The evaluation and surgical management of patients with acquired esotropia in the setting of high myopia can be complex. These patients classically present with diplopia secondary to progressive esotropia and hypotropia with limitation of abduction and elevation, although exotropia and hypotropia have also been described . Traditional recession–resection surgery can be ineffective and even exacerbate the esotropia . Proper surgical planning in these cases must account for preoperative strabismic measurement artifacts and aim to correct the pathophysiology contributing to this form of acquired strabismus.
The aim of the present article is to describe the cause of esotropia in patients with high myopia and to discuss the evaluation and surgical management in these challenging patients.
Strabismus fixus convergence, or more commonly known as ‘Heavy Eye’ syndrome [1,3,4], was initially thought to be caused by the increased weight of an elongated myopic eye and subsequent prolapse of its anterior portion. Over the years, many theories have been presented. Researchers have attributed this progressive esotropia to compression of the lateral rectus muscle against the lateral orbital wall [5,6], whereas Demer and von Noorden  showed mechanical restriction from contact between the posterior globe and bones of the orbital apex.
Although many theories can be confounding, Krzizok et al. went further into describing the pathophysiology. Using MRI scans on 37 patients with high myopia, they showed that in the 13 who demonstrated esotropia and hypotropia, the lateral rectus was inferiorly displaced 3.4 mm. In the two patients with exotropia and hypotropia, the medial rectus was downwardly displaced. This was further characterized by Aoki et al.. In their cohort of patients with acquired esotropia in the setting of high myopia, MRI studies showed superotemporal prolapse of the elongated posterior portion of the eyeball, leading to an inferior shift of the lateral rectus and nasal shift of the superior rectus. This was previously described by Yokoyama et al.. The superotemporal quadrant is particularly susceptible to globe prolapse, as the ligament that joins the lateral rectus and superior rectus band degenerates over time [11,12].
‘SAGGING EYE’ SYNDROME
A similar phenomenon, termed ‘sagging eye’ syndrome, was described by Demer, Rutar and Chaudhuri [13,14] for elderly patients in the absence of high myopia. In these patients, age-related thinning or elongation of the lateral rectus and superior rectus band was noted. They classically present with diplopia with horizontal and vertical strabismus, although not as severe as in heavy eye syndrome, along with typical age-related changes to the levator aponeurosis, such as ptosis or superior sulcus deformities.
In these patients with progressive esotropia with high myopia (greater than −9.00 diopters but generally greater than −15.00 diopters), further workup is generally necessary. Although they may have a decompensated, long standing esotropia or ocular myasthenia, neuroimaging, preferably with MRI, should be obtained with particular attention to the paths of the rectus muscles. In Yamaguchi et al. all patients were evaluated using axial and coronal T2 weighted spin-echo imaging with 3 mm slices and the eyes infraducted, as many patients with strabismus fixus cannot maintain primary position. Coronal images of the globes were then analyzed 9 mm anterior to the optic nerve-globe junction. The angle created between the lateral and superior rectus with respect to the center of the globe was analyzed (see Fig. 1). They found the average angle in patients with heavy eye syndrome to be 179.9 ± 30.8 degrees whereas control patients had an angle of 102.9 ± 6.8 degrees . If altered paths of the muscles are noted, the surgical options, discussed below, will aim to correct that deviation. However, if no abnormality is seen and in the absence of other causes such as thyroid eye disease or neurogenic or microvascular sixth nerve palsy, classical recession–resection surgery may be beneficial.
An important consideration when determining the dose of recess–resect surgery to perform is calculating the amount that the deviation is effected by the spectacles themselves. All spectacles induce a prismatic effect but this can be clinically significant in both high hyperopic and high myopic patients . As Scattergood and Guyton described, plus lenses measure less than the true deviation whereas minus lenses measure more. Although a perfectly linear relationship does not exist, for myopic corrections up to −15 diopters, the true distance deviation can be determined by correcting the measured deviation by 2× the lens power as a percentage. For example, for a −10 patient wearing their full eyeglass correction, the true deviation is 20% less than measured through the eyeglasses. This needs to be considered to prevent significant overcorrection in these patients.
