Corneal Touch Research Articles

Local anaesthetic delivery through indwelling retrobulbar catheters for ocular pain control in horses

AbstractBackgroundEquine corneal disease is common and painful. Current pain mitigation strategies are often suboptimal, especially early in the disease.ObjectivesTo evaluate the effects of local anaesthetic delivery via indwelling retrobulbar catheter on corneal sensitivity, pupil size, pupillary light responses (PLRs), and ocular motility in normal horses.Study designRandomised, controlled crossover experiment.MethodsOne eye was randomly selected from seven horses. A 20‐gauge catheter was placed in the retrobulbar space and injected with 10 mL of 0.5% bupivacaine or 0.9% saline. Cochet–Bonnet esthesiometry (CBE), pupil photogrammetry, PLRs, and oculocephalic reflexes were evaluated before injection (t = 0) and t = 0.25, 1, 3, 6, 9 and 12 h after injection. Following a 7–14 day washout period, this procedure was repeated using the alternative injection solution. Corneal touch thresholds (CTTs) derived from CBE and pupillary areas (PA; as measured from photographs) were compared across time for each group. PLRs and oculocephalic reflexes were compared between groups at each evaluation time point.ResultsSaline did not affect CBE, PA, PLRs or oculocephalic reflexes at any time point. Bupivacaine reduced CTT compared with saline for 6 h, with maximum reduction at t = 1 h (bupivacaine: 0.08 ± 0.20 cm; saline: 4.21 ± 0.39 cm; p < 0.001). Bupivacaine increased PA compared with saline for 3 h, with maximum increase at t = 3 h (bupivacaine: 349.75 ± 84.80 mm2; saline: 194.65 ± 27.03 mm2; p = 0.04). Bupivacaine injection reduced PLRs for 9 h and oculocephalic reflexes for 3 h; saline had no effect. Mild adverse effects included chemosis, blepharoedema, and transiently reduced palpebral reflex.Main limitationsReduction in CTT may not directly translate to pain control in clinical horses with corneal disease. Adverse effects of repeated injections were not evaluated.ConclusionsInjection of bupivacaine via an indwelling retrobulbar catheter in horses reduces corneal sensitivity and may be useful in reducing pain in horses with corneal disease.

Comparison of Proparacaine, Tetracaine, and Oxybuprocaine in Corneal Sensitivity Measurement.

Purpose: This study aimed to determine the onset and duration of action of 3 commercially available topical anesthetic solutions in Brazil, using the Cochet-Bonnet esthesiometer (Luneau®, Paris, France) and to quantitatively assess patient-reported discomfort during application. Methods: A prospective, randomized, masked, and double-blind study was conducted, involving 40 eyes from 21 patients. Patients were administered each one of the topical anesthetics weekly, and corneal sensitivity was measured using the Cochet-Bonnet esthesiometer's corneal touch threshold (CTT). Patients rated the burning sensation using a visual analogue scale (VAS). Results: Among the 21 patients (42.9% male), with a mean age of 31.95 years (±standard deviation = 10.17, range = 22.0-58.0), corneal sensitivity significantly decreased 30 s after application, returning to baseline after 30 min for all groups (P < 0.0001). Significant differences in CTT were observed at 5 min, with proparacaine exhibiting a superior anesthetic effect (P = 0.0003), at 10 min, where tetracaine displayed the most substantial anesthetic effect (P = 0.0135), and at 20 min, where tetracaine demonstrated the highest anesthetic efficacy (P < 0.0001). VAS scores indicated the most intense burning sensation with tetracaine (P < 0.0001). Men reported experiencing more discomfort during instillation compared with women (P = 0.0168). Conclusions: Proparacaine exhibited the fastest onset of action among the 3 topical anesthetics and provided a more comfortable eye sensation during instillation. However, tetracaine demonstrated the longest duration of action despite causing more discomfort.

