Journal of Pediatric Ophthalmology and Strabismus

Original Article Supplemental Data

A Comparative Study of Prism Adaptation and the Augmented Surgery Formula in the Management of Acquired Comitant Esotropia

Rehab R. Kassem, MD, FRCS(Glasg); Hala M. Elhilali, MD; Mohammad A. El-Sada, MD; Said A. El-Antably, MD

Abstract

Purpose:

To compare two methods of surgical augmentation (prism adaptation and the augmented surgery formula) in the management of acquired comitant esotropia.

Methods:

Forty patients were included in this prospective study and assigned to either the prism adaptation (20 patients) or augmented surgery (20 patients) group. After preoperative prism adaptation, patients in the prism adaptation group were classified as prism adaptation responders (fusers) or non-responders (non-fusers). All patients in the prism adaptation group underwent surgery for the prism-adapted angle. Patients in the augmented surgery group underwent surgery based on the augmented surgery formula, defined as the average of the near deviation without correction and the distance deviation with correction.

Results:

In the prism adaptation group, 6 patients (30%) were prism responders, whereas 14 (70%) were non-responders. The 3-month motor success rate was significantly higher in the prism adaptation group (90%) than the augmented surgery group (55%) (P = .013). The 6-month motor success rate was not significantly higher in the prism adaptation group (95%) than the augmented surgery group (80%) (P = .151). The improvement in the 6-month outcome was mainly attributed to hyperopic spectacle power reduction after 3-month postoperative evaluation to correct consecutive exotropia.

Conclusions:

Although prism adaptation is superior in precisely determining the surgical target angle, the success rates were comparable between the two groups after hyperopic spectacle power reduction. This obviates the need for prism adaptation, except in cases of non-accommodative esotropia. To maximize the benefit of prism adaptation, it is recommended that all patients with prism adaptation (responders and non-responders) undergo surgery for the prism-adapted angle.

[J Pediatr Ophthalmol Strabismus. 2020;57(2):108–119.]

Abstract

Purpose:

To compare two methods of surgical augmentation (prism adaptation and the augmented surgery formula) in the management of acquired comitant esotropia.

Methods:

Forty patients were included in this prospective study and assigned to either the prism adaptation (20 patients) or augmented surgery (20 patients) group. After preoperative prism adaptation, patients in the prism adaptation group were classified as prism adaptation responders (fusers) or non-responders (non-fusers). All patients in the prism adaptation group underwent surgery for the prism-adapted angle. Patients in the augmented surgery group underwent surgery based on the augmented surgery formula, defined as the average of the near deviation without correction and the distance deviation with correction.

Results:

In the prism adaptation group, 6 patients (30%) were prism responders, whereas 14 (70%) were non-responders. The 3-month motor success rate was significantly higher in the prism adaptation group (90%) than the augmented surgery group (55%) (P = .013). The 6-month motor success rate was not significantly higher in the prism adaptation group (95%) than the augmented surgery group (80%) (P = .151). The improvement in the 6-month outcome was mainly attributed to hyperopic spectacle power reduction after 3-month postoperative evaluation to correct consecutive exotropia.

Conclusions:

Although prism adaptation is superior in precisely determining the surgical target angle, the success rates were comparable between the two groups after hyperopic spectacle power reduction. This obviates the need for prism adaptation, except in cases of non-accommodative esotropia. To maximize the benefit of prism adaptation, it is recommended that all patients with prism adaptation (responders and non-responders) undergo surgery for the prism-adapted angle.

[J Pediatr Ophthalmol Strabismus. 2020;57(2):108–119.]

Introduction

Acquired esotropia is a leading cause of amblyopia in the pediatric population.1 The goal of management of acquired esotropia is to align the eyes as soon as possible to reestablish binocular fusion and prevent sensory and motor complications. The first line of treatment is to reverse any amblyopia and prescribe the full hyperopic correction. If a residual esotropia is present, strabismus surgery is performed.2 Various strategies have been proposed to determine the surgical target angle (the angle of esotropia on which the amount of muscle surgery is based),3 including the standard surgery formula,4 prism adaptation,3,5 and the augmented surgery formula.6

The standard surgery formula is based on the residual deviation after prescribing full hypermetropic correction.4 However, undercorrection was frequently encountered after standard surgery.2,3,5,6 Consequently, two methods (prism adaptation3,5 and the augmented surgical formula)6 were devised to reduce the rate of undercorrection and minimize the need for reoperation.

Prism adaptation is defined as the preoperative use of Fresnel prisms for patients with acquired esotropia to determine the maximum angle of strabismus and to estimate fusional potential. A prism adaptation responder is a patient who demonstrates fusion with prisms, whereas a prism adaptation non-responder is a patient who fails to develop fusion with prisms. Prism-adapted surgery refers to surgery for the angle of deviation for which the prism wearer achieves fusion. This is equivalent to the power of the worn Fresnel prism plus the residual distance esotropia measured with the worn prisms through the alternate cover and prism test (ACPT) at the time prism response is determined.3

The augmented surgery formula is based on the average of near deviation with and without correction, and the alternative augmented surgery formula is based on the average of near deviation without correction (largest deviation) and the distance deviation with correction (smallest deviation). The formulas were devised as alternative tools to increase the amount of surgery without the need for wearing prisms.6

Prism adaptation and the augmented surgical formula are different tools of surgical augmentation that produce superior postoperative ocular alignment.7 The purpose of the current study was to compare the two methods of surgical augmentation in the management of acquired comitant esotropia.

