Topical bupivacaine and proparacaine: a comparison of toxicity, onset of action, and duration of action

TFOS Lifestyle: Impact of elective medications and procedures on the ocular surface

The word "elective" refers to medications and procedures undertaken by choice or with a lower grade of prioritization. Patients usually use elective medications or undergo elective procedures to treat pathologic conditions or for cosmetic enhancement, impacting their lifestyle positively and, thus, improving their quality of life. However, those interventions can affect the homeostasis of the tear film and ocular surface. Consequently, they generate signs and symptoms that could impair the patient's quality of life. This report describes the impact of elective topical and systemic medications and procedures on the ocular surface and the underlying mechanisms. Moreover, elective procedures performed for ocular diseases, cosmetic enhancement, and non-ophthalmic interventions, such as radiotherapy and bariatric surgery, are discussed. The report also evaluates significant anatomical and biological consequences of non-urgent interventions to the ocular surface, such as neuropathic and neurotrophic keratopathies. Besides that, it provides an overview of the prophylaxis and management of pathological conditions resulting from the studied interventions and suggests areas for future research. The report also contains a systematic review investigating the quality of life among people who have undergone small incision lenticule extraction (SMILE). Overall, SMILE refractive surgery seems to cause more vision disturbances than LASIK in the first month post-surgery, but less dry eye symptoms in long-term follow up.

Prolonged Retrobulbar Local Anesthesia of the Cornea Does Not Cause Keratopathy in Mice

Purpose

Prolonged local anesthesia (PLA) of the cornea is currently assumed to cause neurotrophic keratitis and is strongly discouraged. We investigate whether PLA of the cornea per se causes neurotrophic keratitis.

Methods

PLA of the cornea was induced in 12 female albino BALB/c mice by retrobulbar injection of a polymeric prodrug (PGS-TTX) where the site 1 sodium channel blocker tetrodotoxin (TTX) was slowly released from the polymer polyglycerol sebacate. The duration and depth of corneal anesthesia was monitored by the Cochet-Bonnet esthesiometer. Corneal injury from PLA was assessed by slit lamp examination with 2% sodium fluorescein dye, histology, corneal nerve density by immunohistochemistry with anti-β III tubulin antibody and confocal microscopy, and corneal neurotrophin levels (substance P and neurokinin A) by an enzyme-linked immunosorbent assay. PLA was also induced by topical amitriptyline (80 mM), used as a positive control for local anesthetic-induced corneal injury. Frequent ocular lubrication was provided.

Results

Retrobulbar PGS-TTX resulted in complete corneal anesthesia lasting 50.1 ± 3.6 hours and mean time to complete resolution of block of 55.1 ± 3.6 hours with no keratopathy provided lubrication was provided. Topical 80 mM amitriptyline induced complete corneal anesthesia for 24 hours and developed keratopathy. There was no difference in the histology, levels of corneal neurotrophins, and corneal nerve density between the retrobulbar PGS-TTX group and normal cornea.

Conclusions

In the absence of topical toxicity or corneal exposure, PLA of the cornea per se does not cause keratitis.

Translational Relevance

PLA of the cornea could be highly beneficial in acute and chronic painful corneal conditions.

High fat diet induced gut dysbiosis alters corneal epithelial injury response in mice

PURPOSE

Commensal microbiome secretes various metabolites that can exert important effects on the host immunity and inflammation and can alter cellular functions. However, little is known regarding the effect of microbiome on corneal immunity and genetic expression. The purpose of this study is to describe the effect of diet-induced gut dysbiosis on corneal immunity and corneal gene expression after wounding.

METHODS

This study is approved by the Animal Care and Use of the University of Illinois. Six-week-old female C57BL6 mice were fed on a normal chow diet (ND), isocaloric low-fat control diet (LFD), or a 21% milk high-fat diet (HFD) for six weeks. 2 mm corneal epithelial debridement was performed (n = 10). Fecal samples from mice were used for microbial diversity analysis (n > 3). Immunofluorescence staining of corneal wholemount tissue post-debridement was used to visualize immune cell distribution. RNA Seq was performed on tissue samples from corneas following debridement.

RESULTS

Mice fed differing diets had significant alterations in gut microbial diversities. After corneal debridement, HFD mice experienced delayed wound healing in comparison to LFD mice and ND mice groups. However, fecal transplantation led to normalization of wound closure rates. Increased γδTCR staining was observed in the LFD group, and decreased LY6G was observed in HFD group (p < 0.05). Gene Ontology terms of differentially expressed genes included response to external stimulus, cell proliferation, migration, adhesion, defense response and leukocyte migration. Top over-represented pathways included ECM-receptor interaction, Cytokine-cytokine receptor interaction, Focal adhesion and Leukocyte trans-endothelial migration.

