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Ocular ischaemic syndrome (OIS) is most commonly caused by severe ipsilateral carotid artery stenosis.1–3 Occasionally it is caused by ophthalmic artery stenosis.4,5 Features commonly observed are iris neovascularisation, angle neovascularisation, rubeotic glaucoma, and iritis. In the posterior segment common signs are narrowing of the retinal arterioles, mid-peripheral retinal haemorrhages, optic disc pallor or neovascularisation and, rarely, retinal neovascularisation. Fluorescein angiography characteristically demonstrates delayed filling of the retinal circulation and occasionally patchy filling of the choroidal circulation is also observed.1–3 To the best of our knowledge OIS has not previously been described in thyroid eye disease. We report a case of OIS in thyroid eye disease confirmed by magnetic resonance angiography (MRA) and treated by orbital decompression.
A 48 year old woman with known thyroid eye disease presented with a 4 week history of pain, redness, and reduced visual acuity in her right eye. Eight years previously she had undergone bilateral three wall orbital decompression for severe corneal exposure. On examination visual acuity was counting fingers in the right eye and 6/9 in the left. There was bilateral lid retraction and mild generalised restriction of eye movements. There was bilateral proptosis measuring 24 mm in the right eye and 23 mm in the left (Keeler exophthalmometer). A right relative afferent pupillary defect was present. Intraocular pressures were 50 mm Hg in the right eye and 20 mm Hg in the left. There was right corneal oedema, rubeosis iridis (Fig 1), and moderate anterior chamber activity. Gonioscopy showed an open, grade 2 angle (Shaffer’s classification) with rubeotic vessels present in the angle. Fundal examination was limited by the corneal oedema but no specific abnormality was identified. Examination of the left eye was normal.
Fluorescein angiography showed delayed filling of the retinal vasculature in the right eye relative to the left. Computed tomography scans of the orbits showed previous bilateral three wall orbital decompression and diffuse enlargement of extraocular muscles. Carotid duplex ultrasound examination was normal. An MRA of the orbits demonstrated that blood flow in the right ophthalmic artery was reduced. Blood flow in the left ophthalmic artery was normal (Fig 2).
The patient was admitted and treated with intravenous mannitol and acetazolamide and topical apraclonidine 0.5% and betaxolol 0.5% but intraocular pressure remained elevated at 29 mm Hg. A further right orbital decompression was performed (where the lateral orbital wall was removed as far posteriorly as the anterior wall of the middle cranial fossa and superiorly to the floor of the anterior cranial fossa). Postoperatively the right proptosis measured 21 mm, the relative afferent pupillary defect resolved and the intraocular pressure was controlled (⩽20 mm Hg) with oral acetazolamide and topical apraclonidine 0.5% and betaxolol 0.5%. The corneal oedema resolved and the visual acuity gradually improved to 6/9. At the 3 month follow up postoperatively the rubeotic iris vessels had regressed. An MRA performed 4 months postoperatively demonstrated normal blood flow in both ophthalmic arteries (Fig 3).
Imaging methods available for evaluating the ophthalmic artery include duplex ultrasonography and cerebral angiography. Duplex ultrasonography is a non-invasive technique that gives quantitative information about flow; however, it requires an experienced operator and it is not always possible to positively identify the ophthalmic artery. Cerebral angiography is an invasive technique with the inherent risk of embolisation and stroke. MRA is a relatively new technique and has not previously been used to investigate disturbances of blood flow in the ophthalmic artery. It is non-invasive and does not require the level of technical experience required for Doppler studies. MRA detects blood flowing at a defined velocity. In this case 25 mm/s was chosen as it has been shown in many studies using Doppler ultrasound to be the mean ophthalmic artery blood flow. The absence of signal from the right ophthalmic artery in the preoperative MRA demonstrates that at no stage during the cardiac cycle was blood flowing at this velocity in the artery. The images shown in Figures 2 and 3 are composites of all slices taken through the orbits. Hence it is not possible that one of the ophthalmic arteries could have been missed as a result of the orientation of any one particular slice.
Various abnormalities of the orbital circulation have been reported in thyroid ophthalmopathy. Blood flow in the superior ophthalmic vein has been shown to be reduced,6–8 or even reversed7,8 in some patients. Increased central retinal artery,8 ophthalmic artery,8 and retinal blood flow9 have also been demonstrated. Ischaemia of the optic nerve head has been postulated to have a role in the development of optic neuropathy in some patients with thyroid ophthalmopathy.10 However, to the best of our knowledge ophthalmic artery obstruction as a result of thyroid eye disease has not previously been described.
In summary, this case demonstrates for the first time, the ocular ischaemic syndrome as a result of ophthalmic artery obstruction in thyroid eye disease. Furthermore, it demonstrates the usefulness of MR imaging in evaluation of the ophthalmic artery.