Ophthalmic Parameters of Healthy Captive Blue-Tongued Skinks (Tiliqua scincoides)

Abstract Normal ophthalmic parameters of the blue-tongued skink (Tiliqua scincoides), one of the largest members of the skink family of lizards, have yet to be evaluated. The objective of this study was to establish baseline ophthalmic parameters for a captive population of 12 healthy, one year old, blue-tongued skinks. Ophthalmic examination, corneal touch threshold, tear production including phenol red thread test (PRTT) and modified Schirmer tear test-2 (mSTT-2), horizontal palpebral fissure length (HPFL), rebound tonometry (TONOVET and TONOVET Plus), and bacterial and fungal culture were performed. The blue-tongued skinks were all amenable to ocular diagnostic testing. Corneal touch threshold (mean ± SD) was 5.48 ± 0.81 cm. PRTT (mean ± SD) was 9.17 ± 6.62 mm/15 seconds. mSTT-2 (mean ± SD) was 2.54 ± 2.72 mm/60 seconds. HPFL (mean ± SD) was 6.96 ± 0.62 mm and was positively correlated with body weight. Intraocular pressure (IOP) assessed using TONOVET (mean ± SD) was 8.43± 1.51 mmHg, while IOP assessed using TONOVET Plus (mean ± SD) was 12.39± 1.54 mmHg. Differences in TONOVET and TONOVET Plus tonometry values were statistically significant (P&amp;lt;0.0001) and TONOVET values positively correlated with body weight. The most common bacterial species identified were Staphylococcus xylosus (10/12) and Staphylococcus sciuri (8/12). Fungal cultures were all negative. One animal had superficial corneal ulceration which resolved with treatment. Ophthalmic examination and testing is readily performed in blue-tongued skinks. These parameters may be useful for ocular assessment of this species in a clinical setting.

Improving rat welfare through the development of a peribulbar anaesthesia technique for ophthalmic procedures: A preliminary study.

Rats are a commonly used animal model for the study of the pathogenesis and novel treatments of glaucoma, which is induced experimentally using invasive, painful procedures. Peribulbar anaesthesia (PBA) is frequently used in people and domestic animals prior to ophthalmic surgeries to provide excellent perioperative analgesia. Our goal was to develop a PBA technique adapted to rat anatomy, improving the welfare of animals used as a model for glaucoma. Eighteen rat cadavers (n = 36 eyes) were used to establish the optimal needle insertion location. Five injection techniques using 0.1 mL/100 g lidocaine 2% and a contrast agent (1:1 volume ratio) were compared via computed tomography (CT). CT images were scored for injectate distribution at four locations: extraconal, intraconal, around the optic nerve and at the orbital fissure (scale 0-8, where 0 = none and 8 = excellent). Median scores using the dorso-medial-75° (5; range 2-6) and medial-canthus (4.5; range 2-8) injection techniques were not different from the dorso-medial-45° (4; range 3-6) technique and were higher (better distribution) compared with mid-ventral (3; range 2-5) and ventro-lateral (2; range 1-3) techniques. The two superior techniques were used in two experimental rats (n = 4 eyes) to determine the volume of bupivacaine 0.5% necessary to affect corneal touch threshold (CTT) and periocular skin sensitivity (PSS). A volume of 0.05 mL/100 g decreased CTT and PSS for several hours, while a larger volume produced excessively long effects. Dorso-medial-75° or medial-canthus PBA using 0.05 mL/100 g bupivacaine are likely to provide ocular and periocular analgesia in rats, with minor transient adverse effects.

Topical ropivacaine hydrochloride 0.5% and lidocaine hydrochloride 2% significantly reduce corneal sensitivity without short-term negative side effects in horses.

