Toxicity of Xylocaine to rabbit corneal endothelium

Induction of apoptosis of rabbit corneal endothelial cells by preservative-free lidocaine hydrochloride 2%, ropivacaine 1%, or levobupivacaine 0.75%

PURPOSE

To determine and compare the amount of apoptosis and changes in rabbit corneal endothelial cell morphology after intracameral administration of different anesthetic agents.

SETTING

Department of Ophthalmology, Baskent University Medical Faculty, Ankara, Turkey.

METHODS

Right eyes of 64 Vienna white rabbits were injected intracamerally with preservative-free lidocaine hydrochloride 2%, ropivacaine 1%, levobupivacaine 0.75%, or fortified balanced salt solution (BSS Plus) (control). Animals were humanely killed 1 day or 7 days later. Terminal deoxynucleotidyl transferase deoxy-UTP-nick end labeling was used to detect apoptosis. Corneal endothelial cells and apoptotic cells were counted by light microscopy. The morphologic appearance was determined by transmission electron microscopy (TEM).

RESULTS

Apoptotic cell density was high in the anesthetic groups on day 1 (P<.01); there was no significant difference between groups at 7 days. Apoptotic cell density declined significantly between 1 day and 7 days in the anesthetic groups (P<.05) but not in the control group. There was no difference in endothelial cell density between the 4 groups at 1 or 7 days. All anesthetic groups showed degenerative changes on TEM, with the least change in the preservative-free lidocaine hydrochloride 2% group.

CONCLUSIONS

Intracameral injections of preservative-free lidocaine, ropivacaine, and levobupivacaine induced significantly more apoptotic endothelial cell loss than BSS Plus and led to morphologic changes in the corneal endothelial cells in the early period. This effect was temporary, with recovery by 7 days. Considering the limited proliferative capacity in human eyes, the induced apoptosis might result in the permanent cell loss and enlargement in human corneal endothelium.

Corneal endothelial safety with the irradiation system for light-adjustable intraocular lenses

PURPOSE

To assess the safety to the corneal endothelium of the irradiation delivered through a system developed for noninvasive postoperative power adjustments of the Light Adjustable Lens (LAL) (Calhoun Vision).

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

METHODS

After anesthesia, 12 cats had a light beam of near ultraviolet light (365 nm), with an intensity of 250 mW/cm(2), applied to the central 6.0 mm of the right cornea for 120 seconds. The cats were killed 1 day, 1 week, and 1 and 3 months after light application (3 cats/time point). Their corneas were then removed and evaluated for evidence of morphological damage to the corneal endothelial cells by staining with trypan blue and alizarin red and quantification with a digital imaging program (EPCO system).

RESULTS

The overall size and shape of the corneal endothelial cells were qualitatively similar in irradiated and nonirradiated eyes. Four corneas in the irradiated group and 3 corneas in the control group had small areas of cell damage (staining with trypan blue) within the central 6.0 mm. These areas were generally close to corneal folds. The differences in damaged areas between both groups at each time point, as well as the difference considering the overall results in both groups, were not significant (P>.05).

CONCLUSIONS

Irradiation of cat corneas with the therapeutic dose used to lock in the power of the LAL was not associated with damage to endothelial cells. Further studies are necessary to confirm the absence of damage at the ultrastructural level.

Experimental evaluation of ophthalmic devices and solutions using rabbit models

OBJECTIVE

To analyze and compare the geometry of the anterior segment of rabbit and human eyes, with relevance for the evaluation of intraocular lenses, and to review rabbit models used in our laboratory for the evaluation of different ophthalmic devices and solutions.

PROCEDURES

Fifteen rabbit and 15 human eyes (10 phakic and 5 pseudophakic/group) obtained postmortem were used. Anterior-posterior length, equatorial diameter, and white-to-white (corneal diameter) were measured with calipers. The eyes were then analyzed with a very high-frequency ultrasound (Artemis, Ultralink) for measurements of the anterior chamber depth, and anterior chamber and ciliary sulcus diameters. The capsular bag diameter was measured with calipers from a posterior view, and the diameter and thickness of the crystalline lenses were measured after their excision from the phakic eyes.

RESULTS

Although the size of the rabbit eye is overall smaller than the size of the human eye, the dimensions of the anterior segment of rabbit eyes are generally larger. The differences between rabbit and human eyes were statistically significant (Wilcoxon rank sum test) in terms of anterior-posterior length, equatorial diameter, white-to-white measurements (P < 0.0001), anterior chamber diameter (P = 0.0004), ciliary sulcus diameter (P = 0.0012), and crystalline lens diameter and thickness (P = 0.0003).

