C L I N I C A L
A N D
E X P E R I M E N T A L
OPTOMETRY RESEARCH PAPER
The impact of prism adaptation test on surgical outcomes in patients with primary exotropia DOI:10.1111/cxo.12219
Clin Exp Optom 2015; 98: 224–227 Ayse Kiyak Yilmaz MD Suheyla Kose PhD Suzan Guven Yilmaz MD Onder Uretmen PhD Ophthalmology Department, School of Medicine, Ege University, Izmir, Turkey E-mail: [email protected]
Submitted: 18 April 2014 Revised: 19 August 2014 Accepted for publication: 23 August 2014
Background: We aimed to determine the impact of the preoperative prism adaptation test (PAT) on surgical outcomes in patients with primary exotropia. Methods: Thirty-eight consecutive patients with primary exotropia were enrolled. Preoperative PAT was performed in 18 randomly selected patients (Group 1). Surgery was based on the angle of deviation at distance measured after PAT. The remaining 20 patients in whom PAT was not performed comprised Group 2. Surgery was based on the angle of deviation at distance in these patients. Surgical success was defined as ocular alignment within eight prism dioptres (PD) of orthophoria. Results: Satisfactory motor alignment (± 8 PD) was achieved in 16 Group 1 patients (88.9 per cent) and 16 Group 2 patients (80 per cent) one year after surgery (p = 0.6; chi-square test). There were no statistically significant differences in demographic parameters, preoperative and post-operative angle of deviation between the two groups (p > 0.05; MannWhitney U and chi-square tests). Nine patients in Group 1 (50 per cent) and two patients in Group 2 (10 per cent) had increased binocular vision one year post-operatively. A statistically significant difference was determined in terms of change in binocular single vision between the two groups (p = 0.01; chi-square test). Conclusion: Although the prism adaptation test did not lead to a significant increment in motor success, it may be helpful in achieving a more favourable functional surgical outcome in patients with primary exotropia.
Key words: exotropia, prism adaptation test, surgery The prism adaptation test (PAT) was first described for acquired esotropia1 and its efficacy confirmed by later studies.2,3 Improved surgical results were reported when the increase of the deviation under the influence of correcting prisms (prism adaptation) was taken into account when determining the surgical dosage. The Prism Adaptation Study Research Group2 showed that the success rate in patients with acquired esotropia whose angle increased under the influence of prisms base-out was higher after augmented surgery (89 per cent) than when conventional surgery was performed (79 per cent) (p < 0.05). In addition, the PAT might be helpful in achieving a favourable surgical outcome in intermittent exotropia.4 Results from previous studies indicate that preoperative prism correction allows a more accurate determination of the amount of surgery, prevents the risk of undue overcorrection and promotes the development of binocularity.5 In this prospective study, we aimed to determine Clinical and Experimental Optometry 98.3 May 2015
224
the impact of pre-operative PAT on the surgical outcome in patients with primary exotropia and whether the preoperative prism adaptation test is useful for achieving a more favourable functional surgical outcome. METHODS In this prospective study, conducted between 2009 and 2011, 38 (23 female) consecutive patients aged five to 49 years (mean 17.5 ± 10.9 years) with basic-type primary exotropia, who were scheduled to undergo strabismic surgery were enrolled. Basic-type primary exotropia is present when the exodeviation is approximately the same at distance and near fixation and there may or may not be binocular single vision. The difference between the prism cover test measurements for near and distant fixation does not exceed 10 PD.1 Patients with amblyopia, dissociated vertical deviation, A or V pattern, oblique or vertical rectus muscle dysfunction
or nystagmus were not included in the study. Patients who had undergone previous surgery for strabismus, with a diagnosis of intellectual disability or underlying neurologic disorder were excluded. Ethics approval for this prospective study was obtained from the Ege University local research ethics committee. Written and informed consent from patients was obtained prior to study inclusion. The angle of exodeviation in the study patients ranged from 16 to 50 PD (median, 32.7 ± 10.1 PD) at distance and from 18 to 52 PD (median, 34.7 ± 10.1 PD) at near. The measurement of deviation was obtained after 45 minutes of unilateral occlusion, while the patient was wearing fully corrective lenses without cycloplegia and fixated on an accommodative target at distances of 6.0 metres and 0.3 metres with the prism and alternate cover test. While the patient was fixating at 0.3 metres and looking through +3.00 D lenses, which were added over the distance correction and were placed in the © 2014 The Authors
Clinical and Experimental Optometry © 2014 Optometrists Association Australia
