fulfilled the following criteria: (1) Greater preoperative exodeviation was present at 20 feet and beyond compared to near measurement at approximately 14 inches. If a refractive error was present the full optical correction was used in recording these measurements. Additional +3.00 lenses were not used for the near mea surement. (2) Parents observed their chil dren for two months before surgery and agreed that exodeviation was manifest at distant fixation when the patient was day dreaming or tired. (3) Presumed or tested equal vision was in both eyes. (4) No orthoptic treatment was done pre- or postoperatively. (5) Patients were sufficiently cooperative to perform the cover and cross-cover tests preoperatively, demon strate fusional amplitudes on the troposcope, and perform the Wirth stereoscop-
689
690
AMERICAN JOURNAL OF OPHTHALMOLOGY
ic test postoperatively. These require ments necessitated a follow-up period lasting until most patients were over 6 years of age. (6) Associated vertical stra bismus was no more than 6 prism diop ters at 20 feet. (7) Neurological status was normal. (8) There was a follow-up period of at least one year. Some of the patients in the study had been followed for eight years. Seven patients who had reoperation for recurrent intermittent exotropia were included because a follow-up period of more than one year was present between surgeries. We added patients to the series consec utively over the past eight years as they were found to fulfill all the criteria. We measured all deviations with prisms by using the cover and cross-cover tests at near fixation, 20 feet, and looking out the window at a target at infinity. Further measurements in side gaze, straight up, and downgaze with fixation at 20 feet were done whenever possible. Using the Wirth vectograph, we recorded stereoacuity if patients were sufficiently mature. If a refractive error was present, the full optical correction was worn for all measurements and tests. All patients had surgery on at least two horizontal rectus muscles; 95 had reces sion of both lateral rectus muscles, five had recession-resection surgery on the same eye. Eleven patients with a V pat tern had bilateral inferior oblique myectomies at the same time as their horizon tal muscle surgery; one patient had a single inferior oblique myectomy at the same time as the horizontal surgery. We examined all patients on the first or second postoperative day and these meas urements were recorded as the immediate postoperative results. At this time, prism cover and cross-cover tests were done with the patient fixing targets at near, 20 feet, and out of the window at infinity. Patients were examined at intervals until at least one year after surgery and until
NOVEMBER, 1977
they had attained an age and level of maturity necessary to understand and perform the sensory tests. We then evalu ated their sensory and motor status and we used this information as the final assessment. Results of cover and crosscover tests using prisms for measurement fixing at near, 20 feet, and out of the window at infinity, were reported. Wirth stereoacuity at near was recorded. Paying particular attention to the presence of divergence amplitudes, we tested all pa tients with fusion slides on the troposcope. A normal response was recorded only if the divergence amplitudes were at least five prism diopters and only if the patient had diplopia when the divergence amplitudes were exceeded. All patients with normal divergence amplitudes also had good convergence amplitudes, the total amplitudes were at least 20 prism diopters. Although we measured stereoacuity at near with the Wirth test on all patients, we paid particular attention to this test in those patients with any postoperative eso tropie deviation to exclude a monofix ation syndrome with fusion but with de fective stereoscopic acuity.2 The risk of permanent esotropia is pres ent, not only in those patients who are esotropie in the immediate postoperative period, but also in those who are orthophoric. Careful follow-up of this group is essential as the following case report demonstrates. CASE REPORT At the age of 2V2 years this girl had an intermittent exotropia of 45 prism diopters in the distance. Ductions and versions were normal. There was no in crease in the deviation past 20 feet. The cycloplegic refraction was +0.50 in both eyes. The fundi were normal. At age 23 months an 8-mm-recession of the right lateral rectus muscle and a 6-mm-resection of the right medial rectus muscle were performed under general anesthesia. On the first postoperative day, at 20 feet and at near, we detected an obvious over correction of 20 prism diopters of esotropia. This esotropia disappeared within a month and thé child appeared to be orthophoric at 20 feet in the