CONCLUSIONS

Gut microbial dysbiosis alters corneal immune cell distribution, corneal response to injury, and genes related to epithelial function and corneal immunity.

Topical Application of Lidocaine and Bupivacaine to Disbudding Wounds in Dairy Calves: Safety, Toxicology and Wound Healing

Simple Summary

Disbudding is a common, but painful procedure performed on calves to prevent horn growth. Tri-Solfen^® is a combination local anaesthetic and antiseptic formulation which, applied topically to the disbudding wound, is reported to reduce calf pain. Applied in this manner, the local anaesthetics in Tri-Solfen^®, lidocaine and bupivacaine, are reported to be poorly absorbed, resulting in low risk of neurological or cardiotoxic effects. The potential impacts on other blood, urine and tissue parameters and on wound healing when used in this manner, and/or accidental overdose situations are unknown, however. We performed experiments investigating (i) the safety of Tri-Solfen^® (including overdose situations) and (ii) the impact of Tri-Solfen^® on disbudding wound healing under field conditions. No adverse health effects were observed in Tri-Solfen^®-treated animals, even those receiving 5× the recommended dose, with no clinically significant differences in measured parameters between placebo and Tri-Solfen^® groups. No negative impacts on wound healing were noted. Conversely, lower levels of bacterial wound colonisation were evident, and there was reduced incidence of abnormal wounds at days 11–12 in Tri-Solfen^®-treated animals.

Abstract

Tri-Solfen^® is a combination topical anaesthetic and antiseptic solution containing lidocaine, bupivacaine, adrenaline and cetrimide. Applied to wounds, it is reported to reduce the pain experienced by calves following thermocautery disbudding. While lidocaine and bupivacaine are widely used in medicine, conflicting data exist on the impact of these compounds when applied directly to the surgical wound. To investigate the safety of Tri-Solfen^® applied to thermocautery disbudding wounds of calves, experiments were performed to measure (i) the safety of Tri-Solfen^® (including in overdose situations); and (ii) the impact of Tri-Solfen^® application at recommended doses on disbudding wound healing under field conditions. Haematological, biochemical and urinalysis parameters did not show clinically significant differences between placebo and Tri-Solfen^® groups (1×, 3× and 5× dose). No adverse health impacts were reported. Histopathological analysis of wounds noted a reduction in bacterial colonies in Tri-Solfen^®-treated wounds. Under field conditions, no negative impacts on wound healing were noted. Conversely, there was reduced incidence of abnormal wounds, with an associated trend toward improved average daily gain at days 11–12 in Tri-Solfen^®-treated animals. These data are considered to support the safety of topical anaesthesia, as formulated in Tri-Solfen^®, to the thermocautery disbudding wound in calves.

Effects of topical application of tramadol with/without dexmedetomidine and proparacaine on corneal sensitivity in rats

PURPOSE

To evaluate the corneal anesthetic effect following topical application of tramadol alone and in combination with dexmedetomidine, and compare it to proparacaine, in clinically healthy rats.

METHODS

A randomized, crossover study was performed. Twenty Wistar albino rats (n = 40 eyes) were used. Corneal touch threshold (CTT) measurements (in mm) were obtained using a Cochet-Bonnet aesthesiometer. CTT measurements were obtained at baseline, 1-min following application of the topical anesthetic agent, and repeated at 5-min intervals up to 75 min. The topical protocol involved 3 treatment conditions, separated by a 2-week washout period: proparacaine, tramadol alone, and tramadol in combination with dexmedetomidine.

RESULTS

CTT values were significantly decreased compared to baseline at each timepoint until completion of the 75-min evaluation in all treated eyes, regardless of the assigned treatment (p < 0.0083). With tramadol, complete corneal anesthesia (CTT = 0) was achieved within 1-5 min in 18 eyes and ranged from 5 to 25 min. Co-administration of dexmedetomidine to tramadol resulted in significantly increased CTT values from 5 to 20 min following topical application, compared to tramadol alone (p < 0.0083), and complete corneal anesthesia was achieved in only 14 out of 20 treated eyes.

CONCLUSION

Tramadol might be a useful alternative to topical anesthetic agents, providing a dose-related corneal anesthetic effect. Co-administration of dexmedetomidine does not potentiate its anesthetic effect. The underlying mechanism(s) of drug antagonism between tramadol and dexmedetomidine remains to be determined.

