Intracameral anesthesia: in vitro iris and corneal uptake and washout of 1% lidocaine hydrochloride

Sodium Ferulate Attenuates Lidocaine-Induced Corneal Endothelial Impairment

The introduction of intracameral anaesthesia by injection of lidocaine has become popular in cataract surgery for its inherent potency, rapid onset, tissue penetration, and efficiency. However, intracameral lidocaine causes corneal thickening, opacification, and corneal endothelial cell loss. Herein, we investigated the effects of lidocaine combined with sodium ferulate, an antioxidant with antiapoptotic and anti-inflammatory properties, on lidocaine-induced damage of corneal endothelia with in vitro experiment of morphological changes and cell viability of cultured human corneal endothelial cells and in vivo investigation of corneal endothelial cell density and central corneal thickness of cat eyes. Our finding indicates that sodium ferulate from 25 to 200 mg/L significantly reduced 2 g/L lidocaine-induced toxicity to human corneal endothelial cells, and 50 mg/L sodium ferulate recovered the damaged human corneal endothelial cells to normal growth status. Furthermore, 100 mg/L sodium ferulate significantly inhibited lidocaine-induced corneal endothelial cell loss and corneal thickening in cat eyes. In conclusion, sodium ferulate protects human corneal endothelial cells from lidocaine-induced cytotoxicity and attenuates corneal endothelial cell loss and central corneal thickening of cat eyes after intracameral injection with lidocaine. It is likely that the antioxidant effect of sodium ferulate reduces the cytotoxic and inflammatory corneal reaction during intracameral anaesthesia.

[Toxic anterior segment syndrome]

Toxic anterior segment syndrome (TASS) is a general term used to describe acute, sterile postoperative inflammation due to a non-infectious substance that accidentally enters the anterior segment at the time of surgery and mimics infectious endophthalmitis. TASS most commonly occurs acutely following anterior segment surgery, typically 12-72h after cataract extraction. Anterior segment inflammation is usually quite severe with hypopyon. Endothelial cell damage is common, resulting in diffuse corneal edema. No bacterium is isolated from ocular samples. The causes of TASS are numerous and difficult to isolate. Any device or substance used during the surgery or in the immediate postoperative period may be implicated. The major known causes include: preservatives in ophthalmic solutions, denatured ophthalmic viscosurgical devices, bacterial endotoxin, and intraocular lens-induced inflammation. Clinical features of infectious and non-infectious inflammation are initially indistinguishable and TASS is usually diagnosed and treated as acute endophthalmitis. It usually improves with local steroid treatment but may result in chronic elevation of intraocular pressure or irreversible corneal edema due to permanent damage of trabecular meshwork or endothelial cells.

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.

Safety and efficacy of two ocular anesthetic methods for phacoemulsification: topical anesthesia and viscoanesthesia (VisThesia)

PURPOSE

VisThesia is a new ophthalmic viscosurgical device (OVD) which has 1% lidocaine combined with 1.5% sodium hyaluronate. This is a prospective evaluation of the safety and efficacy of VisThesia used in association with phacoemulsification.

METHODS

A total of 114 eyes were divided into two groups. Fifty-nine eyes were treated with tetracaine + oxybuprocaine topical anesthesia and DuoVisc OVD and 55 eyes were treated with VisThesia, for use as both topical anesthetic and OVD. Endothelial cell counts were measured at 30 days postoperatively and compared to preoperative baseline values. Pain and discomfort was subjectively evaluated by patients using a visual analog pain scale (0-10).

RESULTS

All surgeries were uneventful with no intraoperative or immediate postoperative complications. Patients receiving topical anesthesia had a mean pain score of 1.1+/-6.8 compared to a mean score of 1.3+/-4.6 for patients receiving VisThesia (p=0.59). Postoperatively, endothelial cell loss at 1 month was greater for patients receiving VisThesia (20.32%+/-43.75) than for those receiving the topical anesthetic (8.8%+/-59.6; p<0.0001).

CONCLUSIONS

The results from the visual analog pain scale were comparable between groups, showing that VisThesia provides similar pain relief to topical anesthesia. Specular microscopy performed at 30 days postoperatively showed a significantly greater loss of endothelial cells with the use of VisThesia, suggesting that the 1% lidocaine concentration used in VisThesia may be toxic to corneal endothelial cells.

