Journal of Pediatric Ophthalmology and Strabismus

Surgery for Congenital Esotropia - An Age Comparison Study

Stephen P Kraft, MD, FRCS(C); William E Scott, MD

Abstract

Introduction

In the surgical treatment of congenital esotropia, controversy has arisen concerning the optimal age for initial surgery and the type of surgical procedure to perform to align the eyes.

Controversy has existed between those individuals who adamantly feel that successful alignment must be accomplished within the first year or two of life ("early") to achieve best results for sensory fusion and motor stability,19 and others who feel that there are serious disadvantages to operating this early and suggest that aligning the eyes after age three may be more beneficial.1014 Other authors have concluded that early surgery is best even though their studies showed that good results can be obtained with surgery at later ages.15·16

Concerning the surgical plan, two approaches have been used. Most authors have advocated two-muscle procedures, either bimedial recession or a monocular recess/resect procedure, as the initial procedure regardless of the size of the preoperative deviation2,13,17,18 to be followed by further surgery if the patient is not successfully aligned to less than 10 diopters of orthotropia. Others1,3,6 have advised a "selective" approach by which three or four horizontal rectus muscles are operated upon according to the preoperative angle in order to reduce the angle to less than 10 diopters. Parks6 suggests a two-muscle procedure if the child is less than four years old, but states that the horizontal recti may be operated upon if the child is older than four, and the deviation is large.

Regardless of one's bias in either issue, the goal of surgery for congenital esotropia is the reduction of the distance and near deviation to as close to orthotropia as possible. It is hoped that this result will allow development of sensory fusion, motor alignment or both and thus longterm stability. In order to determine a surgical plan, it is helpful to have some guidelines as to the amount of correction one can expect with specific amounts of surgery.

Tables are available giving rough guidelines for the amount of surgery to perform (either unilateral or bilateral) for various amounts of the preoperative deviation.6 In addition, one study19 analyzed the amount of correction with a specific monocular recess/resect procedure. However, none of these data take the age at time of surgery into account. One source14 suggests that there is more effect from a given amount of surgery in a very young child than in an older child. The assumption made is that anatomic factors are involved due to the relatively small size of the globe in a very young child in whom a specific amount of recession or resection will bring about relatively more effect. This fact is also used to support a widely held clinical impression that the larger the preoperative deviation the more effect from a given amount of surgery.14

Inferior oblique overactions are commonly seen as part of the spectrum of motility abnormalities in congenital esotropia, along with dissociated vertical divergence (DVD) and latent nystagmus. Inferior oblique overaction can cause a significant "V' pattern which requires surgical correction at the same time as the esotropia repair. Stager and Parks20 found no significant average shift in a horizontal alignment in primary position from bilateral inferior oblique weakening procedures. These patients all had less than 10 diopters of horizontal deviation in primary position preoperatively. Other authors21-23 state that bilateral oblique weakening for "V" pattern induces no significant change in esodeviation in primary position and some14,24,25 advise performing the same amount of horizontal surgery for the esotropia irrespective of whether the inferior obliques are to be weakened at the same time. To our knowledge, no study has looked at the effect on deviation…

Introduction

In the surgical treatment of congenital esotropia, controversy has arisen concerning the optimal age for initial surgery and the type of surgical procedure to perform to align the eyes.

Controversy has existed between those individuals who adamantly feel that successful alignment must be accomplished within the first year or two of life ("early") to achieve best results for sensory fusion and motor stability,19 and others who feel that there are serious disadvantages to operating this early and suggest that aligning the eyes after age three may be more beneficial.1014 Other authors have concluded that early surgery is best even though their studies showed that good results can be obtained with surgery at later ages.15·16

Concerning the surgical plan, two approaches have been used. Most authors have advocated two-muscle procedures, either bimedial recession or a monocular recess/resect procedure, as the initial procedure regardless of the size of the preoperative deviation2,13,17,18 to be followed by further surgery if the patient is not successfully aligned to less than 10 diopters of orthotropia. Others1,3,6 have advised a "selective" approach by which three or four horizontal rectus muscles are operated upon according to the preoperative angle in order to reduce the angle to less than 10 diopters. Parks6 suggests a two-muscle procedure if the child is less than four years old, but states that the horizontal recti may be operated upon if the child is older than four, and the deviation is large.

