- Email: [email protected]
Corneal endothelial toxicity of topical anesthesia
Ophthalmology
Volume 105, Number
optic. Retained viscoelastic causes an osmotic gradient across the capsule, leading to an accumulation of viscous fluid in the bag. This causes distention of the bag, with posterior displacement of the posterior capsule and anterior displacement of the IOL and anterior capsule. It is reversible with either anterior or posterior capsulotomy. We have noticed that acrylic IOLs are more adherent to capsular tissue than silicone. This may cause a higher incidence of capsular block in the acrylic group. However, this syndrome was not observed with either type of IOL in this study. The relative elevation of IOP at I month in the acrylic group occurred despite nearly twice as many suture releasesor lysis. This suggeststhat the underlying mechanism is probably more related to differences in aqueous production rather than obstruction of outflow. We have no direct evidence to support either theory in a study of this design. We may gain more understanding of the underlying mechanism(s)if the study was repeated utilizing postoperative flaremeter readings and/or fluorophotometry. Dr. Safran’s suggestion of trying a dyed viscoelastic, instead of the usual colorless preparation, may also be worthwhile. LANCEC. LEMON, MD DONG H. SHIN, MD, PhD Detroit,
Cornea1 Endothelial Anesthesia
Toxicity
Michigan
of Topical
Dear Editor: I appreciate the interest of Drs. Judge, Najafi, Lee, and Miller in intraocular and topical anesthesia.I thought the use of intraocular anesthesiawould be very slow to catch on; however, the majority of my colleagues with large practices now routinely use 0.5 cc of unpreserved intraocular Xylocaine 1% for their cataract surgery. No problems have been reported. Before using Xylocaine intraocularly. 1 was familiar with reports of inadvertent injections with no adverse effect.’ After dose-ranging work on eyes with limited prognoses and not a single adverse reaction, I began routinely using 0.5 cc unpreserved Xylocaine 1% (Astra Pharmaceuticals, West Borough, MA) as an adjunct to my topical anesthesiaprotocol. I’ve administered other anesthetics intracamerally in partially sighted eyes. In fact, I’ve usedall the anestheticscited in the paper without recognizing a single case of decreased endothelial cell count or increased cornea1thickening. I find it interesting that humans respond so differently from rabbits. In our randomized, controlled study, we did not have a single untoward effect.’ It’s fortunate that we can use0.5 cc of intraocular Xylocaine becauseit is possibly the safest, most effective method of anesthesia for cataract surgery. It has decreasedmany of the problems associatedwith other forms of anesthesia.It is my experience that at least 90% of cataract patients prefer topical anesthesiawith 0.5 cc of unpreserved Xylocaine. We anticipate other similar papers. The rabbit versus
7, July 1998
human cornea responsesdiffer for unknown reasons. I greatly appreciate the study conducted by the authors, but it does not correlate with our human experience. JAMES P. GILLS, MD Tarpon Springs, Florida References
FichmanRA. Phacaemulsification with topical anesthesia. In: Fine IH, FichmanRA, GrabowHB. Clear-Cornea1 Cataract Surgery and Topical Anesthesia. Thorofare, NJ: SLACK, Inc., 1993;113-8. Gills JP, Cherchio Mn, RaananMG. UnpreservedlidoCaineto control discomfort during cataract surgery using topical anesthesia.J Cataract Refract Surg 1997;23:54550. Authors’ reply Dear Editor: We anticipated that someone would raise the issue, and we appreciate the opportunity to respond. The age-old adage applies to Dr. Gills’ concern: “The devil’s in the details,” or in this case, the experimental protocol. We are aware of the relatively widespread use of intracameral anesthesiaand the lack of apparent clinical toxicity. We conceived this rabbit study before anyone had reported injecting anesthetic agent into the eye. We were motivated by a concern that topically applied anesthetic might inadvertently slip inside the eye during cataract surgery, thereby placing the cornea1 endothelium at risk. We did not anticipate that ophthalmologists would soon be injecting the same anesthetics deliberately. Nevertheless, our rabbit study was timely given that evolution. We designed the study to determine if toxicity would be demonstrated under the most severe circumstances. If we did not find it under such conditions, we would not concern ourselves with lesser circumstances. We therefore injected 0.2 cc of each of four different anesthetic agents at strengths supplied commercially into the anterior chambersof rabbit eyes and deliberately left the anesthetic agents in. Our experimental protocol was different from its counterpart in human cataract surgery in that the lidocaine injected intracamerally during cataract surgery is immediately washed out with viscoelastic material or balance salt solution. We found clinically significant toxicity with all four agents (bupivicaine, lidocaine, proparaCaine, and tetracaine) and statistically significant cornea1 opacification and thickening with three of the four agents (bupivicaine, lidocaine, and proparacaine). Clearly, it would be unethical to do the same study in humans, but if it could be done, similar or worse toxicity would probably be seen. Rabbit cornea is resilient and endothelial cells undergo mitotic activity to replenish damaged cells, unlike their human counterparts. We caution ophthalmologists to be aware of the potential for endothelial toxicity. The widespread use of intracamera1lidocaine and the lack of reported toxicity in its current clinical application are reassuring. Nevertheless,