Lidocaine effects on corneal endothelial cell ultrastructure

The purpose of this study was to determine whether intracameral commercial lidocaine 2% induces alterations on the rabbit corneal endothelium. Forty white rabbits received different substances inside the anterior chamber: group (G)1, no substance; G2 and G3 received lidocaine 2% with preservative in aqueous solution; G4 and G5, lidocaine 2% with preservative in gel solution; G6 and G7, the anesthetic preservative (metilparahydroxybenzoate 0.1%); and G8 and G9, lidocaine 2% without preservative in aqueous solution. The animals from G2, 4, 6 and 8 were sacrificed after 1 h, and from G3, 5, 7 and 9 after 24 h after injection of the substance inside the anterior chamber. The corneas were clinically evaluated and assessed by transmission and scanning electron microscopy. G1, 2, 6, 7, 8 and 9 animals had very similar characteristics in clinical, ultrastructural and morphometric evaluations; the G3 and G4 animals showed discrete edema and one animal in G5 had intense corneal edema. We conclude that lidocaine 2% with preservative induces few ultrastructural alterations in the corneal endothelial cells.

Clinical evaluation of endothelial cell decrease with VisThesia in phacoemulsification surgery

PURPOSE

To assess the endothelial cell decrease after the use of sodium hyaluronate 0.3% and lidocaine hydrochloride 2% (VisThesia) to determine whether the addition of lidocaine 1% to sodium hyaluronate 1.5% makes the solution more toxic to the cornea.

SETTING

Instituto de Oftalmologia Avanzada, Madrid, Spain, and Unita Operative Oculistica, Cesena, Italy.

METHODS

VisThesia is an ophthalmic viscosurgical device (OVD) that incorporates lidocaine 1% to provide better comfort to patients under topical anesthesia. Fifty eyes 50 patients were operated on following the same patient selection and surgical technique. After the povidone-iodine (Betadine) ocular asepsis, 1 full ampoule of VisThesia Topical was applied over the corneal surface. The intracameral product was used as a routine OVD during the phacoemulsification procedure. The endothelium of the central cornea was examined preoperatively and 3 months after surgery using a noncontact endothelium microscope.

RESULTS

At the last follow-up visit, the mean best corrected visual acuity was 0.88 +/- 0.18 and the mean manifest SE was -0.36 +/- 1.78 D. The mean endothelial cell density had decreased from 2363.57 +/- 435.4 cells/mm2 preoperatively to 2222.6 +/- 537.69 cells/mm2 at 3 months. These values are comparable with results obtained in other investigations published in the literature using other, similar OVD.

CONCLUSIONS

The results observed in this investigation indicate that the addition of lidocaine to the sodium hyaluronate in VisThesia does not induce additional toxicity nor does it result in increased endothelial cell loss when compared with other, similar OVDs.

Toxic anterior segment syndrome

Toxic anterior segment syndrome (TASS) is a sterile postoperative inflammatory reaction caused by a noninfectious substance that enters the anterior segment, resulting in toxic damage to intraocular tissues. The process typically starts 12 to 48 hours after cataract/anterior segment surgery, is limited to the anterior segment of the eye, is always Gram stain and culture negative, and usually improves with steroid treatment. The primary differential diagnosis is infectious endophthalmitis. Review of the literature indicates that possible causes of TASS include intraocular solutions with inappropriate chemical composition, concentration, pH, or osmolality; preservatives; denatured ophthalmic viscosurgical devices; enzymatic detergents; bacterial endotoxin; oxidized metal deposits and residues; and factors related to intraocular lenses such as residues from polishing or sterilizing compounds. An outbreak of TASS is an environmental and toxic control issue that requires complete analysis of all medications and fluids used during surgery, as well as complete review of operating room and sterilization protocols.

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.

Effects of intracameral injection of preservative-free lidocaine on the anterior segment of the eyes in dogs

OBJECTIVE

To evaluate effects of intracameral injection of preservative-free 1% and 2% lidocaine hydrochloride solution on the anterior segment of the eyes in dogs.

ANIMALS

16 adult healthy dogs (8 male and 8 female) judged to be free of ocular disease.

PROCEDURE

Dogs were randomly assigned to 2 groups of 8 dogs each. Group 1 dogs received an intracameral injection of 0.10 mL of preservative-free 1% lidocaine solution in the designated eye, and group 2 dogs received 0.10 mL of preservative-free 2% lidocaine solution in the designated eye. After injection, intraocular pressure was measured every 12 hours for 48 hours and then every 24 hours until 168 hours after injection. Slit-lamp biomicroscopy was performed preceding intracameral injection, 8 hours after injection, and then every 24 hours until 168 hours after injection. Ultrasonic pachymetry and specular microscopy were performed preceding intracameral injection and 72 and 168 hours after injection. Corneal thickness and endothelial cell density and morphology were compared with baseline measurements.

