Corneal sensation after topical anesthesia

Treatment of Non-Infectious Corneal Injury: Review of Diagnostic Agents, Therapeutic Medications, and Future Targets

Corneal injuries can occur secondary to traumatic, chemical, inflammatory, metabolic, autoimmune, and iatrogenic causes. Ocular infection may frequently occur concurrent to corneal injury; however, antimicrobial agents are excluded from this present review. While practitioners may primarily rely on clinical examination techniques to assess these injuries, several pharmacological agents, such as fluorescein, lissamine green, and rose bengal, can be used to formulate a diagnosis and develop effective treatment strategies. Practitioners may choose from several analgesic medications to help with patient comfort without risking further injury or delaying ocular healing. Atropine, cyclopentolate, scopolamine, and homatropine are among the most frequently used medications for this purpose. Additional topical analgesic agents may be used judiciously to augment patient comfort to facilitate diagnosis. Steroidal anti-inflammatory agents are frequently used as part of the therapeutic regimen. A variety of commonly used agents, including prednisolone acetate, loteprednol, difluprednate, dexamethasone, fluorometholone, and methylprednisolone are discussed. While these medications are effective for controlling ocular inflammation, side effects, such as elevated intraocular pressure and cataract formation, must be monitored by clinicians. Non-steroidal medications, such as ketorolac, bromfenac, nepafenac, and diclofenac, are additionally used for their efficacy in controlling ocular inflammation without incurring side effects seen with steroids. However, these agents have their own respective side effects, warranting close monitoring by clinicians. Additionally, ophthalmologists routinely employ several agents in an off-label manner for supplementary control of inflammation and treatment of corneal injuries. Patients with corneal injuries not infrequently have significant ocular surface disease, either as a concurrent pathology or as an exacerbation of previously existing disease. Several agents used in the management of ocular surface disease have also been found to be useful as part of the therapeutic armamentarium for treatment of corneal injuries. For example, several antibiotics, such as doxycycline and macrolides, have been used for their anti-inflammatory effects on specific cytokines that are upregulated during acute injuries. There has been a recent wave of interest in amniotic membrane therapies (AMTs), including topical, cryopreserved and dehydrated variants. AMT is particularly effective in ocular injuries with violation of corneal surface integrity due to its ability to promote re-epithelialization of the corneal epithelium. Blood-based therapies, including autologous serum tears, plasma-enriched growth factor eyedrops and autologous blood drops, have additionally been explored in small case series for effectiveness in challenging and recalcitrant cases. Protection of the ocular surface is also a vital component in the treatment of corneal injuries. Temporary protective methods, such as bandage contact lenses and mechanical closure of the eyelids (tarsorrhaphy) can be particularly helpful in selective cases. Glue therapies, including biologic and non-biologic variants, can also be used in cases of severe injury and risk of corneal perforation. Finally, there are a variety of recently introduced and in-development agents that may be used as adjuvant therapies in challenging patient populations. Neurotrophic corneal disease may occur as a result of severe or chronic injury. In such cases, recombinant human nerve growth factor (cenegermin), topical insulin, and several other novel agents may be an alternate and effective option for clinicians to consider.

Topical pain control for corneal abrasions: A systematic review and meta-analysis

OBJECTIVES

Corneal abrasions are common ophthalmic presentations to emergency departments. Among emergency physicians and ophthalmologists, there are highly variable practice patterns with regard to management of resultant pain and discomfort. The goal of this study was to review and analyze the efficacy and safety of topical pain therapies for corneal abrasions, including topical anesthetics, nonsteroidal anti-inflammatory drugs (NSAIDs), cycloplegics, steroids, pressure patching, and the use of a bandage contact lens (BCL).

METHODS

The review followed the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines. The protocol was established a priori and published on PROSPERO (CRD42020201288). MEDLINE, EMBASE, CENTRAL, and Web of Science were searched until December 31, 2020. Primary studies comparing topical pain therapies to another therapy or control were included. Primary outcomes included percentage of corneal abrasions healed at 24, 48, and 72 hours, as well as pain control at 24 and 48 hours. Secondary outcomes included use of oral analgesia and incidence of complications. Risk of bias was assessed using validated tools. Quality of evidence was assessed using the GRADE methodology.

RESULTS

Overall, 33 studies (31 randomized controlled trials [RCTs], two cohort studies) comprising 4,167 patients with corneal abrasions were analyzed. Only the data for topical NSAIDs were of adequate evidence from which to draw conclusions; topical NSAIDs demonstrated significantly reduced pain scores at 24 hours (standardized mean differences [SMD] -0.69, 95% CI = -0.98 to -0.41) and 48 hours (SMD = -0.56, 95% CI = -1.02 to -0.10) as well as 53% (95% CI = 34% to 67%) lower oral analgesia use compared to control. Based on available data, topical anesthetics, cycloplegics, patching, and the use of a BCL did not result in any significant difference in pain scores or use of oral analgesia, while no studies examined topical steroids. No interventions resulted in healing delays or significantly higher rates of complications compared to controls.