To evaluate corneal sensitivity and acute side effects following application of ropivacaine hydrochloride 0.5% and lidocaine hydrochloride 2% on the healthy equine cornea. Eight healthy adult horses. A randomized, masked, crossover study design was utilized. Baseline Semiquantitative Preclinical Ocular Toxicology (SPOT) scores and corneal touch thresholds (CTT) using a Cochet-Bonnet esthesiometer were recorded and measured, respectively, for eight healthy adult horses before medication application. Commercially available eyewash was used as a negative control. Ropivacaine hydrochloride 0.5% or lidocaine hydrochloride 2% solution was sprayed on a randomly selected eye, and the contralateral eye received eyewash. CTT was measured in both eyes at 1, 5, 15, 25, 35, 45, 55, 65, and 75 min post-application. Post-application SPOT scores were recorded immediately following the trial. Linear mixed model statistical analyses (mean ± standard error) were performed (p < .05). Mean eyewash CTT (3.41 cm ± 0.464) was significantly different from ropivacaine-treated (1.44 cm ± 0.562) (p = .008) and lidocaine-treated eyes (1.75 cm ± 0.562) (p = .024); CTT was not significantly different between drug groups (p = .88). Time to maximum anesthesia was not significantly different between ropivacaine (13.25 min ± 3.353) and lidocaine (16.25 min ± 3.353) (p = .40). No side effects were appreciated as confirmed by SPOT. Ropivacaine and lidocaine similarly decreased corneal sensitivity when applied topically without clinically evident short-term ocular side effects. Lidocaine may be preferable in clinical settings due to its large, multi-use vials and similar effects to ropivacaine.

Minimally invasive approach for the management of tube–corneal touch in aniridic glaucoma

Aniridic glaucoma, with a prevalence of around 50% in aniridia patients, often requires surgical management with glaucoma drainage device implantation. It is associated with many complications related to the tube or plate. We present a case of tube endothelial touch in aniridic glaucoma where repositioning of the Ahmed glaucoma valve tube was performed using transcameral prolene suture fixation. The advantage of this technique is that it is minimally invasive and maintains the stability of the anterior chamber throughout the surgery.

Proliferative feline eosinophilic keratitis: Case Report

A mixed-breed cat was presented at the Federal Rural University of Pernambuco’s veterinary hospital. The animal showed an irrigated corneal lesion, congestive conjunctiva and touch sensitivity. We carried out tests for pupillary reflexes and the fluorescein test. From those tests, it was found that pupil reflexes remained unchanged and the fluorescein test was negative. Definitive diagnosis was made upon a second visit to the hospital, through observation of corneal material strips taken via swab, scraping and imprint. The definitive diagnosis was Eosinophilic keratoconjunctivitis.

Effects of subconjunctival ropivacaine, liposomal bupivacaine, and mepivacaine on corneal sensitivity in healthy horses.

To evaluate corneal sensitivity and adverse events following subconjunctival administration of three local anesthetics in horses. Randomized, masked, crossover study. Twelve healthy adult mares. The subconjunctival space of the treated eye was injected with 0.2 mL of liposomal bupivacaine (1.3%), ropivacaine (0.5%), or mepivacaine (2%). All horses received each medication once and the contralateral eye received saline (control). Corneal touch threshold (CTT) was measured using a Cochet-Bonnet esthesiometer before sedation, after sedation, and at specified intervals until it returned to baseline. Ocular examinations were performed at 24-, 72, and 168 h post-injection to monitor for adverse effects. The mean total time of anesthesia (TTA) was 168.3 min for ropivacaine, 169.2 min for liposomal bupivacaine, 103.3 min for mepivacaine and 30.7 min for the control. TTA for liposomal bupivacaine (p < .001) and ropivacaine (p = .001) was longer than the control. TTA for mepivacaine was not different from the control (p = .138), liposomal bupivacaine (p = .075) or ropivacaine (p = .150). Injection site hemorrhage reduced TTA regardless of treatments (p = .047). No adverse effects attributed to injections were noted. All three medications were well tolerated. Subconjunctival administration of ropivacaine and liposomal bupivacaine resulted in longer TTAs compared to the control; however, their TTAs were not different from that of mepivacaine. Subconjunctivally administered liposomal bupivacaine and ropivacaine are viable options to provide prolonged corneal analgesia in horses. Future studies are needed to assess the efficacy in diseased eyes.

Decreased corneal subbasal nerve fiber length and density in diabetic dogs with cataracts using in vivo confocal microscopy.

