RETROBULBAR ANESTHESIA RISK - DO SHARP NEEDLES REALLY PERFORATE THE EYE MORE EASILY THAN BLUNT NEEDLES

Purpose: Conventional wisdom in ophthalmology is that the force requir ed to perforate an eye during retrobulbar injection is noticeably grea ter with a specially designed blunt needle than with a standard hypode rmic needle. A search of the literature showed no measurements of scle ral perforation pressure with specific needle tips. The authors invest igated this concept. Methods: A computerized search for eye perforatio ns of the surgical records over a 5-year period at Wilford Hall United States Air Force Medical Center was conducted. A double-masked trial by experienced ophthalmologists, using preserved eye bank eyes and sev eral commercially available needles, subjectively assessed the force r equired to perforate the globe. The authors designed and built a porta ble transducer system to objectively measure the perforation pressure of human globes with the needles. Measurements were done with preserve d and unpreserved human cadaver eyes. Results: No globe penetrations o r perforations were found in this consecutive series of over 4000 retr obulbar anesthesia procedures. A subjective difference between the hyp odermic and blunt needles was detected. Objective measurements showed a significant difference between the hypodermic and blunt needles, and between types of blunt needles. The difference was present with both eye bank eyes and fresh cadaver eyes. Conclusion: Blunt-tipped needles do require greater force to penetrate the eye. The noncutting edge, b lunt-tipped needles have higher scleral perforation pressures than tho se with cutting edges.