The effects of lidocaine and bupivacaine on the rabbit retina

Effect of Peribulbar Anesthesia with and Without Adrenaline on Retinal Thickness in Patients Undergoing Elective Cataract Surgery

Background

The toxic effect of local anesthesia on the retina has been previously investigated in animal studies but not in humans.

Objectives

The objective of this study was to clarify the effect of local anesthesia with lidocaine versus local anesthesia with lidocaine with extra administration of adrenaline on the retinal layer thickness measured by optical coherence tomography (OCT) in patients indicated for elective cataract surgery.

Methods

This is a randomized controlled trial conducted on 60 patients indicated for elective cataract surgery under local anesthesia with lidocaine. Thirty participants received local anesthesia with lidocaine 2% with extra administration of adrenaline (adrenaline group), and 30 participants received local anesthesia with lidocaine 2% only (control group). The retinal thickness was measured for all participants preoperatively and one week postoperatively using OCT.

Results

The OCT findings showed statistically significant decreases postoperatively in superior (P value = 0.028), inferior (P value = 0.017), and average (P value = 0.021) retinal thickness in the adrenaline group. Moreover, there were statistically significant decreases postoperatively in superior (P value = 0.032), inferior (P value = 0.046), and average (P value = 0.028) retinal thickness in the control group. Comparing the adrenaline and control groups for the OCT findings, there was no statistically significant difference between the groups regarding the decreases in superior (P value = 0.325), inferior (P value = 0.642), and average (P value = 0.291) retinal thickness.

Conclusions

Local anesthesia with lidocaine significantly decreased the retinal thickness. The extra administration of adrenaline to lidocaine did not affect the post-anesthetic changes in the retinal thickness.

Effects of intravitreal ropivacaine on retinal thickness and integrity in the guinea pig

BACKGROUND

Retrobulbar anesthesia is widely used for ocular surgery.Ocular complications are possible when retrobulbar anesthesia is accidentally injected intravitreally.

OBJECTIVE

The aim of this study was to determine the relative retinal toxicitiesof ropivacaine hydrochloride, a local anesthetic, using various concentrations in guinea pigs.

METHODS

This randomized, investigator-masked, experimental study wasconducted at the Department of Anesthesiology, Dicle University, Diyarbakir, Turkey. The right eyes of 18 guinea pigs were assigned to 1 of 3 treatment groups: 1%, 0.75%, or 0.5% ropivacaine. The right eye of each animal was injected intravitreally with 0.1 mL of 1%, 0.75%, or 0.5% ropivacaine. The left eye of each animal was injected with a balanced saline solution (control). The guinea pigs were euthanized 7 days after injection, and the retinal structures were examined using light microscopy. The total thickness of each retina was measured using an ocular micrometer.

RESULTS

No histologic abnormalities were observed in the control eyes.Retinal damage of most of the retinal section was seen in the eyes receiving study drug. The eyes injected with 0.5% ropivacaine had a generally intact appearance, with the exception of some atrophy and disorganization. Overall, the eyes injected with 1% ropivacaine had significantly more extensive retinal thinning compared with the eyes injected with 0.75% or 0.5% ropivacaine (both, P < 0.01). In the eyes injected with 0.75% or 1% ropivacaine, disorganization of the structure of the retinal layers and atrophy were noted on histopathology. The mean total thicknesses of the retina were significantly less in all ropivacaine-treated eyes compared with that in the controls (P < 0.001).

CONCLUSIONS

In this small experimental study, ropivacaine had concentration-dependent toxic effects on guinea pig retinas.

Testing retinal toxicity of drugs in animal models using electrophysiological and morphological techniques

Drugs are frequently tested for retinal toxicity in animal models in order to address applied and basic research questions. When a retinal toxicity study is designed, the researcher needs to consider several factors depending on his/her research questions. Among the factors that need to be addressed before a toxicity study is conducted are: the animal species to be used, choice of experimental (functional and/or morphological) techniques, procedure of testing, period of follow-up, and modes of data analysis. This review is a summary of 20 years' experience of studying retinal toxicity of different drugs in rabbits and rats. The use of the electroretinogram and the visual evoked potential for assessment of outer and inner retinal function, respectively, is described as well as the use of morphological techniques (histology, histochemistry, and immunocytochemistry). The advantages and limitations of functional and morphological techniques are discussed with specific examples from my experience. Recommendations for future drug toxicity studies are summarized.

Long-term endothelial cell loss after phacoemulsification: peribulbar anesthesia versus intracameral lidocaine 1%: prospective randomized clinical trial

PURPOSE

To evaluate endothelial cell loss after phacoemulsification with posterior chamber intraocular lens implantation using peribulbar anesthesia or topical anesthesia combined with intracameral unpreserved lidocaine 1%.

SETTING

Department of Ophthalmology, Charité, Humboldt-University of Berlin, Berlin, Germany.

METHODS

Before and 20 months +/- 5.1 (SD) after surgery, specular microscopy was used to evaluate the number and morphology of endothelial cells in 78 eyes having peribulbar anesthesia or topical anesthesia combined with an intracameral injection of 0.15 cc unpreserved lidocaine 1%.

RESULTS

The mean endothelial cell loss was 11.11% in the peribulbar group and 12.55% in the topical/lidocaine group. There was no statistically significant difference in the amount of endothelial cell loss or cell morphology between the 2 groups.