The impact of prism adaptation test on surgical outcomes Kiyak Yilmaz, Kose, Guven Yilmaz and Uretmen
trial frame, measurement for near was repeated for all patients. These measurements were performed to make sure that the type of exotropia was basic. Refractive error was obtained by cycloplegic refraction measured after 45 minutes following two topical instillations of 1% cyclopentolate chloride administered five minutes apart. Cycloplegic refraction and Snellen visual acuity (VA) were recorded for each patient. Sensory examination (with full correction but without +3.00 D lenses or cycloplegia), included Bagolini’s striated glass test (directing the patient to fixate on a spotlight held 33 cm from the eyes) (Oculus, Wetzler, Germany) and TNO test (Lameris Ootech BV, AG Veenendaal). The prism adaptation test was performed in18 randomly selected patients (Group 1) using Fresnel Press-OnTM prisms (Health Care Specialties Division/3M, St. Paul, Minnesota, USA), while the patients were wearing full corrective lenses without cycloplegia. The power of the prism was divided equally between the two eyes. The power of each prism was gradually increased according to the response to deviation as determined by the prism and alternate cover test. The PAT continued for three or four hours until no additional prism was required to neutralise the deviation as described by Ohtsuki and colleagues.5 Patients who showed an increase in exodeviation by five PD or more with the PAT were defined as having a positive prism adaptation response. Surgery was performed based on the angle of deviation at distance measured after PAT. The remaining 20 patients, in whom PAT was not performed, composed Group 2. Surgery was performed, based on the original angle of deviation at distance in these patients. Surgical success was defined as ocular alignment within eight PD of orthophoria at distance. Surgery was performed by one of the authors (SK) on the non-fixating eye with recession of the lateral rectus muscle combined with resection of the medial rectus muscle in all groups. The surgeon was masked to which patients had the PAT and which did not. The amount of surgery is described in Table 1. Patients were examined one week, one month, three months, six months and one year after surgery. Group 1 was divided into two subgroups (Group 1A and Group 1B), based on the results of PAT. Patients with a negative response comprised Group 1A and patients with a positive response comprised Group 1B.
Deviation
Amount of recession and resection Lateral rectus Medial rectus recession resection
20 PD
5 mm
4 mm
25 PD
6 mm
5 mm
30 PD
6.5 mm
6 mm
35 PD
6.5 mm
7 mm
40 PD
7 mm
7.5 mm
45 PD
7 mm
8 mm
50 PD
7 mm
8.5 mm
PD: prism dioptre
Table 1. Amount of surgical recession and resection according to deviation
Comparisons between groups regarding measures were performed with chi-square, Mann-Whitney U, Fisher’s Exact and Kruskal–Wallis tests. Statistical significance was defined as p less than 0.05. RESULTS Visual acuity was 0.01 ± 0.2 logMAR in all patients. Demographic data and clinical characteristics of patients are presented in Table 2. There was no statistically significant difference between Group 1 and Group 2 regarding age at the diagnosis, age at the time of surgery, duration between diagnosis and strabismic surgery, demographic data and refractive error (p > 0.05, Mann-Whitney U and chi-square test). The mean preoperative angle of exodeviation was 31.2 ± 7.7 PD (range: 16 to 40 PD) for Group 1 before PAT and 33.8 ± 11.7 PD (range: 16 to 50 PD) for Group 2. After PAT, the mean target angle for distance increased to 36.3 ± 8.1 PD (range: 20 to 50 PD) in Group 1. There were no statistically significant differences in preoperative angle of deviation and binocular single vision between the two groups (p = 0.696, Mann-Whitney U test and p = 0.157, chisquare test, respectively). Surgical success rates were 100 per cent at one month and 88.9 per cent at one year in Group 1 and 85 per cent at one month and 80 per cent at one year in Group 2. There were no statistically significant differences regarding the surgical outcome between
© 2014 The Authors Clinical and Experimental Optometry © 2014 Optometrists Association Australia
Group 1 and Group 2 at one week, one, three, six and 12 months post-operatively (p = 0.186, p = 0.852, p = 0.696, p = 0.710 and p = 0.606, chi-square test; respectively). There was no statistically significant difference between the groups in relation to the amount of alignment obtained per each millimetre of surgical intervention (for Groups 1 and 2, 2.30 PD and 2.38 PD, respectively; p = 0.158, Mann-Whitney U test). For a detailed analysis of the impact of PAT response on the surgical success rate, we also evaluated patients with negative PAT responses (Group 1A), patients with positive PAT responses (Group 1B) and patients in whom PAT was not performed (Group 2). The mean increase in the target angle of deviation after PAT was 0.2 ± 0.4 PD for Group 1A