Abstract
Drug loss due to tear drainage and blinking was one of the factors considered early as being responsible for poor efficacy of topical therapy. Then other factors were studied, such as the role of preservatives, vehicles, drug carriers, and adjunct agents, together with the influence of molecular weight, pH, tonicity, and drug volume in improving drug penetration into the eye. To date, topical anesthesia has been practiced using currently available eyedrop or gel formulations. Indeed, the gel we have used and are using is intended as a skin and mucosal anesthetic and instrument lubricant. Work on the pharmacokinetics of topically applied ophthalmic drugs aimed for a long time to obtain high intraocular drug levels, mainly to reduce inflamation, defeat infection, or lower intraocular pressure. As for modern cataract surgery, intraocular penetration of anesthetics has been recently questioned as a crucial factor in obtaining proper analgesia and good intraoperative and postoperative comfort. Intracameral injection of lidocaine leads to intraocular levels that are 100 times higher than those after instillation,1Behndig A. Linden C. Aqueous humor lidocaine concentrations in topical and intracameral anesthesia.J Cataract Refract Surg. 1998; 24: 1598-1601Abstract Full Text PDF PubMed Scopus (32) Google Scholar yet fails to prove superior to topical anesthesia alone in controlled clinical trials.2Crandall A.S. Zabriskie N.A. Patel B.C. et al.A comparison of patient comfort during cataract surgery with topical anesthesia versus topical anesthesia and intracameral lidocaine.Ophthalmology. 1999; 106: 60-66Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar, 3Gillow T. Scotcher S.M. Deutsch J. et al.Efficacy of supplementary intracameral lidocaine in routine phacoemulsification under topical anesthesia.Ophthalmology. 1999; 106: 2173-2177Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar, 4Tan J.H. Burton R.L. Does preservative-free lignocaine 1% for hydrodissection reduce pain during phacoemulsification?.J Cataract Refract Surg. 2000; 26: 733-735Abstract Full Text Full Text PDF PubMed Scopus (12) Google Scholar, 5Boulton J.E. Lopatatzidis A. Luck J. Baer R.M. A randomized controlled trial of intracameral lidocaine during phacoemulsification under topical anesthesia.Ophthalmology. 2000; 107: 68-71Abstract Full Text Full Text PDF PubMed Scopus (33) Google Scholar, 6Pang M.P. Fujimoto D.K. Wilkens L.R. Pain, photophobia, and retinal and optic nerve function after phacoemulsification with intracameral lidocaine.Ophthalmology. 2001; 108: 2018-2025Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar It therefore appears that in cataract surgery all efforts should point towards maximizing corneal, conjunctival, and lid analgesia, at least in case of uncomplicated clear cornea small-incision phacoemulsification. Starting from the theoretical observations made by Dr Gaynes, it will probably be possible to develop a more efficient agent for topical anesthesia for cataract surgery.
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