Regardless of one's bias in either issue, the goal of surgery for congenital esotropia is the reduction of the distance and near deviation to as close to orthotropia as possible. It is hoped that this result will allow development of sensory fusion, motor alignment or both and thus longterm stability. In order to determine a surgical plan, it is helpful to have some guidelines as to the amount of correction one can expect with specific amounts of surgery.

Tables are available giving rough guidelines for the amount of surgery to perform (either unilateral or bilateral) for various amounts of the preoperative deviation.6 In addition, one study19 analyzed the amount of correction with a specific monocular recess/resect procedure. However, none of these data take the age at time of surgery into account. One source14 suggests that there is more effect from a given amount of surgery in a very young child than in an older child. The assumption made is that anatomic factors are involved due to the relatively small size of the globe in a very young child in whom a specific amount of recession or resection will bring about relatively more effect. This fact is also used to support a widely held clinical impression that the larger the preoperative deviation the more effect from a given amount of surgery.14

Inferior oblique overactions are commonly seen as part of the spectrum of motility abnormalities in congenital esotropia, along with dissociated vertical divergence (DVD) and latent nystagmus. Inferior oblique overaction can cause a significant "V' pattern which requires surgical correction at the same time as the esotropia repair. Stager and Parks20 found no significant average shift in a horizontal alignment in primary position from bilateral inferior oblique weakening procedures. These patients all had less than 10 diopters of horizontal deviation in primary position preoperatively. Other authors21-23 state that bilateral oblique weakening for "V" pattern induces no significant change in esodeviation in primary position and some14,24,25 advise performing the same amount of horizontal surgery for the esotropia irrespective of whether the inferior obliques are to be weakened at the same time. To our knowledge, no study has looked at the effect on deviation in primary of combined bilateral inferior oblique weakenings with esotropia surgery compared to the effect with esotropia surgery alone.

A final clinical point is related to the comparison of the effect of a bimedial recession with a monocular recess/ resect procedure on the near-distance disparity of the esodeviation. According to Miles and Burian26 bimedial recessions have a greater effect at near than at distance and this effect is stronger in acquired accommodative esotropia.

Because of the implications of these unsolved issues in the treatment of congenital esotropia, we undertook a study to determine the effect of a standard amount of horizontal surgery (bimedial recession of 5.0 mm) on reducing the esotropia in various age groups of young children and compared the results of this horizontal surgery alone to horizontal surgery with simultaneous bilateral inferior oblique weakening. We also analyzed the effect of the horizontal surgery on the near-distance disparity to determine if it had more effect on the near than the distance deviation in the various age groups. We looked at the stability of the postoperative result over time to observe if any overall eso or exo drift occurred over the follow-up course. Finally, the relative effect of the surgery on the various preoperative esotropia angles was examined.

Materials and Methods

Charts were obtained of all patients with congenital esotropia, who were between the ages of six months and 10 years at surgery and who underwent bimedial recessions with or without simultaneous bilateral inferior oblique weakening at the University of Iowa Hospitals from January 1972 to December 1982. All patients had a history of constant esotropia from before six months of age and were examined by an ophthalmologist before age one year.

Prior to surgery, any patient with amblyopia was treated with patching until the visual acuities in the two eyes were less than one line's difference or, in preverbal children, until the fixation pattern was equal.27 Any child with greater than +2.00 spherical equivalent cycloplegic refraction was given glasses prior to surgery to try to decrease the angle. In no case did hyperopic correction decrease the angle more than 10 diopters.

For each patient, in addition to acuities, the preoperative esodeviation was measured by prism and cover test in primary position at 6 meters (distance) and at 33 centimeters (near) while fixing on an accommodation-controlled target. Patients were examined for "A" and "V" patterns. Versions were examined and graded bilaterally from extreme underaction ( -4) to extreme overaction (+4) with 0 being normal action. Two children less than one year old would not cooperate for distance fixation and only a measurement at near could be performed. A complete examination including anterior segment evaluation and funduscopy were performed preoperatively.