and 7.2 ± 4.1 PD for Group 1B (p = 0.001, Mann-Whitney U test). There was an increase more than eight PD in four patients in Group 1B. The post-operative angle of deviation and the surgical outcome in the three groups are presented in Table 3. There was no case with post-operative overcorrection in any group. The post-operative angle of deviation at one year in Group 1B was significantly smaller than in Group 2 (p = 0.04, Mann-Whitney U test). There was no statistical difference among the groups in the surgical outcome at six months and at one year (p = 0.490 and p = 0.488, respectively by Fisher’s exact test). Nine patients (50 per cent) in Group 1 and two patients (10 per cent) in Group 2 had shown an increment of binocular single vision at one year post-operatively and this difference was statistically significant (p = 0.01, chi-square test). Three patients in Group 1 and one patient in Group 2, who did not have binocular single vision preoperatively, developed binocular single vision after surgery. Stereopsis was improved from gross to fine levels in the remaining cases. For further analysis of binocular single vision, the patients were evaluated in Groups 1A, 1B and 2. Two patients in Group 1A (40 per cent), seven patients in Group 1B (53.8 per cent) and two patients in Group 2 (10 per cent) had shown an increment of binocular single vision at one year postoperatively. The patients in Group 1B showed a significantly better improvement in binocular single vision compared to patients in Group 2 with regards to the percentage of patients who showed improvement after surgery (p = 0.013; chi-square test). The increments in binocular single Clinical and Experimental Optometry 98.3 May 2015
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The impact of prism adaptation test on surgical outcomes Kiyak Yilmaz, Kose, Guven Yilmaz and Uretmen
Group 1 (18 patients)
Group 2 (20 patients)
p-value
Age (years), mean ± SD 3.5 ± 3.7
4.2 ± 6.1
0.806*
Strabismus surgery
18.0 ± 12.8
17.0 ± 9.1
0.988*
Duration between diagnosis and surgery (years)
14.5 ± 13.1
12.8 ± 7.2
0.874†
Diagnosis
Gender (% of patients) Male
9 (50.0%)
6 (30.0%)
0.320‡
Female
9 (50.0%)
14 (70.0%)
0.843‡
0 to -3.00 sphere
11 (30.6%)
13 (32.5%)
0 to +3.00 sphere
22 (61.1%)
24 (60.0%)
0 to -2.00 cylinder
9 (25.0%)
12 (30.0%)
0 to +2.00 cylinder
15 (41.7%)
13 (32.5%)
Preoperative deviation (PD)
Before PAT
Mean ± SD
31.2 ± 7.7
Refractive error (D)
33.8 ± 11.7
After PAT
0.933†
36.3 ± 8.1
0.696†
Binocular single vision Stereopsis (+)§
12 (67%)
10 (50%)
§
6 (33%)
10 (50%)
Stereopsis (-) † §
0.157‡
Mann-Whitney U test, ‡ Chi-square test, SD: Standard deviation, PAT: prism adaptation test Stereopsis was determined using the TNO test and Bagolini’s striated glass
Table 2. Demographic data and clinical characteristics of patients
Post-operative duration
Group 1A (5 patients)
Group 1B (13 patients)
Group 2 (20 patients)
p-value
4.0 ± 7.6
3.8 ± 6.1
4.0 ± 5.4
0.716†
80.0%
92.3%
85.0%
0.490‡
4.4 ± 6.4
1.5 ± 4.1
5.3 ± 5.1
0.042†
80.0%
92.3%
80.0%
0.488‡
Six months Angle of deviation (PD) ± SD Surgical success rate One year Angle of deviation (PD) ± SD Surgical success rate
Kruskal–Wallis test, ‡ Fisher’s exact test SD: Standard deviation, PD: prism dioptre
†
Table 3. Post-operative angle of deviation and surgical success in Group 1A, Group 1B and Group 2 vision in the three groups are presented in Table 4. DISCUSSION The prism adaptation test was claimed to improve the results of strabismus surgery Clinical and Experimental Optometry 98.3 May 2015
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and many studies confirmed the efficacy of PAT for esotropia.2,3 The mechanism of progressive increase in prism power is not well understood in relation to exotropia. Prisms are useful to facilitate preoperative or post-operative binocular sensory fusion and surgical over- or under-correction in
primary exotropes. Veronneau-Troutman, Traykovski and DeRosa6 reported that PAT improved the prognosis and predictability of surgery for strabismus in intermittent exotropia. In contrast, Shippman and colleagues7 did not find PAT useful in this type of strabismus. Many studies indicate that preoperative prism correction allows a relatively accurate determination of the amount of the prism for surgery.4,6,8 Thus, it prevents the risk of under-correction and also promotes the development of binocular sensory vision.9,10 In our study, 13 of 18 patients (72.2 per cent) on whom PAT was conducted, showed an increment of five or more prism dioptres in the angle of deviation from six metres compared to the initial angle measured by prism. Consequently, surgical treatment for these patients consisted of larger muscle resection and recession. If the PAT had not been performed pre-operatively, patients would probably have been under-corrected. Dadeya, Kamlesh and Nanival4 reported that satisfactory motor alignment (± 5 PD of orthophoria) was achieved in 14 (53.8 per cent) PAT-negative and 24 (88.8 per cent) PAT-positive patients with