Volume 105, Number
optic. Retained viscoelastic causes an osmotic gradient across the capsule, leading to an accumulation of viscous fluid in the bag. This causes distention of the bag, with posterior displacement of the posterior capsule and anterior displacement of the IOL and anterior capsule. It is reversible with either anterior or posterior capsulotomy. We have noticed that acrylic IOLs are more adherent to capsular tissue than silicone. This may cause a higher incidence of capsular block in the acrylic group. However, this syndrome was not observed with either type of IOL in this study. The relative elevation of IOP at I month in the acrylic group occurred despite nearly twice as many suture releasesor lysis. This suggeststhat the underlying mechanism is probably more related to differences in aqueous production rather than obstruction of outflow. We have no direct evidence to support either theory in a study of this design. We may gain more understanding of the underlying mechanism(s)if the study was repeated utilizing postoperative flaremeter readings and/or fluorophotometry. Dr. Safran’s suggestion of trying a dyed viscoelastic, instead of the usual colorless preparation, may also be worthwhile. LANCEC. LEMON, MD DONG H. SHIN, MD, PhD Detroit,
Cornea1 Endothelial Anesthesia
Toxicity
Michigan
of Topical
Dear Editor: I appreciate the interest of Drs. Judge, Najafi, Lee, and Miller in intraocular and topical anesthesia.I thought the use of intraocular anesthesiawould be very slow to catch on; however, the majority of my colleagues with large practices now routinely use 0.5 cc of unpreserved intraocular Xylocaine 1% for their cataract surgery. No problems have been reported. Before using Xylocaine intraocularly. 1 was familiar with reports of inadvertent injections with no adverse effect.’ After dose-ranging work on eyes with limited prognoses and not a single adverse reaction, I began routinely using 0.5 cc unpreserved Xylocaine 1% (Astra Pharmaceuticals, West Borough, MA) as an adjunct to my topical anesthesiaprotocol. I’ve administered other anesthetics intracamerally in partially sighted eyes. In fact, I’ve usedall the anestheticscited in the paper without recognizing a single case of decreased endothelial cell count or increased cornea1thickening. I find it interesting that humans respond so differently from rabbits. In our randomized, controlled study, we did not have a single untoward effect.’ It’s fortunate that we can use0.5 cc of intraocular Xylocaine becauseit is possibly the safest, most effective method of anesthesia for cataract surgery. It has decreasedmany of the problems associatedwith other forms of anesthesia.It is my experience that at least 90% of cataract patients prefer topical anesthesiawith 0.5 cc of unpreserved Xylocaine. We anticipate other similar papers. The rabbit versus
7, July 1998
human cornea responsesdiffer for unknown reasons. I greatly appreciate the study conducted by the authors, but it does not correlate with our human experience. JAMES P. GILLS, MD Tarpon Springs, Florida References
FichmanRA. Phacaemulsification with topical anesthesia. In: Fine IH, FichmanRA, GrabowHB. Clear-Cornea1 Cataract Surgery and Topical Anesthesia. Thorofare, NJ: SLACK, Inc., 1993;113-8. Gills JP, Cherchio Mn, RaananMG. UnpreservedlidoCaineto control discomfort during cataract surgery using topical anesthesia.J Cataract Refract Surg 1997;23:54550. Authors’ reply Dear Editor: We anticipated that someone would raise the issue, and we appreciate the opportunity to respond. The age-old adage applies to Dr. Gills’ concern: “The devil’s in the details,” or in this case, the experimental protocol. We are aware of the relatively widespread use of intracameral anesthesiaand the lack of apparent clinical toxicity. We conceived this rabbit study before anyone had reported injecting anesthetic agent into the eye. We were motivated by a concern that topically applied anesthetic might inadvertently slip inside the eye during cataract surgery, thereby placing the cornea1 endothelium at risk. We did not anticipate that ophthalmologists would soon be injecting the same anesthetics deliberately. Nevertheless, our rabbit study was timely given that evolution. We designed the study to determine if toxicity would be demonstrated under the most severe circumstances. If we did not find it under such conditions, we would not concern ourselves with lesser circumstances. We therefore injected 0.2 cc of each of four different anesthetic agents at strengths supplied commercially into the anterior chambersof rabbit eyes and deliberately left the anesthetic agents in. Our experimental protocol was different from its counterpart in human cataract surgery in that the lidocaine injected intracamerally during cataract surgery is immediately washed out with viscoelastic material or balance salt solution. We found clinically significant toxicity with all four agents (bupivicaine, lidocaine, proparaCaine, and tetracaine) and statistically significant cornea1 opacification and thickening with three of the four agents (bupivicaine, lidocaine, and proparacaine). Clearly, it would be unethical to do the same study in humans, but if it could be done, similar or worse toxicity would probably be seen. Rabbit cornea is resilient and endothelial cells undergo mitotic activity to replenish damaged cells, unlike their human counterparts. We caution ophthalmologists to be aware of the potential for endothelial toxicity. The widespread use of intracamera1lidocaine and the lack of reported toxicity in its current clinical application are reassuring. Nevertheless,