A specific type of surgery was chosen for the various analyses. Only patients who underwent bilateral medial rectus recessions of 5.0 mm from the insertion or bilateral medial rectus recessions of 5.0 mm from the insertion combined with bilateral symmetrical inferior oblique weakening as a primary procedure were included in the study. The medial recessions were done through either Park's inferonasal fornix incision, or by a limbal approach with no recession of conjunctiva. The inferior oblique weakening was a bilateral recession of 10.0 mm through an inferotemporal fornix incision. Inferior oblique weakening was added if their overactions were at least +2 in both eyes.

We also limited the study to patients who had a "normal" distance of the insertion of the muscle from the limbus. There are no tables, to our knowledge, documenting the distance of the medial rectus insertion from the limbus in different age groups. Burian and von Noorden14 list normal insertions for the newborn as 3.6 mm and for the adult as 5.5 mm. Since the cornea and anterior sclera and anterior segment reaches adult size by two years of age2fi any child over two years was included only if in surgery the muscle insertion was found 5.5 mm from the limbus bilaterally. Under the age of two years patients were included if the medial rectus insertions were between 3.6 and 5.5 mm from the limbus.

Patients included had to have at least six weeks' follow-up postoperatively. The average follow-up time for all patients was 22.3 months with a range of six weeks to seven years. Postoperatively, distance and near measurements in primary position were done under the same refractive conditions. Sensory status was tested with the Worth 4-dot at 33 cm. Versions were recorded and note was made specifically of dissociated vertical divergence (DVD) and inferior oblique overactions. Where available, data were collected on these patients at six weeks, six months, and two years follow-up.

From these criteria, 79 patients were included in the study, 61 of whom underwent bilateral rectus recessions alone and 18 of whom had bimedial rectus recessions combined with inferior oblique recessions. Data were available for all patients at six weeks' follow-up. Seventy patients had follow-up to six months and 61 had follow-up of two years or longer. Groups of data were compared by the students ttest. P values were recorded, and a P value less than 0.05 was considered significant.

Results

Patients were divided into groups by age at time of surgery: (1) less than one year, (2) one-two years, (3) two-three years, (4 ) three-four years, and (5 ) four-ten years. The mean preoperative deviations and the postoperative reductions in deviation with the ranges are recorded at distance and near for patients with bimedial recessions alone (Table 1 ) and for those with combined bimedial recessions and inferior oblique recessions (Table 2). There were no statistically significant differences among the average preoperative deviations in the different age groups. There was no patient less than one year of age who had a combined horizontaloblique surgery as no significant oblique overaction (greater than or equal to +2) was detected in any of the patients operated upon below this age.

Table

TABLE 1REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS ALONE AT VARIOUS FOLLOW-UP TIMES BY AGE GROUP

TABLE 1

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS ALONE AT VARIOUS FOLLOW-UP TIMES BY AGE GROUP

Table

TABLE 2REDUCTION OF PREOPERATIVE ESODEVIATION BY B(MEDIAL RECESSIONS WITH BILATERAL INFERIOR OBLIQUE WEAKENING AT VARIOUS FOLLOW-UP TIMES BY AGE GROUP

TABLE 2

REDUCTION OF PREOPERATIVE ESODEVIATION BY B(MEDIAL RECESSIONS WITH BILATERAL INFERIOR OBLIQUE WEAKENING AT VARIOUS FOLLOW-UP TIMES BY AGE GROUP

Table

TABLE 3REDUCTION OF PREOPERATIVE ESODEVIATION AT VARIOUS FOLLOW-UP TIMES COMPARING BIMEDIAL RECESSIONS ALONE VS. WITH BILATERAL INFERIOR OBLIQUE WEAKENING

TABLE 3

REDUCTION OF PREOPERATIVE ESODEVIATION AT VARIOUS FOLLOW-UP TIMES COMPARING BIMEDIAL RECESSIONS ALONE VS. WITH BILATERAL INFERIOR OBLIQUE WEAKENING

FIGURE I: Mean reduction of preoperative esodeviation comparing bilateral medial rectus recessions to bimedial recessions with bilateral inferior oblique weakening. Bars indicate standard deviations. PD. - Prism Diopters; N.S. - Difference not statistically significant.

