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ORIGINAL ARTICLE
Year : 1997  |  Volume : 45  |  Issue : 1  |  Page : 31-35

Torsional changes in surgery for A-V phenomena


Dr. R.P. Centre for Ophthalmic Sciences, AIIMS, New Delhi

Correspondence Address:
P Sharma
Dr. R.P. Centre for Ophthalmic Sciences, AIIMS, New Delhi

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Source of Support: None, Conflict of Interest: None


PMID: 9475009

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  Abstract 

The role of torsion in the aetiopathogenesis of A-V phenomena has not been sufficiently emphasized. The success of vertical displacement of horizontal recti in correction of A or V has not been attributed to torsional changes. To evaluate this aspect, 21 cases of A or V phenomena were subjected to monocular recession-resection procedure with vertical shifting. Preoperative and postoperative torsional changes were evaluated on synoptophore (subjective torsion), and confirmed by fundus photography (objective torsion). Intorsion with A phenomenon was seen preoperatively in 5 of 8 cases which increased after surgery and was seen postoperatively in the other 3 cases also. Extorsion was observed in 5 of 13 cases pre operatively in 'V' phenomenon, but the changes in extorsion after surgery were less dramatic than those in intorsion. The oblique overactions were reduced in cases where they were present. Correction of A-V phenomena by torsion induced by vertical shifting of horizontal recti muscles is proposed, highlighting the role of torsion in A-V phenomena.

Keywords: A-V phenomena, Torsion, Horizontal recti surgery, Vertical displacement


How to cite this article:
Sharma P, Halder M, Prakash P. Torsional changes in surgery for A-V phenomena. Indian J Ophthalmol 1997;45:31-5

How to cite this URL:
Sharma P, Halder M, Prakash P. Torsional changes in surgery for A-V phenomena. Indian J Ophthalmol [serial online] 1997 [cited 2024 Mar 29];45:31-5. Available from: https://journals.lww.com/ijo/pages/default.aspx/text.asp?1997/45/1/31/15027

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A-V phenomena in concomitant strabismus have generated interest both for their aetiopathogenesis and management. The lack of consensus about the former is reflected in the diverse schools of thoughts.[1][2][3] Torsional imbalance as a result of sagitallization of oblique has been proposed[4] which could explain the secondary overaction or underaction of the corresponding cyclovertical muscles. Cases have been reported to support this proposition.[5],[6] Also anomalous insertion of horizontal recti, medial recti higher and lateral recti lower than normal, causing V pattern and reverse in A pattern have been reported.[7],[8] The success of vertical shifting of horizontal recti also supports this proposition, and torsion has been demonstrated by fundus photographs,[9] or by blindspot charting.[10] However lack of complaints by patients and inability to document torsion before and after surgery,[11],[12] has retarded enthusiasm to support the torsional imbalance as a cause for A-V phenomena or confirm consistently that torsional changes do occur in the corrective surgery of A-V phenomena.

This study was undertaken to evaluate the torsional changes induced by vertical shifting of horizontal recti for A-V phenomena and changes induced in the pre existing superior and inferior oblique overaction after such a surgery.

For this, monocular recession - resection with vertical shifting model was chosen, the effects of which on the A and V phenomena and also the incomitances induced by such a surgery have been reported earlier.[13]


  Material and methods Top


Twenty one consecutive patients of A and V phenomena (8 cases of A pattern and 13 cases of V pattern) were selected for the study, if the horizontal measurements between 25 ± up-and downgaze differed by 15 prism dioptres (pd) for V phenomena and 10 pd for A phenomena, and if they had mild or no inferior or superior oblique overactions. Measurements of horizontal and vertical deviations in all 9 positions of gaze were done by Prism bar cover test and cephalodeviometer,[14] and by synoptophore. Of the 21 cases there were 13 cases of 'V'exotropia, 5 cases of 'A'exotropia and 3 cases of 'A' esotropia. Half (10) of these had mild to moderate oblique overaction (superior oblique in 'A' phenomena and inferior oblique in 'V' phenomena). The grading of mild, moderate and severe was based on the degree of elevation or depression of the adducted eye in the extreme lateral version - mild (upto 15 p.d), moderate (16-30 p.d), and severe (more than 30 p.d.). Cyclotorsion was subjectively measured by synoptophore and objectively documented by fundus photography. For analysing the torsion of fundus picture, two horizontal lines were drawn, one passing through the middle of the disc and another line passing through the lower border of disc. It was labelled as intorsion if the fovea was above the upper line and as extorsion if it was below the lower line.[15] The cyclotorsion values given in the tables are as observed on synoptophore (subjective torsion). The fundus photographs objectively document the torsion but could not be used for accurate quantification. All measurements were performed by the second author (MH) and the surgery performed by the first author (PS). Multiple readings were taken and no variability was observed. No significant refractive error changes were noted after surgery.

