|Year : 1994 | Volume
| Issue : 4 | Page : 203-206
Postequatorial horizontal rectus recession in the management of congenital nystagmus
Himadri Datta, Somdutta Prasad
Regional Institute of Ophthalmology, Medical College, Calcutta, India
Regional Institute of Ophthalmology, Medical College, 88 College Street, Calcutta 700 073
Source of Support: None, Conflict of Interest: None
Postequatorial (12 mm) recession of all four horizontal recti was done in nine patients with congenital nystagmus. Fifteen of 18 eyes showed decreased amplitude of nystagmus while 12 eyes also showed an increase in visual acuity. Functionally, significant limitation of ocular motility was not encountered despite unconventionally large recessions.
Keywords: Congential nystagmus - Postequatorial recession - Horizontal recti
|How to cite this article:|
Datta H, Prasad S. Postequatorial horizontal rectus recession in the management of congenital nystagmus. Indian J Ophthalmol 1994;42:203-6
Surgical options in the management of nystagmus have been very limited to date. Among the methods in vogue are fixation of the extraocular muscles to the periosteum of the lateral orbital wall  transposition of parts of the horizontal and vertical rectus muscles, or a free tenotomy of opposing rectus muscles,  and retroequatorial myopexy of all four horizontal recti.  However, none of these have gained widespread acceptance due to their limited success.
A more recent approach has been to artificially create an exotropia to utilise the stabilising effect of fusion convergence on nystagmus. However, further studies are needed to validate this as a mode of surgical correction for nystagmus.
Some reports have suggested that the intensity of nystagmus could be decreased by retroequatorial recessions (12 mm) of the horizontal recti in one or both eyes. von Noorden and Sprunger  reported encouraging results with this technique in their series of three cases. Helveston et al  recessed all recti muscles either upto or 1 mm behind the equator in their series of 10 cases.
We report the details of nine patients with manifest congenital nystagmus on whom we have used this procedure.
| Materials and methods|| |
Patients with manifest horizontal congenital nystagmus wherein the nystagmus remained horizontal on upgaze were included in the present series. Patients who could not cooperate with visual acuity testing and electronystagmography were excluded. Further exclusion criteria were a best corrected visual acuity of less than 1/60 in either eye, any vertical nystagmus, any head tilt, torticollis or strabismus, and patients who had any previous surgery for nystagmus. None of the eyes had previous history of any eye surgery (cataract, squint, etc.). Informed consent was obtained from all patients or their guardians.
All patients underwent a complete examination, including measurement of visual acuity with correction of refractive error, examination of ocular movements, fundoscopy, and electronystagmography preoperatively. All patients had detailed systemic examination by an internist.
Electronystagmograms were recorded for all patients with full refractive corrections before and following surgery using a dynograph coupled with a direct nystagmus transducer in alternating current mode, using a tracing speed of 5 mm per second. On calibration this corresponded to 1 mm of deflection per degree of eye movement. Rectilinear tracings were obtained with the patient fixing with both eyes in the primary position on a fixation light at 100 cm fixation distance.
We evaluated recordings by averaging the amplitudes of all wave peaks recorded above 1 mm during 4 or 5 seconds. It was felt that below 1 mm of displacement of the tracing pen, electronic noise became too much of a variable for these readings to be included.
All patients underwent recession of all four horizontal recti. In three patients both eyes were operated during the same session with appropriate attention to all aseptic measures. Six patients underwent surgery in two sessions, 3 to 7 days apart. A standard 12 mm recession was performed on each horizontal rectus, thus placing it behind the equator.