FIGURE I: Mean reduction of preoperative esodeviation comparing bilateral medial rectus recessions to bimedial recessions with bilateral inferior oblique weakening. Bars indicate standard deviations. PD. - Prism Diopters; N.S. - Difference not statistically significant.

In Table 3, the overall data for the patients with bimedial rectus recessions alone were compared with those of combined bimedial-oblique recessions in order to determine if any difference existed. Although there were no patients under one year of age in the latter group, the average age of the patients in this group (2.8 years) was not significantly different statistically from that of the group who had bimedial recessions alone (2.6 years).

Table

TABLE 4REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS COMPARING PATIENTS LESS THAN ONE YEAR OF AGE TO THOSE OVER ONE YEAR OF AGE

TABLE 4

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS COMPARING PATIENTS LESS THAN ONE YEAR OF AGE TO THOSE OVER ONE YEAR OF AGE

Table

TABLE 5REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS COMPARING PATIENTS LESS THAN 18 MONTHS OLD TO THOSE OVER 18 MONTHS OF AGE

TABLE 5

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS COMPARING PATIENTS LESS THAN 18 MONTHS OLD TO THOSE OVER 18 MONTHS OF AGE

The data are recorded graphically in Figure 1. The mean preoperative deviations in the two groups were not significantly different. At six weeks postoperatively there was no . significant difference in the mean reduction of esodeviation between the two groups. However, by six months, a trend existed whereby a lower correction was obtained at distance and near in the bimedial plus oblique group, and at two years' follow-up there was a statistically significant difference in the average correction at distance and near in the two groups. Because of this finding, the two groups could not be combined for analysis of other parameters and instead the data for the bimedial recessions group alone were used.

Table

TABLE 6REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS COMPARING PATIENTS LESS THAN TWO YEARS OLD TO THOSE OVER TWO YEARS OF AGE

TABLE 6

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS COMPARING PATIENTS LESS THAN TWO YEARS OLD TO THOSE OVER TWO YEARS OF AGE

Postoperatively, two patients in each group developed an amblyopia and it was successfully treated with patching therapy in each case. On sensory testing 43.3% of the patients who had bimedial recessions and 41.7% of the patients with the combined procedure had fusion of the Worth 4-dot.

In order to determine if the effect of the surgery was greater below compared to above a certain age, we grouped the data from different age groups to compare three combinations: (1) patients less than age one compared to patients over age one, (2) patients less than 18 months old compared to patients greater than 18 months of age, (3) patients less than age two compared to patients greater than age two. These means are tabulated in Tables 4,5, and 6 and are represented graphically in Figures 2, 3, and 4.

The only significant differences in any of these three analyses were in the comparison of ages less than one versus greater than one year in the six-week follow-up period (Table 4). Patients less than one year old had a significantly greater effect from the surgery than patients greater than one year at this follow-up time at near (P = 0.04) and a barely significant difference at distance (P = 0.06). However, this difference was no longer significant at six months' follow-up although the children less than one year had a larger mean reduction in deviation. By two years there was no difference detected and, in fact, the mean change at distance in the children over one year old was slightly greater.

The data for the comparison of surgery at age less than two years versus greater than two years (Table 6) shows an opposite trend in that the means were similar at distance and near at six weeks and six months, but at two years a trend emerged in favor of greater correction in the children less than two years of age. These means, however, were not statistically significant.