Prolonged Duration Topical Corneal Anesthesia With the Cationic Lidocaine Derivative QX-314

Purpose

Topical corneal local anesthetics are short acting and may impair corneal healing. In this study we compared corneal anesthesia and toxicity of topically applied N-ethyl lidocaine (QX-314) versus the conventional local anesthetic, proparacaine (PPC).

Methods

Various concentrations of QX-314 and 15 mM (0.5%) PPC were topically applied to rat corneas. Corneal anesthesia was assessed with a Cochet-Bonnet esthesiometer at predetermined time points. PC12 cells were exposed to the same solutions to assess cytotoxicity. Repeated topical corneal administration in rats was then used to assess for histologic evidence of toxicity. Finally, we created uniform corneal epithelial defects in rats and assessed the effect of repeated administration of these compounds on the defect healing rate.

Results

QX-314 (15 mM) and PPC (15 mM) caused similar total duration (114 ± 17 and 87 ± 16 minutes, respectively; P = 0.06) of anesthesia. The depth of anesthesia was similar between these low-dose groups at 15 minutes after application (1.8 ± 0.3- and 2.0 ± 0.8-cm filament lengths). QX-314 (100 mM) provided more prolonged corneal anesthesia (174 ± 13 minutes; P < 0.0001), with improved depth at 15 minutes (0.7 ± 0.3-cm filament length; P = 0.007). All tested concentrations of QX-314 demonstrated similar or less toxicity than 0.5% PPC.

Conclusions

Topical administration of QX-314 is effective for corneal anesthesia and demonstrates no histologic signs of local toxicity in a rodent model. In higher concentrations, QX-314 provides more than twofold the duration of anesthetic effect than does 0.5% PPC.

Translational Relevance

Our study reveals a clinically relevant compound providing prolonged duration topical corneal anesthesia.

Long-acting liposomal corneal anesthetics

Eye drops producing long-acting ocular anesthesia would be desirable for corneal pain management. Here we present liposome-based formulations to achieve very long ocular anesthetic effect after a single eye drop instillation. The liposomes were functionalized with succinyl-Concanavalin A (sConA-Lip), which can bind corneal glycan moieties, to significantly prolong the dwell time of liposomes on the cornea. sConA-Lip were loaded with tetrodotoxin and dexmedetomidine (sConA-Lip/TD), and provided sustained release for both. A single topical instillation of sConA-Lip/TD on the cornea could achieve 105 min of complete analgesia and 608 min of partial analgesia, which was significantly longer than analgesia with proparacaine, tetrodotoxin/dexmedetomidine solution or unmodified liposomes containing tetrodotoxin and dexmedetomidine. sConA-Lip/TD were not cytotoxic in vitro to human corneal limbal epithelial cells or corneal keratocytes. Topical administration of sConA-Lip/TD provided prolonged corneal anesthesia without delaying corneal wound healing. Such a formulation may be useful for the management of acute surgical and nonsurgical corneal pain, or for treatment of other ocular surface diseases.

The effects of subconjunctival bupivacaine, lidocaine, and mepivacaine on corneal sensitivity in healthy horses

OBJECTIVE

To compare the efficacy and duration of effect of three local anesthetics on corneal sensitivity when administered subconjunctivally in horses.

ANIMALS STUDIED

Eight healthy adult horses.

PROCEDURE

A randomized, masked, crossover study design was used, with a two-week washout period between trials. The subconjunctival space of the randomly selected eye was injected with 0.2 mLs of bupivacaine (0.5%), lidocaine (2%), mepivacaine (2%), or saline. All horses received each medication once. The contralateral eye served as a control. The corneal touch threshold (CTT) was measured in both eyes with a Cochet-Bonnet esthesiometer prior to sedation with xylazine, after sedation, and at 10-min intervals after subconjunctival injection until corneal sensitivity returned to baseline. The total time of decreased CTT and the maximum decrease in CTT were compared for each medication using a general linear mixed model (P < 0.05).

RESULTS

Total time of decreased CTT was 105.0 min for bupivacaine, 103.8 min for lidocaine, 138.8 min for mepivacaine, and 7.5 min for saline. All local anesthetics decreased CTT longer than saline (P < 0.001) and mepivacaine decreased CTT longer than lidocaine (P = 0.04). The mean minimum CTT was 1.67 cm for bupivacaine, 1.42 cm for lidocaine, and 0.73 cm for mepivacaine, which were all significantly less (P < 0.001) than saline (4.73 cm). No evidence of corneal toxicity was noted with any treatment.