VOL. 84, NO. 5
INTERMITTENT EXOTROPIA
primary position, in up-, down-, and sidegaze. There was also no deviation at near or infinity. The child was brought back four years later and we then found the visual acuity was R.E.: 6/9 (20/30), and L.E.: 6/6 (20/20). A small angle right esotropia of four prism diopters at 20 feet and 6 prism diopters at near was noted. Weak peripheral fusion with amplitudes of eight prism diopters in the presence of anomalous retinal correspondence on the troposcope was re corded. This case shows the danger of permanent esotropia developing even though the patient had no deviation one month after operation. It is possible that a tiny esotropie flick might have been missed one month postoperatively; one must look carefully and repeatedly for any persistent esotropie devia tion. RESULTS
Patients were divided into cured and noncured groups. The 41 cured patients fulfilled the following criteria at least one year postoperatively: (1) absence of clo sure of one eye in sunlight; (2) no mani fest tropia at any distance; (3) Wirth test results indicating equal vision with stereopsis at near of 40 seconds; (4) divergence amplitude of at least five prism diopters on the troposcope using a foveal fusion slide; (5) the recognition of diplopia im mediately when the divergence ampli tude was exceeded; (6) good convergence amplitude was present, the total conver gence and divergence amplitude exceed ed 20 prism diopters on the troposcope. Fifty-nine patients did not fulfill the above criteria and were listed as noncured. We compared the immediate postopera tive muscle balance of the eyes at 20 feet
691
in the primary position with the full opti cal correction in place and the final result under the same circumstances (Table 1). Statistical analysis of the cure rate in the three groups (orthophoric, esotropie, and exotropic deviations) showed no signifi cant difference with the chi-square test at any level. Comparison of a pooled orthophoric plus esotropie deviation vs exotropic de viation also showed the same cure ratio in both groups. Therefore, the immediate postoperative muscle balance does not statistically influence the final result. Per manent esotropia only occurred in pa tients who were orthophoric or esotropie immediately after operation. The chisquare test showed this to be highly sig nificant (P=.005). We examined the muscle imbalance measured at 20 feet at least a year postop eratively in the noncured group (Table 2). Forty of these 59 patients were within ten prism diopters of being straight and were thus cosmetically satisfactory; adding these 40 to the cure group yields an over all result of 8 1 % cosmetically satisfactory patients. Eleven patients showed the characteristics of a monofixating syn drome with fusion arid gross stereoscopic acuity associated with a small angle esotropia. 1 Only one of these 11 patients was younger than age 6 at the time of the final evaluation, the median age of the group was 8 years. The importance of including the Wirth four-dot stereoscopic
TABLE 1 COMPARISON OF THE IMMEDIATE POSTOPERATIVE MUSCLE BALANCE AND THE FINAL POSTOPERATIVE RESULT
Immediate Postoperative Position
No. of Patients (%)
Cured (%)
Esotropia
Exòtropia
Orthophoria Esotropie Exotropic Total
27 (27) 40 (40) 33 (33) 100
13 (48) 18 (45) 10 (30) 41
5 10 0 15
9 12 23 44
Noncured
692
AMERICAN JOURNAL OF OPHTHALMOLOGY
NOVEMBER, 1977
TABLE 2 MUSCLE IMBALANCE IN NONCUHED GROUP AT LEAST ONE YEAR POSTOPERATIVE
Esotropia under 10 prism diopters with fusion and stereopsis (monofixation syndrome) Esotropia under 10 prism diopters without fusion Esotropia (blind spot) 35 prism diopters Exotropia under 10 prism diopters Exotropia over 10 prism diopters Total no. of patients
test in the final evaluation was to help identify the monofixation syndrome after treatment.2 We divided the 100 patients into two age groups (Table 3); 39 were under age 4 years and 61 were aged 4 or older at the time of surgery. The median age of the under-4 group was 2V2 years, whereas in those 4 and over, it was 5V2 years. The patients in the younger group were often those noticed by observant parents and brought for examination before age 3; and the older group consisted of those who were likely being teased at school. The youngest patient was IV2 years old at the time of surgery. Only four patients were over 7 years of age, the oldest was 11 years old. The oldest patient to be cured was operated on at age 10 years. Sixty-one percent of the patients in the under-fouryear age group were cured, compared to only 28% of the 4-and-over age group. The chi-square test showed this differ ence to be highly significant (P<.001).