At surgery, monocular recession-resection requisite for the horizontal deviation in primary position was performed and the insertion shifted up (medial rectus in A and lateral rectus in V) or down (medial rectus in V and lateral rectus in A) by 5 mm or 8 mm, parallel to the limbus.[16] The choice of 5mm or 8mm was done on a purely random basis in both the groups of A-V phenomena with or without oblique overactions. The difference in correlation of A or V phenomena between the two groups was statistically insignificant as reported earlier,[13] as also the changes in A-V phenomena and horizontal and vertical incomitance.

Measurements performed preoperatively were repeated on the first post operative day and after one week, one month and three months. Fundus photography was done preoperatively and three months postoperatively.


  Results Top


Torsion was found preoperatively only in the 5 cases of 'A' pattern with superior oblique overaction on the synoptophore and confirmed on fundus photography. It was intorsion in all cases and the amount of intorsion was more in down gaze (mean = + 3.2° + 0.74°) than in primary gaze (mean = + 1.8° ± 1.16°) [Table.:1]. The mean amplitude of A pattern (difference in up and down positions) in all these 5 cases was 23.6 pd whereas the mean of the three cases without intorsion, and without superior oblique overaction was 18.33 p.d. This difference was, however, not statistically significant.

No torsion was detected in any of the 13 cases of V pattern with or without inferior oblique overaction.

[Table.:2] shows the preoperative and postoperative torsion and the postoperative change in torsion after vertical shifting of horizontal recti. The maximum change in torsion was produced in A patterns, the mean being 5.25° ± 1.16° (intorsion) compared to the same in V patterns being 1.69° ± 2.32° (extorsion). The difference of the means between A and V patterns appears to be marked (p<0.01, two sample t-test) because all the 8 cases with A pattern (5 of which had intorsion even preoperatively) showed a significant intorsion, whereas only 5 of the 13 cases with V pattern showed significant extorsion. However the mean of these 5 cases alone had extorsion of 4.4°, which is similar to those of A cases. The analysis of cases which had 8mm shift in A pattern showed a mean intorsion of +6.5° compared to +4.25° mean in 5 mm shift group.

Similarly in V patterns the 8 mm shift group had a mean extorsion of -5.0° compared to -3.5° extorsion in 5 mm shift group. However, this difference was not statistically significant.

[Figure - 1] shows the preoperative and postoperative photographs of a case of A phenomenon where the right eye was operated showing the intorsion of the operated eye. The preoperative intorsion was not so apparent in the fundus picture of this eye as it is about one degree only in the primary position. The post operative picture of right eye shows an intorsion, the fovea shifted above the horizontal line passing through the middle of disc. However the left fundus shows the fovea between the two horizontal lines passing through the middle of the disc and lower pole.

Analysing the change in overaction of obliques after surgery, it was observed that in 3 out of 5 cases the overaction persisted postoperatively, though it was less in severity and it disappeared in two cases. A similar observation was seen in the 5 cases of V pattern which had inferior oblique overaction preoperatively, that the preoperative overaction disappeared in two cases and decreased in others.