CONCLUSION

Subconjunctival injections of lidocaine, bupivacaine, and mepivacaine effectively and safely reduce corneal sensitivity in eyes of healthy horses for 1.5-2 h, and may be useful for providing perioperative analgesia for equine corneal procedures.

Corneal Anesthesia With Site 1 Sodium Channel Blockers and Dexmedetomidine

PURPOSE

Amino-amide or amino-ester local anesthetics, which are currently used for topical ocular anesthesia, are short acting and may delay corneal healing with long-term use. In contrast, site 1 sodium channel blockers (S1SCBs) are potent local anesthetics with minimal adverse tissue reaction. In this study, we examined topical local anesthesia with two S1SCBs, tetrodotoxin (TTX) or saxitoxin (STX) individually or in combination with α2-adrenergic receptor agonists (dexmedetomidine or clonidine), and compared them with the amino-ester ocular anesthetic proparacaine. The effect of test solutions on corneal healing was also studied.

METHODS

Solutions of TTX ± dexmedetomidine, TTX ± clonidine, STX ± dexmedetomidine, dexmedetomidine, or proparacaine were applied to the rat cornea. Tactile sensitivity was measured by recording the blink response to probing of the cornea with a Cochet-Bonnet esthesiometer. The duration of corneal anesthesia was calculated. Cytotoxicity from anesthetic solutions was measured in vitro. The effect on corneal healing was measured in vivo after corneal debridement followed by repeated drug administration.

RESULTS

Addition of dexmedetomidine to TTX or STX significantly prolonged corneal anesthesia beyond that of either drug alone, whereas clonidine did not. Tetrodotoxin or STX coadministered with dexmedetomidine resulted in two to three times longer corneal anesthesia than did proparacaine. S1SCB-dexmedetomidine formulations were not cytotoxic. Corneal healing was not delayed significantly by any of the test solutions.

CONCLUSIONS

Coadministration of S1SCBs with dexmedetomidine provided prolonged corneal anesthesia without delaying corneal wound healing. Such formulations may be useful for the management of acute surgical and nonsurgical corneal pain.

Topical drug formulations for prolonged corneal anesthesia

PURPOSE

Ocular local anesthetics currently used in routine clinical practice for corneal anesthesia are short acting and their ability to delay corneal healing makes them unsuitable for long-term use. In this study, we examined the effect of the site 1 sodium channel blocker tetrodotoxin (TTX) on the duration of corneal anesthesia, applied with either proparacaine (PPC) or the chemical permeation enhancer octyl-trimethyl ammonium bromide (OTAB). The effect of test solutions on corneal healing was also studied.

METHODS

Solutions of TTX, PPC, and OTAB, singly or in combination, were applied topically to the rat cornea. The blink response, an indirect measure of corneal sensitivity, was recorded using a Cochet-Bonnet esthesiometer, and the duration of corneal anesthesia was calculated. The effect of test compounds on the rate of corneal epithelialization was studied in vivo after corneal debridement.

RESULTS

Combination of TTX and PPC resulted in corneal anesthesia that was 8 to 10 times longer in duration than that from either drug administered alone, whereas OTAB did not prolong anesthesia. The rate of corneal healing was moderately delayed after coadministration of TTX and PPC.

CONCLUSIONS

Coadministration of TTX and PPC significantly prolonged corneal anesthesia, but in view of delayed corneal reepithelialization, caution is suggested in the use of the drug combination.

Toxicity of topical ophthalmic anesthetics

INTRODUCTION

Topical ocular anesthetics are generally well tolerated in clinical settings but have great potential for abuse if used by patients at home. This abuse can lead to significant ocular complications. Topical ocular anesthetic abuse can lead to superficial punctate keratitis, persistent epithelial defects, stromal/ring infiltrates, corneal edema, endothelial damage and ocular inflammation, even when used in a dilute concentration. Patient characteristics may include a healthcare association and/or psychiatric illness. In these instances, patients often do not admit to anesthetic use and are often initially treated for acanthamoeba keratitis. Local anesthetics are thought to cause direct toxicity to the corneal epithelium, stroma and endothelium. This in turn may lead to release of antigens and from there an inflammatory response in the form of infiltrate and edema. It is thought that preservatives in anesthetics may play a further role in toxicity.

AREAS COVERED

The authors provide a brief history on topical ocular anesthetics and review the most recent literature on reported ocular toxicities of topical anesthetics.

EXPERT OPINION

Practitioners must maintain high suspicion for topical ocular anesthetic abuse to identify it early. Topical ocular anesthetic abuse is often misdiagnosed as acanthamoeba keratitis. Early identification is one of the most important factors for a successful outcome. It is also imperative to give proper alternative pain control to avoid topical anesthetic abuse.

