In a university ophthalmology department, a cluster of postoperative diplop
ia and ptosis cases occurred in the initial 3 months after hyaluronidase (W
ydasel (R)) became unavailable for use with injection anesthesia. These cas
es suggest that hyaluronidase, when used with injection anesthesia, may pro
tect extraocular muscles and nerves from the toxic effects of local anesthe
tic agents. The spreading action of hyaluronidase facilitates uniform diffu
sion of anesthetic agents. This prevents elevated extracellular tissue pres
sure, a cause of ischemic damage to extraocular muscles or nerves. Hyaluron
idase may also prevent focal accumulations and concentrations of local anes
thetic agents, which at high enough levels may cause myotoxic or neurotoxic
damage, fibrosis, and contracture of extraocular muscles or nerves. (C) 20
01 ASCRS and ESCRS.