Patients and Methods

This was a prospective study conducted in the Department of Ophthalmology at Cairo University and was approved by the Cairo University Council, after approval from the Department of Ophthalmology and the Faculty of Medicine Councils. The study conformed to all local laws and the principles of the Declaration of Helsinki.

Forty consecutive patients met the inclusion criteria and were included in the study. Inclusion criteria were patients aged 3 years or older who had an acquired, comitant, non-accommodative or partially accommodative esotropia. Exclusion criteria included any of the following: refusal to participate, previous ocular or extraocular surgery, fully accommodative esotropia, high or low accommodative convergence/accommodation (AC/A) ratio, vertical strabismus exceeding 3 prism diopters (PD), dissociated vertical deviation, inferior oblique muscle over-action exceeding +2 PD in either eye, A/V pattern, nystagmus, inability to perform the Worth 4-dot test, inability to assess visual acuity, corrected visual acuity worse than 20/40 in either or both eyes despite amblyopia therapy, eccentric fixation, other associated ocular disorders, or systemic or neurological diseases.3

The clinical evaluation included history taking, measurement of best corrected visual acuity, sensory testing, ocular-motor examination, cycloplegic refraction, and funduscopy. Sensory testing was performed with the Worth 4-dot test at 6 and 0.33 m, the Bagolini Lens Test, and the Titmus Stereo Test. Ocular deviation was measured with the simultaneous prism and cover test (SPCT) and the ACPT at 6 m in straight, vertical, and horizontal gazes, and at 0.33 m in straight gaze. Measurements were recorded with and without correction (1 month after spectacle prescription). Measured angles of esotropia had to be within 5 PD on two consecutive visits within 1 week to ensure stability of deviation. Spectacle correction was prescribed within 0.50 diopters (D) of the patient's cycloplegic refraction, if the latter exceeded 1.50 D of hyperopia, astigmatism, or anisometropia, or 1.00 D of myopia.3

Eligible patients were assigned to either the prism adaptation (20 patients) or augmented surgery (20 patients) group.

Images of the patients' eyes were taken on entry into the study, at the end of prism adaptation, and 6 months postoperatively. Consent was obtained from the children's guardians to publish the images of their eyes.

Prism Adaptation Group

Prism adaptation was based on the method described by the Prism Adaptation Study Research Group.3

Prism Prescription. The prism prescription was based on the deviation measured with the ACPT through worn spectacles while the patient fixated on an accommodative target at 6 m while in the primary position. Neutralizing base-out Fresnel press-on prisms were stuck with water on the rear surface of the spectacles. Ten minutes later, the deviation was measured with the SPCT through worn prisms at 6 and 0.33 m. If an esotropic shift greater than 8 PD was detected, prisms of a higher power were substituted. Patients left the office wearing the prisms, with an esotropic shift between 0 and 8 PD at distance and near. An exotropic shift of 5 PD or less was permissible.3

Follow-up and Prism Adjustment. Patients were seen at weekly intervals. Follow-up visits comprised visual acuity measurement, sensory testing, and ocular alignment assessment. If an esotropic shift greater than 8 PD was detected, prisms of a higher power were substituted. Patients again left the office after each follow-up visit wearing the appropriate prisms,3 which were readjusted when necessary until the prism response status was determined.3

Prism Response Status. A patient was considered a prism adaptation responder (fuser) if, while wearing spectacles, a stable esotropia between 0 and 8 PD was detected with the SPCT and fusion at near at 6 and 0.33 m. The patient was considered a prism adaptation non-responder (non-fuser) when a stable esotropia between 0 and 8 PD was present for 30 days without developing fusion, an exotropic shift with suppression was detected, or the prescribed prism power exceeded 60 PD.3

Surgery. Patients in the prism adaptation group (responders and non-responders who underwent pre-operative prism adaptation) underwent surgery for the prism-adapted angle. This was equivalent to the power of the worn Fresnel prisms plus the distance deviation measured with the ACPT through worn prisms on the final follow-up during prism adaptation.8

Augmented Formula Group

Patients in the augmented surgery group underwent surgery based on the augmented surgery formula, defined as the average of the near deviation without correction and the distance deviation with correction.6 The amount of surgery performed per target angle is presented in Table 1.

Amount of Surgery for Range of Target Angle

Table 1:

Amount of Surgery for Range of Target Angle

The total duration of postoperative follow-up was 6 months. Follow-up examinations for all patients were scheduled 1 week, 1 month, 6 weeks, 3 months, and 6 months postoperatively. Postoperative evaluations comprised visual acuity measurement, sensory testing, and ocular alignment assessment with the SPCT through worn spectacles. Certain restrictions were placed on postoperative therapy. Specifically, no repeated surgery or prism therapy was allowed prior to the 6-month follow-up visit. No change in spectacle prescription was allowed prior to the 3-month follow-up examination, unless the patient's visual acuity was worse than 20/40.

A successful motor outcome was defined as orthotropia or a horizontal tropia of 10 PD or less at distance and near, measured with the SPCT through worn spectacles. A tropia exceeding 10 PD was considered a successful outcome if intermittent. A successful sensory outcome was defined as motor success and fusion or intermittent fusion on the Worth 4-dot test at near.8 A successful outcome was synonymous with motor success.