Determination of tear break-up time reference values and ocular tolerance of tetracaine hydrochloride eyedops in healthy horses

REASONS FOR PERFORMING STUDY

Tetracaine hydrochloride (THCl) has been reported to cause irritation in dogs. In man, some topical anaesthetics have been shown to disrupt the tear film. Tear break-up time (TBUT) is a useful test allowing an assessment of the quality of the precorneal tear film. Only one TBUT value has been reported in horses with no information on the technique used.

OBJECTIVES

To provide a method for performing the TBUT in horses and to report any side effects of a single application of THCl in clinically normal horses, particularly on the stability of the tear film.

METHODS

In Study 1, one drop of 0.5 or 1% THCl was applied to one eye of 20 horses divided in 2 groups. Treated eyes were assessed for the development of side effects 2.5 and 5 min after treatment. In Study 2, the TBUT was measured in both eyes of 2 groups of 10 horses, before and 2.5 and 5 min after, instillation of one drop of either 0.5 or 1% THCl.

RESULTS

No animals developed any ocular side effect after instillation. Basal TBUT was 8.3±1.3 s. TBUT decreased from baseline 5 and 2.5 min after application of one drop of 0.5% THCl and one drop of 1% THCl, respectively.

CONCLUSIONS

A technique to measure the TBUT in healthy horses is described and normal range values that could be used as a reference were obtained.

POTENTIAL RELEVANCE

THCl is well tolerated in horses but lowers the TBUT.

Influence of topical anesthetics on oculocardiac reflex and corneal healing in rabbits

AIM

To investigate the incidence of oculocardiac reflex (OCR) with two anesthetic regimens and its prevention using topical anesthetics in a rabbit model, and to explore the effect of topical anesthetics on corneal healing.

METHODS

Forty-eight clinically healthy adult New Zealand white rabbits of either sex were divided into two groups (Group A and B) and anesthetized with either ketamine (Group A, n =24) or propofol (Group B, n =24). he incidence of OCR was recorded in each group with a variety of ocular manipulation with or without the use of topical anesthetics (40g/L lignocaine, 5g/L proparacain, 5g/L bupivacaine). Corneal toxicity and healing following the use of each topical anesthetic was assessed one day after surgery and up to 7 days postoperatively by clinical examination of the eye, histopathology and collagen staining and transmission electron microscopy.

RESULTS

No incidence of OCR was recorded with ocular manipulation under ketamine anesthesia, whereas significant reduction in heart rate (P<0.01) was recorded under propofol anesthesia. Topical anesthetics could successfully prevent the OCR without affecting the corneal healing.

CONCLUSION

Topical anesthetics may be recommended for prevention of OCR without any local adverse effect.

Limbal anaesthesia versus topical anaesthesia for clear corneal phacoemulsification

PURPOSE

To compare the safety and clinical efficacy provided by limbal anaesthesia with topical anaesthesia in cataract surgery.

METHODS

A total of 117 consecutive patients undergoing routine cataract surgery were randomly assigned to receive limbal or topical anaesthesia. Limbal anaesthesia was administered with a cellulose ophthalmic sponge soaked in preservative-free lidocaine hydrochloride 4% applied to the temporal perilimbal area for 45 seconds immediately before surgery. For topical anaesthesia lidocaine 4% was instilled in each patient at 10-min intervals four times before surgery. We studied phaco time, perioperative pain, visual outcome and intraoperative complications. The level of intraoperative pain was scored on a scale of 1-10, where 1 = no pain and 10 = severe pain.

RESULTS

55 patients (91.6%) in the topical group and 54 patients (94.7%) in the limbal group tolerated the procedure well, giving pain scores of 1-3, with no statistical difference. No patients in either group required supplemental anaesthesia and no intraoperative complications were recorded. No eyes had epithelial defects at the end of surgery or at postoperative check-ups.

CONCLUSION

Limbal anaesthesia in cataract surgery is safe and the two anaesthesia techniques do not present differences in the degree of analgesia achieved.

Flap suturing with proparacaine for recurrent epithelial ingrowth following laser in situ keratomileusis surgery

PURPOSE

To evaluate the safety and efficacy of flap suturing with proparacaine application for the management of recurrent epithelial ingrowth following laser in situ keratomileusis (LASIK).

SETTING

Private consultation practice and Department of Ophthalmology, Rush University, Chicago, Illinois, USA.