To determine whether there is a difference in corneal sensitivity and corneal subbasal nerve plexus (CSNP) morphology in cataractous dogs with diabetes mellitus (DM) versus without DM. Twenty six domestic dogs with cataracts of various breeds presented for phacoemulsification, 13 with DM and 13 without DM. The inclusion criteria for the study were dogs with bilateral cataracts and no clinical evidence of corneal disease. The diabetic group had documented hyperglycemia and was currently treated with insulin. The non-diabetic group had no evidence of DM on examination and bloodwork. Complete ophthalmic examination, corneal esthesiometry, and in vivo confocal microscopy of the CSNP was performed for both eyes of each dog. The CSNP was evaluated using a semi-automated program and statistically analyzed. The mean (±SD) CSNP fiber length was significantly decreased in diabetic (3.8 ± 3.0 mm/mm2 ) versus non-diabetic (6.7 ± 1.9 mm/mm2 ) dogs. Likewise, the mean (±SD) fiber density was significantly decreased in diabetic (8.3 ± 3.1 fibers/mm2 ) versus non-diabetic (15.5 ± 4.9 fibers/mm2 ) dogs. The corneal touch threshold was significantly reduced in diabetic (2.1 ± 0.8cm) versus non-diabetic (2.8 ± 0.4cm) dogs. There was a non-significant trend towards subclinical keratitis in diabetic (9/13) versus non-diabetic (4/13) dogs. Morphological and functional abnormalities of the CSNP were present in dogs with DM, including decreased fiber length, fiber density, and corneal sensitivity. These findings are consistent with diabetic neuropathy and could contribute to clinically significant corneal complications after cataract surgery.

Single Administration of Intracameral Bimatoprost Implant 10µg in Patients with Open-Angle Glaucoma or Ocular Hypertension.

IntroductionThis study evaluated the intraocular pressure (IOP)-lowering efficacy and safety of a single intracameral administration of bimatoprost implant 10 µg in adults with open-angle glaucoma or ocular hypertension.MethodsTwo identically designed, randomized, 20-month, parallel-group, phase 3 clinical trials (one study eye/patient) compared three administrations of 10- or 15-µg bimatoprost implant (day 1, weeks 16 and 32) with twice-daily topical timolol maleate 0.5%. An open-label, 24-month, phase 1/2 clinical trial compared one or two implants administered in the study eye with once-daily topical bimatoprost 0.03% in the fellow eye. Separate analyses of the pooled phase 3 and phase 1/2 study datasets evaluated outcomes in the 10-µg bimatoprost implant and comparator treatment arms after a single implant administration, up to the time of implant re-administration or rescue with IOP-lowering medication.ResultsIn the phase 3 studies, 10-µg bimatoprost implant single administration demonstrated IOP reductions (hour 0) of 4.9–7.0 mmHg through week 15 from a mean (standard deviation, SD) baseline IOP of 24.5 (2.6) mmHg (n = 374); IOP in the topical timolol BID group was reduced by 6.0–6.3 mmHg from a mean (SD) baseline IOP of 24.5 (2.6) mmHg (n = 373). In the phase 1/2 study (n = 21), median time to use of additional IOP-lowering treatment (Kaplan–Meier analysis) was 273 days (approximately 9 months), and 5 of 21 enrolled patients (23.8%) required no additional IOP-lowering treatment up to 24 months after single administration. In each study, after a single implant administration there were no reports of corneal edema, corneal endothelial cell loss, or corneal touch, and no patients had 20% or greater loss in corneal endothelial cell density.ConclusionsBimatoprost implant single administration lowers IOP and has a favorable safety profile. Additional studies are needed to further evaluate the duration of effect and factors predicting long-term IOP lowering after a single implant administration.Trial registration numbersClinicalTrials.gov NCT02247804, NCT02250651, and NCT01157364.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40123-022-00527-6.

The crested caracara (Caracara plancus) eye: Morphologic observations and results of selected diagnostic tests.