  Discussion Top


For A-V pattern with horizontal squint diverse surgical plans are proposed by different investigators.[1][2][3] The general consensus is to weaken the overacting oblique whenever significant and to shift the horizontal recti vertically in other cases, apart from a few cases where differential or slanting insertions are done. Both the approaches have resulted in success raising the possibility of a common pathway in the form of torsional changes each can induce. The role of torsion was highlighted by Gobin[4] and the possibility of the oblique getting sagittalized is not infrequent. The fact that patients do not complain of torsion is another matter but torsional changes have been described.[9],[10] We also observed preexisting intorsion of 5 of 8 cases of A phenomenon, all these 5 cases also had superior oblique overaction. The other three cases that had no superior oblique overaction did not show intorsion, indicating a direct cause-effect relationship between torsion and superior oblique overaction. This was confirmed by the observation that intorsion increased on depression. It may be of interest to note that a similar extorsion was not detected in case of V phenomenon even with inferior oblique overaction. This observation which was also similar in postoperative change of torsion is interesting. This may be due to the extorsion being more amenable to sensory adaptation compared to intorsion. It may have some bearing on the directional discrepancy between subjective and objective vertical meridians described as disclination with each eye having a subjective extorsion of about 4° to 5°.[17]

After the operation of shifting as advocated by Knapp[16], medial rectus up and lateral rectus down for A and vice versa for V, all the cases of A phenomenon had more severe intorsion and cases with V phenomena, also started showing extorsion, though the latter observation was limited to fewer cases. The surgery that was proposed by Knapp for A phenomenon actually causes intorsion as can be seen if one evaluates the vertical torques of the shifted recti.

[Figure - 2] shows the effect on muscle torque, M when the right lateral rectus is shifted down (as for A phenomenon). The obliquely angulated muscle torques M now can be resolved into a horizontal vector H which contributes to abduction, and a vertical vector, V upwards. Similarly, as the medial rectus is shifted up, the vertical vector for that becomes, Vm which will be acting downwards.

[Figure - 3] shows the composite effect of both the vertical vectors of lateral rectus upwards and medial rectus downwards causing an intorsion. The induced intorsion in the postoperative cases of A phenomenon where medial rectus were shifted upwards and lateral rectus downward can be explained by the vectors created by the muscle torque being inclined due to the shift. Resolving the two vectors of this torque for the medial rectus the horizontal vector provides the adduction force while the vertical vector provides a downward force. A similar inclination of the lateral rectus (shifted down) also produces a horizontal vector for abduction and a vertical vector (upwards) which together with the downwards vector of medial rectus contributes to the lntorsion. It may be noted here that if both the horizontal recti were shifted in the same direction, the vertical vectors of both medial and lateral recti would have been downward, with a net downward movement causing or correcting a vertical incomitance. This will also be expected whenever the two vertical vectors are not balanced, explaining vertical incomitance in some cases with cyclovertical muscle imbalance as also reported by us earlier.[13] The surgery of vertical shifting of horizontal recti proposed by de Decker[18] and the recently described horizontal shifting of vertical recti by Von Noorden et al[19] for correcting ocular torticollis are based on the same principle.

The [Table - 3] describes the dynamic changes that occur in primary position, upgaze and downgaze after the vertical shifting medial rectus up and lateral rectus down in the case of A Phenomenon. It may be observed that while in the primary position a net intorsion is observed, there is no significant change in horizontal position. However in upgaze since the abduction improved and adduction weakerns there is a net divergence opening the top of A. In the down gaze there is, similarly a net convergence causing the collapse of base of A. Thus A phenomenon gets corrected. A similar analysis of surgery done for V phenomenon, medial rectus shifted down and lateral rectus up, can explain how the V phenomena gets corrected. It may not be possible at this stage to establish whether primarily it is the horizontal recti, or obliques that are at fault. In all probability, in different cases, different causes are present. It appears, however, that the common denominator is torsion, and different surgical methods owe their success to this being changed. In our cases, the A and V patterns were effectively corrected even in cases with oblique overaction. Moreover, the oblique overactions were diminished or eliminated in a period of 3 months indicating that they may be secondary, and once the vertical shifting procedure induced requisite torsion the requirement on obliques reduces, causes a relaxation of the obliques, which is corroborated by the observation. This relaxation may keep on occurring over a period of time and a study with longer followup may give further answers. It may also be noted that due to vertical incomitance which can be induced, one should be careful while doing vertical shifting as a monocular recession resection procedure, especially, if there are preexisting cyclovertical muscle imbalance.

