Magnetic resonance imaging (MRI) scans are frequently and routinely used to view the orbit; however, problems with imaging quality can arise from the patient’s voluntary ocular movements. Several nonanesthetic techniques have been implemented to prevent any ocular motility during scans. One such technique involves placing water-soaked gauze over one eye and taping it shut, while the contralateral eye fixates on a target ( ). In response to the article describing this technique, we report a case of a subject who suffered transient ischemic ocular events after taping the eyes with water-soaked gauze.
Case report
As part of an on going research project, a 56-year-old neuroradiologist at the University of Texas, with no history of vascular disease, volunteered herself to obtain an MRI scan of her head and neck. To ensure negligible ocular movements, the technique described in the aforementioned article was carried out. Two 4 × 4 gauzes were folded, soaked in water, and taped tightly down to both of her eyes. The gauze was also taped down to the head rest to guarantee that neither ocular nor head movements caused increase tissue noise. No topical, retrobulbar, or general anesthesia was used.
After the MRI scan, the soaked gauze and tape was removed and the subject was temporarily unable to see out of either eye. She experienced severe photopsia and a black curtain effect in both eyes, which lasted 15–20 minutes. No headaches or intraocular pain were reported and full visual acuity returned after 20 minutes. After ophthalmic examination and discussion, no ocular findings were noted and a bilateral ischemic ocular event was inferred.
Comment
It is speculated that the external globe pressure, created by the soaked gauze, resulted in an elevated intraocular pressure (IOP) greater than the perfusion pressure, thereby causing a temporary ischemic event. Ophthalmic blood flow was impeded secondary to the decrease in perfusion pressure, resulting in a reduction in systemic blood pressure and a rise in venous pressure of IOP. A previously reported case described a patient who developed loss of vision because of elevated IOP from external orbital compression which they speculate compromised retinal and choroidal perfusion as a result ( ).
Ocular Perfusion Pressure (OPP) is determined by the mean difference of the blood pressure (BP) and the IOP (i.e., OPP = Mμ(BP – IOP)). Given this formula, it can be derived that the OPP was significantly decreased in the reported case, as the mean BP was decreased in the supine position and that the IOP was increased because of the pressure exerted from the soaked gauze and tape.
This transient decrease in OBF may have caused bilateral amaurosis fugax. Mainstream thought is that amaurosis fugax is primarily a large vessel disease; however, reports in the literature have shown that small vessel disease may also be involved ( ). We report a case in which bilateral amaurosis fugax was likely caused by the placement of soaked-gauze taped to both eyes during an MRI scan of the head. It is therefore the opinion of the authors that the technique described in the March 2006 article should not be employed for patients requiring an MRI scan of the head or orbits to avoid the risk of an ocular ischemic event.
References
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