Tube Shunt Related Complications of the Orbit

Orbital complications during or after glaucoma filtering or tube shunt surgery are relatively rare but may pose a significant treatment challenge or threat to vision. The incidence of complications is highly variable, and transient events may not be reported as frequently as those that persist. A variety of orbital complications occur following glaucoma surgery. Complications may be categorized as mechanical, infectious, neurogenic, or myogenic. However, each complication may be multimodal and fall into more than one category. Mechanical complications are the most frequent type of orbit complication related to glaucoma surgery and more specifically to tube shunt implantation. Mechanical complications include ptosis, lid retraction, strabismus, and proptosis. Several theories address why ptosis may occur after ocular surgery and why it may be either transient or permanent. The levator muscle may be damaged or dehisced by an eyelid speculum, leading to a lid droop. Bridle sutures, which are often used during glaucoma surgery, have also been implicated as they apply counter traction against the superior rectus muscle. Prolonged eyelid edema and local anesthesia have each been more strongly associated with postoperative ptosis. For more information on ptosis, see Chapter 25. Strabismus after tube shunt implantation is most commonly related to either the device itself or to scarring and fibrosis that develop postoperatively. Transient strabismus may be related to swelling or edema of local tissues and may also follow retrobulbar injection. The strabismus is usually incomitant and does not present with a characteristic pattern of deviation; thus, prisms and other nonsurgical treatments are seldom adequate. Although strabismus following tube shunt surgery is usually transient, persistent diplopia may occur. The type of implant, size, location, and material each play a role. Implants with larger surface areas have a higher incidence of motility disturbance due to mass effect. Tube shunt plates that require placement below the rectus muscles risk direct muscle injury or adhesion scarring to the implant. In addition, a pseudo-Brown’s syndrome may be created by a superonasal implant due to interference with the superior oblique muscle function. The bleb that develops around the tube shunt reservoir can also act as a mass.