Bilateral myopic strabismus fixus with fat prolapse treated by silicone band loop myopexy and excision of fat.

Description

A 60-year-old man presented to our outpatient clinic with chief complaints of progressive inward deviation of both eyes and presence of a yellowish mass in both eyes for 2 years. On examination, the best-corrected visual acuity in the right eye (RE) was perception of light with accurate projection of rays and 20/126 in the left eye (LE). On ocular motility evaluation, there was limitation of abduction and elevation of −4 (figure 1A). The modified Krimsky test showed a large esotropia of about 110 prism diopters (PD) and 14 PD hypotropia in both eyes. A subconjunctival, yellow, soft, avascular, non-pulsatile, mobile mass was noticed supero-temporally in both eyes (figure 1B). While the palpebral part of the lacrimal gland was not visible, the orbital part could not be palpated. Examination of the anterior segment showed surgical aphakia in the RE and nuclear cataract in the LE. Fundus examination showed severe myopic tessellations in both eyes with normal optic discs, and there was a chorio-retinal atrophic patch involving the macula, suggestive of myopic maculopathy in the RE. The axial length was 34.21 and 34.41 mm in the RE and LE, respectively. CT scan of the orbit showed nasal shift of the superior rectus (SR) and inferiorisation of the lateral rectus (LR) with extraconal fat prolapse bilaterally (figure 1C).

Figure 1

(A) Nine gaze clinical photographs depicting esotropia with hypotropia in primary gaze (yellow arrows) with marked limitation of abduction and elevation (white arrows). (B) Clinical photograph of severe orbital fat prolapse in the supero-temporal quadrant of the globe (blue asterisk). (C) Coronal cut of CT image depicting orbital fat prolapse in the supero-temporal quadrant of the orbit (blue star) with nasalisation of superior rectus and inferiorisation of lateral rectus (encircled).

A diagnosis of myopic strabismus fixus (MSF) with orbital fat prolapse was made. The patient underwent an LR and SR muscle union using a silicone band and a medial rectus muscle recession with orbital fat excision bilaterally. Intraoperatively, the forced duction test was positive for the medial rectus muscle. The silicone loop myopexy and orbital fat excision were both done in a single sitting. There was minimal inflammation in the immediate postoperative period, for which we prescribed topical anti-inflammatory agents. The surgical procedure led to a desirable outcome; the patient had a residual esotropia of 25–30 PD and an improvement in the abduction (−4 limitation to −1, on a scale of 0–4), in the immediate postoperative period with complete resolution of fat prolapse. The patient was however lost to follow-up.

Horizontal strabismus associated with myopia can manifest in various forms, that is, infantile, intermittent, constant, sensory and occasionally even with a small vertical component. However, MSF can manifest in two forms: esotropia–hypotropia complex and exotropia-hypotropia complex.1

This patient exhibited an esotropia–hypotropia complex form of MSF. In such patients, there is a supero-temporal dislocation of the posterior portion of the elongated globe from the muscle cone due to increased axial length. This causes an inferior displacement of the LR leading to abduction limitation and nasal displacement of the SR, thereby causing an elevation limitation.2

This could be appreciated on coronal cuts of a CT scan of the orbit (figure 1C). However, the best modality for soft tissue and extraocular muscle path delineation is MRI. The socio-economic status of the patient precluded getting an MRI done. While the inferior displacement of LR leads to weakening of abducting force and converts it to a depressor, nasalisation of the SR weakens its elevating force and converts it to an adductor, thereby leading to esotropia and hypotropia. The majority of these patients tend to have a myopia of >15 D and axial length of >31 mm.2

The surgical procedure to restore the dislocated globe back into muscle cone by uniting muscle bellies of SR and LR is very effective for MSF.3 Bilateral silicone band loop myopexy of LR–SR with or without bilateral medial rectus muscle recession is a good procedure to improve the alignment and extra-ocular motility. The intraoperative and postoperative complications like globe perforation, splitting of muscle, suture-related complications and anterior segment ischaemia are less seen in loop myopexy as compared with suture myopexy.4

Subconjunctival orbital fat prolapse is the prolapse of intraconal fat through a weakness in the tenon’s capsule.5 Management of orbital fat prolapse includes either excision of the fat or conjunctival suturing of the fat to the sclera.6

In this case, both procedures were approached via a forniceal conjunctival incision made between SR and LR. The LR was then exposed and hooked. The prolapsed fat was approached through the same incision. The septa over the prolapsed fat was dissected to expose the fat globules. The base of the globules was clamped with an artery forceps and the fat was excised using a bipolar radiofrequency cautery. The visible fat was debulked and no attempt was made to pull out residual extraconal fat. In order to induce fibrosis and prevent further fat prolapse, the base of the debulked fat pad was cauterised using a bipolar cautery. Care was taken to avoid injuring the palpebral lobe of the lacrimal gland and the insertion of the LR muscle while dissection. The SR was then exposed and hooked. Using a crescent knife, a scleral tunnel was made 14 mm behind the limbus, midway between the SR and the LR muscles. A number 240 silicone band was passed around the SR, passed through the scleral tunnel and then around the LR, thereby approximating the SR and LR muscles.

This case was unique in terms of bilaterality, displacements of SR and LR muscles and fat prolapse. Although MSF has been widely reported, fat prolapse in MSF is unknown or has not been published to the best of our knowledge.

Modified scleral fixated silicone band loop myopexy with or without medial rectus (MR) recession is a safe and effective procedure in the management of esotropia–hypotropia in myopic strabismus fixus, since this procedure normalises the vector forces of the lateral rectus and superior rectus.

Intraoperatively, if there is a tight MR in addition to a large esotropia in primary position, this procedure can be combined with bi-MR recession.

Muscle and fat prolapse can occur simultaneously which is amenable to surgery with good outcome.