11 2 2 27 17 59
Amblyopia occurred as a complication of secondary esotropia only in the young er group. Three patients had vision of 6/12 (20/40) in the poorer eye, and one had 6/9 (20/30). The chi-square test com paring the amblyopia rates in the age groups under 4 years and 4 years and older, showed a significant difference (.01
TABLE 3 RELATIONSHIP BETWEEN THE AGE AT TIME OF SURGERY AND THE FINAL RESULT
Exotropia Exotropia Blind Under Over Total Cured Monofixators Monofixators Spot 10 prism 10 prism Patients (%) With Fusion Without Fusion Mechanism diopters diopters Amblyopia Under 4 years of age (median age 2V2) 4 years of age and over (median age 5VÎ) Total
39
24 (61)
61
17 (28) 41
100
3
24
14
11
27
17
VOL. 84, NO. 5
INTERMITTENT EXOTROPIA
Two patients who had increased small postoperative esotropie deviations to 35 prism diopters were considered to have blind spot mechanisms. Both these pa tients were still being treated with prisms one year after surgery. In five (12%) of those cured and in 18 (30%) of the noncures, a small associated vertical strabis mus was detected either before or after surgery, at 20 feet in the primary position. Many vertical deviations seen for the first time postoperatively may have been pre sent before surgery, but were undetected. All five patients in the cure group exhibit ed a vertical strabismus under six prism diopters preoperatively, and no measur able vertical discrepancy postoperatively. In only one case was vertical muscle sur gery aimed specifically to cure the small vertical imbalance present before surgery. Thirty percent of the noncured group had a measurable vertical strabismus at 20 feet in the primary position after surgery and, in most cases, this was not detected before surgery. The cure rate was decreased by the presence of a vertical strabismus. The chi-square test showed this to be significant (.025
Although 81% of the patients were cosmetically satisfactory with a manifest strabismus of 10 prism diopters or less one year after surgery, only 41% were cured. The most important factor in obtaining a cure was the age at which surgical realignment was undertaken. Surgery performed at a median age of 2l/2 years was associated with a higher cure rate than surgery three years later. The pres ence of a vertical strabismus decreased the chance of a cure being obtained. Strabismic amblyopia from persistent overcorrection occurred only in the younger age group and is an inherent danger of early surgery. The possibility of changing intermittent exotropia, by surgical over-
693
correction, into a permanent small angle esotropia with monofixating syndrome is more likely in the younger age group. This study did not support previous data recommending over-correction of in termittent exotropia for best results. 3-5 Statistical analysis of our data showed no significant difference as to whether the eyes were esotropically or exotropically deviated, or orthophoric, in the immedi ate postoperative period. Preoccupation with the motor and cosmetic effects, rath er than the sensory result, may confuse the issue. This study demonstrates the danger of neglecting over-correction with the production of a monofixating syn drome with or without amblyopia or an esotropia without fusion. The cure rate was also adversely affect ed by the presence of a small vertical strabismus. In most of the cases, an asso ciated paretic muscle weakness was not identifiable but a concomitant difference in height was. Every effort should be made, before operation, to identify a vertical strabismus and fashion treatment to cure it. SUMMARY
We studied the results of surgery on 100 patients with intermittent exotropia of the divergence excess type. The pres ence of normal divergence and conver gence amplitudes, with diplopia when these were exceeded, and the presence of 40 seconds of arc stereoscopic acuity at near were used as evidence of a sensory cure. Forty-one patients were cured. Surgery before the age of 4 years was the most significant factor in obtaining a cure. The presence of a small vertical strabismus decreased the chances of ob taining a cure. Over-correction in the im mediate postoperative period was not a significant factor. The danger of persistent esotropia, par ticularly in young patients, was demon strated by 11 patients with the monofix ation syndrome, four with amblyopia.
694
AMERICAN JOURNAL OF OPHTHALMOLOGY REFERENCES
1. Parks, M. M.: Ocular Motility and Strabismus, Hagerstown, Harper and Row, 1975, pp. 123-131. 2. : Stereoacuity as an indicator of bifixation. In Arruga A. (ed): International Strabismus Symposium, Giessen, 1966, Basel, S. Karger, 1968.
NOVEMBER, 1977
3. Cooper, E. L.: Purposeful overcorrection of exotropia. In Arruga, A. (ed): International Strabis mus Symposium, Giessen, 1966, Basel, S. Karger, 1968. 4. Raab, E. L., and Parks, M. NI.: Recession of the lateral recti. Arch. Ophthalmol. 82:203,1969. 5. : Recession of the lateral recti. Arch. Ophthalmol. 93:584,1975.