Statistical Analysis

Data were presented as the mean ± standard deviation and percentages. Numerical variables between the study groups were compared with the Student's t test for independent samples (for two groups of normally distributed data) and the Mann–Whitney U test (for independent samples of data not normally distributed). The chi-square test was used to compare categorical data. Fisher's exact test was used instead of the chi-square test when the expected frequency was less than 5. Comparisons before and after treatment were performed with the McNemar test. Correlation between various variables was performed with the Pearson moment correlation equation for linear relation of normally distributed variables and the Spearman rank correlation equation for variables not normally distributed or non-linear monotonic relationships. Two-sided P values less than .05 were considered statistically significant. All statistical calculations were performed with IBM SPSS software for Windows (Statistical Package for the Social Sciences version 22; IBM Corporation, Armonk, NY).

Results

Forty patients met the inclusion criteria and were included in the study. The number of patients in each group and the abbreviations used in reference to the various groups are shown in Figure 1.

Design diagram of the study.

Figure 1.

Design diagram of the study.

Patient Characteristics. The patient characteristics of the groups are presented in Table 2. Most of the baseline characteristics between the two groups are the same, with the exception that the mean initial angles of esotropia are larger in the augmented surgery group than the prism adaptation group.

Preoperative, Intraoperative, and Postoperative DataPreoperative, Intraoperative, and Postoperative Data

Table 2:

Preoperative, Intraoperative, and Postoperative Data

Prism Adaptation. In the prism adaptation group, 6 patients (30%) were prism responders (fusers), whereas 14 patients (70%) were non-responders (non-fusers). An angle build-up with prisms was noted in 16 patients (80%) from the prism adaptation group: 9 (45%) had an increase in deviation of 1 to 9 PD, whereas 7 (35%) had a build-up of esotropia of more than 10 PD (Figure 2A). Of the 4 patients (20%) who demonstrated no prism build-up (Figure 2B), 1 (5%) had a decrease in the initial angle of esotropia with prisms. All 6 prism responders (100%) and 10 of 14 non-responders (71.4%) showed angle build-up with prisms. The relationship between prism response and build-up was not statistically significant (Pearson chi-square = 2.143, P = .143).

(A) Build-up of 25 prism diopters (PD). (i) Non-accommodative esotropia with an initial angle of 25 PD. (ii) Orthotropia with 50-PD Fresnel press-on prisms. (iii) Esotropia of 50 PD after prism adaptation. (iv) Orthotropia after surgery for a target angle of 50 PD (5-mm bimedial muscle recession and 5-mm right lateral rectus muscle resection). (B) No prism build-up. (i) Partially accommodative esotropia with an initial angle of 25 PD. (ii) Orthotropia through 25-PD press-on Fresnel prisms. (iii) Esotropia of 25 PD after prism adaptation. (iv) Orthotropia after surgery for a target angle of 25 PD (4-mm bimedial muscle recession).

Figure 2.

(A) Build-up of 25 prism diopters (PD). (i) Non-accommodative esotropia with an initial angle of 25 PD. (ii) Orthotropia with 50-PD Fresnel press-on prisms. (iii) Esotropia of 50 PD after prism adaptation. (iv) Orthotropia after surgery for a target angle of 50 PD (5-mm bimedial muscle recession and 5-mm right lateral rectus muscle resection). (B) No prism build-up. (i) Partially accommodative esotropia with an initial angle of 25 PD. (ii) Orthotropia through 25-PD press-on Fresnel prisms. (iii) Esotropia of 25 PD after prism adaptation. (iv) Orthotropia after surgery for a target angle of 25 PD (4-mm bimedial muscle recession).

The amount of angle build-up with the prism is shown in Figure 3. In the prism adaptation group, the mean angle of esotropia before and after prism adaptation was 29 ± 6.2 and 37.2 ± 9.66 PD, respectively. Therefore, the mean angle build-up was 8.2 ± 10.14 PD. The increase in the angle of esotropia with prisms was significant (t = 3.617, P = .002).

Mean angles of esotropia (ET) before and after prism adaptation (PA). PRB = prism responders; PNRB = prism non-responders; PB = prism build-up; P = prism adaptation group

Figure 3.

Mean angles of esotropia (ET) before and after prism adaptation (PA). PRB = prism responders; PNRB = prism non-responders; PB = prism build-up; P = prism adaptation group

Surgery. Table 1 shows the mean surgical target angles and the amount of surgery performed for the different groups. The mean surgical target angle was significantly higher in the augmented surgery group than the prism adaptation group. Moreover, the mean surgical target angles in the augmented surgery group (52.88 ± 13.3 PD) were higher than the angles in the subgroup of patients with prism adaptation with angle build-up (39.62 ± 8.47 PD, P = .001). Therefore, a significantly smaller target angle was documented in the prism adaptation group even after angle build-up with prisms.

The chi-square test revealed a significant linear-by-linear association value of 3.886 (P = .049) between the presence or absence of prism build-up and the amount of surgery performed on the medial rectus muscle.

3-Month Postoperative Follow-up Visit and Outcome Assessment. Results of the 3-month postoperative follow-up are presented in Table 2. Evaluations were performed prior to spectacle power adjustment. Figure 4 shows the motor and sensory success rates obtained by different study groups at the 3-month postoperative follow-up visit. The motor success rate was significantly higher and the sensory success rate was not significantly higher in the prism adaptation group than the augmented surgery group. The difference in motor success rates between prism responders and non-responders was not significant (P = .502). In contrast, the difference in sensory success rates between prism responders and non-responders was significant (P = .001). The differences in motor and sensory success rates between patients showing a prism build-up and those not showing a prism build-up were not significant (P = .264 and .608, respectively).

Sensory and motor success rates at 3 months postoperatively. PRB = prism responders; PNRB = prism non-responders; PB = prism build-up; P = prism adaptation group; A = augmented surgery group

Figure 4.