Table 7 tabulates the effect of the surgery at reducing the esodeviation at near compared to at distance. The neardistance disparity (N-D), defined as the difference between the measurement fixating at a near target and the measurement while fixating at distance in primary position, was calculated for each patient. In all age groups the average N-D was slightly greater than 0 preoperatively indicating slightly larger esodeviations at near than at distance. The postoperative values show the change in this (N-Di value over time. A minus value indicates that the surgery had a greater effect at near than at distance. A plus value, conversely, indicates a lesser effect at near compared to distance.

In all but the three-four year age group, there was a trend at six weeks and six months to a slightly greater effect of bilateral medial rectus recession at near than at distance. This trend was no longer present at two years' follow-up except in children over four years old. In no instance, however, was the mean change in N-D significant. Thus, the surgery had no greater effect at near than at distance.

In Table 8, the mean change in distance esodeviation by bimedial recessions is recorded according to the preoperative angle of deviation. There was a definite trend by six months that was even clearer at two years of a larger effect of the surgery the more the preoperative deviation. The amount of correction increased with time in the patients with preoperative deviations between 41 and 70 prism diopters.

The data from Tables 1 and 8 indicate that for patients operated on between ages two and four, or with preoperative deviations over 41 prism diopters, there was an increase in the effect of the surgery (that is, reduction in preoperative esodeviation) over time. There was a small exo shift in these groups seen between six weeks' and six months' follow-up and a further exo drift in the six months to two years interval. In the other age groups with preoperative deviations of less than 40 diopters, the surgery had an effect that remained relatively stable over time.

FIGURE 2: Mean reduction of preoperative esodeviation by bimedial recessions comparing patients under one year old to those over one year of age. Bars indicate standard deviations. P.D. - Prism Diopters; N.S. - Difference not statistically significant.

FIGURE 2: Mean reduction of preoperative esodeviation by bimedial recessions comparing patients under one year old to those over one year of age. Bars indicate standard deviations. P.D. - Prism Diopters; N.S. - Difference not statistically significant.

FIGURE 3: Mean reduction of preoperative esodeviation by bimedial recessions comparing patients under 18 months old to those over 18 months of age. Bars indicate standard deviations. P.D. - Prism Diopters.

FIGURE 3: Mean reduction of preoperative esodeviation by bimedial recessions comparing patients under 18 months old to those over 18 months of age. Bars indicate standard deviations. P.D. - Prism Diopters.

FIGURE 4: Mean reduction of preoperative esodeviation by bimedial recessions comparing patients under two years old to those over two years of age. Bars indicate standard deviations. P.D. - Prism Diopters.

FIGURE 4: Mean reduction of preoperative esodeviation by bimedial recessions comparing patients under two years old to those over two years of age. Bars indicate standard deviations. P.D. - Prism Diopters.

Overall reductions in esodeviation at distance and near including all age groups are tabulated in Table 9. Between six weeks' and six months' follow-up there was a mean increase in effect, or average exo drift, of 2.8 prism diopters at distance and 2.1 prism diopters at near. Between six months and two years, there was an exo drift of 4.3 prism diopters at distance and 3.3 diopters at near.

Of the 61 patients who had bimedial recessions alone, 28 (45.9%) had DVDs and 29 (47.5%) had an inferior oblique overaction of at least +1 noted at the time of the first visit to the clinic or on a subsequent preoperative or postoperative visit. None of those who had an inferior oblique overaction documented preoperatively were judged to be significant enough to require surgical correction.

Of the 18 patients who had inferior oblique recession with the bimedial recessions, all had "V" patterns (pattern greater than or equal to 15 prism diopters) with inferior oblique overactions of at least +2 preoperatively and 10 (55.6%) had DVD in addition to the inferior oblique overaction. Thirteen (72.2%) had an associated bilateral superior oblique underaction of -1 or -2, and 2 (11.1%) had no superior oblique underaction. In three patients the preoperative superior oblique actions were not recorded.

Of the 18 patients, only two (11.1%) were converted to "A" patterns (greater than or equal to 10 prism diopters), one of 10 and one of 15 prism diopters.

Two of the 18 patients had residual +1 overactions of the inferior oblique muscles postoperatively. One of these two individuals had fusion postoperatively. The remaining 16 patients had -1 underactions or normal actions of the inferior oblique muscles.