basic type of intermittant exotropia. In our study, satisfactory motor alignment (± 8 PD of orthophoria) was achieved in 80 per cent PAT-negative and 92.3 per cent PAT-positive patients one year post-operatively. In our study group, the rate of satisfactory motor alignment appeared better in PAT-positive than in PAT-negative patients; however, this difference did not reach statistical significance, most probably due to the limited number of patients. A further randomised prospective study with large numbers of cases is needed for generalised conclusions of a large population. Ohtsuki and colleagues10 concluded that patients who show marked response to prism correction had a tendency to have a better outcome with regard to the single binocular vision examined with Bagolini lens test during a longer follow-up (three years). In contrast, Dadeya, Kamlesh and Nanival4 observed similar sensory success for PATpositive and PAT-negative patients. The authors4 suggested that the reason for poor sensory results might be that most of their patients had poor control of deviation. We determined that sensory results were significantly better in PAT-conducted than control patients post-operatively. It could be due to the fact that the residual angle of deviation was closer to the orthophoria in Group 1; © 2014 The Authors
Clinical and Experimental Optometry © 2014 Optometrists Association Australia
The impact of prism adaptation test on surgical outcomes Kiyak Yilmaz, Kose, Guven Yilmaz and Uretmen
Group
Preoperative
Post-operative
TNO test (arcsec)
TNO test (arcsec)
Group 1A
Patient 1: 120
60
Two of five patients
Patient 2: 120
60
Group 1B Seven of 13 patients
Patient 1: 120
60
Patient 2: 120
60
Patient 3: 120
15
Patient 4: 120
60
Patient 5: Stereopsis (-)
Group 2 2 of 20 patients †
480
Patient 6: Stereopsis (-)
480
Patient 7: Stereopsis (-)
Fusion (+)† no stereopsis
Patient 1: 960
60
Patient 2: Stereopsis (-)
480
Tested with Bagolini’s striated glass
Table 4. Post-operative increment of binocular single vision in Group 1A, Group 1B and Group 2 however, all patients in both groups had manifest exotropia preoperatively and thus might have poor stereopsis. This stereopsis may have been lost when the patients developed their constant strabismus. Whether or not this stereopsis is recoverable after strabismic surgery that provides good alignment may be dependent upon how soon the intervention is performed. In our study, we could not determine how long the patients had manifest strabismus before surgery. This point was one of the limitations of this study. In this prospective study with a control group, our results revealed that the prism adaptation test might be helpful to determine the largest exotropic angle and to achieve a more favourable binocular function in patients with primary exotropia. As the small sample was the major limitation of this study, additional studies with longer follow-up and an increased number of patients are required to substantiate our results. ACKNOWLEDGEMENT
Part of this material was presented at the XI Meeting of the International Strabismological Association, Istanbul, 2010. REFERENCES 1. Jampolsky A. A simplified approach to strabismus diagnosis. In: Burian HM, ed. Symposium on Strabismus: Transactions of the New Orleans Academy of Ophthalmology. St. Louis: CV Mosby, 1971. p 342–365.
2. Repka MX, Connett JE, Baker JD, Rosenbaum AL. Surgery in the prism adaptation study: accuracy and dose response. Prism Adaptation Study Research Group. J Pediatr Ophthalmol Strabismus 1992; 29: 150–156. 3. Scott WE. Office use of prisms. In: Burian HM, ed. Symposium on Strabismus: Transactions of the New Orleans Academy of Ophthalmology. St. Louis: CV Mosby, 1978. p 91–102. 4. Dadeya S, Kamlesh, Nanival S. Usefulness of the preoperative prism adaptation test in patients with intermittent exotropia. J Pediatr Ophthalmol Strabismus 2003; 40: 85–89. 5. Ohtsuki H, Hasebe S, Kono R, Yamane T, Fujiwara H, Shigara F. Prism adaptation response is useful for predicting surgical outcome in selected types of intermittent exotropia. Am J Ophthalmol 2001; 131: 117–122. 6. Veronneau-Troutman S, Traykovski E, DeRosa J. The influence of prisms adaptation test on surgery for intermittent exotropia. In: Lennerstrand G, ed. Update on Strabismus and Pediatric Ophthalmolgy. Boca Raton, Florida: CRC Press, 1995. p 220–223. 7. Shippman S, Weintraub D, Cohen KR, Weseley AC. Prisms in the pre-operative diagnosis of intermittent exotropia. Am Orthopt J 1988; 38: 101–106. 8. Ron A, Merin S. The pre-op prism adaption test in the surgery of exotropia. Acta Strabologica 1985; 2: 57–64. 9. O’Neal TD, Rosenbum AL, Stathacopoulos RA. Distance stereo acuity improvement in intermittent exotropic patients following strabismus surgery. J Pediatr Ophthalmol Strabismus 1995; 32: 353–357. 10. Ohtsuki H, Hasebe S, Okono M, Furuse T. Comparison of surgical results of responders and non-responders to the prism adaptation test in intermittent exotropia. Acta Ophthalmol Scand 1997; 75: 528–531.