Sensory and motor success rates at 3 months postoperatively. PRB = prism responders; PNRB = prism non-responders; PB = prism build-up; P = prism adaptation group; A = augmented surgery group

6-Month Postoperative Follow-up and Outcome Assessment. Results of the 6-month postoperative follow-up are presented in Table 2 and Figure 5.

Sensory and motor success rates at 6 months postoperatively. PRB = prism responders; PNRB = prism non-responders; PB = prism build-up; P = prism adaptation group; A = augmented surgery group

Figure 5.

Sensory and motor success rates at 6 months postoperatively. PRB = prism responders; PNRB = prism non-responders; PB = prism build-up; P = prism adaptation group; A = augmented surgery group

Adjusting the spectacle power at the 3-month postoperative follow-up to correct esotropia had an impact on the success rates 6 months postoperatively. Two patients in the prism adaptation group had spectacle discontinuation, whereas 4 patients in the augmented surgery group had hyperopic power reduction, which corrected a consecutive exotropia to within 10 PD of orthotropia (Table 3). Spectacle power reduction was 100% successful in correcting a consecutive exotropia to within 10 PD of orthotropia, but was not applicable in patients with residual esotropia or patients with non-accommodative esotropia without an initial spectacle prescription.

Reduction of Hyperopic Correction

Table 3:

Reduction of Hyperopic Correction

Although not statistically significant, the success rates 6 months postoperatively were higher in the prism adaptation group (19 of 20 patients [95%]) than in the augmented surgery group (16 of 20 patients [80%]) (P = .151). In the prism adaptation group, 1 patient with an unsuccessful outcome had a residual esotropia of 16 PD. In the augmented surgery group, 3 patients with unsuccessful outcomes had a residual esotropia between 12 and 14 PD, whereas 1 patient had an exotropia of 25 PD. The latter had a refractive error that was not significant and, therefore, no initial spectacle prescription.

The differences in motor success rates between prism responders and non-responders and between patients with and without prism build-up were not significant (P = .502 and .608, respectively). The difference in sensory success rates between prism responders and non-responders was significant (P = .003), but the difference between patients with and without prism build-up was not significant (P = .264).

Discussion

The goal of strabismus surgery is to align the eyes to permit fusion with a minimum number of operations, reducing morbidity, stress, and cost.3 The standard surgical formula has resulted in an unacceptably high rate of undercorrections,2,3,5,6 in contrast to prism adaptation3 and the augmented surgical formulas,6 which have remarkably improved the success rate of surgery for acquired comitant esotropia. In addition to the current study, the superiority of one strategy over another has been previously investigated.6,7,9

The current study is a prospective evaluation of prism adaptation versus the augmented surgical formula. At the 3-month postoperative follow-up (prior to spectacle power adjustments), the study revealed significantly higher success rates in patients undergoing prism adaptation (90% success) than those receiving surgery based on the augmented surgery (55% success) (P = .013), which contradicts results from previous studies.6,7,9

Wright and Bruce-Lyle6 reported equal to slightly better results on comparing the results of the augmented surgery formula with those of prism adaptation, previously obtained in the Prism Adaptation Study.3 The success rate was 88% with augmented surgery and 81% with prism adaptation.10 Hwang et al.7 were the first to conduct a prospective study comparing the two methods of surgical augmentation: augmented surgery formula and prism adaptation. Reporting the results of the 3-,7 6-, and 12-month9 postoperative follow-up visits, Hwang et al.,9 suggested there were no significant differences between the two methods. The authors reported a 6-month postoperative motor success rate of 85%, 89%, and 100% for the augmented surgery group, prism responders, and prism non-responders, respectively.7 However, Hwang et al. also reported a sensory success rate of 37%, 100%, and 43% for the augmented surgery group, prism responders, and prism non-responders, respectively.7

The current study differs from former studies7,9 in two respects. First, the alternative augmented surgical formula (based on the average of near deviation without correction and the distance deviation with correction)6 was used rather than the augmented surgical formula (based on the average of the near deviation with and without correction)6 used by the authors.7,9 However, this did not result in a remarkable difference in the surgical target angle because only patients with a normal AC/A ratio were included. Second, all patients with prism adaptation in the current study (responders and non-responders) underwent surgery based on the prism-adapted angle, whereas in the previous studies3,7,9,11 only prism responders underwent prism-adapted surgery and non-responders underwent surgery for the preadaptation angle.

The Prism Adaptation Study Research Group3 reported that it was not clear whether systematically increasing the amount of surgery for all patients would produce alignment comparable to that obtained in their study with prism adaptation. Their data suggested that the prism adaptation process identified a group of patients who could safely undergo a larger amount of surgery without increasing the risk of overcorrection. Later, Wright and Bruce-Lyle6 devised the augmented surgery formula to systematically increase the amount of surgery for all patients with acquired accommodative esotropia. However, overcorrection was a threat associated with that method. Nevertheless, the authors6 stated that innate, large fusional amplitudes would compensate for overcorrections. Therefore, the current study addressed whether prism adaptation is superior to the augmented surgery formula in precisely identifying the group of patients who can safely undergo a larger amount of surgery, and determining the amount of surgery needed.

In the current study, we noted that 35% of the prism adaptation group showed a build-up of esotropia of more than 10 PD with prisms. In the Prism Adaptation Study, 45% of patients showed a similar build-up of esotropia with prism adaptation.3 These rates conform to the 25% to 30% undercorrection rates noted in previous studies with standard surgery.3,6,11,12 Thus, it can be concluded that approximately one-third of the patients with acquired esotropia require surgical augmentation. By systematically increasing the amount of surgery for all patients, two-thirds of the patients would acquire a consecutive exotropia.

