Spontaneous carotid-cavernous sinus fistula diagnosed by ophthalmodynamometry.

Abstract

Sir, The episcleral veins communicate upstream through the aqueous veins with Schlemm's canal in the eye, and downstream via the superior ophthalmic vein with the cavernous sinus. A spontaneous dilatation of episcleral veins can pose diagnostic problems, especially if imaging techniques are unremarkable. The present report describes a patient who presented with dilated episcleral veins of primarily unknown aetiology, and in whom ophthalmodynamometric determination of the central retinal vein collapse pressure was diagnostically helpful. A 59-year-old female patient experienced binocular diplopia and increasing redness of both eyes. Ophthalmologic examination revealed bilaterally dilated episcleral veins, blood staining of Schlemm's canal upon gonioscopy, slightly dilated retinal veins, a reduction in horizontal motility of the left eye corresponding with sonographic thickening of the left horizontal rectus muscles, and slight exophthalmos of 3 mm. Cerebral nuclear magnetic imaging was unremarkable. A preliminary diagnosis of endocrine orbitopathy was made and treated accordingly. Dilatation of the episcleral veins increased, however, and intraocular pressure (IOP) was elevated to 25 mmHg. A choroidal detachment developed in the left eye. Visual acuity remained unchanged at 20/20. Modified ophthalmodynamometry was performed as follows. Under topical anaesthesia, a conventional Goldmann contact lens with a pressure sensor mounted into its holding ring was put onto the cornea (Fig. 1). The contact lens was slightly pressed onto the cornea and the pressure values at the time when the central retinal vein or artery started to pulsate were noted. The measurements were repeated nine times, and the mean of the 10 values was taken for further statistical analysis. A previous study determined the reproducibility of the technique for measurements of the collapse pressures of the central retinal vein and artery to be 16.3 ± 11.4% and 8.5 ± 4.1%, respectively (Jonas 2003). The method has already been described in detail (Jonas & Niessen 2002; Jonas 2003; Jonas & Harder 2003). Photograph depicting the ophthalmodynamometer consisting of a conventional Goldmann contact lens and a pressure sensor mounted into the holding ring grip. Central retinal vein collapse pressure (OD: 24.1 ± 4.8 relative units; OS: 88.0 ± 6.3 relative units) measured significantly (p = 0.02) higher in the patient presented in this report than in a normal control group (6.1 ± 8.4 relative units) consisting of 27 subjects with a mean age of 69.6 ± 12.5 years. Central retinal artery collapse pressure did not vary significantly between the patient of the present report and the subjects of the control group (88.8 ± 1.7 relative units versus 78.0 ± 19.2 relative units; p = 0.44). As the central retinal vein and the episcleral veins drain into the same intracranial venous system, suggesting an abnormality in the cavernous sinus, neuroradiological examination was repeated. Cerebral angiography indicated a carotid-cavernous sinus fistula as the reason for increased central retinal vein pressure and dilatation of the episcleral veins. After endovascular embolization of the shunt with detachable platinum coils, exophthalmos, ocular motility, dilatation of the episcleral veins and IOP were reduced or normalized. After 4 months follow-up, IOP has remained normal, and the dilatation of the episcleral veins has regressed. The present report shows that using a modified type of ophthalmodynamometry for estimation of central retinal vein collapse pressure can be helpful in the diagnosis of carotid-cavernous sinus fistula. It is paralleled by other studies in which ophthalmodynamometric measurement of central retinal vein collapse pressure was shown to be useful in determining increased intracerebral pressure (Firsching et al. 1998; Jonas & Harder 2003).