Discussion

The aim of surgery in congenital esotropia is the reduction of the tropia to orthotropia if possible. Rogers et al.29 have documented significant improvement in fine motor skills and various visually directed tasks in infants with congenital esotropia who were aligned to less than 10 prism diopters of orthotropia by surgery and were otherwise developmentally normal. Tolchin and Lederman30 stressed that early alignment of congenital esotropia was important in the normal development of parent-child relationships because of the improvement of the general appearance of the child.

At this institution we use the selective approach to surgical treatment of congenital esotropia as originally advocated by Taylor.1 In general, for preoperative deviations under 45-50 prism diopters, we perform two-muscle surgery with amounts proportional to the amount of deviation. Beyond this we add a third muscle to the procedure, and we will do a fourth horizontal muscle for deviations above about 70 prism diopters. However, in order to assess the comparative effect of surgery in different age groups and different preoperative deviations, a specific amount and type of surgery had to be selected. A bimedial recession of 5.0 was the most frequent amount and type of muscle procedure performed over the past 10 years. Therefore the results from this procedure hopefully provided a sufficient amount of data to allow analysis. In reviewing the charts of patients in the early years included in the study, we would no longer consider performing bimedial recessions of 5.0 for the entire range of the preoperative deviations, especially for the large deviations (over 50 prism diopters). For deviations above this amount we perform surgery on three or four horizontal rectus muscles.

Table

TABLE 7EFFECT OF BIMEDIAL RECESSIONS ON NEAR (N) - DISTANCE (D) DISPARITY (N-D) OF ESODEVIATION AT VARIOUS FOLLOW-UP TIMES BY AGE GROUPS

TABLE 7

EFFECT OF BIMEDIAL RECESSIONS ON NEAR (N) - DISTANCE (D) DISPARITY (N-D) OF ESODEVIATION AT VARIOUS FOLLOW-UP TIMES BY AGE GROUPS

The data indicate that the weakening of the inferior oblique coincident with bimedial rectus recessions reduced the effect of the horizontal muscle surgery in primary position. This difference became progressively more impressive with time and was significant at the two-year follow-up period. This finding could not be attributed to a difference in the fusion status postoperatively as the percentage of patients who achieved fusion was almost identical in the two groups (43-3% vs. 41.7%). In addition, only two patients in each group developed an amblyopia after surgery and in each case it was treated successfully with patching. Therefore, this factor cannot be responsible for the observed difference. Finally, inadequate or ineffective inferior oblique surgery was not a causative factor as demonstrated by the postoperative versions.

The patients with bimedial rectus recessions alone had, on the average, 10.9 prism diopters more reduction of esodeviation at distance and 13.4 prism diopters at near than those who had this combined with oblique recessions. The six-week postoperative results agree with Stager and Parks'20 results at three months' follow-up in patients who had bilateral inferior oblique weakening, although they had less than 10 diopters of tropia in primary position preoperatively. We are unaware of any source documenting the long-term results of inferior oblique weakening on the horizontal deviation in primary. The references that advise not altering the amount of horizontal muscle surgery in treating "V" esotropia that require combinations of inferior oblique and horizontal rectus muscle surgery14,24,25 or claim no significant change in primary position by inferior oblique weakening21 do not indicate the length of follow-up.

Table

TABLE 8REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS GROUPED ACCORDING TO PREOPERATIVE DEVIATION COMBINING ALL AGE GROUPS

TABLE 8

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS GROUPED ACCORDING TO PREOPERATIVE DEVIATION COMBINING ALL AGE GROUPS

Table

TABLE 9OVERALL REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS AT VARIOUS FOLLOW-UP TIMES

TABLE 9

OVERALL REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS AT VARIOUS FOLLOW-UP TIMES

The results suggest that if bilateral inferior oblique weakening is done in conjunction with bimedial recessions, the amount of horizontal surgery should be appropriately increased. The difference we found between the two groups is not unexpected as the tertiary action of the oblique muscles is that of abduction in the primary position.14 Jampol31 showed experimentally that in the horizontal plane in primary there was a small abduction effect of the inferior obliques. Therefore, it could be expected that by weakening the obliques one would lose their abducting effect and this would counteract some of the effect of recessing the medial recti.