SURGICAL OPTIONS FOR ‘HEAVY EYE’ SYNDROME
Many surgical options have been proposed to correct myopic strabismus fixus with variable results. Hayashi et al. reported success with recession–resections in 23 patients with less severe abduction deficiencies but limited effectiveness for more advanced cases. For the more severe cases, transposition of the superior and inferior rectus was effective but run the risk of anterior segment ischemia. Others have proposed bimedial rectus disinsertion with lateral fixation of the sclera to the periosteum in a severe case but were limited by significant postoperative motility deficiencies .
These approaches were refined when Krizizok [2,8] described the dislocation of the lateral rectus muscle path. His 13 patients with high myopia and esotropia underwent large medial rectus recession (12 mm) with retroequatorial posterior fixation suture on the lateral rectus with a 4-0 nonabsorbable suture. Although he obtained good postoperative results, this procedure is technically difficult, particularly in high myopes with thin sclera.
However, the most successful outcomes have come from correcting the muscle paths of both the superior and lateral rectus muscles. Initially, hemitransposition of the superior and lateral rectus with scleral fixation was used . Now, most surgeons prefer a surgical technical without sclera fixations. The most commonly performed surgery involves loop myopexy of the superior and lateral rectus muscles either with muscle splitting (e.g. partial Jensen's) [20–22] or without muscle splitting [15,23–25]. This technique is performed by isolating both the superior and lateral rectus muscles through either a superotemporal fornix based conjunctival incision or a limbal peritomy. Once the muscles are isolated, a 5-0 nonabsorbable suture is passed through the lateral one-half of the superior rectus and the superior one-half of the lateral rectus at, approximately, 14–16 mm posterior to the limbus and securely tied. Scleral fixation is not necessary. This eliminates the risk of sclera perforation as no sclera suture is placed and minimizes the risk of anterior segment ischemia as the anterior ciliary circulation is not compromised. In their study of 23 eyes in 14 patients who underwent this procedure, Yamaguchi et al. showed that preoperatively, these patients had orbital imaging studies confirming superotemporal dislocation of the posterior portion of the globe outside of the muscle cone correlating with the amount of limitation of abduction and elevation. However, following surgical correction, the globe was restored to within the muscle cone and motility was significantly improved. No surgical complications were noted.
THE ROLE OF CONCURRENT MEDIAL RECTUS SURGERY
Medial rectus recession needs to be considered at the time of loop myopexy in these patients. In particular, if preoperative forced duction testing is positive or if the esotropia is long standing with likely contracture of the medial rectus, recession with the possible use of an adjustable suture can improve outcomes but can result in exotropia [25,26]. However, in the absence of these findings, medial rectus recession may be staged for a second surgery or may be unnecessary. In Yamaguchi's et al. study, of the 23 eyes operated, seven did not undergo concurrent medial rectus surgery. Of these, three needed medial recessions for residual esotropia within the next year but in four cases, further surgery was not necessary. Additionally, Akar et al.[27▪] studied 35 eyes that underwent loop myopexy with or without medial rectus recession. In their study, 11 eyes did not have medial rectus recession at the time of myopexy. Of these, two needed medial recessions for residual esotropia but the remaining nine (26%) were cured with the myopexy alone with 4 years of follow-up.
If large medial rectus recession is to be performed, hang back or hemi-hang back techniques can be employed in order to avoid passing suture needles within the thin sclera seen in patients with high myopia and increased axial lengths, and therefore decrease the risk of scleral perforation.
UNILATERAL VERSUS BILATERAL SURGERY
Another consideration in patients with bilateral high myopia and ‘heavy eye syndrome’ is whether to perform unilateral or bilateral surgery, especially in the setting of a significant difference in visual acuity in each eye. If possible, bilateral loop myopexy should be performed to correct the deviant muscle paths, with or without unilateral or bilateral medial rectus recession. Medial rectus recession can be staged if necessary. However, if unilateral myopexy is preferred, augmentation with ipsilateral medial rectus recession can provide satisfactory postoperative outcomes with additional gradual improvements in ductions occurring over time [20,26].
Correcting the underlying pathophysiology is vital to treating patients with esotropia with high myopia. If orbital imaging demonstrates dislocated superior and lateral rectus muscles, loop myopexy is a well tolerated and effective surgical procedure in these patients. This can be performed with concurrent medial rectus recession in the setting of muscle contracture to treat myopic strabismus fixus or ‘heavy eye syndrome.’
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Conflicts of interest
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REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
- ▪ of special interest
- ▪▪ of outstanding interest
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