To provide a descriptive investigation about relevant features of the crested caracara's eye (Caracara plancus) and bony orbit, as well as provide data for ophthalmic tests. Morphological observations and the following diagnostic tests were performed: Schirmer tear test (STT), conjunctival flora evaluation, corneal touch threshold (CTT), intraocular pressure (IOP), central corneal thickness (CCT), B-mode ocular biometry, palpebral fissure length (PFL), and corneal diameter (CD) in 19healthy birds, plus two macerated skulls. Not all birds were used for each test. STT: 7.84±3.05mm/min; CTT: 2.46±1.10cm; IOP: 19.18±3.07mmHg; CCT: 0.31±0.02mm; PFL: 13.32±1.06mm; CD: 10.26±2.43mm; Axial globe length: 1.89±0.06cm; Anterior chamber depth: 0.27±0.06cm; Lens axial length: 4.55±0.06cm; Vitreous chamber depth: 1.2±0.07cm. The most frequent conjunctival bacterial isolates were Corynebacterium sp. (10/23.8%), Staphylococcus sp. (9/21.42%), Streptococcus sp. (7/16.6%), and E.coli (7/16.66%). The large lateral part of the palatine bone likely plays a role in the ventral protection of the globe against the impact of prey. Observed results are generally reflective of increased body mass compared to other Falconiformes, with values approaching those of similar sized Accipitriformes. These data may help veterinarians recognize peculiar morphologic features and perform a more accurate diagnosis of eye diseases of this avian species.

Evaluation of corneal anaesthesia after the application of topical 0.5% bupivacaine, 2% lidocaine and 0.4% oxybuprocaine in normal horses

ObjectiveTo compare the corneal anaesthetic effect of 0.5% bupivacaine, 2% lidocaine and 0.4% oxybuprocaine on normal equine eyes. Study designProspective, blinded crossover study. AnimalsA group of 10 clinically healthy horses. MethodsCorneal sensitivity was determined in each eye by measuring corneal touch threshold (CTT). The study had three phases. Each subject was randomly given one of the three treatments followed by a 72 hour washout period. Every horse received all treatments. Baseline CTT was recorded prior to anaesthetic instillation (T0) then CTT was measured 5 and 10 minutes after (T1 and T2, respectively), then 20 to 90 minutes (T3 to T10) at 10 minute intervals. CTT data were compared among treatments at each time point using the Friedman test p < 0.05. ResultsMedian (range) baseline CTT was 51.3 (25.0–60.0) mm for bupivacaine, 50.0 (40.0–55.0) mm for oxybuprocaine and 55.0 (30.0–60.0) mm for lidocaine. All treatments caused a significant decrease in CTT at T1. The lowest CTT was observed at T3 with bupivacaine and oxybuprocaine treatments. Median CTTs at this time point were 18.7 (5.0–25.0) mm and 28.7 (25.0–40.0) mm, respectively. The lowest CTT with lidocaine treatment was 28.7 (20.0–50.0) mm at T6 (50 minutes). At T3, CTT was significantly lower with the bupivacaine treatment compared with oxybuprocaine and lidocaine treatments (p < 0.0074). There was no significant difference in CTT values between T1 and T6 for bupivacaine, between T1 and T7 for lidocaine, and between T1 and T8 for oxybuprocaine. Duration of the maximum effect was 45 minutes for the bupivacaine, 55 minutes for the lidocaine and 65 minutes for the oxybuprocaine treatment. Conclusions and clinical relevanceAdministration of a 0.5% injectable solution of bupivacaine or a 2% lidocaine had similar anaesthetic effect to the commonly used oxybuprocaine. Therefore, they might be used as alternatives for corneal anaesthesia.

Age and Sex Variation in the Duration of Action and Corneal Touch Threshold (CTT) following Instillation of 0.5% Topical Ophthalmic Proparacaine and Tetracaine Hydrochlorides.

Purpose We investigated the effect of age and sex on corneal touch threshold (CTT) and duration of action following administration of 0.5% topical ophthalmic proparacaine and tetracaine hydrochlorides. Methods A prospective, randomized, subject-masked, crossover study design was used. Two hundred and forty human volunteers were enrolled in the study. Corneal touch threshold (CTT) was determined using a Cochet-Bonnet esthesiometer. CTT was measured every 15 seconds for the first 1-minute and at 5-minute intervals subsequently for a period of 40 minutes after the application of each anesthetic. CTT and duration of action of the ophthalmic solutions were tested for statistical significance using repeated measures ANOVA. Results The total duration of effect was 20 minutes for females and 25 minutes for males for both anesthetics. The total duration of the effect of both solutions decreased with increasing age; however, elderly participants had the longest duration (5 minutes) of the maximal effect (minimum CTT) of the two ophthalmic preparations. There was a significant influence of sex, F (2.39, 569.65) = 2.86, p=0.04; F (3.48, 828.19) = 4.41, p=0.003, and age, F (4.78, 566.18) = 8.97, p < 0.001; F (7.19, 852.56) = 20.55, p < 0.001 on CTT following application of proparacaine hydrochloride and tetracaine hydrochloride, respectively. Conclusion CTT and duration of anesthetic effect after instillation of 1 drop of 0.5% proparacaine hydrochloride and 0.5% tetracaine hydrochloride vary based on sex and age.