The results of bilateral 5.0 mm medial rectus muscle recessions at two years' follow-up do not support that more esodeviation is corrected in very young children. While Burian and von Noorden14 do not specifically state the age below which this premise holds true nor the follow-up on which this is based we analyzed the data according to the ages during which the globe, and specifically the anterior segment, undergoes almost all of its growth.

There was a significant difference in the effect of the surgery in patients less than one year of age than in patients over one year of age six weeks postoperatively. This trend was no longer present by six months, and by two years the average reductions of the esodeviation in the two groups of patients were not significantly different. There was no statistically significant difference in the other two analyses, those of patients less than 18 months of age at surgery compared to those older and those less than two years of age at surgery compared to those over two years of age, at any of the follow-up times.

These findings may be explained by Beisner's32 studies on the physiological changes induced by recessing a rectus muscle. He found that the muscle is weakened primarily because of a change in the length-tension relationship. A newborn medial rectus muscle has an average length of 28.0 mm compared to an adult's 40.7 mm.14 A very young child would have a greater alteration in the length-tension curve by a 5.0 mm recession than would an older child and thus greater effect from surgery. With muscle growth the curve will change so that by age two or three the lengthtension relationship may be equivalent to that of the muscle of a child operated upon at this age or older.

This same hypothesis could also explain the fact that no significant increased effect at near compared to distance was found. If the muscle length is the critical factor in reducing the muscle's effect, more so than the torque, then no difference in effect between distance and near deviation would occur. The finding of no significant decrease in neardistance disparity over time was present in all age groups including those less than one year of age. This finding agrees with Miles and Burian2· who found an average of only 1.0 prism diopter difference between the decrease in esodeviation at distance compared to near with bimedial recessions for congenital esotropia.

In our 79 patients with congenital esotropia, we found 38 cases (48.1%) had DVD and 47 (59.5%) had inferior oblique overactions of at least + 1 detected at some time during the pre or postoperative course. These figures are slightly lower than those quoted by various sources.ii·14·'*'

Of the 47 patients with inferior oblique overactions, 18 (38.3%) had significant overactions (that greater or equal to + 2 and requiring correction) and had inferior oblique weakening procedures with the horizontal surgery. The diagnosis of overaction of an inferior oblique was contingent upon finding on cover test a corresponding hypotropia of the abducting eye while the adducting eye was fixating on a target. This is a differential diagnostic feature to rule out DVD alone as the cause of an upshoot in adduction. Of those patients who had superior oblique function noted on versions preoperatively, 13 of 15 patients (86.7%) had at least -1 overaction of these muscles and 2 had normal actions. This suggests that most patients with significant inferior oblique overactions (greater than or equal to +2) and congenital esotropia may have partially recovered bilateral superior oblique palsies to explain the versions and "V' patterns. Therefore, we feel that most significant inferior oblique overactions are secondary overactions and not primary overactions.

Only two of the 18 patients (11.1%) with simultaneous medial and oblique recessions were converted into an "A" pattern postoperatively, much lower than the 33% (8 of 24 cases) reported by Foster et al.16 in patients treated with bimedial recessions and bilateral inferior oblique myectomies. Neither of our two patients had a pattern over 15 diopters while four of their eight patients did.

The results with bimedial recessions show a consistent exo drift (or decreased esodeviation) over time postoperatively in certain age groups and overall across all age groups. This drift was observed between the six weeks' and six months' follow-up visits and between the six months' and two years' follow-up visits. Seaber33 also found an exo drift in 20 patients with bimedial recessions, but she found an average postoperative exo drift at distance of 12 prism diopters in the first six months and further drift of 4 diopters in the next 18 months. Our overall drift of about 7 diopters at distance at two years comprised a 3 diopter change at six months and further drift of 4 diopters in the next 18 months. Unfortunately, Seaber did not divide her patients by age group, and so no comment can be made as to whether her trend was true of all age groups.

