Thyroid Eye Disease
Thyroid eye disease (TED) affects the eye and the orbit in various ways. Only motility disturbances are covered in this volume.
Edema, inflammation, and fibrosis of the EOMs due to lymphocytic infiltration occur in this disease. Not only do these pathologies restrict motility, but the massively enlarged muscles can cause compressive optic neuropathy. Detection of muscle enlargement by orbital imaging helps confirm the diagnosis.
The myopathy is not caused by thyroid dysfunction. Rather, both conditions probably result from a common autoimmune disease. Thyroid-stimulating immunoglobulins likely mediate TED and may be regarded as a functional biomarker for this condition. Some patients also have myasthenia gravis (another autoimmune disease, discussed later in this chapter), complicating the clinical findings. An association between severity of TED and smoking has recently become apparent; the hazard ratio for strabismus surgery is almost double in patients with thyroid disease who smoke.
The muscles affected in TED, in decreasing order of severity and frequency, are the inferior rectus, medial rectus, superior rectus, and lateral rectus. The condition is usually bilateral but is often asymmetric. Forced duction testing almost always shows restriction in one or more directions.
Most often, the patient presents with some degree of upper eyelid retraction, proptosis, hypotropia, and esotropia (Fig 12-7). TED is a common cause of acquired vertical deviation in adults, especially women, but rarely causes motility problems in children.
Diplopia and abnormal head position are the principal indications for strabismus surgery. The operation may eliminate diplopia in primary gaze but rarely restores normal motility because of the restrictive myopathy, the need for large recessions in some cases to place the eye in primary position, and the ongoing underlying disease.
Figure 12-7 Thyroid eye disease. Note right upper eyelid retraction and restrictive right hypotropia with very limited elevation. Other rotations are not affected in this patient.
It is best to perform surgery after strabismus measurements and thyroid function tests have stabilized. In cases in which orbital decompression is necessary, strabismus surgery should be delayed until after that has been done. In the meantime, prisms may alleviate diplopia. Botulinum toxin may reduce the severity of fibrosis when injected into tight muscles in the acute phase. In studies of surgery performed before stability was achieved in patients with severe head positions, the results were favorable, but half the patients required further surgery.
Recession of the affected muscles is the preferred surgical treatment, addressing the tight muscles in 1 or both eyes. Resection procedures usually worsen restriction, but in carefully selected cases they may be helpful as part of the surgical plan. Slight initial undercorrection of hypotropia is desirable because late progressive overcorrection is common, especially with inferior rectus muscle recessions. Limited depression of the eyes after inferior rectus muscle recessions can interfere with patients’ bifocal use.
Because proptosis and eyelid retraction can increase after EOM surgery, eyelid surgery is best delayed until after all EOM surgery has been completed.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.