METHODS

Six eyes of 5 patients with recurrent epithelial ingrowth had flap lifting followed by debridement of interface epithelial cells, interface application of proparacaine, and the placement of interrupted 10-0 nylon sutures.

RESULTS

Four eyes achieved a best corrected visual acuity (BCVA) of 20/40 or better. Two eyes required repeat debridement with suturing and were stable with at least a 1-year follow-up. No eye lost more than 1 line of BCVA. Three eyes regained excellent uncorrected visual acuity due to a reduction in induced astigmatism.

CONCLUSIONS

Recurrent epithelial ingrowth following LASIK surgery can be a visually debilitating condition. Flap suturing with interface proparacaine application may be effective in preventing further recurrences of epithelial ingrowth after initial debridement.

Efficacy and safety of three ophthalmic inserts for topical anaesthesia of the cornea. An exploratory comparative dose-ranging, double-blind, randomized trial in healthy volunteers

BACKGROUND

Cataract surgery requires prolonged anaesthesia, concomitant with permanent hydration and lubrication of the cornea, in order to provide a clear view of the operation area.

AIMS

The primary objective of the study was to assess several formulae of a soluble ophthalmic insert: TOPICSERT [bupivacaine (Bupi) + hyaluronic acid (HA) or sodium hyaluronate] in terms of complete and long-lasting anaesthesia of the cornea. The hydration properties of HA were not assessed in this study.

METHODS

In a prospective double-blind, cross-over, randomized study, with latin-square allocation of treatments, 16 healthy volunteers received a single dose of each formula (A, 1 mg Bupi and 0.1 mg HA; B, 0.5 mg Bupi and 0.1 mg HA; C, 1 mg Bupi and 0 mg HA, and D acting as a placebo) via the ocular route with 1 week of wash-out between each period. Corneal anaesthesia was measured using a Cochet-Bonnet esthesiometer.

RESULTS

There was a statistically significant difference between treatments with regard to the main criterion (complete anaesthesia lasting at least 20 min) when general association statistics were used (Mantel-Haenzel test, P < 0.0001): 68.75% (n = 11) of subjects receiving treatment A, 37.5% (n = 6) receiving treatment B, and 87.5% (n = 14) on treatment C reached complete and satisfactory anaesthesia, while this was not achieved in any of the subjects receiving placebo. Ninety-five percent confidence intervals of the difference between treatments were as follows: treatment A vs. B (-0.03, 0.66), treatment A vs. C (-0.47, 0.10), treatment B vs. C (-0.84, - 0.16). Only the difference between B and C was statistically significant (adjusted probability by the method of Bonferroni, P < 0.001). When complete anaesthesia was reached, mean (+/-SD) duration of anaesthesia was as follows: 20.7 (+/-6.5), 15.3 (+/-11.4) and 24.7 (+/-7.6) min for treatments A, B, C, respectively.

CONCLUSIONS

Bupivacaine 1 mg seems to be the efficient and safe dose. The value of hyaluronic acid as a corneal hydration agent and used in association with bupivacaine will be the subject of further studies.

Duration of effect and effect of multiple doses of topical ophthalmic 0.5% proparacaine hydrochloride in clinically normal dogs

OBJECTIVE

To determine the duration of effect and the effect of multiple doses of topical ophthalmic application of 0.5% proparacaine hydrochloride on corneal sensitivity in clinically normal dogs.

ANIMALS

8 clinically normal dogs.

PROCEDURE

Dogs were randomly allocated to treatment order in a 2 x 2 (period X treatment) crossover study. Treatments consisted of topical application of ophthalmic 0.5% proparacaine (1 drop or 2 drops at a 1-minute interval); treatments were applied to both eyes. A Cochet-Bonnet aesthesiometer was used to determine corneal touch threshold (CTT) before corneal application, 1 and 5 minutes after corneal application, and at 5-minute intervals thereafter for 90 minutes.

RESULTS

The CTT value before treatment differed significantly from CTT values after treatment until 45 minutes after application in the 1-drop group and until 55 minutes after application in the 2-drop group. As determined by use of the Cochet-Bonnet aesthesiometer, a significantly greater anesthetic effect was detected for the 2-drop treatment, compared with the effect for the 1-drop treatment, at 30, 35, 40, 45, 50, and 55 minutes after application. Maximal anesthetic effect lasted for 15 minutes for the 1-drop treatment and 25 minutes for the 2-drop treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Duration of corneal anesthetic effect induced by topical ophthalmic application of 0.5% proparacaine in dogs of this study is considerably longer than that reported elsewhere. Serial application of doses of 0.5% proparacaine increases the duration and magnitude of corneal anesthetic effects.