The initial surgical plan should include enough surgery to eliminate the deviation. There is only a 40-50% success rate reported in congenital esotropes using two-muscle horizontal surgery as the first procedure.213·17 This low success rate is due primarily to the significant number of large preoperative deviations (over 50 diopters) in these series. Furthermore, the predictability of the effect of twomuscle surgery for esodeviations over 50 diopters is poorer than for deviations under this amount.19

We feel that appropriate planning including selective surgery when indicated, or augmenting the effect of the medial recti with conjunctival recessions where appropriate, will improve the results with initial surgery in these children. The frequency of second or third anesthetics because of undercorrections from the first surgery would be reduced. Close follow-up for several years postoperatively is still essential since up to 60% of patients aligned successfully early in life can drift eso or exo even after years of stable angles of less than 10 diopters.18

Acknowledgment

We wish to thank Mr. Tom O'Gorman for his assistance in the statistical analysis.

References

1. Taylor DM: How early is early surgery in the management of strabismus? Arch Ophthalmol 1963; 70:752-756.

2. Ing M, Costenbader FD, Parks MM, et al: Early surgery for congenital esotropia. Am J Ophthalmol 1966; 61:1419-1427.

3. Fisher NF, Flom MC, Jampolsky A: Early surgery of congenital esotropia. Am J Ophthalmol 1968; 65:439-443.

4. Taylor DM: Is congenital esotropia functionally curable? Trans Am Ophthalmol Soc 1972; 70:571-576.

5. Gale D: The surgical management of esotropia in infancy. Trans Ophthalmol Soc UK 1972; 92:675-683.

6. Parks MM: Ocular Motility and Strabismus. New York, Harper and Row. 1975.

7. Vazquez R, Calhoun JH, Harley RD: Development of monofixation syndrome in congenital esotropia. J Pediatric Ophthalmol & Strabismus 1981; 18:42-44.

8. Zak TA, Morin JD: Early surgery for infantile esotropia: Results and influence of age upon results. Can J Ophthalmol 1982; 17:213-218.

9. Ing MR: Early surgical alignment for congenital esotropia. J Pediatr Ophthalmol & Strabismus 1983; 20:11-18.

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TABLE 1

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS ALONE AT VARIOUS FOLLOW-UP TIMES BY AGE GROUP

TABLE 2

REDUCTION OF PREOPERATIVE ESODEVIATION BY B(MEDIAL RECESSIONS WITH BILATERAL INFERIOR OBLIQUE WEAKENING AT VARIOUS FOLLOW-UP TIMES BY AGE GROUP

TABLE 3

REDUCTION OF PREOPERATIVE ESODEVIATION AT VARIOUS FOLLOW-UP TIMES COMPARING BIMEDIAL RECESSIONS ALONE VS. WITH BILATERAL INFERIOR OBLIQUE WEAKENING

TABLE 4

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS COMPARING PATIENTS LESS THAN ONE YEAR OF AGE TO THOSE OVER ONE YEAR OF AGE

TABLE 5

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS COMPARING PATIENTS LESS THAN 18 MONTHS OLD TO THOSE OVER 18 MONTHS OF AGE

TABLE 6

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS COMPARING PATIENTS LESS THAN TWO YEARS OLD TO THOSE OVER TWO YEARS OF AGE

TABLE 7

EFFECT OF BIMEDIAL RECESSIONS ON NEAR (N) - DISTANCE (D) DISPARITY (N-D) OF ESODEVIATION AT VARIOUS FOLLOW-UP TIMES BY AGE GROUPS

TABLE 8

REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS GROUPED ACCORDING TO PREOPERATIVE DEVIATION COMBINING ALL AGE GROUPS

TABLE 9

OVERALL REDUCTION OF PREOPERATIVE ESODEVIATION BY BIMEDIAL RECESSIONS AT VARIOUS FOLLOW-UP TIMES

10.3928/0191-3913-19840301-05

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