CONCLUSIONS

Experimental evaluation of design features of new phakic intraocular lenses in rabbit eyes may be inconclusive without adaptation of their size/design, contrary to the evaluation of new pseudophakic lenses by implantation in the capsular bag. The rabbit is a very valuable model for the experimental evaluation of different ophthalmic devices and solutions.

Cytotoxicity of Lidocaine or Bupivacaine on Corneal Endothelial Cells in a Rabbit Model

PURPOSE

To investigate the corneal endothelial cytotoxicity of commercial formulations of agents used for intracameral anesthesia in cataract and other ocular surgery.

METHODS

Cultured corneal endothelial cells (CECs) of New Zealand White rabbits were exposed for 1 minute to balanced salt solution (control); Xylocaine (lidocaine) 1% E (with epinephrine), 2% E, 2%, or 4%; or Marcaine (bupivacaine) 0.5% or 0.5% spinal heavy. The degree of cytotoxicity was determined by in vitro staining with trypan blue and light microscopic evaluation of cell morphology. The effect of longer exposure (up to 16 minutes) to lidocaine 1% E was also investigated.

RESULTS

CECs were not significantly damaged by 1-minute exposure to lidocaine 1% E or 2% E; however, significant cytotoxicity was seen after 1-minute exposure to lidocaine 2% or 4% or bupivacaine 0.5% or 0.5% spinal heavy. Exposure to lidocaine 1% E showed a trend toward time-dependent cytotoxicity that reached significance at 16 minutes.

CONCLUSIONS

One-minute exposure to lidocaine 1% E or 2% E appears to be safe for cultured rabbit CECs, although longer exposures could cause time-dependent cytotoxicity, which should be considered in planning cataract or other ocular surgery. Because bupivacaine 0.5% and 0.5% spinal heavy cause cytotoxic effects within the first minute of contact with CECs, they should be used with great caution, if at all, in the anterior chamber of human eyes.

Randomized comparative clinical study of cryoanalgesia versus topical anesthesia in clear corneal phacoemulsification

PURPOSE

To compare intraoperative pain scores and objective stress signs during clear corneal phacoemulsification under cryoanalgesia and topical anesthesia.

SETTING

Hospital Ramón y Cajal, Madrid, and Hospital Universitario Nuestra Sra. de la Candelaria, Tenerife, Canary Islands, Spain.

METHODS

Eighty-two patients were randomized to have phacoemulsification under cryoanalgesia or topical anesthesia. Uncooperative patients and those with shallow anterior chamber and small pupils were excluded. In case of breakthrough pain during the surgery, a supplemental anesthesia protocol was established. Each patient was asked to grade the severity of pain on a 4-point scale (verbal description score; 0=none, 1=little, 2=some, or 3=much). Immediately after surgery, the general discomfort and pain were evaluated. Surgeon stress was evaluated during surgery. A comparison of the 2 groups was performed using a statistical analysis of variance.

RESULTS

Supplemental anesthesia was required in 1 patient in each group. A total of 95.23% of patients would repeat the same technique under cryoanalgesia versus 97.5% under topical anesthesia. Similar pain levels and surgical stress scores were noted in both groups.

CONCLUSIONS

Cryoanalgesia clear corneal phacoemulsification was safe with an acceptable level of pain. It induced a physiological stress response to that of topical anesthesia (blood pressure and heart rate). Cryoanalgesia was preferred over topical anesthesia by some patients. It is a suitable technique for anesthetic allergy cases.

Evaluation of the cataractogenic effect of viscoanesthetic solutions on the rabbit crystalline lens

PURPOSE

To evaluate the toxicity and cataractogenic effect of solutions combining sodium (Na) hyaluronate 1.0% and 1.5% with lidocaine 1.0% on the rabbit crystalline lens. The amount of pupil dilation provided by the addition of lidocaine to the Na hyaluronate solutions was also assessed.

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

METHODS

Five solutions were injected into the anterior chamber of 18 pigmented rabbits in a randomized manner by the same surgeon, the intraocular component of VisThesia (Na hyaluronate 1.5%/lidocaine 1.0%), the intraocular component of VisThesia Light (Na hyaluronate 1.0%/lidocaine 1.0%), Ophthalin Plus (Na hyaluronate 1.5%), and a balanced salt solution; and both eyes of 2 other rabbits were injected with nonpreserved aqueous lidocaine 1.0%. The pupil diameter of each eye was measured before injection, immediately after, and 1 and 5 minutes after injection. After a follow-up of 3 months with slitlamp examinations, the rabbits were killed, and their eyes were enucleated. The crystalline lenses were evaluated from a posterior or Miyake-Apple view, and the eyes were fixated in 10% formalin for histopathologic analyses.