Aqueous humor levels of topically applied bupivacaine 0.75% in cataract surgery

PURPOSE

To measure the intraocular levels of bupivacaine 0.75% topically applied before phacoemulsification and to develop standards for topical anesthesia in cataract surgery.

SETTING

Department of Ophthalmology, University Hospitals of Leicester, Leicester, United Kingdom.

METHODS

Forty eyes having phacoemulsification for senile cataract under topical anesthesia without sedation were randomly assigned to 1 of 2 preoperative topical anesthesia regimens. Bupivacaine 0.75% was applied in 0.1 mL drops 3 times in the 30 minutes before surgery in 18 eyes and 6 times in the 60 minutes before surgery in 22 eyes. Aqueous humor and serum samples were taken at the start of surgery and the bupivacaine levels measured. A visual analog pain score scale was used to indicate intraoperative pain.

RESULTS

The mean aqueous humor level of bupivacaine was 5.9 microg/mL +/- 4.3 (SD) after 3 drops and 5.7 +/- 4.0 microg /mL after 6 drops. The blood levels were less than 1.0 microg/mL. There was no statistically significant difference in the intraocular level of bupivacaine between the 2 groups. There was no difference in the age or sex distribution between the 2 groups, although there was an increase in the intraocular level of bupivacaine with age (approximately 1.4 microg/mL per decade; P =.048). There was no clear pattern associating the pain score with age, sex, or intraocular level of bupivacaine.

CONCLUSIONS

A 3-drop regimen of bupivacaine 0.75% in the half hour before cataract surgery penetrated the eye as effectively as 6 drops in the 1 hour before surgery and provided good analgesia for phacoemulsification. Bupivacaine 0.75% penetrated the eye increasingly effectively with increasing age.

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.

Corneal sensation after topical anesthesia

PURPOSE

To compare the topical effects of tetracaine, lidocaine, and bupivacaine on corneal sensitivity in normal eyes.

METHODS

Corneal touch sensitivity was measured with a Cochet-Bonnet anesthesiometer before and at 2.5-minute intervals after instillation of the anesthetic agent, until baseline levels had been reestablished. Seventeen healthy volunteers were randomized into five groups. Group 1 included 0.5% tetracaine (n = 6); group 2, 4% lidocaine (n = 8); group 3, 0.75% bupivacaine (n = 8); group 4, 0.5% tetracaine + 4% lidocaine (n = 5); and group 5, 0.5% tetracaine + 0.75% bupivacaine (n = 7).

RESULTS

The duration of anesthesia showed no differences between groups 1, 3, and 5. Although there was no difference between groups 2 and 4, both groups demonstrated significantly longer effects than groups 1, 3, and 5 (p < 0.005).

CONCLUSION

The application of 4% lidocaine results in a significantly prolonged topical anesthetic effect when compared with tetracaine and bupivacaine.

Perilimbal topical anesthesia for clear corneal phacoemulsification

PURPOSE

To evaluate the efficacy of perilimbal topical anesthesia for clear corneal cataract surgery.

SETTING

Department of Ophthalmology, University of Udine, Udine, Italy.

METHODS

Seventy-five consecutive patients were studied for perioperative pain, visual outcome, and intraoperative complications. Topical anesthesia was administered with a cellulose sponge soaked in preservative-free lidocaine 2%. The perilimbal area was touched 360 degrees for 30 seconds with the sponge tip under the operating microscope just before surgery. No sedation or adjunctive anesthetic drops were given. Surgery was performed through a temporal corneal tunnel with the easy-chop technique. Pain was scored on a subjective scale from 0 (no pain) to 3 (severe pain). Visual acuity was measured 1 day and 1 week after surgery. Mean operating time was recorded.

RESULTS

Sixty-nine patients (92%) tolerated the procedure well, giving a pain score of 0 or 1. Six (8%) of the 40 patients who had a single stitch at the end of surgery scored 2. No patient reported pain during iris touch, intraocular lens implantation, or conjunctiva manipulation. No intraoperative complications were recorded. Mean operating time was 12.7 minutes +/- 3.7 (SD) (range 7 to 34 minutes). Mean preoperative visual acuity was 0.4 +/- 0.2 (range 0.01 to 0.80). Visual acuity of 0.5 or better was attained in 93.6% of eyes 1 day and in 96% 1 week postoperatively.

CONCLUSIONS

Perilimbal topical anesthesia was an effective and easy-to-administer anesthetic procedure for phacoemulsification, providing good perioperative pain tolerance by patients and rapid visual recovery.