OPHTHALMIC MINIATURE
There exists another variety of false sight, that Plenk has denomi nated metamorphopsia, and in which objects appear changed in their natural qualities, producing error of form, error of motion, error of number, and error of colour. I had a patient in Lisbon who fancied that all the horses he saw carried horns or extensive antlers. A young lady whom I attended beheld every one of a gigantic height. Dr. Priestley has given a curious case of error of colour in five brothers and two sisters, all adults. One of the brothers could form no idea whatever of colours, though he judged very accurately of the form and other qualities of objects; hence he thought stockings were sufficiently distinguished by the name of stockings, and could not conceive the necessity of calling them white or black. He could perceive cherries on a tree; but only distinguished them, even when red-ripe, from the surrounding leaves by their size and shape. One of the brothers appeared to have a faint sense of a few colours, but still a very imperfect notion; and, upon the whole, they did not seem to possess any other distinguishing power than that of light and shade, into which they resolved all the colours presented to them,—so that dove or straw colour were regarded as white; and green, crimson, and purple, as black or dark. J. G. Millingen, Curiosities of Medical Experience London, Richard Bentley, 1839
PRATT-JOHNSON,
F.R.C.S.(C), J. M.
B A R L O W , AND
G.
TILLSON
Vancouver, British Columbia
Intermittent exotropia of the diver gence excess type is characterized by an exodeviation that is greater at a distance of 20 feet or more than at a near distance. In a child with intermittent exotropia, unconscious divergence of one eye is often noted before 18 months of age, par ticularly when the child is tired, day dreaming, or looking into the distance. H e may close and rub one eye in bright sunlight. Suppression associated with in termittent exotropia permits the eye to become divergent without diplopia and usually without the patient's awareness. Vision is suppressed in the deviated eye when the eye diverges, and disappears when the eye is straight or convergent. In contrast, the exophoric patient experienc es diplopia every time his eye diverges. The causes of the initial divergence in intermittent exotropia are not clear, but the suppression makes it impossible for patients to control the deviation. Diver gence fusional amplitudes are character istically absent in intermittent exotropia. Despite excellent articles on the treat ment of intermittent exotropia, the effect of such treatment on the sensory state has been insufficiently emphasized. Suppres sion, in intermittent exotropia, is "switched off" when the eyes are straight or in the esotropie position. Hence, at near, where most patients with intermit tent exotropia control, 40 seconds of arc stereopsis with the Wirth four-dot stereo scopic test can usually be recorded before any treatment has been instituted. Thus, From the Department of Ophthalmology, Univer sity of British Columbia and the Vancouver General Hospital, Vancouver, British Columbia, Canada. Reprint requests to John A. Pratt-Johnson, M.B., Department of Ophthalmology, University of Brit ish Columbia, 2550 Willow St., Vancouver, British Columbia, V5Z 3N9, Canada.
assessment of the sensory state must in volve tests for the presence or absence of suppression while the eyes are divergent. Such tests must include the demonstra tion of the presence or absence of a nor mal divergence fusional amplitude with diplopia on exceeding it. Preoccupation with the final motor position of the eyes and overall appearance has preempted the possibility of converting an intermittent exotropia to a tiny, almost unnoticeable secondary esotropia with a monofixating syndrome 1 (one fovea suppressed with peripheral fusion under binocular condi tions). We designed this study to deter mine whether the suppression associated with intermittent exotropia of the diver gence excess type could be eradicated with surgery, and whether there was a danger of producing a different type of suppression in over-corrected patients. S U B J E C T S AND M E T H O D S
All 100 cases included in this study fulfilled the following criteria: (1) Greater preoperative exodeviation was present at 20 feet and beyond compared to near measurement at approximately 14 inches. If a refractive error was present the full optical correction was used in recording these measurements. Additional +3.00 lenses were not used for the near mea surement. (2) Parents observed their chil dren for two months before surgery and agreed that exodeviation was manifest at distant fixation when the patient was day dreaming or tired. (3) Presumed or tested equal vision was in both eyes. (4) No orthoptic treatment was done pre- or postoperatively. (5) Patients were sufficiently cooperative to perform the cover and cross-cover tests preoperatively, demon strate fusional amplitudes on the troposcope, and perform the Wirth stereoscop-
689
690
