Purpose: Conventional wisdom in ophthalmology is that the force required to perforate an eye during retrobulbar injection is noticeably greater with a specially designed blunt needle than with a standard hypodermic needle. A search of the literature showed no measurements of scleral perforation pressure with specific needle tips. The authors investigated this concept. Methods: A computerized search for eye perforations 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 several commercially available needles, subjectively assessed the force required to perforate the globe. The authors designed and built a portable transducer system to objectively measure the perforation pressure of human globes with the needles. Measurements were done with preserved and unpreserved human cadaver eyes. Results: No globe penetrations or perforations were found in this consecutive series of over 4000 retrobulbar anesthesia procedures. A subjective difference between the hypodermic 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, blunt-tipped needles have higher scleral perforation pressures than those with cutting edges.
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