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A N D
E X P E R I M E N T A L
OPTOMETRY RESEARCH PAPER
The impact of prism adaptation test on surgical outcomes in patients with primary exotropia DOI:10.1111/cxo.12219
Clin Exp Optom 2015; 98: 224–227 Ayse Kiyak Yilmaz MD Suheyla Kose PhD Suzan Guven Yilmaz MD Onder Uretmen PhD Ophthalmology Department, School of Medicine, Ege University, Izmir, Turkey E-mail: [email protected]
Submitted: 18 April 2014 Revised: 19 August 2014 Accepted for publication: 23 August 2014
Background: We aimed to determine the impact of the preoperative prism adaptation test (PAT) on surgical outcomes in patients with primary exotropia. Methods: Thirty-eight consecutive patients with primary exotropia were enrolled. Preoperative PAT was performed in 18 randomly selected patients (Group 1). Surgery was based on the angle of deviation at distance measured after PAT. The remaining 20 patients in whom PAT was not performed comprised Group 2. Surgery was based on the angle of deviation at distance in these patients. Surgical success was defined as ocular alignment within eight prism dioptres (PD) of orthophoria. Results: Satisfactory motor alignment (± 8 PD) was achieved in 16 Group 1 patients (88.9 per cent) and 16 Group 2 patients (80 per cent) one year after surgery (p = 0.6; chi-square test). There were no statistically significant differences in demographic parameters, preoperative and post-operative angle of deviation between the two groups (p > 0.05; MannWhitney U and chi-square tests). Nine patients in Group 1 (50 per cent) and two patients in Group 2 (10 per cent) had increased binocular vision one year post-operatively. A statistically significant difference was determined in terms of change in binocular single vision between the two groups (p = 0.01; chi-square test). Conclusion: Although the prism adaptation test did not lead to a significant increment in motor success, it may be helpful in achieving a more favourable functional surgical outcome in patients with primary exotropia.
Key words: exotropia, prism adaptation test, surgery The prism adaptation test (PAT) was first described for acquired esotropia1 and its efficacy confirmed by later studies.2,3 Improved surgical results were reported when the increase of the deviation under the influence of correcting prisms (prism adaptation) was taken into account when determining the surgical dosage. The Prism Adaptation Study Research Group2 showed that the success rate in patients with acquired esotropia whose angle increased under the influence of prisms base-out was higher after augmented surgery (89 per cent) than when conventional surgery was performed (79 per cent) (p < 0.05). In addition, the PAT might be helpful in achieving a favourable surgical outcome in intermittent exotropia.4 Results from previous studies indicate that preoperative prism correction allows a more accurate determination of the amount of surgery, prevents the risk of undue overcorrection and promotes the development of binocularity.5 In this prospective study, we aimed to determine Clinical and Experimental Optometry 98.3 May 2015
224
the impact of pre-operative PAT on the surgical outcome in patients with primary exotropia and whether the preoperative prism adaptation test is useful for achieving a more favourable functional surgical outcome. METHODS In this prospective study, conducted between 2009 and 2011, 38 (23 female) consecutive patients aged five to 49 years (mean 17.5 ± 10.9 years) with basic-type primary exotropia, who were scheduled to undergo strabismic surgery were enrolled. Basic-type primary exotropia is present when the exodeviation is approximately the same at distance and near fixation and there may or may not be binocular single vision. The difference between the prism cover test measurements for near and distant fixation does not exceed 10 PD.1 Patients with amblyopia, dissociated vertical deviation, A or V pattern, oblique or vertical rectus muscle dysfunction
or nystagmus were not included in the study. Patients who had undergone previous surgery for strabismus, with a diagnosis of intellectual disability or underlying neurologic disorder were excluded. Ethics approval for this prospective study was obtained from the Ege University local research ethics committee. Written and informed consent from patients was obtained prior to study inclusion. The angle of exodeviation in the study patients ranged from 16 to 50 PD (median, 32.7 ± 10.1 PD) at distance and from 18 to 52 PD (median, 34.7 ± 10.1 PD) at near. The measurement of deviation was obtained after 45 minutes of unilateral occlusion, while the patient was wearing fully corrective lenses without cycloplegia and fixated on an accommodative target at distances of 6.0 metres and 0.3 metres with the prism and alternate cover test. While the patient was fixating at 0.3 metres and looking through +3.00 D lenses, which were added over the distance correction and were placed in the © 2014 The Authors
Clinical and Experimental Optometry © 2014 Optometrists Association Australia