CONCLUSION

The long-term postoperative endothelial cell course showed that topical anesthesia combined with an intracameral injection of 0.15 cc unpreserved lidocaine 1% is a safe alternative to peribulbar anesthesia.

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.

Retinal toxicity of gentamicin after subconjunctival injection performed adjacent to thinned sclera

OBJECTIVE

To investigate the potential toxicity to the retina of gentamicin injected near surgically thinned scleral areas in a rabbit model.

DESIGN

Experimental study.

METHODS

Scleral scraping to half thickness was performed in the superotemporal scleral area in both eyes of adult rabbits (n = 10). Gentamicin sulfate was injected subconjunctivally to the right eye and saline to the left eye, which always served as a control eye. Four weeks after the procedure, electroretinography (ERG) was performed to assess retinal function. Then, the eyes were enucleated and prepared for histologic evaluation of structural damage. In four eyes of two additional rabbits, vitreous gentamicin concentrations were measured using a fluorescence polarization assay.

MAIN OUTCOME MEASURES

Dark- and light-adapted ERG responses and histopathologic damage.

RESULTS

Dark- and light-adapted ERG responses in all rabbits were similar in the experimental and control eyes. Gentamicin levels were more than 10 microg/ml after subconjunctival injection of gentamicin with scraping and 0.29 microg/ml after subconjunctival injection of gentamicin with no scraping. Histopathologic examination revealed significant local damage to the photoreceptors adjacent to the area of scraping and subconjunctival injection. A significantly lesser degree of damage was seen if gentamicin was injected in pigmented rabbits or in albino rabbits, but only 4 weeks after scleral scraping.

CONCLUSIONS

Increased penetration of gentamicin through thinned sclera may lead to toxic levels of the drug in a localized area adjacent to the site of injection. These toxic effects are also influenced by the degree of pigmentation and acute inflammation.

Lidocaine toxicity to rat retinal ganglion cells

PURPOSE

To examine the effects of the local anesthetic, lidocaine, on rat retinal ganglion cells (RGC) in vitro and in a modified in vivo assay.

METHODS

For in vitro experiments, RGC were dissociated from freshly harvested Long Evan's rat pup retinas. The RGC were incubated overnight with varying concentrations of lidocaine (0.5-12.0 mM). Surviving cells were assayed at 24 hours. In an in vivo assay, 7-day-old Long-Evans rat pups were anesthetized and 2 microl of lidocaine (final intraocular concentration: 0.03-15 mM) or vehicle was injected intravitreally. Intravitreal coinjection of nimodipine or MK801 (dizocilpine) were also performed in a subset of animals. A week after injection, rat pups were sacrificed and each retina removed, dissociated and plated separately. RGC survival was immediately assessed. Living RGC were identified on the basis of morphology and counted in a masked fashion.

RESULTS

Lidocaine is toxic in a dose dependent fashion to RGC in vitro. Lower concentrations (0.5 mM and 1.0 mM) were non-toxic; 2.0, 6.0 and 12.0 mM lidocaine killed 25%, 88% and 99% of the RGC respectively. Intravitreal lidocaine was also toxic to RGC in a dose dependent fashion. Lidocaine concentrations of 3.0 mM, 7.5 mM and 15 mM killed 25%, 38% and 44% of the RGC. This effect was blocked by the simultaneous administration of either nimodipine or MK801.

CONCLUSIONS

Lidocaine is toxic to RGC both in vitro and in vivo. This effect is blocked in vivo by the simultaneous administration of agents known to block glutamate mediated neuronal death, suggesting that excitotoxicity may be involved in this process.

Toxicity of intraocular lidocaine and bupivacaine

PURPOSE

To study the toxicity of intraocular lidocaine, bupivacaine, and a combination of the two anesthetics.

METHODS

The right eyes of 34 rabbits were divided into eight groups, and each was injected intravitreally with 0.2 ml of lidocaine hydrochloride in a 2%, 1%, 0.5%, or 0.25% concentration, or bupivacaine hydrochloride in a 0.75%, 0.5%, or 0.25% concentration, or a 1:1 mixture of lidocaine 2% and bupivacaine 0.75%. The left eyes of four of these rabbits received an injection of balanced saline solution. Electroretinograms were recorded before injection and 30 minutes, 90 minutes, 3 hours, 6 hours, 24 hours, and 1 week after injection. The amplitude and the implicit time were analyzed. The rabbits were killed 1 week after injection and the eyes evaluated histologically.

RESULTS

No adverse clinical reaction and no histologic abnormality was observed in any of the nine groups after injection. The a- and b-waves of the electroretinograms in the control group injected with balanced saline solution, and the a-waves of the experimental groups that received injections of lidocaine, bupivacaine, or the mixture, were normal. The b-waves of the experimental groups demonstrated a marked decrease in the amplitude and an increase (P < .05) in the implicit time after intravitreal injection. Electroretinogram responses recovered within 24 hours.

CONCLUSIONS

Intravitreal injection of 0.2 ml of lidocaine up to 2%, or of bupivacaine up to 0.75%, and the mixture of lidocaine 2% and bupivacaine 0.75%, induced reversible electroretinogram changes in the rabbit retina. No histologic abnormalities were observed.