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

Intracameral lidocaine as supplement to classic topical anesthesia for relieving ocular pain in cataract surgery

AIM

To evaluate safety, efficacy, and patient adherence of intracameral lidocaine as supplement of classic topical anesthetic drops in cataract surgery.

METHODS

A prospective and controlled trial including a large cohort of 1650 individuals suffering with bilateral cataract not complicated, in program by phacoemulsification surgery, were randomly assigned to 2 different groups for the type of anesthesia received, 0.4% oxybuprocaine hydrochloride (INN) drops, and INN drops associated to intracameral 1% lidocaine hydrochloride monohydrate. At the end of surgery, tables were assigned to each patient indicating the degree of pain (0-3) felt during the operation.

RESULTS

Thirty-two percent of patients in group 1 declared to have not felt any pain against the 77% of patients in group 2. Fifty-nine percent of patients in group 1 complained about only a slight discomfort against 20% of group 2 patients. Only a small percentage of patients in group 1 (5%) admitted severe pain, while no patient in group 2 admitted severe pain. Four patients of group 2 reported an episode of transient amaurosis, lasting several hours after surgery.

CONCLUSION

Intracameral administration of lidocaine is a simple and secure method able to increase the analgesia during the cataract surgery, eliminating the discomfort and increasing also the cooperation of the patients during the steps of manipulation.

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.

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.

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.

Injection intravitréenne accidentelle de lidocaïne au cours d’une anesthésie palpébrale : toxicité rétinienne de la lidocaïne ?

INTRODUCTION

We report an atypical case of scleral perforation due to an inadvertent intravitreal lidocaine injection following palpebral anesthesia. We discuss the management of this rare complication and focus on the transient lidocaine toxicity on human retina.

OBSERVATION

A 29-year-old man presented with unilateral decreased vision during a lower right palpebral anesthetic injection for a chalazion removal procedure. The patient's vision was light perception. Examination revealed intraocular pressure at 55 mmHg, a wound of the posterior crystalloid, an intraocular gas bubble, and a central retinal artery spasm. On ERG, the b wave was decreased. The central retinal artery spasm resolved with prompt reduction of hypertony. Twenty-four hours later, the vision was 6/10 and the ERG showed an increased b wave activity. No clinical retinal toxicity of lidocaine was observed. Only a subcapsular cataract was observed, which had caused the loss of vision.

CONCLUSION

This case confirms that lidocaine is well tolerated by the retina and reminds us that superficial palpebral anesthetic injection should be done with great caution.

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.

Survey of ophthalmic viscosurgical devices

PURPOSE OF REVIEW

Cataract treatment is evolving, thanks to new phaco systems and innovative surgical techniques. Recent ophthalmic viscosurgical devices (OVDs) play an important role in the development of new approaches to surgery. Knowledge of the new techniques and advances in new OVDs is crucial to performing routine and complicated surgeries.

RECENT FINDINGS

Viscoadaptive substances have been introduced as a particular kind of OVD and are distinguished by high viscosity at a low flow rate and a tendency to fracture at higher flow rates, assuming pseudodispersive behavior. The ultimate soft shell technique emphasizes the rheology of viscoadaptive OVDs to perform phacoemulsification procedures, exploiting all the useful properties of these OVDs in terms of space maintenance and tissue protection. Recent studies have highlighted some new and interesting aspects of the use of OVDs. Current reports suggest that the association of lidocaine and OVD seems to be safe and useful in providing anesthesia during cataract surgery. Concern has been expressed in other studies regarding the presence of contaminants, such as endotoxins, which may be responsible for postoperative uveitis-like reactions. Finally, OVDs are widely known to protect the corneal endothelium during cataract surgery. Their role is also assuming relevance in vitreoretinal surgery.

SUMMARY

New OVDs and related techniques represent an advancement in cataract surgery.

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 III: removal time of OVD/viscoanesthetic solutions from the capsular bag of postmortem human eyes

PURPOSE

To investigate and evaluate the removal time of various ophthalmic viscosurgical device (OVD)/viscoanesthetic solutions containing sodium hyaluronate 1.5% with different concentrations of lidocaine (0.5%, 1.0%, and 1.65%).

SETTING

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

METHODS

Six postmortem human eyes were prepared per the Miyake-Apple posterior video technique. Capsulorhexis, hydrodissection/delineation, and nuclear emulsification were performed, followed by thorough cleaning of the capsular bag using an irrigation/aspiration (I/A) tip. The time and ease of removal of 4 solutions from the capsular bag were evaluated. The solutions were Ophthalin Plus (sodium hyaluronate, 15 mg/mL) and sodium hyaluronate 15 mg/mL mixed with lidocaine 0.5%, lidocaine 1.0%, and lidocaine 1.65%. The solutions were dyed with fluorescein to enhance visualization. After the capsular bag was filled with 1 of the solutions, a posterior chamber intraocular lens was implanted. The solution was then aspirated using an automated I/A device set at 250 mm Hg of aspiration. The time required to remove most and then all the material was recorded.

RESULTS

The mean time required for removal of most of the Ophthalin Plus, viscoanesthesia 0.5%, viscoanesthesia 1%, and viscoanesthesia 1.65% solutions was 8.7 seconds +/- 2.1 (SD), 7.7 +/- 1.1 seconds, 9.7 +/- 0.6 seconds, and 6.3 +/- 1.5 seconds, respectively (P =.1). The mean time to remove all the solutions was 21.3 +/- 3.2 seconds, 19.7 +/- 2.5 seconds, 18.3 +/- 3.2 seconds, and 15.7 +/- 2.1 seconds, respectively (P =.166). No subjective difference in viscosity or consistency was found among the solutions.

CONCLUSIONS

The addition of lidocaine to the OVD solution did not significantly alter the viscosity or consistency of the solution or change its removal time from the capsular bag.