 
  References Top

1.
Urist MJ: The etiology of the so called A& V syndrome. Am J Ophthalmol; 46:835-844, 1958.  Back to cited text no. 1
    
2.
Brown HW. Vertical Deviations. In Symposium, Strabismus, Trans Am Acad Ophthalmol Otolaryngol; 57:157-173, 1953.  Back to cited text no. 2
    
3.
Urrets-Zavalia A, Solares-Zamora J Olmos HR. Anthropological studies on the nature of cyclovertical squint. Br J Ophthalmol; 45:578-596, 1961.  Back to cited text no. 3
    
4.
Gobin MH: Sagittalization of the oblique muscle as possible cause for A-V and phenomena Br J Ophthalmol; 52:13-18, 1968.  Back to cited text no. 4
    
5.
Bagolini B, Campos E and Chiesi C. Plagiocephaly causing superior oblique deficiency and ocular torticollis. Arch Ophthalmol; 100:1093-1096, 1982.  Back to cited text no. 5
    
6.
France T. Strabismus in hydrocephalus: Am Orthopt J; 25:101-105, 1975.  Back to cited text no. 6
    
7.
Postic G: Etiopthogenie des syndromes A. et V. Bull Mem Soc. Fr. Ophthalmil; 78:240, 1965.  Back to cited text no. 7
    
8.
Nakamura T. Awaya S. Miyama E: Insertion anomalies of horizontal muscles in A & V pattern: Nippom Ganka-Gakka-Zazzhi; 95:698-703, 1991.  Back to cited text no. 8
    
9.
Weiss JB. Ectopies et pseudo ecctopies macularies parrotation. Bull Soc Ophthal Fr; 79:329. 1966.  Back to cited text no. 9
    
10.
Locke JC. Heterotropia of the blind spot in ocular vertical muscle imbalance. Am J Ophthalmol; 65:362-375. 1968.  Back to cited text no. 10
    
11.
Almeida HC. Correction of A & V Syndrome acting upon only one eye: International Strabismological Association Proceeding, Marseille, France 1974, pp 134-137.  Back to cited text no. 11
    
12.
Metz HS. The treatment of A & V pattern by monocular surgery. Arch Ophthalmol; 95:251-253. 1987  Back to cited text no. 12
    
13.
Sharma P, Haider M, Prakash P. Effect of vertical displacement of horizontal recti in A-V phenomena Indian J. Ophthalmol; 43:9-11, 1995.  Back to cited text no. 13
    
14.
Prakash P. Khadka KB, Menon V: Cephalodeviometer: a new instrument for diagnosis of A-V pattern: Campos E, ed. in: Proceedings of Fifth International Strabismologist Association, Rome, 1986, pp 251-254.  Back to cited text no. 14
    
15.
Bixenmann WW and Noorden GK Von. Apparent foveal displacement in normal subjects and in cyclotropia. Ophthalmologica; 89:58-61, 1982.  Back to cited text no. 15
    
16.
Knapp P. Vertically incomitant horizontal strabismus-the so called A and V syndrome. Trans Am Acad Ophthalmol Soc; 57:666-669, 1959.  Back to cited text no. 16
    
17.
Tschermak-Seysenegg A von: Introduction to physiological optics. Translated by Paul Boeder S. Springfield, USA: Charles C Thomas Publisher 1952, P 234.  Back to cited text no. 17
    
18.
de Decker W. Rotatorischer Kestenbaum an geraden Augenuskein, Zeitschr F Prakt Augenheilk; 11:111-114, 1990.  Back to cited text no. 18
    
19.
Noorden GK Von, Jenkins RH, Rosenbaun AL. Horizontal transposition of the vertical rectus muscles for treatment of ocular torticollis. J Ped Ophthalmol Strabis; 30:8-14, 1993.  Back to cited text no. 19
    


    Figures

  [Figure - 1], [Figure - 2], [Figure - 3]
 
 
    Tables

  [Table - 1], [Table - 2], [Table - 3]



 

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