RESULTS

No significant differences were found in intraocular pressure, corneal thickness, endothelial cell density, and morphologic features in either group, compared with baseline. A significant difference in aqueous flare was found for treated and control eyes 8, 24, and 48 hours after injection, compared with baseline. No significant difference in aqueous flare was found between treated and control eyes within either group.

CONCLUSIONS AND CLINICAL RELEVANCE

No adverse ocular effects were detected after intracameral injection of preservative-free 1% or 2% lidocaine solution; thus, its use would be safe for intraocular pain management in dogs.

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.

Phacoemulsification with topical anesthesia performed by resident surgeons

PURPOSE

To evaluate and compare the outcomes in phacoemulsification cases performed by resident surgeons using topical anesthesia or retrobulbar anesthesia.

SETTING

Department of Ophthalmology, Emory University, Atlanta, and Department of Veterans Affairs Medical Center, Decatur, Georgia, USA.

METHODS

This was a retrospective review of phacoemulsification cases performed by resident surgeons during 1 academic year. Variables analyzed included patient age and sex, preexisting conditions limiting final acuity, and type of anesthesia used. Outcomes measured included intraoperative and postoperative complications and final visual acuity.

RESULTS

Of the 291 cases analyzed, 119 (40.9%) were retrobulbar and 172 (59.1%) were topical. Residents began using topical anesthesia after a brief introductory period with retrobulbar anesthesia. Vitreous loss occurred in 15 cases (5.1%), 8 retrobulbar (6.7%) and 7 topical (4.1%) (P =.42). Postoperative complications occurred in 30 cases (10.3%), 17 topical (9.9%) and 13 retrobulbar (10.9%) (P =.85). Overall, 245 cases (84.2%) achieved a final best corrected visual acuity (BCVA) of 20/40 or better. When cases with preexisting conditions limiting final acuity were eliminated, 92.1% achieved a final BCVA of 20/40 or better. More topical cases (112, 65.1%) than retrobulbar cases (64, 53.8%) achieved a final BCVA of 20/25 or better (P =.06), and more topical cases (149, 86.6%) than retrobulbar cases (96, 80.7%) achieved a final BCVA of 20/40 or better (P =.19).

CONCLUSION

Topical anesthesia is safe and efficacious for phacoemulsification performed by resident surgeons early in training after a brief introduction to phacoemulsification using retrobulbar anesthesia.

Ocular surgical pharmacology: corneal endothelial safety and toxicity

The purpose of this review is to discuss the recently published literature related to corneal endothelial toxicity and safety. We discuss postoperative complications, such as toxic endothelial cell destruction syndrome and toxic anterior segment syndrome, that cause significant injury to the patient and anxiety to the physician. Additionally, we review recent papers related to intraocular medications, preservatives, and devices, including antibiotics, anesthetics, viscoelastics, and enzymatic sterilization detergents, that have potentially toxic effects on the corneal endothelium.

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.

Viscoanesthesia. Part II: toxicity to intraocular structures after phacoemulsification in a rabbit model

PURPOSE

To investigate the toxicity of a solution that combines sodium hyaluronate 1.5% with lidocaine (0.5%, 1.0%, or 1.65%) to intraocular structures.

SETTING

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

METHODS

Phacoemulsification was performed in both eyes of 29 rabbits. They were divided into 3 groups; in each group (n = 7), 1 viscoanesthetic solution was used before capsulorhexis. After irrigation/aspiration, 0.2 mL of the solution was purposely left in the capsular bag. In 1 rabbit in each group, the solution was injected into the vitreous cavity through a posterior capsulorhexis. In 8 rabbits used as controls, balanced salt solution (BSS(R)) (n = 4) or sodium hyaluronate 1.5% (n = 4) was injected into the vitreous cavity. Enucleations were performed 15, 30, and 60 days postoperatively. Histological sections were cut and stained with hematoxylin-eosin, periodic acid-Schiff, and Masson trichrome stains.