CONCLUSIONS

There was strong evidence to support that topical NSAIDs reduce pain associated with corneal abrasions in the first 48 hours and the need for oral analgesia. The existing evidence was insufficient to support or refute the use of topical anesthetics, cycloplegics, steroids, or BCL for pain control in corneal abrasions. Pressure patching was ineffective at pain reduction and may increase the risk of complications. Delays in healing or other complications were not significantly different between any intervention or control for simple, uncomplicated corneal abrasions; however, larger RCTs are required to identify any differences in rare complications.

Postoperative Behaviour after Primary Strabismus Surgery in Children: Is There an Influence of Intraoperative Topical Anaesthesia?

INTRODUCTION

The course of the recovery phase after general anaesthesia, during which consciousness and pain gradually return, is essentially determined by the choice of anaesthetic drug, and its total dose or duration of application. This phase is often complicated by more or less severe agitation, especially in children. In the present study we investigated whether the application of a topical anaesthetic to the conjunctiva at the end of a strabismus operation had a positive effect on the recovery behaviour of the child.

PATIENTS/METHODS

This prospective, randomised, blinded study was conducted with 50 healthy, ASA class I or II children, aged 3 to 8 years undergoing their first strabismus operation. Following the surgeon's randomisation two drops of a 0,5% tetracaine-HCl ophthalmic solution were applied to the operated conjunctiva three times at 30-s intervals immediately following wound closure. The postoperative evaluation encompassed heart rate, as well as COMFORT and CHEOPS scores. The first assessment was directly postoperatively with repetitions at 15, 30, 45, 60, 75, 90 and 120 min, as well as on the day after surgery.

RESULTS

The CHEOPS scores did not differ significantly between children with or without topical anaesthesia at any time during the observation period. The COMFORT scores revealed a slight, but non-significant analgesic effect at 15 and 30 min. The 60 min score showed the opposite effect, possibly indicating a slight disadvantage of the topical anaesthesia. There were no significant differences with regard to time to first request for additional systemic analgesia, to the total dose of systemic pain medication, or to when the patient was eligible for discharge to the ward.

CONCLUSION

The application of topical tetracaine-HCl immediately after wound closure had no positive effects on the course of the postoperative recovery period after strabismus surgery in children. There was no evidence of an effect on pain or emergence agitation.

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.

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.

Prospective, randomized, contralateral eye comparison of tetracaine and proparacaine for pain control in laser in situ keratomileusis and photorefractive keratectomy

Background

Tetracaine and proparacaine are two of the most commonly used medications for providing topical anesthesia in laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). These agents have not been previously compared in a prospective manner to determine their efficacy in these settings.

Methods

This prospective, single-masked, randomized study comprised 256 eyes from 128 consecutive patients being treated with LASIK or PRK who were randomized to receive tetracaine in one eye and proparacaine in the other. The patients were blinded as to which anesthetic agent was used in each eye. Pain levels were graded on a 0–10 scale, and were assessed upon instillation, during surgery, immediately postoperatively, 30 minutes postoperatively, overnight, and on postoperative day 1. Patients were asked 30 minutes after surgery which anesthetic agent they would choose.

Results

Both anesthetic agents resulted in diminished amounts of subjective pain in patients undergoing LASIK and PRK. Tetracaine caused significantly more pain upon instillation than proparacaine for both LASIK and PRK patients. LASIK patients noted significantly less pain 30 minutes after surgery when treated with tetracaine. Significantly more LASIK patients preferred the eye treated with tetracaine. These differences were not present in the PRK group.

Conclusion

Both tetracaine and proparacaine are effective methods of topical anesthesia in LASIK and PRK. Tetracaine caused significantly more pain upon instillation in all patients, but resulted in greater analgesia 30 minutes after surgery in the LASIK group. Patients in the LASIK group expressed a preference for tetracaine over proparacaine. There was no significant drop preference among PRK patients.

Synthetic neurotensin analogues are nontoxic analgesics for the rabbit cornea

PURPOSE

To characterize the analgesic potency and toxicity of topical synthetic neurotensin analogues, and localize neurotensin receptors in the cornea and trigeminal ganglion.

METHODS

Cochet-Bonnet esthesiometry was performed on the rabbit cornea to test the analgesic dose response and duration of effect for two synthetic neurotensin analogues: NT71 and NT72. Receptors for neurotensin were localized in the murine cornea and trigeminal ganglion using quantitative PCR (qPCR), Western blotting, and immunohistochemistry. In vitro toxicity of NT71, NT72, and sodium channel blockers was evaluated using cytotoxicity, single-cell migration, and scratch closure assays performed on rabbit corneal epithelial cells. In vivo toxicity of these agents was assessed using a rabbit laser phototherapeutic keratectomy (PTK) model and histology.

