Heavy Eye Syndrome
Strabismus fixus convergence or ‘Heavy Eye’ syndrome (HES) is a cause of acquired esotropia in the setting of high myopia. Patients classically present with diplopia secondary to progressive esotropia and hypotropia with limitation of abduction and elevation, although exotropia and hypertropia have also been described . Heavy eye syndrome should be differentiated from sagging eye syndrome (SES) which is mostly seen in non-myopic elderly population and presents with esotropia worse at distance along with degenerative changes such as, bilateral blepharoptosis, and deepening of the lid sulci .
It is hypothesized that HES is the result of LR and SR shifts caused by the elongated posterior portion of the eyeball due to high myopia. Inferior shift of LR causes reduced abduction and increased infraduction. Nasal shift of SR causes reduced supraduction and increased adduction. Consequently, HES shows esodeviation and hypodeviation due to increased adduction, reduced abduction, reduced supraduction with an increased infraduction .
There are no definitive diagnostic criteria for HES ; however, findings are described below. Table 1 compiles key findings in HES.
Heavy eye syndrome is not typically seen in childhood. Patients typically have high myopia - Hayashi et al. found an average diopter of -18.00D among their cases. Some patients will complain of new onset diplopia in adulthood . Some patients may present with concerns about appearance of the eye . The older and more myopic the patient, the more likely the patient will have an acquired esotropia and/or a vertical heterotropia .
Neuroimaging, preferably with MRI, should be obtained with attention to the paths of the rectus muscles  . If altered paths of the muscles are noted, the surgical options will aim to correct the deviation. If no abnormality is found and in the absence of other causes, classical recession-resection surgery may be beneficial .
Yamaguchi et al. investigated the anatomic relationships between the globe, SR, and LR muscles with coronal MRI. The angle formed by the globe, LR, and SR was calculated and referred to as the angle of dislocation of the globe . Their study found patients with highly myopic strabismus to have a mean angle of dislocation of 179.9° ± 30.8° while in the control group the mean angle of dislocation was 102.9° ± 6.8° (P < .001) . This finding is represented by Figure 1.
Tan et al. measured this angle in HES vs SES patients. The mean angle between the lateral rectus and superior rectus muscles in HES was 121° ± 7° while in SES, the mean angle between the lateral rectus and superior rectus muscles was 104° ± 11°, significantly less than in HES (P < 0.001) .
Mansour et al. reported two cases of acquired convergent strabismus fixus that developed ocular ischemia, atrophy of the optic nerve, and central retinal artery occlusion. They believed these complications to be secondary to mechanical stretching and torsion of the optic nerve with subsequent strangulation of its blood supply. They recommended early surgical correction of strabismus fixus .
- Endocrine ophthalmopathy 
- Sagging Eye Syndrome 
- Uncorrected hyperopic refractive error 
- High accommodative convergence/accommodation ratio 
- Duane syndrome 
- Myasthenia gravis 
- Thyroid eye disease
- Cranial nerve palsy (Third, fourth, or sixth nerves)
In patients with highly myopic strabismus, it is important to distinguish HES from SES as the distinction drives appropriate surgery. There is overlap of motility findings; therefore, imaging should be obtained. Orbital MRI demonstrates inferior lateral rectus displacement and medial superior rectus displacement with severe superotemporal prolapse of the myopic globe in HES, whereas only inferior displacement of the lateral rectus results from degeneration of the LR-SR band is seen in SES . Distinctions and similarities have been compiled into Table 2.
Hayashi et al. found the recession and resection (R&R) procedure to be easy and effective when the abducting disorder is not severe. However, R&R was less successful in patients with more severe disease, which they defined as cases where the patient could not abduct to the midline or had a fixed eyeball in the extreme adducting position .
The most successful outcomes have come from correcting the muscle paths of both the superior and lateral rectus muscles. The most commonly performed surgery involves loop myopexy of the superior and lateral rectus muscles either with or without muscles splitting . Yamaguchi et al. demonstrated the efficacy of loop myopexy±medial rectus recession in 23 patients. They were successful in decreasing the angle of dislocation of the globe, increasing the angles of maximum abduction and sursumduction, and decreasing the angle of ocular deviation. All 23 patients had positive forced duction tests preoperatively; and postoperatively, only 1 patient had a positive forced duction test. Dislocation of the globe, restriction of ocular movements, and ocular deviation did not relapse during follow up (mean 48.8 months) . Akbari et al. modified this procedure by using two sutures for muscle belly union which resulted in favorable outcomes in 16 patients 
•Concurrent Medial Rectus Recession at Time of Loop Myopexy
While many experts have performed medial rectus recession at the same time as loop myopexy, Bansal et al. demonstrated the efficacy of loop myopexy alone. In their case series, 21/29 (72%) did not require medial rectus recession and had a successful outcome with loop myopexy alone. A combined approach eliminates the need for a second procedure, while a staged approach reduces the overall amount of surgery required .
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- Akbari MR, Bayat R, Mirmohammadsadeghi A, Inanloo B, Mirshahi R. Surgical outcome of a new modification to muscle belly union surgery in heavy eye syndrome. Strabismus. 2018;26(4):198-202. doi:10.1080/09273972.2018.1502793