RESULTS

Pupil diameter was significantly larger 1 and 5 minutes after injection in the VisThesia (P = .01 and P = .007) and VisThesia Light (P = .008 and P = .007) groups, whereas the differences were not significant in the Ophthalin Plus (P = .317 and P = .102) and balanced salt solution groups (P = .317 and P = .180). Fast and large pupillary dilation was observed in the aqueous lidocaine group, starting during the injection. No differences in the transparency of the natural lens and the red fundus reflex were noted during slitlamp examinations. Postmortem analyses from a posterior view also showed no differences in the transparency of the crystalline lens. The histopathologic appearance of the lens capsule, anterior and equatorial lens epithelial cells, and epithelial lens bow was comparable in the eyes, without signs of cell vacuolization or disruption.

CONCLUSIONS

Intracameral injection of the solutions used in this study caused no localized opacity or overall change in the transparency of the crystalline lenses as observed during clinical and postmortem examinations as well as histopathologic analyses of the enucleated rabbit eyes. Viscoanesthesia may have application in phakic intraocular lens implantation.

L’anesthésie topique en chirurgie de la cataracte ambulatoire de l’adulte sans anesthésiste présent

To review the local anesthesia environment in France in adult out-patient cataract surgery. The author considers the presence or absence of an anesthesiologist in the operating room. The report shows that in many circumstances there is no need for an anesthesiologist if the following criteria are respected: the adult is fully informed, in rather good health, with no acute risk factors, and surgery is performed by a senior surgeon in a certified operating room. In France, a move toward more flexible regulations is expected, with a new cooperation between ophthalmologists and anesthesiologists that will lead to a new true risk/benefit/obligation ratio. Respect of the individual and safety remain crucial requirements making systematic generalizations impossible.

Corneal endothelial cell damage after lens extraction using the fluid-based system compared to ultrasound phacoemulsification in human cadaver eyes

PURPOSE

To compare the endothelial cell damage after lens removal using a fluid-based system to conventional ultrasound.

METHODS

Twenty human cadaver eyes were randomized to undergo phacoemulsification using either a fluid-based system or conventional ultrasound. After surgery, each corneoscleral button was removed, stained and damaged endothelial cells per square millimeter were assessed using light microscopy.

RESULTS

Fluid-based system mean damaged endothelial cells/mm was 60.2 +/- 24.1 compared with 60.4 +/- 42.6 when using conventional ultrasound (P = 0.248).

CONCLUSION

The fluid-based system is as safe for the corneal endothelium as conventional ultrasound during cataract removal in human cadaver eyes.

Effect of intracameral injection of lidocaine and carbachol on the rabbit corneal endothelium

PURPOSE

To determine the effect of intracameral injection of preservative-free lidocaine 1% and carbachol 0.01% on corneal endothelial cells of rabbits.

SETTING

Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan.

METHODS

Forty eyes of 20 New Zealand White rabbits were divided into 2 equal groups. In the first group, 1 eye was injected with 0.02 mL of preservative-free lidocaine 1% and the fellow eye was injected with 0.02 mL of normal saline as a control. In the second group, 1 eye was injected with 0.02 mL of carbachol 0.01% and the fellow eye was injected with 0.02 mL of normal saline. Specular microscopy was used to evaluate corneal endothelial cell loss and corneal thickness 1 week and 1 month postinjection. For morphologic studies, corneal buttons were excised and stained with alizarin red with trypan blue. Scanning electron microscopy (SEM) examination was performed.

RESULTS

Specular microscopy revealed no significant endothelial cell loss and normal endothelial thickness with the intracameral injection of preservative-free lidocaine 1% and carbachol 0.01% compared with the control eye. Alizarin red with trypan blue stain and SEM examinations revealed smooth, distinct, and intact intercellular borders and normal viability of corneal endothelial cells in both groups.

CONCLUSIONS

Intracameral injections of preservative-free lidocaine 1% and carbachol 0.01% do not produce morphologic and functional changes in the corneal endothelial cells of rabbits.

Pharmacologic prevention of posterior capsule opacification: in vitro effects of preservative-free lidocaine 1% on lens epithelial cells

PURPOSE

To assess the in vitro effectiveness of preservative-free lidocaine 1% in removing lens epithelial cells (LECs) from the anterior capsule and to evaluate the effect of lidocaine on the LECs.