The impact of prism adaptation test on surgical outcomes Kiyak Yilmaz, Kose, Guven Yilmaz and Uretmen
trial frame, measurement for near was repeated for all patients. These measurements were performed to make sure that the type of exotropia was basic. Refractive error was obtained by cycloplegic refraction measured after 45 minutes following two topical instillations of 1% cyclopentolate chloride administered five minutes apart. Cycloplegic refraction and Snellen visual acuity (VA) were recorded for each patient. Sensory examination (with full correction but without +3.00 D lenses or cycloplegia), included Bagolini’s striated glass test (directing the patient to fixate on a spotlight held 33 cm from the eyes) (Oculus, Wetzler, Germany) and TNO test (Lameris Ootech BV, AG Veenendaal). The prism adaptation test was performed in18 randomly selected patients (Group 1) using Fresnel Press-OnTM prisms (Health Care Specialties Division/3M, St. Paul, Minnesota, USA), while the patients were wearing full corrective lenses without cycloplegia. The power of the prism was divided equally between the two eyes. The power of each prism was gradually increased according to the response to deviation as determined by the prism and alternate cover test. The PAT continued for three or four hours until no additional prism was required to neutralise the deviation as described by Ohtsuki and colleagues.5 Patients who showed an increase in exodeviation by five PD or more with the PAT were defined as having a positive prism adaptation response. Surgery was performed based on the angle of deviation at distance measured after PAT. The remaining 20 patients, in whom PAT was not performed, composed Group 2. Surgery was performed, based on the original angle of deviation at distance in these patients. Surgical success was defined as ocular alignment within eight PD of orthophoria at distance. Surgery was performed by one of the authors (SK) on the non-fixating eye with recession of the lateral rectus muscle combined with resection of the medial rectus muscle in all groups. The surgeon was masked to which patients had the PAT and which did not. The amount of surgery is described in Table 1. Patients were examined one week, one month, three months, six months and one year after surgery. Group 1 was divided into two subgroups (Group 1A and Group 1B), based on the results of PAT. Patients with a negative response comprised Group 1A and patients with a positive response comprised Group 1B.
Deviation
Amount of recession and resection Lateral rectus Medial rectus recession resection
20 PD
5 mm
4 mm
25 PD
6 mm
5 mm
30 PD
6.5 mm
6 mm
35 PD
6.5 mm
7 mm
40 PD
7 mm
7.5 mm
45 PD
7 mm
8 mm
50 PD
7 mm
8.5 mm
PD: prism dioptre
Table 1. Amount of surgical recession and resection according to deviation
Comparisons between groups regarding measures were performed with chi-square, Mann-Whitney U, Fisher’s Exact and Kruskal–Wallis tests. Statistical significance was defined as p less than 0.05. RESULTS Visual acuity was 0.01 ± 0.2 logMAR in all patients. Demographic data and clinical characteristics of patients are presented in Table 2. There was no statistically significant difference between Group 1 and Group 2 regarding age at the diagnosis, age at the time of surgery, duration between diagnosis and strabismic surgery, demographic data and refractive error (p > 0.05, Mann-Whitney U and chi-square test). The mean preoperative angle of exodeviation was 31.2 ± 7.7 PD (range: 16 to 40 PD) for Group 1 before PAT and 33.8 ± 11.7 PD (range: 16 to 50 PD) for Group 2. After PAT, the mean target angle for distance increased to 36.3 ± 8.1 PD (range: 20 to 50 PD) in Group 1. There were no statistically significant differences in preoperative angle of deviation and binocular single vision between the two groups (p = 0.696, Mann-Whitney U test and p = 0.157, chisquare test, respectively). Surgical success rates were 100 per cent at one month and 88.9 per cent at one year in Group 1 and 85 per cent at one month and 80 per cent at one year in Group 2. There were no statistically significant differences regarding the surgical outcome between
© 2014 The Authors Clinical and Experimental Optometry © 2014 Optometrists Association Australia
Group 1 and Group 2 at one week, one, three, six and 12 months post-operatively (p = 0.186, p = 0.852, p = 0.696, p = 0.710 and p = 0.606, chi-square test; respectively). There was no statistically significant difference between the groups in relation to the amount of alignment obtained per each millimetre of surgical intervention (for Groups 1 and 2, 2.30 PD and 2.38 PD, respectively; p = 0.158, Mann-Whitney U test). For a detailed analysis of the impact of PAT response on the surgical success rate, we also evaluated patients with negative PAT responses (Group 1A), patients with positive PAT responses (Group 1B) and patients in whom PAT was not performed (Group 2). The mean increase in the target angle of deviation after PAT was 0.2 ± 0.4 PD for Group 1A and 7.2 ± 4.1 PD for Group 1B (p = 0.001, Mann-Whitney U