AMERICAN JOURNAL OF OPHTHALMOLOGY
ic test postoperatively. These require ments necessitated a follow-up period lasting until most patients were over 6 years of age. (6) Associated vertical stra bismus was no more than 6 prism diop ters at 20 feet. (7) Neurological status was normal. (8) There was a follow-up period of at least one year. Some of the patients in the study had been followed for eight years. Seven patients who had reoperation for recurrent intermittent exotropia were included because a follow-up period of more than one year was present between surgeries. We added patients to the series consec utively over the past eight years as they were found to fulfill all the criteria. We measured all deviations with prisms by using the cover and cross-cover tests at near fixation, 20 feet, and looking out the window at a target at infinity. Further measurements in side gaze, straight up, and downgaze with fixation at 20 feet were done whenever possible. Using the Wirth vectograph, we recorded stereoacuity if patients were sufficiently mature. If a refractive error was present, the full optical correction was worn for all measurements and tests. All patients had surgery on at least two horizontal rectus muscles; 95 had reces sion of both lateral rectus muscles, five had recession-resection surgery on the same eye. Eleven patients with a V pat tern had bilateral inferior oblique myectomies at the same time as their horizon tal muscle surgery; one patient had a single inferior oblique myectomy at the same time as the horizontal surgery. We examined all patients on the first or second postoperative day and these meas urements were recorded as the immediate postoperative results. At this time, prism cover and cross-cover tests were done with the patient fixing targets at near, 20 feet, and out of the window at infinity. Patients were examined at intervals until at least one year after surgery and until
NOVEMBER, 1977
they had attained an age and level of maturity necessary to understand and perform the sensory tests. We then evalu ated their sensory and motor status and we used this information as the final assessment. Results of cover and crosscover tests using prisms for measurement fixing at near, 20 feet, and out of the window at infinity, were reported. Wirth stereoacuity at near was recorded. Paying particular attention to the presence of divergence amplitudes, we tested all pa tients with fusion slides on the troposcope. A normal response was recorded only if the divergence amplitudes were at least five prism diopters and only if the patient had diplopia when the divergence amplitudes were exceeded. All patients with normal divergence amplitudes also had good convergence amplitudes, the total amplitudes were at least 20 prism diopters. Although we measured stereoacuity at near with the Wirth test on all patients, we paid particular attention to this test in those patients with any postoperative eso tropie deviation to exclude a monofix ation syndrome with fusion but with de fective stereoscopic acuity.2 The risk of permanent esotropia is pres ent, not only in those patients who are esotropie in the immediate postoperative period, but also in those who are orthophoric. Careful follow-up of this group is essential as the following case report demonstrates. CASE REPORT At the age of 2V2 years this girl had an intermittent exotropia of 45 prism diopters in the distance. Ductions and versions were normal. There was no in crease in the deviation past 20 feet. The cycloplegic refraction was +0.50 in both eyes. The fundi were normal. At age 23 months an 8-mm-recession of the right lateral rectus muscle and a 6-mm-resection of the right medial rectus muscle were performed under general anesthesia. On the first postoperative day, at 20 feet and at near, we detected an obvious over correction of 20 prism diopters of esotropia. This esotropia disappeared within a month and thé child appeared to be orthophoric at 20 feet in the
VOL. 84, NO. 5
INTERMITTENT EXOTROPIA
primary position, in up-, down-, and sidegaze. There was also no deviation at near or infinity. The child was brought back four years later and we then found the visual acuity was R.E.: 6/9 (20/30), and L.E.: 6/6 (20/20). A small angle right esotropia of four prism diopters at 20 feet and 6 prism diopters at near was noted. Weak peripheral fusion with amplitudes of eight prism diopters in the presence of anomalous retinal correspondence on the troposcope was re corded. This case shows the danger of permanent esotropia developing even though the patient had no deviation one month after operation. It is possible that a tiny esotropie flick might have been missed one month postoperatively; one must look carefully and repeatedly for any persistent esotropie devia tion. RESULTS
