Acute comitant esotropia with binocular single vision for near can be found both in myopes, as described by von Graefe and Bielschowsky, and in young emmetropes or low hypermetropes, as described by Burian and Franceschetti [4
]. DPE is usually considered as a neurological disorder and the presence of normal electro-oculographically determined saccadic velocities may help distinguish it from a bilateral deficit of the abducens [5
]. DPE shares with Burian-Franceschetti’s acute comitant esotropia, often caused by brain tumour, the reduction of divergence fusion amplitudes [6
], so that they could probably be considered the same entity. Sagging eye syndrome seems to represent a variant in elderly people. The main signs that differentiate SES and deficit of abducens are the normal ocular motility, the stability of the angle of deviation in both left and right ductions and the normal horizontal saccadic velocity. MRI is also pathognomonic because it shows lower slippage of the lateral rectus muscle.
Many surgical approaches have been described [2
] for esotropia with incomitance among distance and near in DPE (Table 1).
The recent hypothesis that considers DPE as a mechanical (and not neurological) disease, also called “sagging eye syndrome,” allows a modification of the surgical approach. Accordingly, some patients with clinical signs and symptoms of DPE, as demonstrated by coronal section of orbital MRI, evidence an inferior displacement of LR muscle probably due to age-related orbital connective tissues degeneration, with no variations in its original insertion. It has been supposed that bilateral inferior displacement of LR may induce a mechanical divergence paralysis esotropia (DPE), characterized by orthophoria or asymptomatic esophoria of no more than 10? at 33 cm, with symptomatic distance esotropia (ET), and normal saccadic velocities in adduction and abduction. Asymmetrical inferior shift of the LR pulley has been postulated to induce cyclovertical strabismus (CVS), and may result in hypotropia with excyclotropia; it is important to differentiate this from controlateral oblique superior palsy, characterized by an excyclotropia of the hypertropic eye [2
]. Sagging eye syndrome is similar in its pathogenesis to “heavy eye syndrome” in which, however, an association with high myopia, profound esotropia, and hypotropia is always present [2
]. In axial myopia, inferior lateral rectus displacement is also combined with medial rectus inferior displacement, an enlarged, irregular staphylomatous globe which could also be involved in the appearance of profound esotropia. One of the surgical approaches described to correct heavy eye syndrome is an equatorial loop myopexy associated with medial rectus recession and lateral rectus resection [13
]. Rutar et al. [2
] and Durnian et al. [9
] have only suggested in SES cases a loop of silicone between the superior and lateral rectus muscle bellies to suspend the lateral rectus muscle, a tecnique that has been described however in “heavy eye” syndrome. Based on MRI, in such cases of bilateral SES or mechanic DPE a bilateral lateral rectus muscles scleral fixation at 10 mm distance from original insertion seems to be sufficient in order to normalize the pathological path of LR. The goal of this surgery is to correct the body muscle slippage in order to eliminate the esotropia coming from the “disfunction” of the slipped lateral rectus muscle. We have fixed only one-third of the lateral rectus muscle with a loop miopexy because by involving the entire body muscle, we would have performed a muscle transposition. At the same time, the loop miopexy allows the muscle fibers to contract without changing the insertion, this is the reason why it differs from the classical retroequatorial miopexy. Equatorial loop myopexy in bilateral sagging eye syndrome is a rapid and safe surgical approach with satisfactory clinical results. Further follow-up will be necessary to assess the incidence of recurrence beyond six months.