SETTING

Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.

METHODS

Eight rabbits (16 eyes) were used in the study. After the rabbits were killed, the eyes were enucleated and divided into 2 groups. In Group 1 (n = 8 eyes), LECs were exposed to preservative-free lidocaine 1% or balanced salt solution (BSS) for 1, 2, or 5 minutes. The anterior capsules were then stained with trypan blue and alizarin red. Photomicrographs of each capsule were taken and analyzed for LEC damage. In Group 2 (n = 8 eyes), hydrodissection was performed with 1 of the agents, followed by phacoemulsification and cortical cleanup. The LEC attachment to the anterior capsule was evaluated by histopathology.

RESULTS

Anterior capsule fragments irrigated with BSS showed no LEC nuclear staining; ie, no direct toxic effect. In those irrigated with preservative-free lidocaine 1%, the LECs showed mild toxicity; some cells showed blue nuclear staining. After hydrodissection with lidocaine, the capsules were almost free of LECs; after hydrodissection with BSS, the capsules showed a normal layer of LECs attached to the anterior capsule.

CONCLUSIONS

Preservative-free lidocaine 1% may help diminish the amount of live LECs by facilitating cortical cleanup, by loosening the desmosomal area of cell-cell adhesion with decreased cellular adherence, or by a direct toxic effect. The use of this agent may help prevent posterior capsule opacification.

Viscoanesthesia. Part I: toxicity to corneal endothelial cells in a rabbit model

PURPOSE

To evaluate the toxicity of a solution combining sodium hyaluronate 1.5% with lidocaine (0.5%, 1.0%, or 1.65%) to the rabbit corneal endothelium.

SETTING

Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.

METHODS

Each rabbit cornea was excised, and the endothelium was exposed to 1 of the following solutions for 20 minutes: viscoanesthetic solution (0.5%, 1.0%, or 1.65% lidocaine in sodium hyaluronate 1.5%; 5 corneas each), sodium hyaluronate 1.5% (n = 5), balanced salt solution (BSS(R)) (n = 5), mitomycin-C 0.02% (n = 2), dextran 15% (n = 2), or distilled water (n = 2). The endothelium was then stained with trypan blue and alizarin red. Two corneas were stained immediately after excision. Cell morphology and damage to the corneal endothelium were analyzed by microscopic examination.

RESULTS

The endothelium in the corneas of the viscoanesthetic groups was comparable to that in the sodium hyaluronate 1.5% and the BSS groups and to the corneas not exposed to any solution. In some areas of the 1.0% and the 1.65% viscoanesthesia groups, the corneal endothelial cells presented irregular intercellular borders. Staining with trypan blue, which indicates cellular damage, was observed in some linear areas corresponding to corneal folds in all groups. The folds were probably caused during manipulation for corneal excision and staining. The corneal endothelium was destroyed in the mitomycin group. In the dextran and distilled-water groups, morphological alterations probably resulting from osmotic changes were observed.

CONCLUSIONS

The 3 concentrations of viscoanesthetic solutions appeared to be safe to rabbit corneal endothelium.

Effects of intracameral lidocaine on ocular tissues

PURPOSE

To investigate the ultrastructural changes in iris and corneal tissue induced by intracameral 1% lidocaine infusion applied during lens extraction in a rabbit model.

METHODS

The study was conducted using New Zealand rabbits. Eight rabbits received 0.2 mL 1% lidocaine hydrochloride intracamerally and lens extraction was performed, keeping the posterior capsule intact. After lens extraction, cornea and iris tissue samples were obtained for electron microscopy. Eight eyes were included as a control group.

RESULTS

Electron microscopy revealed morphological abnor-malities in both cornea and iris of the lidocaine injected eyes, different from the control group. Cytoplasmic vacuolization, phagosomes and residual bodies were observed in epithelial cells. Corneal fibroblasts contained fluid-filled vacuoles, which could be due to the influx of water into the cells as a result of corneal endothelial damage. Mitochondrial swelling and residual bodies were also seen in the cytoplasm of fibroblasts. Blood vessels in the iris contained fluid material composed of fibrin and proteinaceous material and many vacuoles showed vascular endothelial injury.

CONCLUSION

Even a short period of exposure of intra-cameral lidocaine to the ocular tissues can induce histo-logical changes that may result in functional defects.

Alkalinization increases penetration of lidocaine across the human cornea

PURPOSE

To test the hypothesis that corneal permeability of lidocaine complies with the principle of nonionic diffusion.