RESULTS

Light microscopic evaluation of the eyes enucleated after 15, 30, and 60 days in the study and control groups showed similar findings in intraocular structures such as the ciliary body and retina. No evidence of an inflammatory reaction, cell necrosis, or cell degeneration was observed in the histological sections.

CONCLUSIONS

The use of viscoanesthesia during phacoemulsification appeared to be safe, with no histologic abnormalities observed with the 3 lidocaine concentrations. The efficacy of the anesthetic effects of these solutions will be addressed in clinical trials.

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.

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.

Circumcorneal perilimbal anesthesia in extracapsular cataract extraction with intraocular lens implantation

PURPOSE

To evaluate the effectiveness of subconjunctival anesthesia in conventional extracapsular cataract extraction (ECCE) with intraocular lens (IOL) implantation.

SETTING

Eye Hospital, Colombo, Sri Lanka.

METHODS

This prospective study evaluated the complications related to the use of subconjunctival anesthesia in conventional ECCE with IOL implantation. Patient-reported pain during surgery in the first 100 consecutive cases was also evaluated.

RESULTS

Complications from the subconjunctival anesthesia technique were few. Patients did not report intraoperative pain severe enough to cause the procedure to be abandoned or the anesthesia reinforced; surgery was successfully performed in all cases.

CONCLUSIONS

Circumcorneal perilimbal anesthesia was effective for ECCE with IOL implantation. It is important that the surgeon is experienced in the technique and that patients are carefully selected.

Corneal endothelial toxicity of different lidocaine concentrations

PURPOSE

To examine the potential damaging effect on the corneal endothelium of unpreserved lidocaine in concentrations of 1%, 5%, and 10%.

SETTINGS

Department of Ophthalmology, Charité Medical Faculty, Humboldt University, Berlin, Germany.

METHODS

Experimental porcine corneas (n = 18) were exposed to 100 microL of unpreserved lidocaine hydrochloride at concentrations of 1%, 5%, and 10% for 60 minutes. Additional corneas (n = 6) were treated with lidocaine hydrochloride 1% for 30 minutes to simulate clinical conditions. Balanced salt solution (BSS((R))) served as a control to evaluate corneal endothelial cell damage using Janus Green photometry. Morphology, damage pattern, and changes in the ultrastructural appearance of corneal endothelial cells were examined by light and scanning electron microscopy.

RESULTS

Lidocaine 1% used for 30 or 60 minutes did not cause significantly more corneal endothelial damage (mean 3.00% +/- 0.76% [SD] and 3.26% +/- 1.00%, respectively) than in the control group (mean 3.32% +/- 0. 86%) (P >.01). Significant corneal endothelial cell loss was observed with lidocaine 5% (mean 10.7% +/- 6.4%) (P <.001) and lidocaine 10% (42.3% +/- 17.0%) (P <.001).

CONCLUSION

Experimental exposure of corneal endothelial cells to higher concentrations of lidocaine resulted in significant cell loss, indicating that the 1% concentration only should be used clinically.

The resiliency of the corneal endothelium to refractive and intraocular surgery

PURPOSE

To describe stress factors (phenylephrine and contact lenses) from the corneal epithelium that can affect the corneal endothelium, and to describe the effects of refractive and intraocular surgery on the corneal endothelial structure and function.

METHODS

Significant clinical and experimental publications are reviewed and recent experiments conducted in the author's laboratory to describe the corneal endothelial stresses.

RESULTS

The corneal epithelium serves as a barrier to topical phenylephrine (2.5-10%). In a compromised epithelium, topical phenylephrine will cause drug-induced stromal edema and endothelial vacuolization. Contact lenses are capable of stimulating the epithelial arachidonic acid cascade to release 12(R)hydroxyeicosatetraenoic acid (12(R)HETE) and 8(R)hydroxy-hexadecatrienoic acid (8(R)HHDTrE) to cause endothelial Na+/K+ adenosine triphosphatase (ATPase)-inhibition and polymegethism. Specular microscopy of the corneal endothelial cells after refractive surgery (photorefractive keratectomy [PRK], laser in situ keratomileusis [LASIK], intrastromal rings [INTACs]) has shown that there is minimal effect. However, laser ablation of the stroma within 200 microm of the corneal endothelium will result in endothelial cell structural changes and the formation of the amorphous substance deposited onto Descemet's membrane. Phacoemulsification with a high flow of the irrigation solution can alter the endothelial surface glycoprotein layer. Lidocaine hydrochloride (1%) used as intracameral anesthesia readily diffuses through the corneal endothelium, resulting in stromal uptake and endothelial cell swelling. With phacoemulsification, however, the washout of lidocaine from the cornea (T1/2, 5 minutes) and iris (T1/2, 9 minutes) occurs quickly. Corneal endothelial wound healing after keratoplasty occurs in the following sequence: migration of endothelial cells, development of tight junctions, and the formation of Na+/K+ ATPase pump sites.