Results of the augmented surgical formula may be orthotropia (Figure AA, available in the online version of this article), a residual esotropia (Figure AB), or a consecutive exotropia (Figure AC). These variable outcomes can be explained by the following hypothesis: if the amount of surgical augmentation (using the augmented surgery formula) was equivalent to the amount of prism build-up (if prism adaptation was undertaken), then the result would be postoperative orthotropia. However, if the amount of surgical augmentation was either less than or more than the amount of presumed prism build-up, a residual esotropia or a consecutive exotropia would result. The significant and substantial difference in the success rates between the prism adaptation group (90%) and the augmented surgery group (55%) supports this hypothesis.

(A) (Top) Postoperative orthotropia. (Middle) Partially accommodative esotropia of 70 prism dipoters (PD) (sc) and 50 PD (cc). (Bottom) Orthotropia (cc) after surgery for a target angle of 60 PD (5-mm bimedial muscle recession and 7-mm right lateral rectus muscle resection). (B) (Top) Postoperative residual esotropia. (Middle) Partially accommodative esotropia of 54 PD (sc) and 25 PD (cc). (Bottom) Residual esotropia of 18 PD (cc) after surgery for a target angle of 39.5 PD (5.5-mm bimedial muscle recession). (C) (Top) Postoperative consecutive exotropia. (Middle) Partially accommodative esotropia of 59 PD (sc) and 30 PD (cc). (Bottom) Consecutive exotropia of 14 PD (cc) after surgery for a target angle of 44.5 PD (6-mm bimedial muscle recession). sc = without spectacles; cc = with spectacles

Figure A.

(A) (Top) Postoperative orthotropia. (Middle) Partially accommodative esotropia of 70 prism dipoters (PD) (sc) and 50 PD (cc). (Bottom) Orthotropia (cc) after surgery for a target angle of 60 PD (5-mm bimedial muscle recession and 7-mm right lateral rectus muscle resection). (B) (Top) Postoperative residual esotropia. (Middle) Partially accommodative esotropia of 54 PD (sc) and 25 PD (cc). (Bottom) Residual esotropia of 18 PD (cc) after surgery for a target angle of 39.5 PD (5.5-mm bimedial muscle recession). (C) (Top) Postoperative consecutive exotropia. (Middle) Partially accommodative esotropia of 59 PD (sc) and 30 PD (cc). (Bottom) Consecutive exotropia of 14 PD (cc) after surgery for a target angle of 44.5 PD (6-mm bimedial muscle recession). sc = without spectacles; cc = with spectacles

It can be concluded that prism adaptation is superior to the augmented surgical formula in precisely determining the amount of surgery to be performed and identifying the group of patients who can safely receive larger amounts of surgery. However, if the surgical target angle in the prism adaptation group is calculated with the augmented surgery (the average of distance deviation with correction [29 PD] and near deviation without correction [48.35 PD]), the angle will be 38.7 PD, which is approximately the same as the prism-adapted angle in the prism adaptation group (37.7 PD). Based on this observation, is the time, cost, and effort necessary to perform prism adaptation really worth it?

Wright and Bruce-Lyle6 suggested a reduction or removal of the amount of plus in the spectacles, thus titrating a small consecutive exotropia (following augmented surgery) to orthotropia. Therefore, the motor success rate of 88% obtained with the augmented surgery formula could improve to 98% and 100% after reduction or removal of hyperopic correction.6 We investigated this option in the current study 6 month postoperatively, after spectacle power reduction or removal following the 3-month postoperative evaluation to titrate a consecutive exotropia. This resulted in a rise of the success rates in the augmented surgery group from 55% to 80% (P = .063). Accordingly, the difference in success rates between the augmented surgery group (80%) and the prism adaptation group (95%) were insignificant 6 months postoperatively (P = .151).

Comparing the success rates from the current study with previous studies,3,6,7 we found that the success rates for the prism adaptation group were superior and the success rates for the augmented surgery group were inferior to previous studies. The superior surgical outcome in the prism adaptation group can be attributed to the fact that all patients with prism adaptation (responders and non-responders) underwent surgery based on the prism-adapted angle. However, in previous studies3,7,9,11 responders underwent prism-adapted surgery, whereas nonresponders underwent surgery for the preadaptation angle. Non-responders did not benefit from prism adaptation in previous studies,3,7,9,11 lowering the overall rate of success, whereas non-responders did benefit in the current study.

Is performing surgery for the prism-adapted angle in all patients with prism adaptation regardless of prism response superior to performing surgery for the prism-adapted angle only in prism responders and performing surgery for the angle prior to prism adaptation in prism non-responders? The current study performed prism-adapted surgery in all patients with prism adaptation. We reported success rates of 90% at 3 months postoperatively and 95% at 6 months postoperatively. The Prism Adaptation Study Research Group only performed prism-adapted surgery on prism responders. At 6 months postoperatively, the highest motor success rate was recorded in prism adaptation responders who underwent surgery for the prism-adapted angle (89%) versus prism adaptation responders who underwent surgery for their entry angle of deviation (79%). Among non-responders, the motor success rate was 73%.3 Similar to the current study, other studies performed surgery for all patients with prism adaptation, regardless of prism response.13–15 Six months postoperatively, Altman et al.13 reported alignment within 8 PD of orthotropia at 20 feet in 90% of patients. Ela-Dalman et al.15 reported postoperative alignment between 6 PD of exotropia and 5 PD of esotropia at distance in 100% of patients. Therefore, surgery for the prism-adapted angle is superior to surgery for the initial angle of esotropia.

