To the Editor:
We read with interest the elegant article by Dubost et al.1
documenting a correlation between increased optic nerve sheath diameters and preeclampsia. At Bascom Palmer Eye Institute we have been studying the potential application of sonography for ophthalmic regional anesthesia.
The application of sonic energy around the eye is not without risk. Thermal and mechanical bio-effects are well described. Multiple international regulatory authorities, including the U.S. Food and Drug Administration2
and Health Canada* have imposed stricter physical parameters for the use of ophthalmic ultrasound. In particular, limits on Mechanical Index and Thermal Index have been reduced to 0.23 and less than 1, respectively.
We recently published a rabbit model study that compared thermal and mechanical changes induced by exposure to ophthalmic- and nonophthalmic-rated transducers.3
Our data showed significant changes in intraorbital temperature after exposure to the nonorbital rated Sonosite Micromaxx 6-13 MHz linear transducer (Bothell, WA).
Great benefit may emanate from intra- or perioperative ultrasonic ocular examinations, whether for optic nerve sheath diameters, regional anesthesia, or other applications. Investigators must remain cognizant of the potential deleterious ocular effects of sonic energy, and ensure that only orbital-approved technology is used in future research.
Howard D. Palte, M.B.Ch.B., F.C.A.(SA).,† Steven Gayer, M.D., M.B.A.
†University of Miami, Miller School of Medicine, Miami, Florida. firstname.lastname@example.org
1. Dubost C, Le Gouez A, Jouffroy V, Roger-Christoph S, Benhamou D, Mercier FJ, Geeraerts T. Optic nerve sheath diameter used as ultrasonographic assessment of the incidence of raised intracranial pressure in preeclampsia: A pilot study. ANESTHESIOLOGY. 2012;117:1066–71
2. U.S. Food and Drug Administration. Guidance for Industry and FDA Staff Information for Manufacturers Seeking Marketing Clearance of Diagnostic Ultrasound Systems and Transducers. 2008 Silver Spring, MD U.S. Food and Drug Administration
3. Palte HD, Gayer S, Arrieta E, Scot Shaw E, Nose I, Lee E, Arheart KL, Dubovy S, Birnbach DJ, Parel JM. Are ultrasound-guided ophthalmic blocks injurious to the eye? A comparative rabbit model study of two ultrasound devices evaluating intraorbital thermal and structural changes. Anesth Analg. 2012;115:194–201
© 2012 American Society of Anesthesiologists, Inc.