To the Editor:
We read with interest the elegant article by Dubost et al. 1documenting 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 Administration2and 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.3Our 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.
†University of Miami, Miller School of Medicine, Miami, Florida. firstname.lastname@example.org