In the current study, the reason for the inferior surgical outcome among the augmented surgery group as compared with previous studies performing surgery based on the augmented surgical formula can be explained by the fact that this group comprised 8 patients (40%) with non-accommodative esotropia and 12 patients (60%) with partially accommodative esotropia, whereas previous studies6,7 included only patients with partially accommodative esotropia. The failure rate in the augmented surgery group was 45% (9 patients) at 3 months postoperatively. Of the 9 patients, 6 had non-accommodative esotropia and 3 had partially accommodative esotropia. Moreover, the 3-month postoperative success rates in the augmented surgery group were estimated to be as low as 2 of 8 (25%) among patients with non-accommodative esotropia, and as high as 9 of 12 (75%) among patients with partially accommodative esotropia (P = .028). Six months postoperatively, the success rates in the augmented surgery group were 5 of 8 (62.5%) in patients with non-accommodative esotropia and 11 of 12 (91.7%) in patients with partially accommodative esotropia (P = .11).

The substantial difference in the success rates between patients with non-accommodative esotropia and patients with partially accommodative esotropia can be explained by the fact that the former had surgery based on a formula that was more aligned to a standard one than an augmented one. The mean increase in the surgical target angle, by using an augmented rather than a standard formula, in patients with partially accommodative esotropia was approximately 11.46 ± 3.33 PD, in contrast to 5.88 ± 3.84 PD in patients with non-accommodative esotropia. The difference between the two means was significant (P = .005).

The prism adaptation group was not significantly affected by the type of esotropia (non-accommodative or partially accommodative). This group included 13 (65%) and 7 (35%) patients with partially accommodative and non-accommodative esotropia, respectively. The 3-month postoperative success rates were 12 of 13 (92.3%) in patients with partially accomodative esotropia and 6 of 7 (85.7%) in patients with non-accommodative estropia (P = .639). The 6-month postoperative success rates were 92.3% in patients with partially accommodative esotropia, whereas the rates reached 100% in patients with non-accommodative esotropia (P = .452). This can be explained because the surgical target angle in the prism adaptation group was equivalent to the power of the press-on prisms worn plus distance deviation measured through worn prisms, without considering deviation without spectacles.

The 3-month postoperative success rates recorded in patients with partially accommodative esotropia assigned to the prism adaptation and augmented surgery groups were 92.3% and 75%, respectively (P = .238). The 6-month postoperative success rates were 92.3% and 91.7% in the prism adaptation group and the augmented surgery group, respectively (P = .953). The difference in the 3-month postoperative success rates between patients with non-accommodative esotropia included in the prism adaptation group (85.7%) versus those included in the augmented surgery group (25%) was substantial and significant (P = .019). However, the 6-month postoperative success rates for those with non-accommodative esotropia were not significantly higher in the prism adaptation group (100%) than in the augmented surgery group (62.5%) (P = .07). The augmented surgery formula might have a beneficial role, approaching that of prism adaptation, in cases of partially accommodative esotropia. However, it has no role in non-accommodative esotropia, where prism adaptation is ideal.

However, the process of prism adaptation has limitations that are not encountered when using the augmented surgical formula. Prism adaptation requires additional time and expense prior to surgery,3,7,9 whereas the augmented surgical formula provides rapid treatment without needing prisms or multiple preoperative visits.6,7,9 Moreover, Fresnel prisms cause a reduction and distortion in visual acuity during the process of prism adaptation.3,16 Finally, to allow the expected build-up of deviation with prisms, prism adaptation is not a feasible option in patients with angles of esotropia exceeding 40 PD.3

In the current study, the prism adaptation group required a mean duration of wearing prisms for 32.6 ± 18.3 days prior to surgery. During that period, an average of five clinic visits (2 to 9) were necessary for prism prescription and adjustments. An average of 2.7 prism changes (1 to 5) were required during the process of prism adaptation. Moreover, the prism power had to be split between the two eyes, adding to the expenses.

Ela-Dalman et al.15 conducted a study to evaluate results of surgery based on prism adaptation for only 1 hour. The preoperative angle of deviation at distance was 20.4 ± 4.2 PD. It increased to 36.2 ± 4.2 PD after the maximum motor fusion test17 followed by 1 hour of prism adaptation testing. Following prism-adapted surgery, the final postoperative deviation was 1.3 ± 3.3 PD at distance, and 5.2 ± 1.5 PD at near, after a mean postoperative follow-up of 18 ± 2.6 months. The success rate was 100%.15 Ela-Dalman et al.'s15 results suggest that the limitations of a lengthy prism adaptation test, which we encountered in the current study, may be avoided with a short prism adaptation test.

A frequent complication in the current study was the reduction in visual acuity with press-on prisms. In the prism adaptation group, the mean aided visual acuity before prism adaptation was 0.88 ± 0.17 (decimal) for each eye. Press-on prisms reduced the mean visual acuity to 0.65 ± 0.22 and 0.63 ± 0.19 (decimal) in the right and left eyes, respectively. The mean reduction in visual acuity with press-on prisms was 0.23 ± 0.21 (decimal) (P = .001) and 0.25 ± 0.13 (decimal) (P < .001) in the right and left eyes, respectively.