Patients were divided into cured and noncured groups. The 41 cured patients fulfilled the following criteria at least one year postoperatively: (1) absence of clo sure of one eye in sunlight; (2) no mani fest tropia at any distance; (3) Wirth test results indicating equal vision with stereopsis at near of 40 seconds; (4) divergence amplitude of at least five prism diopters on the troposcope using a foveal fusion slide; (5) the recognition of diplopia im mediately when the divergence ampli tude was exceeded; (6) good convergence amplitude was present, the total conver gence and divergence amplitude exceed ed 20 prism diopters on the troposcope. Fifty-nine patients did not fulfill the above criteria and were listed as noncured. We compared the immediate postopera tive muscle balance of the eyes at 20 feet
691
in the primary position with the full opti cal correction in place and the final result under the same circumstances (Table 1). Statistical analysis of the cure rate in the three groups (orthophoric, esotropie, and exotropic deviations) showed no signifi cant difference with the chi-square test at any level. Comparison of a pooled orthophoric plus esotropie deviation vs exotropic de viation also showed the same cure ratio in both groups. Therefore, the immediate postoperative muscle balance does not statistically influence the final result. Per manent esotropia only occurred in pa tients who were orthophoric or esotropie immediately after operation. The chisquare test showed this to be highly sig nificant (P=.005). We examined the muscle imbalance measured at 20 feet at least a year postop eratively in the noncured group (Table 2). Forty of these 59 patients were within ten prism diopters of being straight and were thus cosmetically satisfactory; adding these 40 to the cure group yields an over all result of 8 1 % cosmetically satisfactory patients. Eleven patients showed the characteristics of a monofixating syn drome with fusion arid gross stereoscopic acuity associated with a small angle esotropia. 1 Only one of these 11 patients was younger than age 6 at the time of the final evaluation, the median age of the group was 8 years. The importance of including the Wirth four-dot stereoscopic
TABLE 1 COMPARISON OF THE IMMEDIATE POSTOPERATIVE MUSCLE BALANCE AND THE FINAL POSTOPERATIVE RESULT
Immediate Postoperative Position
No. of Patients (%)
Cured (%)
Esotropia
Exòtropia
Orthophoria Esotropie Exotropic Total
27 (27) 40 (40) 33 (33) 100
13 (48) 18 (45) 10 (30) 41
5 10 0 15
9 12 23 44
Noncured
692
AMERICAN JOURNAL OF OPHTHALMOLOGY
NOVEMBER, 1977
TABLE 2 MUSCLE IMBALANCE IN NONCUHED GROUP AT LEAST ONE YEAR POSTOPERATIVE
Esotropia under 10 prism diopters with fusion and stereopsis (monofixation syndrome) Esotropia under 10 prism diopters without fusion Esotropia (blind spot) 35 prism diopters Exotropia under 10 prism diopters Exotropia over 10 prism diopters Total no. of patients
test in the final evaluation was to help identify the monofixation syndrome after treatment.2 We divided the 100 patients into two age groups (Table 3); 39 were under age 4 years and 61 were aged 4 or older at the time of surgery. The median age of the under-4 group was 2V2 years, whereas in those 4 and over, it was 5V2 years. The patients in the younger group were often those noticed by observant parents and brought for examination before age 3; and the older group consisted of those who were likely being teased at school. The youngest patient was IV2 years old at the time of surgery. Only four patients were over 7 years of age, the oldest was 11 years old. The oldest patient to be cured was operated on at age 10 years. Sixty-one percent of the patients in the under-fouryear age group were cured, compared to only 28% of the 4-and-over age group. The chi-square test showed this differ ence to be highly significant (P<.001).
11 2 2 27 17 59
Amblyopia occurred as a complication of secondary esotropia only in the young er group. Three patients had vision of 6/12 (20/40) in the poorer eye, and one had 6/9 (20/30). The chi-square test com paring the amblyopia rates in the age groups under 4 years and 4 years and older, showed a significant difference (.01
TABLE 3 RELATIONSHIP BETWEEN THE AGE AT TIME OF SURGERY AND THE FINAL RESULT
Exotropia Exotropia Blind Under Over Total Cured Monofixators Monofixators Spot 10 prism 10 prism Patients (%) With Fusion Without Fusion Mechanism diopters diopters Amblyopia Under 4 years of age (median age 2V2) 4 years of age and over (median age 5VÎ) Total
39
24 (61)
61
17 (28) 41
100
3
24
14
11
27
17
VOL. 84, NO. 5
INTERMITTENT EXOTROPIA
Two patients who had increased small postoperative esotropie deviations to 35 prism diopters were considered to have blind spot mechanisms. Both these pa tients were still being treated with prisms one year after surgery. In five (12%) of those cured and in 18 (30%) of the noncures, a small associated vertical strabis mus was detected either before or after surgery, at 20 feet in the primary position. Many vertical deviations seen for the first time postoperatively may have been pre sent before surgery, but were undetected. All five patients in the cure group exhibit ed a vertical strabismus under six prism diopters preoperatively, and no measur able vertical discrepancy postoperatively. In only one case was vertical muscle sur gery aimed specifically to cure the small vertical imbalance present before surgery. Thirty percent of the noncured group had a measurable vertical strabismus at 20 feet in the primary position after surgery and, in most cases, this was not detected before surgery. The cure rate was decreased by the presence of a vertical strabismus. The chi-square test showed this to be significant (.025