The criterion for improvement in visual acuity was improvement of at least one line in either eye as recorded with Snellen's chart and for nystagmus, a decrease in the frequency and amplitude of nystagmus postoperatively as measured by electronystagmography. Improvement in cosmesis was measured by the reduction in eye oscillation caused by nystagmus, as observed and reported by the patient. The visual acuity was evaluated in the same examination room at all visits.
| Results|| |
All the patients were followed up for a period ranging from 6 to 15 months. Of the 18 eyes (nine patients) operated, improvement in visual acuity was found in 12 eyes. All 9 patients had visual gain at least in one eye. The amplitude of nystagmus was found to be decreased in 15 eyes [Figure - 1]. The frequency of nystagmus remained unaltered in four patients, increased in two patients [Figure - 2] and decreased in three patients. Thus, all patients displayed some improvement in visual acuity and most displayed a decreased amplitude of nystagmus. Two patients displayed increased frequency of nystagmus, but recorded a decrease in amplitude [Figure - 3] and an improvement in visual acuity of one Snellen line in one eye each [Table - 1]. However, the sample size was not adequate to permit a statistical analysis of the results.
| Discussion|| |
Helveston et al  in their series of 10 cases observed the reduction of amplitude after the surgery and visual improvement of at least 1 line in eight patients. von Noorden et al 4 in their series of three patients observed modest improvement of visual acuity in two patients . [4 ] Controversy exists as to whether younger age group patients really need to undergo surgery, as some are of the view that nystagmus improves with age, while von Noorden has a different opinion. As there is no clear contraindication for surgery in this age group, our 4-year-old patient has been included in this study.
The recti are able to rotate the globe due to the leverage that exists between the centre of rotation and the line of pull of the muscle at the tangential point of contact with the globe.  By shifting the insertion of the horizontal recti behind the tangential point, we decreased this leverage, expecting that due to this a given amount of muscle innervation would have a smaller rotational effect on the globe. Most of our cases showed a decrease in the amplitude of nystagmus but no change in frequency, thus bearing out the above reasoning. Unexpectedly, the frequency of nystagmus increased in two patients and decreased in three, but this did not have an adverse effect. The improved visual acuity recorded by our patients, though only modest, was still significant in our opinion. However, this should not be overemphasized as visual acuity may vary during different examinations in the presence of nystagmus, depending upon the patient's effort and state of anxiety .  Most patients were happy with the cosmetic improvement due to the decreased amplitude of nystagmus.
Unconventionally large recessions did not lead to decreased ocular motility. This may be due to the fact that both the agonist and antagonist were recessed simultaneously, thus their balance was not significantly upset. However, cases 1, 2, 7 and 9 [Table - 1] displayed a minimal limitation of abduction and adduction postoperatively, but these were not functionally significant.
Despite the favourable results recorded in this study, it must be considered only preliminary as a larger sample size and longer follow-up are necessary before these results can be considered to be generally representative. At present, we perform the procedure of bilateral retroequatorial horizontal muscle recessions for cases of congenital nystagmus ' for cosmetic and possible visual improvement. If larger studies substantiate the visual improvement shown in our series, then it may be advisable to recommend this procedure at a younger age.
| References|| |
Colburn JE. Fixation of the external rectus muscle in nystagmus and paralysis. Am J Ophthalmol 23:85-88, 1906.
Keeney AH, Roseman E. Acquired vertical illusory movements of the environment. Am J Ophthalmol 61:1188-1191, 1966.
Arruga A. Posterior suture of rectus muscles in retinal detachment with nystagmus: A preliminary report. J Paediatr Ophthalmol Strabismus 11:36-37, 1974.
von Noorden GK, Sprunger DT. Large rectus muscle recessions for the treatment of congenital nystagmus. Arch Ophthalmol 109:221-224, 1991.
Helveston EM, Ellis FD, Plager DA. Large recession of the horizontal recti for treatment of nystagmus. Ophthalmology 98:1302-1305, 1991.
von Noorden GK. Binocular Vision and Ocular motility: Theory and Management of Strabismus, 4th ed. St. Louis, CV Mosby Co., 1990, pp 485.
von Noorden GK, Munoz M, Wong SY. Compensatory mechanisms in congenital nystagmus. Am J Ophthalmol 104:387-389, 1987.
[Figure - 1], [Figure - 2], [Figure - 3]
[Table - 1]
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