Prism adaptation precisely determines the surgical target angle, with markedly lower subsequent risk of ocular misalignment. Moreover, it is a method that precisely identifies the group of patients who can safely undergo augmentation of surgery. However, the augmented surgery formula is a method of systematically increasing the amount of surgery for all patients, with no precise determination of the exact amount of augmentation required or the true candidates for augmentation. Therefore, theoretically speaking, overcorrections and undercorrections are potential risks of this unpredictable method. However, practically speaking, the surgical target angle would not have been significantly different in the prism adaptation group if the augmented surgery formula was used instead. Moreover, any consecutive exotropia that develops could be titrated to orthotropia or near orthotropia with hyperopic spectacle power reduction. However, this is only applicable in cases of partially accommodative esotropia, not in cases of non-accommodative esotropia.

Prism adaptation, although a precise method for surgical target angle determination in all cases of acquired comitant esotropia, has a peculiar indication in cases of non-accommodative esotropia, whereas the augmented surgical formula has no place. To maximize the benefit of prism adaptation, it is recommended that all patients with prism adaptation, whether responders or non-responders, undergo surgery based on the prism-adapted angle.

References

  1. Seeley MZ, Paul TO, Crowe S, Dahms G, Lichterman S, Traboulsi EI. Comparison of clinical characteristics of familial and sporadic acquired accommodative esotropia. J AAPOS. 2001;5(1):18–20. doi:10.1067/mpa.2001.111784 [CrossRef]
  2. Jotterand VH, Isenberg SJ. Enhancing surgery for acquired esotropia. Ophthalmic Surg. 1988;19(4):263–266.
  3. Prism Adaptation Study Research Group. Efficacy of prism adaptation in the surgical management of acquired esotropia. Arch Ophthalmol. 1990;108(9):1248–1256.
  4. Parks MM. Ocular Motility and Strabismus. Hagerstown, MD: Harper & Row; 1975:100–108.
  5. Scott WE, Thalacker JA. Preoperative prism adaptation in acquired esotropia. Ophthalmologica. 1984;189(1–2):49–53.
  6. Wright KW, Bruce-Lyle L. Augmented surgery for esotropia associated with high hypermetropia. J Pediatr Ophthalmol Strabismus. 1993;30(3):167–170.
  7. Hwang JM, Min BM, Park SC, Oh SY. A randomized comparison of prism adaptation and augmented surgery in the surgical management of esotropia associated with hypermetropia. J Pediatr Ophthalmol Strabismus. 1999;36(4):196–200.
  8. Kassem RR. A pilot study of the value of prism adaptation in planning strabismus reoperations. J Pediatr Ophthalmol Strabismus. 2008;45(2):98–103. doi:10.3928/01913913-20080301-12 [CrossRef]
  9. Hwang JM, Min BM, Park SC, Oh SY, Sung NK. A randomized comparison of prism adaptation and augmented surgery in the surgical management of esotropia associated with hypermetropia: one-year surgical outcomes. J AAPOS. 2001;5(1):31–34. doi:10.1067/mpa.2001.111782 [CrossRef]
  10. Greenwald MJ, Connett JE, Scott WE. Prism adaptation study. Ophthalmology. 1997;104(11):1725–1726.
  11. Repka MX, Connett JE, Scott WEPrism Adaptation Study Research Group. The one-year surgical outcome after prism adaptation for the management of acquired esotropia. Ophthalmology. 1996;103(6):922–928. doi:10.1016/S0161-6420(96)30586-1 [CrossRef]
  12. Repka MX, Wentworth DPrism Adaptation Study Research Group. Predictors of prism response during prism adaptation. J Pediatr Ophthalmol Strabismus. 1991;28(4):202–205.
  13. Altman M, Baker JD, Petrunak J, Schweers M. Can prism adaptation for acquired esotropia be accomplished in a shorter time frame?J AAPOS. 1999;3(5):259–262. doi:10.1016/S1091-8531(99)70019-4 [CrossRef]
  14. Velez FG, Rosenbaum AL. Preoperative prism adaptation for acquired esotropia: long-term results. J AAPOS. 2002;6(3):168–173. doi:10.1067/mpa.2002.123397 [CrossRef]
  15. Ela-Dalman N, Velez G, Thacker N, Britt MT, Velez FG. Maximum motor fusion combined with one-hour preoperative prism adaptation test in patients with acquired esotropia. J AAPOS. 2006;10(6):561–564. doi:10.1016/j.jaapos.2006.09.011 [CrossRef]
  16. Scott WE. Office use of prisms. In: Helveston EM, ed. Symposium on Strabismus: Transactions of the New Orleans Academy of Ophthalmology. St. Louis, MO: CV Mosby Co; 1978:91–103.
  17. Mims JL III, Wood RC. The maximum motor fusion test: a parameter for surgery for acquired esotropia. J AAPOS. 2000;4(4):211–216. doi:10.1067/mpa.2000.105307 [CrossRef]

Amount of Surgery for Range of Target Angle

Target Angle (PD) MR Recession OU (mm) LR Resection (mm)
12 to 15 3
16 to 20 3.5
21 to 25 4
26 to 30 4.5
31 to 35 5
36 to 40 5.5
41 to 45 6
46 to 50 5 5
51 to 55 5 6
56 to 60 5 7
61 to 65 5 8
66 to 70 5 5.5 (OU)
71 to 75 5 6.5 (OU)