Although 81% of the patients were cosmetically satisfactory with a manifest strabismus of 10 prism diopters or less one year after surgery, only 41% were cured. The most important factor in obtaining a cure was the age at which surgical realignment was undertaken. Surgery performed at a median age of 2l/2 years was associated with a higher cure rate than surgery three years later. The pres ence of a vertical strabismus decreased the chance of a cure being obtained. Strabismic amblyopia from persistent overcorrection occurred only in the younger age group and is an inherent danger of early surgery. The possibility of changing intermittent exotropia, by surgical over-
693
correction, into a permanent small angle esotropia with monofixating syndrome is more likely in the younger age group. This study did not support previous data recommending over-correction of in termittent exotropia for best results. 3-5 Statistical analysis of our data showed no significant difference as to whether the eyes were esotropically or exotropically deviated, or orthophoric, in the immedi ate postoperative period. Preoccupation with the motor and cosmetic effects, rath er than the sensory result, may confuse the issue. This study demonstrates the danger of neglecting over-correction with the production of a monofixating syn drome with or without amblyopia or an esotropia without fusion. The cure rate was also adversely affect ed by the presence of a small vertical strabismus. In most of the cases, an asso ciated paretic muscle weakness was not identifiable but a concomitant difference in height was. Every effort should be made, before operation, to identify a vertical strabismus and fashion treatment to cure it. SUMMARY
We studied the results of surgery on 100 patients with intermittent exotropia of the divergence excess type. The pres ence of normal divergence and conver gence amplitudes, with diplopia when these were exceeded, and the presence of 40 seconds of arc stereoscopic acuity at near were used as evidence of a sensory cure. Forty-one patients were cured. Surgery before the age of 4 years was the most significant factor in obtaining a cure. The presence of a small vertical strabismus decreased the chances of ob taining a cure. Over-correction in the im mediate postoperative period was not a significant factor. The danger of persistent esotropia, par ticularly in young patients, was demon strated by 11 patients with the monofix ation syndrome, four with amblyopia.
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AMERICAN JOURNAL OF OPHTHALMOLOGY REFERENCES
1. Parks, M. M.: Ocular Motility and Strabismus, Hagerstown, Harper and Row, 1975, pp. 123-131. 2. : Stereoacuity as an indicator of bifixation. In Arruga A. (ed): International Strabismus Symposium, Giessen, 1966, Basel, S. Karger, 1968.
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3. Cooper, E. L.: Purposeful overcorrection of exotropia. In Arruga, A. (ed): International Strabis mus Symposium, Giessen, 1966, Basel, S. Karger, 1968. 4. Raab, E. L., and Parks, M. NI.: Recession of the lateral recti. Arch. Ophthalmol. 82:203,1969. 5. : Recession of the lateral recti. Arch. Ophthalmol. 93:584,1975.
OPHTHALMIC MINIATURE
There exists another variety of false sight, that Plenk has denomi nated metamorphopsia, and in which objects appear changed in their natural qualities, producing error of form, error of motion, error of number, and error of colour. I had a patient in Lisbon who fancied that all the horses he saw carried horns or extensive antlers. A young lady whom I attended beheld every one of a gigantic height. Dr. Priestley has given a curious case of error of colour in five brothers and two sisters, all adults. One of the brothers could form no idea whatever of colours, though he judged very accurately of the form and other qualities of objects; hence he thought stockings were sufficiently distinguished by the name of stockings, and could not conceive the necessity of calling them white or black. He could perceive cherries on a tree; but only distinguished them, even when red-ripe, from the surrounding leaves by their size and shape. One of the brothers appeared to have a faint sense of a few colours, but still a very imperfect notion; and, upon the whole, they did not seem to possess any other distinguishing power than that of light and shade, into which they resolved all the colours presented to them,—so that dove or straw colour were regarded as white; and green, crimson, and purple, as black or dark. J. G. Millingen, Curiosities of Medical Experience London, Richard Bentley, 1839