SETTING

Department of Ophthalmology and Institute of Pharmacology, Vienna, Austria.

METHODS

Human corneas, mounted in an in vitro perfusion system under short-circuit conditions, were exposed on the epithelial (tear) side to lidocaine 4% in a buffered solution of pH 5 or pH 7. The endothelial bathing solutions had a constant pH of 7.4. Both solutions were adjusted to an osmolarity of 290 mOsm/L. The lidocaine permeability of the isolated corneas was assessed from the fluxes of 14C-labeled lidocaine across the tissue, measured at 15-minute intervals for 180 minutes, and corrected for the unidirectional fluxes of 3H-polyethylene glycol, a marker for the extracellular pathway. The corneal tissue content of lidocaine was estimated from the time span until the unidirectional lidocaine fluxes across the cornea reached a steady state.

RESULTS

The mean transcorneal fluxes of lidocaine in the steady state (90 to 180 minutes) were 72% higher at pH 7 than at pH 5 (101 mmol/min +/- 37 (SD) versus 59 +/- 34 nmol/min.cornea; P <.002). The corneal content of lidocaine in the steady state was 65% higher at pH 7 than at pH 5 (2.8 +/- 0.9 micromol/cornea versus 1.7 +/- 1.2 micromol/cornea; not significant).

CONCLUSIONS

A shift in solution pH from 5 to 7 significantly increased the corneal permeability of topically applied lidocaine. Alkaline pH-adjustment of topical lidocaine solutions is easy to perform by adding sodium bicarbonate. The main clinical advantages of anesthetic solutions buffered at pH 7 are increased penetration rates, effectiveness, prolonged action time, and a reduction in local irritation and lacrimation.

No-anesthesia clear corneal phacoemulsification versus topical and topical plus intracameral anesthesia. Randomized clinical trial

PURPOSE

To compare the intraoperative pain scores during clear corneal phacoemulsification under no anesthesia, topical anesthesia, and topical plus intracameral anesthesia.

SETTING

Dr. Agarwal's Eye Hospital and Eye Research Center, Chennai, India.

METHODS

Seventy-five patients were randomized to have phacoemulsification under no anesthesia, topical anesthesia, or topical plus intracameral anesthesia. Uncooperative or illiterate patients and those with hard cataract, a shallow anterior chamber, or small pupils were excluded. A protocol was established for supplemental anesthesia in case of breakthrough pain during the surgery. Each patient was asked to grade the overall severity of intraoperative pain immediately after surgery on a 10-point visual analog scale. Also evaluated were the general discomfort during surgery, discomfort from the microscope lights, surgeon stress during surgery, and total surgical time. Comparison among the 3 groups was performed using an analysis of variance.

RESULTS

No supplemental anesthesia was required in any group. No significant difference was noted in the mean scores of the subjective sensation of pain with or without topical anesthesia (P =.610). The mean scores of patient discomfort from the microscope lights and surgical time were also statistically insignificant. Patient discomfort and surgeon stress during surgery were significantly greater in the no-anesthesia group than in the topical and topical plus intracameral groups (P =.0235 and P = 0.0206, respectively).

CONCLUSION

No-anesthesia clear corneal phacoemulsification was performed by a highly experienced, skilled surgeon without causing an unacceptable level of pain. However, this technique is not suitable for every cataract surgeon or patient.

Intracameral anesthesia: a report by the American Academy of Ophthalmology

OBJECTIVE

This document describes the technique of intracameral anesthesia and examines the available evidence to address questions about its effectiveness, possible corneal endothelial and retinal toxicity, and the optimal and maximal dose.

METHODS

A literature search conducted for the years 1968 to 2000 retrieved over 180 citations that matched the search criteria. Panel members and a methodologist reviewed this information, and it was evaluated for the quality of the evidence presented.

RESULTS

Some studies report effectiveness of intracameral anesthesia while others report no effect. In those studies showing an effect, levels of pain in the groups that were compared were low. Short-term studies seem to indicate that preservative (methylparaben)-free lidocaine 1% is well tolerated by the corneal endothelium but that higher concentrations of lidocaine are toxic. There is some evidence of electroretinogram changes after exposure to lidocaine or bupivacaine.

CONCLUSIONS

The ideal timing and placement of intracameral anesthesia has not been determined. Because topical anesthesia alone is effective, surgeons may elect to use intracameral anesthesia for incremental pain control in patients who cannot be adequately managed with topical alone. Appropriate patient selection is important when using this method of anesthesia. While short-term studies seem to indicate safety, long-term effects are unknown. Patient preferences for anesthesia are not well studied.