Comparison of 4 topical anesthetic agents for effect and corneal toxicity in rabbits

PURPOSE

To compare the onset time, duration of action, corneal toxicity, and corneal epithelial healing time of 4 topical anesthetic agents in rabbits.

SETTING

Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.

METHOD

Fifty-six rabbits were treated with 4 topical anesthetics (bupivacaine, lidocaine, procaine, and benzocaine) at different concentrations and different pH of solutions. Corneal sensation, corneal toxicity, and corneal epithelial healing time were measured.

RESULTS

The onset time of all 4 anesthetic agents was within 1 minute; however, bupivacaine and lidocaine produced significantly longer action than procaine or benzocaine (P < .05). Buffered bupivacaine and lidocaine had a significantly longer anesthetic effect than that of the nonbuffered solutions (P < .05). No significant effect on corneal epithelial healing time or corneal toxicity was observed.

CONCLUSION

Topical bupivacaine and lidocaine had a longer anesthetic effect, particularly in buffered solutions. No significant corneal toxicity was observed.

Corneal endothelial toxicity of topical anesthesia

PURPOSE

To determine the relative corneal endothelial toxicities of the following topical anesthetic agents: bupivacaine HCl 0.75%, unpreserved lidocaine HCl 4%, proparacaine HCl 0.5%, and tetracaine HCl 0.5%.

METHODS

The experiment was conducted using pigmented rabbits. Approximately nine animals each were randomly assigned to eight groups. Right eyes received injections of 0.2 ml of one of the four anesthetic agents at one of two concentrations and left eyes received injections of 0.2 ml of balanced salt solution. Corneal thickness and clarity were measured before surgery and on postoperative days 1, 3, and 7.

RESULTS

A statistically significant increase (P < 0.05) in corneal thickness and opacification over preoperative measurements was noted with injections of bupivacaine, lidocaine, and proparacaine, controlling for changes occurring in control eyes from surgery alone. Proparacaine was statistically more toxic than were the others. The toxicity of tetracaine was statistically indistinguishable from balanced salt solution, although mild toxicity was evident clinically. Injection of 1:10 dilutions of the same anesthetic agents failed to produce a statistically significant increase in corneal thickness or opacification on any postoperative examination.

CONCLUSIONS

Anterior chamber injection of bupivacaine HCl 0.75%, unpreserved lidocaine HCl 4%, and proparacaine HCl 0.5% produces corneal thickening and opacification that is clinically and statistically significant. Tetracaine HCl 0.5% injection produces corneal thickening and opacification that is clinically apparent in some eyes but statistically insignificant. Ophthalmic surgeons should be aware of the potential for endothelial cell injury if anesthetic agents enter or are injected into the eye during cataract surgery in the concentrations supplied commercially.

Comparison of Corneal Epithelial Wound Healing After Photorefractive and Lamellar Keratectomy

BACKGROUND

The rate of corneal epithelial wound healing may be determined, in part, by the characteristics of the stromal surface. The excimer laser has the ability to produce a highly uniform ablated surface, which may facilitate reepithelialization after photorefractive keratectomy (PRK).

METHODS

The rate of corneal epithelial wound healing after excimer laser PRK was compared with the rate of reepithelialization after manual lamellar keratectomy. Ten rabbits received a 4-mm diameter ablation in one eye (fluence = 160 mJ/cm2) and a shallow, 5-mm diameter, manual lamellar keratectomy in the contralateral eye. At 0, 4, 8, 12, 24, 36, 48, 60, and 72 hours after wounding, sodium fluorescein was instilled, and photographs were taken, converted to video images, and digitized. Wound area was calculated for each time point and converted to wound radius; the slopes of the wound radius, plotted over time, were compared to determine rates of healing. Scanning electron microscopy was performed immediately after wounding to examine surface regularity.

RESULTS

By 24 hours after wounding, corneas that had undergone PRK demonstrated a significantly faster rate of epithelial wound healing compared with eyes that underwent lamellar keratectomy (33.4 +/- 1.9 microns/hr vs 27.8 +/- 1.4 microns/hr, respectively, for 12 to 72 hours) (p < 0.0001). Scanning electron microscopy showed greater stromal surface irregularity in the corneas that had undergone lamellar keratectomy, compared with the laser-ablated corneas.

CONCLUSIONS

This study demonstrates that the rate of epithelial wound healing is significantly faster after excimer laser PRK than after lamellar keratectomy in the rabbit. Variations in surface regularity and wound edge profile may contribute to differences in wound healing.