Preoperative, Intraoperative, and Postoperative Data

Parameter Prism Adaptation (n = 20) Augmented Formula (n = 20) Pa,b
Preoperative
  Sex, n (%) .744
    Male 8 (40) 7 (35)
    Female 12 (60) 13 (65)
  Age (y), mean ± SD 8.82 ± 3.80 8.71 ± 4.76 .655
  Age at onset (y), mean ± SD 3.50 ± 1.70 3.97 ± 2.85 .849
  Duration (y), mean ± SD 5.34 ± 4.02 4.74 ± 3.52 .797
  Sensory testing, Worth 4-dot (6 m) .509
    Suppression 18 (90) 16 (80)
    Diplopia 0 1 (5)
    Intermittent fusion 2 (10) 1 (5)
    Inability to perform test 0 2 (10)
  Sensory testing, Worth 4-dot (0.33 m) .513
    Suppression 18 (90) 18 (90)
    Diplopia 0 1 (5)
    Intermittent fusion 2 (10) 1 (5)
  Sensory testing, Titmus Stereo Test .311
    800 to 40 seconds of arc 1 (5) 0
    Absent stereopsis 19 (95) 20 (100)
    Deviation angle, Dcc (PD), mean ± SDb 29.00 ± 6.20 43.65 ± 13.51 < .001a
    Deviation angle, Nsc (PD), mean ± SDb 48.35 ± 14.34 62.15 ± 14.58 .002a
  Type of esotropia, n (%) .744
    Partially accommodative 13 (65) 12 (60)
    Non-accommodative 7 (35) 8 (40)
    Spherical equivalent OD (D), mean ± SD 3.57 ± 2.03 3.48 ± 1.70 .860
    Spherical equivalent OS (D), mean ± SD 3.64 ± 2.06 3.36 ± 1.59 .704
    Surgical target angle (PD), mean ± SDb 37.70 ± 9.24 52.88 ± 13.30 .001a
Intraoperative
  Medial rectus muscle recession (mm), mean ± SDc 10.05 ± 1.19 9.95 ± 0.76 .483
  Lateral rectus muscle resection (mm), mean ± SDd 1.30 ± 2.32 5.50 ± 3.65 < .001a
3-month postoperative data
  Sensory testing, Worth 4-dot (6 m) .424
    Fusion 8 (40) 10 (50)
    Suppression 7 (35) 3 (15)
    Diplopia 5 (25) 5 (25)
    Intermittent fusion 0 1 (5)
    Inability to perform test 0 1 (5)
  Sensory testing, Worth 4-dot (0.33 m) .494
    Fusion 8 (40) 12 (60)
    Suppression 7 (35) 3 (15)
    Diplopia 4 (20) 4 (20)
    Intermittent fusion 1 (5) 1 (5)
  Sensory testing, Titmus Stereo Test .680
    800 to 40 seconds of arc 6 (30) 4 (20)
    3,000 seconds of arc 1 (5) 2 (10)
    Absent stereopsis 13 (65) 14 (70)
    Deviation angle, Dcc (PD), mean ± SDa −0.45 ± 4.97 −2.35 ± 10.66 .502
    Deviation angle, Ncc (PD), mean ± SDa 0.05 ± 5.53 1.85 ± 11.01 .501
6-month postoperative data
  Sensory testing, Worth 4-dot (6 m) .693
    Fusion 9 (45) 10 (50)
    Suppression 6 (30) 4 (20)
    Diplopia 5 (25) 5 (25)
    Intermittent fusion 0 1 (5)
  Sensory testing, Worth 4-dot (0.33 m) .155
    Fusion 9 (45) 14 (70)
    Suppression 5 (25) 1 (5)
    Diplopia 4 (20) 4 (20)
    Intermittent fusion 1 (5) 1 (5)
    Suppression/diplopia 1 (5) 0
  Sensory testing, Titmus Stereo Test 1.000
    800 to 40 seconds of arc 5 (25) 5 (25)
    3,000 seconds of arc 1 (5) 1 (5)
    Absent stereopsis 14 (70) 14 (70)
    Deviation angle, Dcc (PD), mean ± SDa 1.70 ± 5.92 0.55 ± 8.40 .804
    Deviation angle, Ncc (PD), mean ± SDa 1.90 ± 4.75 2.40 ± 8.55 .551
3-month outcome
  Motor success, n (%) 18 (90) 11 (55) .013a
  Sensory success, n (%) 9 (45) 8 (40) .204
6-month outcome
  Motor success, n (%) 19 (95) 16 (80) .151
  Sensory success, n (%) 10 (50) 14 (70) .102

Reduction of Hyperopic Correction

Group Case No. SE of Rx at Entry (D) Type of ET 3-Month Postoperative Deviation (PD)a SE of Rxb (D) 6-Month Postoperative Deviation (PD)a




OD OS SPCT 6 m SPCT 0.33 m OD OS SPCT 6 m SPCT 0.33 m
P 1 2.50 4.125 NA XT 10 XT 12 0.00 0.00 0 XT 6
P 7 2.00 1.75 NA RXT 16, LXT 10 RDHD 10 0.00 0.00 RDHD 10 LET 6
A 29 5.875 5.625 PA XT 16 XT 14 3.125 3.00 0 0
A 32 1.875 1.25 NA XT 16 XT 6 0.125 0.375 XT 4 ET 2
A 38 0.25 4.25 NA XT 14 XT 6 0.25 3.00 XT 8 XT 8
A 40 6.00 4.375 PA XT 12 0 3.75 2.25 0 0
Authors

From the Department of Ophthalmology, Cairo University, Cairo, Egypt.

The authors have no financial or proprietary interest in the materials presented herein.

Correspondence: Rehab R. Kassem, MD, FRCS(Glasg), Department of Ophthalmology, Kasr Al-Einy Hospital, Cairo University, Cairo, Egypt. E-mail: rehabrkassem@hotmail.com

Received: September 14, 2019
Accepted: November 21, 2019

10.3928/01913913-20200114-01

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