test). There was an increase more than eight PD in four patients in Group 1B. The post-operative angle of deviation and the surgical outcome in the three groups are presented in Table 3. There was no case with post-operative overcorrection in any group. The post-operative angle of deviation at one year in Group 1B was significantly smaller than in Group 2 (p = 0.04, Mann-Whitney U test). There was no statistical difference among the groups in the surgical outcome at six months and at one year (p = 0.490 and p = 0.488, respectively by Fisher’s exact test). Nine patients (50 per cent) in Group 1 and two patients (10 per cent) in Group 2 had shown an increment of binocular single vision at one year post-operatively and this difference was statistically significant (p = 0.01, chi-square test). Three patients in Group 1 and one patient in Group 2, who did not have binocular single vision preoperatively, developed binocular single vision after surgery. Stereopsis was improved from gross to fine levels in the remaining cases. For further analysis of binocular single vision, the patients were evaluated in Groups 1A, 1B and 2. Two patients in Group 1A (40 per cent), seven patients in Group 1B (53.8 per cent) and two patients in Group 2 (10 per cent) had shown an increment of binocular single vision at one year postoperatively. The patients in Group 1B showed a significantly better improvement in binocular single vision compared to patients in Group 2 with regards to the percentage of patients who showed improvement after surgery (p = 0.013; chi-square test). The increments in binocular single Clinical and Experimental Optometry 98.3 May 2015
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The impact of prism adaptation test on surgical outcomes Kiyak Yilmaz, Kose, Guven Yilmaz and Uretmen
Group 1 (18 patients)
Group 2 (20 patients)
p-value
Age (years), mean ± SD 3.5 ± 3.7
4.2 ± 6.1
0.806*
Strabismus surgery
18.0 ± 12.8
17.0 ± 9.1
0.988*
Duration between diagnosis and surgery (years)
14.5 ± 13.1
12.8 ± 7.2
0.874†
Diagnosis
Gender (% of patients) Male
9 (50.0%)
6 (30.0%)
0.320‡
Female
9 (50.0%)
14 (70.0%)
0.843‡
0 to -3.00 sphere
11 (30.6%)
13 (32.5%)
0 to +3.00 sphere
22 (61.1%)
24 (60.0%)
0 to -2.00 cylinder
9 (25.0%)
12 (30.0%)
0 to +2.00 cylinder
15 (41.7%)
13 (32.5%)
Preoperative deviation (PD)
Before PAT
Mean ± SD
31.2 ± 7.7
Refractive error (D)
33.8 ± 11.7
After PAT
0.933†
36.3 ± 8.1
0.696†
Binocular single vision Stereopsis (+)§
12 (67%)
10 (50%)
§
6 (33%)
10 (50%)
Stereopsis (-) † §
0.157‡
Mann-Whitney U test, ‡ Chi-square test, SD: Standard deviation, PAT: prism adaptation test Stereopsis was determined using the TNO test and Bagolini’s striated glass
Table 2. Demographic data and clinical characteristics of patients
Post-operative duration
Group 1A (5 patients)
Group 1B (13 patients)
Group 2 (20 patients)
p-value
4.0 ± 7.6
3.8 ± 6.1
4.0 ± 5.4
0.716†
80.0%
92.3%
85.0%
0.490‡
4.4 ± 6.4
1.5 ± 4.1
5.3 ± 5.1
0.042†
80.0%
92.3%
80.0%
0.488‡
Six months Angle of deviation (PD) ± SD Surgical success rate One year Angle of deviation (PD) ± SD Surgical success rate
Kruskal–Wallis test, ‡ Fisher’s exact test SD: Standard deviation, PD: prism dioptre
†
Table 3. Post-operative angle of deviation and surgical success in Group 1A, Group 1B and Group 2 vision in the three groups are presented in Table 4. DISCUSSION The prism adaptation test was claimed to improve the results of strabismus surgery Clinical and Experimental Optometry 98.3 May 2015
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and many studies confirmed the efficacy of PAT for esotropia.2,3 The mechanism of progressive increase in prism power is not well understood in relation to exotropia. Prisms are useful to facilitate preoperative or post-operative binocular sensory fusion and surgical over- or under-correction in
primary exotropes. Veronneau-Troutman, Traykovski and DeRosa6 reported that PAT improved the prognosis and predictability of surgery for strabismus in intermittent exotropia. In contrast, Shippman and colleagues7 did not find PAT useful in this type of strabismus. Many studies indicate that preoperative prism correction allows a relatively accurate determination of the amount of the prism for surgery.4,6,8 Thus, it prevents the risk of under-correction and also promotes the development of binocular sensory vision.9,10 In our study, 13 of 18 patients (72.2 per cent) on whom PAT was conducted, showed an increment of five or more prism dioptres in the angle of deviation from six metres compared to the initial angle measured by prism. Consequently, surgical treatment for these patients consisted of larger muscle resection and recession. If the PAT had not been performed pre-operatively, patients would probably have been under-corrected. Dadeya, Kamlesh and Nanival4 reported that satisfactory motor alignment (± 5 PD of orthophoria) was achieved in 14 (53.8 per cent) PAT-negative and 24 (88.8 per cent) PAT-positive patients with basic type of intermittant exotropia. In our study, satisfactory motor alignment (± 8 PD of orthophoria) was