CONCLUSIONS

Corneal endothelial resiliency is due to the increased peripheral endothelial cell number for migration, the ability of endothelial cells to form tight junctions to maintain the endothelial barrier, the increase in endothelial Na+/K+ ATPase pump sites under stress, and the ability of the corneal endothelial cells to shift their metabolism of glucose to the hexose monophosphate shunt for the production of nicotinamide adenine dinucleotide phosphate (NADPH) and membrane repair. All of these factors are important, along with the aqueous humor sodium concentration, which establishes the osmotic gradient for corneal deturgescence and transparency.

Anesthesia modalities for cataract surgery

Research articles on anesthesia modalities for cataract surgery are reviewed. A growing trend toward the use of topical anesthesia is apparent. Particular emphasis in the literature is given to determining the safety and efficacy of various forms of topical anesthesia using injectable anesthesia as a frame of reference. A consensus of opinion points toward the use of topical application of anesthetic drops plus intracameral unpreserved lidocaine 1% as the anesthesia modality that provides the best level of analgesia and comfort to patients while not compromising ocular safety. Several articles reporting complications of injectable anesthesia are also reviewed.

Comparison of preservative-free bupivacaine vs. lidocaine for intracameral anesthesia: a randomized clinical trial and in vitro analysis

PURPOSE

To determine whether intracameral bupivacaine hydrochloride 0.5% is as effective as lidocaine hydrochloride 1.0% in controlling discomfort of patients during phacoemulsification and posterior chamber intraocular lens implantation. In rabbits, corneal endothelial cell function, ultrastructure, and viability were evaluated after in vitro perfusion of bupivacaine 0.5%.

METHODS

In a double-masked, controlled trial, 48 eyes of 48 patients with uncomplicated age-related cataract were randomly assigned to receive bupivacaine 0.5% or lidocaine 1.0% intracamerally before phacoemulsification with a posterior chamber intraocular lens. Outcome measures such as pain, visual acuity, amount of sedation, length of surgery, pupil size, intraocular pressure, corneal clarity, and anterior chamber reaction were compared. In laboratory studies, paired rabbit corneas were evaluated by endothelial cell perfusion with either bupivacaine 0.5%, bupivacaine 0.5% and glutathione bicarbonate Ringer solution in a 1:1 ratio or bupivacaine 0.5% buffered to a pH of 7.0. The paired control corneas were perfused with glutathione bicarbonate Ringer solution and rates of corneal swelling were determined. Cell ultrastructure and viability were also evaluated.

RESULTS

In the randomized trial, there was no significant difference in the pain patients had during surgery or in the early or late postoperative period. No statistically significant difference was seen between the two groups in terms of pupil size, intraocular pressure, corneal edema, anterior chamber reaction, or visual acuity immediately after the operation or on postoperative day 1. Paired rabbit corneas perfused with bupivacaine 0.5% and bupivacaine 0.5% buffered to a pH of 7.0 swelled significantly (P<.001, P = .009, respectively), and had corneal endothelial cell damage. Dilution of the bupivacaine 1:1 with glutathione bicarbonate Ringer solution prevented corneal edema and damage to the corneal endothelium. Endothelial cell viability was also decreased after perfusion of bupivacaine 0.5% (P<.001).

CONCLUSIONS

Clinically, bupivacaine 0.5% is as effective as lidocaine 1.0% for anesthesia during phacoemulsification and posterior chamber intraocular lens implantation. However, in vitro perfusion of bupivacaine 0.5% damaged the corneal endothelium of rabbits except when the drug was diluted 1:1 with glutathione bicarbonate Ringer solution. Surgeons who use 0.2 to 0.5 ml of intracameral bupivacaine 0.5% should be aware of its potential to cause endothelial cell damage because of its lipid solubility. The bupivacaine 0.5% should be diluted at least 1:1 with balanced salt solution before intracameral injection, followed immediately by phacoemulsification. The surgeon should ensure that the bupivacaine 0.5% is nonpreserved and packaged in single-use vials or flip-top containers.