RESULTS

NT71 and NT72 induced potent analgesic effects on the rabbit cornea at concentrations between 1.0 and 2.5 mg/mL, lasting up to 180 minutes. A site-specific distribution of neurotensin receptors was observed in the murine cornea and trigeminal ganglion. NT71 and NT72 did not cause any significant in vitro or in vivo toxicity, in contrast to sodium channel blockers.

CONCLUSIONS

Synthetic neurotensin analogues are potent analgesics that avoid the toxicities associated with established topical analgesic agents. Receptors for neurotensin are present in both the cornea and trigeminal ganglion.

Management of Ocular Trauma in Emergency (MOTE) Trial: A pilot randomized double-blinded trial comparing topical amethocaine with saline in the outpatient management of corneal trauma

Background:

It is unclear whether local anesthetic eye drops can be safely used for the topical anesthesia of patients with minor corneal injury who are discharged from the emergency department (ED).

Objectives:

To assess whether topical 0.4% amethocaine self-administered to a maximum recommended frequency of once every hour for 36–48 h is safe in the management of uncomplicated corneal injury in patients discharged from the ED.

Patients and Methods:

A pilot randomized double-blinded trial comparing topical 0.4% amethocaine with topical normal saline.

Results:

Forty-seven subjects were recruited, with 22 randomized to receive amethocaine and 25 to receive placebo (normal saline). Baseline characteristics, including corneal injury type, were similar in both groups. There were no significant functional or clinical adverse sequelae in the majority of enrolled patients who could be contacted at 2 weeks (17/22 for amethocaine and 21/25 for placebo). Follow-up for the primary study outcome was suboptimal, with only 7/22 from the amethocaine group and 9/25 from the saline group presenting for 36–48 h review; there was a statistically nonsignificant trend for persistence of the corneal defect in the amethocaine group as compared with the saline group (2/7 and 1/9, respectively).

Conclusion:

Compared with saline drops, amethocaine eye drops are not definitely safe but they are effective for topical analgesia in minor corneal injury. Until further definitive studies, topical nonsteroidal agents or long-lasting artificial tears may be preferred for the topical analgesia of minor corneal injury. Return for corneal re-evaluation will necessarily remain suboptimal in an otherwise self-limiting condition, leading to a bias even if study recruitment is good.

Duration of corneal anesthesia following topical administration of 0.5% proparacaine hydrochloride solution in clinically normal cats

OBJECTIVE

To determine duration of corneal anesthesia following topical administration of 0.5% proparacaine hydrochloride solution in domestic shorthair (DSH) cats.

ANIMALS

20 clinically normal DSH cats.

PROCEDURES

Baseline corneal touch threshold (CCT) was established by use of a Cochet-Bonnet aesthesiometer. Treatment consisted of a single 50-microL topical application of an ophthalmic preparation of 0.5% proparacaine solution to a randomly selected eye of each cat. The corneal touch threshold was assessed 1 and 5 minutes after application to the cornea and at 5- minute intervals thereafter for 60 minutes.

RESULTS

Corneal sensitivity, as determined by Cochet-Bonnet aesthesiometry, was significantly reduced from baseline for 25 minutes following topical administration of ophthalmic proparacaine. Maximal anesthetic effect lasted 5 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

As determined by Cochet-Bonnet aesthesiometry, duration of anesthetic effects on the cornea induced by a single topical application of an ophthalmic preparation of 0.5% proparacaine solution in DSH cats is considerably shorter than the reported duration of corneal anesthesia in dogs.

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.

Corneal esthesiometry in the healthy horse

OBJECTIVE

To determine corneal sensitivity in healthy adult horses in order to establish reference values.

ANIMALS STUDIED

One hundred eyes of 50 healthy adult horses.

PROCEDURE

Corneal sensitivity was determined by evaluating the corneal touch threshold (CTT) in five different corneal regions using a Cochet-Bonnet esthesiometer.

RESULTS

Comparing CTT values (in mm filament length) of the five prescribed corneal regions revealed regional variations in corneal sensitivity, with the central region (21.15 +/- 6.23 mm) being the most sensitive, followed by the nasal (20.75 +/- 5.14 mm), temporal (20.70 +/- 5.37 mm), ventral (20.15 +/- 5.88 mm) and dorsal (15.85 +/- 3.70 mm) region. However, differences between the central, nasal, temporal and ventral regions were not statistically significant, whereas the dorsal region was significantly (P < 0.0001) less sensitive compared to the other regions. Division of the horses into three age groups revealed an insignificant decrease in corneal sensitivity with age in the nasal, temporal, ventral and central region, and an insignificant increase with age in the dorsal region. Correlation of corneal sensitivity with age was statistically significant in the central, ventral and temporal region. No statistically significant difference in the CTT was found between left and right eyes and between males and females.

CONCLUSIONS

CTT values in 100 eyes of 50 healthy adult horses evaluated with a Cochet-Bonnet esthesiometer generated reference values. Reference values are necessary to determine alterations of corneal sensation accompanying various eye diseases or systemic diseases.