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This 71 year old woman was referred with bilateral optic neuropathy and thyroid associated ophthalmopathy (TAO) of Graves' Disease.
She had been treated for primary hyperthyroidism on three occasions with radioactive iodine and was taking Tapazole 5 mg daily.
Neuro-ophthalmological examination:
Vision was reduced to 20/200 in each eye with bilateral central scotoma and mild disc hyperemia.
She had the classical signs of Graves' Disease.
A prominent stare.
Retraction of all four eyelids
Bilateral exophthalmos
Hertel exophthalmometer 25 OD, 28 OS, base 108.
Tight orbits/reduced orbital resilience
Restricted horizontal eye movements
Marked limitation of upward gaze
Mild limitation of downgaze
Lid lag (persistent elevation of the upper eyelid in
downgaze) – von Graefe sign
Positive forced duction test
Prominent congested scleral blood vessels
A visible rim of sclera on gentle eye closure
Bell's reflex absent, eyes fail to move up under closed
lids)
Convergence normal
Investigations:
Thyroid tests showed TT3 elevated to 243 (6/7/90) and 324 (7/3/90).
CT orbits:
Greatly enlarged extraocular muscles crowding the optic
nerves at the apex
Considerable bilateral proptosis right left.
The inferior rectus and medial rectus muscles were especially enlarged with fusiform dilatation of the midposition of the muscle.
Therapy:
Patient received a course of oral steroids
Surgery:
Bilateral orbital decompression and ethmoidectomy.
CT Orbits Post-Op:
The scan confirmed adequate removal of the medial orbital walls and the orbital floors over the maxillary sinuses.
The surgeon also partly divided the levator muscles because of severe upper lid retraction. Her vision recovered to 20/40 OD and 20/30 OS.
Comment:
Compressive optic neuropathy is the most serious complication of TAO.
The incidence of visual loss is between 2% and 9% in all patients with TAO. However, in patients with "severe" TAO, requiring orbital decompression, as in this case, optic neuropathy occurs in up to 50% of patients.
Vision loss from optic nerve compression requires immediate management.
Clinical
This 71 year old woman with TAO of Graves' Disease has:
A prominent stare.
Retraction of all four eyelids
Bilateral exophthalmos
Hertel exophthalmometer 25 OD, 28 OS, base 108.
Tight orbits/reduced orbital resilience
Restricted horizontal eye movements
Marked limitation of upgaze
Mild limitation of downgaze
Lid lag (persistent elevation of the upper eyelid in
downgaze) – von Graefe sign
Positive forced duction test
Prominent congested scleral blood vessels
A visible rim of sclera on gentle eye closure
Also illustrated is:
• The use of a Hertel exophthalmometer to measure the forward protrusion of the proptotic eye
• How to evaluate reduced orbital resilience by digital pressure on the globe
• The absent Bell's reflex
Comment:
TAO can be differentiated from ocular myasthenia gravis by the lack of ptosis and the presence of proptosis, lid retraction, lid-lag and periorbital edema.
TAO can, however, co-exist with ocular myasthenia gravis. As a result, screening thyroid studies are essential prior to treatment even when the clinical diagnosis of TAO together with ocular myasthenia gravis seems clear.
Forced duction test:
In TAO the limitation of upgaze is due to tethering of the eyeball in the floor of the orbit by soft tissue changes.
Tethering of the eyeball inferiorly can be confirmed by performing a forced duction test. The test requires anesthetizing the eyeball with topical anesthesia. Inability to move the eye up despite pushing on the globe with a cotton tip swab or pulling with a small pair of blunt tweezers, suggests mechanical restriction - interpreted as a positive forced duction test.
Neuroimaging
Computerized tomography (CT) of the orbit is the gold standard for the diagnosis of TAO. The classic finding is enlargement of the extraocular muscle belly with relative sparing of the tendon.
Proptosis may be recognized without extraocular muscle enlargement, presumably resulting from an increased volume of intraorbital fat.
To order an MRI of the orbit, the recommended sequence is STIR (short tau inversion recovery), to highlight the extraocular muscles.
CT orbit:
Illustrative images in another case of TAO show:
Figure 1 Axial CT through the orbit without contrast shows enlargement of the medial rectus muscle bilaterally. Note that the tendinous insertion is spared.
Figure 2 The coronal CT (reformatted from axial data set) without contrast shows enlargement of the medial rectus muscle, inferior rectus muscle and upper muscle complex on both sides.
Courtesy of Hugh Curtin, M.D.
To view CT images go to PowerPoint presentation "Thyroid Associated Orbitopathy".
Anatomy
Orbit - enlargement of extraocular muscles
Pathology
Graves' Disease is an autoimmune condition.
For unknown reasons, the extraocular muscles develop lymphocytic and plasmacytic infiltration with secondary production of acid mucopolysaccharides. In the acute stages, the changes are largely inflammatory. In the chronic inactive stage, there is often fatty infiltration of muscles.
Etiology
Autoimmune disorder
Disease/Diagnosis
Restrictive orbitopathy of Graves' Disease
Treatment
Treatment of TAO associated with Graves' Disease is extremely successful. Irritation and swelling can be treated with a short (1-2month) course of systemic corticosteroids or with low-dose (1500 to 2000 cGy) orbital radiation therapy.
Proptosis can be treated with orbital decompression using a variety of techniques.
(For a full discussion of therapy see reference 3, 6 and 10)
References
1. Bahn RS, Heufelder AE, Pathogenesis of Graves' ophthalmopathy. N Engl J Med 1993;329:1468-1475.
2. Galetta SL, Gray LG, Raps EC, Shatz, NJ. Pretectal eyelid retraction and lag. Ann Neurol 1993;33:554-557.
3. Galetta SL, Raps EC, Liu GT, Saito NG, Kline LB. Eyelid lag without eyelid retraction in pretectal disease. J Neuro-ophthalmol 1996; 16:96-98.
4. Garrity JA, Fatourechi V, Bergstralh EJ, et al. Results of transantral orbital decompression in 428 patients with severe Graves' ophthalmopathy. Am J Ophthalmol 1993;116:533-547.
5. Hoffman PN. In: Walsh and Hoyt's Clinical Neuro-Ophthalmology, 6th edition. Editors Miller NR, Newman NJ, 2005;1(22):1085-1131.
6. Jacobson DM. Acetylcholine receptor antibodies in patients with Graves ophthalmopathy. J Neuro-ophthalmol 1995;15:166-170.
8. Liu GT, Volpe NJ, Galetta SL. Orbit Disease in Neuro-ophthalmology. Chp 18, 651-697. In: Neuro-ophthalmology Diagnosis and Management. W.B. Saunders Company 2001.