achieved in 80 per cent PAT-negative and 92.3 per cent PAT-positive patients one year post-operatively. In our study group, the rate of satisfactory motor alignment appeared better in PAT-positive than in PAT-negative patients; however, this difference did not reach statistical significance, most probably due to the limited number of patients. A further randomised prospective study with large numbers of cases is needed for generalised conclusions of a large population. Ohtsuki and colleagues10 concluded that patients who show marked response to prism correction had a tendency to have a better outcome with regard to the single binocular vision examined with Bagolini lens test during a longer follow-up (three years). In contrast, Dadeya, Kamlesh and Nanival4 observed similar sensory success for PATpositive and PAT-negative patients. The authors4 suggested that the reason for poor sensory results might be that most of their patients had poor control of deviation. We determined that sensory results were significantly better in PAT-conducted than control patients post-operatively. It could be due to the fact that the residual angle of deviation was closer to the orthophoria in Group 1; © 2014 The Authors
Clinical and Experimental Optometry © 2014 Optometrists Association Australia
The impact of prism adaptation test on surgical outcomes Kiyak Yilmaz, Kose, Guven Yilmaz and Uretmen
Group
Preoperative
Post-operative
TNO test (arcsec)
TNO test (arcsec)
Group 1A
Patient 1: 120
60
Two of five patients
Patient 2: 120
60
Group 1B Seven of 13 patients
Patient 1: 120
60
Patient 2: 120
60
Patient 3: 120
15
Patient 4: 120
60
Patient 5: Stereopsis (-)
Group 2 2 of 20 patients †
480
Patient 6: Stereopsis (-)
480
Patient 7: Stereopsis (-)
Fusion (+)† no stereopsis
Patient 1: 960
60
Patient 2: Stereopsis (-)
480
Tested with Bagolini’s striated glass
Table 4. Post-operative increment of binocular single vision in Group 1A, Group 1B and Group 2 however, all patients in both groups had manifest exotropia preoperatively and thus might have poor stereopsis. This stereopsis may have been lost when the patients developed their constant strabismus. Whether or not this stereopsis is recoverable after strabismic surgery that provides good alignment may be dependent upon how soon the intervention is performed. In our study, we could not determine how long the patients had manifest strabismus before surgery. This point was one of the limitations of this study. In this prospective study with a control group, our results revealed that the prism adaptation test might be helpful to determine the largest exotropic angle and to achieve a more favourable binocular function in patients with primary exotropia. As the small sample was the major limitation of this study, additional studies with longer follow-up and an increased number of patients are required to substantiate our results. ACKNOWLEDGEMENT
Part of this material was presented at the XI Meeting of the International Strabismological Association, Istanbul, 2010. REFERENCES 1. Jampolsky A. A simplified approach to strabismus diagnosis. In: Burian HM, ed. Symposium on Strabismus: Transactions of the New Orleans Academy of Ophthalmology. St. Louis: CV Mosby, 1971. p 342–365.
2. Repka MX, Connett JE, Baker JD, Rosenbaum AL. Surgery in the prism adaptation study: accuracy and dose response. Prism Adaptation Study Research Group. J Pediatr Ophthalmol Strabismus 1992; 29: 150–156. 3. Scott WE. Office use of prisms. In: Burian HM, ed. Symposium on Strabismus: Transactions of the New Orleans Academy of Ophthalmology. St. Louis: CV Mosby, 1978. p 91–102. 4. Dadeya S, Kamlesh, Nanival S. Usefulness of the preoperative prism adaptation test in patients with intermittent exotropia. J Pediatr Ophthalmol Strabismus 2003; 40: 85–89. 5. Ohtsuki H, Hasebe S, Kono R, Yamane T, Fujiwara H, Shigara F. Prism adaptation response is useful for predicting surgical outcome in selected types of intermittent exotropia. Am J Ophthalmol 2001; 131: 117–122. 6. Veronneau-Troutman S, Traykovski E, DeRosa J. The influence of prisms adaptation test on surgery for intermittent exotropia. In: Lennerstrand G, ed. Update on Strabismus and Pediatric Ophthalmolgy. Boca Raton, Florida: CRC Press, 1995. p 220–223. 7. Shippman S, Weintraub D, Cohen KR, Weseley AC. Prisms in the pre-operative diagnosis of intermittent exotropia. Am Orthopt J 1988; 38: 101–106. 8. Ron A, Merin S. The pre-op prism adaption test in the surgery of exotropia. Acta Strabologica 1985; 2: 57–64. 9. O’Neal TD, Rosenbum AL, Stathacopoulos RA. Distance stereo acuity improvement in intermittent exotropic patients following strabismus surgery. J Pediatr Ophthalmol Strabismus 1995; 32: 353–357. 10. Ohtsuki H, Hasebe S, Okono M, Furuse T. Comparison of surgical results of responders and non-responders to the prism adaptation test in intermittent exotropia. Acta Ophthalmol Scand 1997; 75: 528–531.
© 2014 The Authors Clinical and Experimental Optometry © 2014 Optometrists Association Australia
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