Corneal neuropathic pain in irritable bowel syndrome: clinical findings and in vivo corneal confocal microscopy.

Ocular discomfort is a common symptom in central sensitization syndromes. The aim of this study was to evaluate ocular surface discomfort and related corneal changes in patients with irritable bowel syndrome. Twenty-nine patients with IBS (20 female, 9 male, mean age: 45.3 ± 10.1years) and 37 healthy control subjects (25 female, 12 male, mean age: 44.95 ± 9.76years) were included. A detailed ophthalmological examination was performed to all participants including tear break-up time (TBUT) and Schirmer test I with anesthetic (SIT). Ocular discomfort was evaluated using the ocular surface disease index (OSDI) questionnaire and corneal sensation was evaluated with Cochet-Bonnet esthesiometer. Corneal subbasal nerve plexus was evaluated with in vivo corneal confocal microscopy (IVCM). There was no significant difference between the groups for age, gender distribution, and visual acuity. OSDI scores were significantly higher (p = 0.008) and TBUT was significantly reduced in patients with IBS compared to controls (p = 0.001 for right eye, p = 0.014 for left eye). However, there was no significant difference in corneal touch sensation and SIT results between the groups. IVCM revealed that corneal nerve fiber density, corneal nerve branch density, and corneal nerve fiber length were significantly reduced in patients with IBS (p < 0.001, p < 0.001, and p = 0.023, respectively). Patients with IBS have increased dry eye-associated ocular surface complaints and nerve fiber loss in corneal subbasal nerve plexus. IBS should be remembered in the differential diagnosis, when there is discordance between the level of ocular surface discomfort and dry eye disease associated corneal findings.

Mini-Scleral Contact Lens for Asian Eyes Post-Penetrating Keratoplasty with Smaller Palpebral Aperture: Case Reports

PurposeTo report the use of miniscleral contact lenses (MSCLs) with diameter of 14.7 mm for Asian eyes to improve vision in patients after penetrating keratoplasty (PKP) surgery.MethodsTwo patients with high corneal astigmatism post-PKP were evaluated for a contact lens fitting. Visual acuity, slit lamp, and anterior segment OCT findings before and after fitted the lens of 14.7 mm diameter were recorded.ResultsA Kmax of case 1 and 2 were 52.8 D and 76.9 D, respectively at the first visit. Both patients were successfully fit with MSCLs, showing adequate corneal clearance of over 250 μm with no corneal touch on OCT and sufficient limbal clearance and edge alignment. MSCLs use resulted in improved comfort and visual acuity of 20/30 or better.ConclusionMSCLs with diameter of 14.7 mm can be considered a safe and effective option for patients with highly steep corneas post-PKP surgery in Asian eyes.

Pigment Epithelium-Derived Factor Peptide Promotes Corneal Nerve Regeneration: An In Vivo and In Vitro Study.

PurposeTo investigate the potential of a pigment epithelium-derived factor (PEDF) peptide 44-mer to promote nerve regeneration in a rabbit corneal nerve injury model to demonstrate its neurotrophic ability in cultivated mouse trigeminal neuron cells.MethodsSubconjunctival or intrastromal injection of 44-mer on the cornea was performed in a rabbit model of corneal nerve injury created by corneal epithelial debridement. Immunocytochemical analysis (44-mer, anti-tubulin III, SMI312, CD11b, and α-SMA) and in vivo confocal microscopy were performed. Corneal sensation was estimated using a Cochet-Bonnet corneal esthesiometer. Primary cultivated mouse trigeminal neurons were used to examine the in vitro neurotrophic ability of 44-mer. The cellular morphology and the immunocytochemical staining with anti-tubulin III and SMI312 in different concentrations of 44-mer were compared, and a quantitative assessment of neurite outgrowth was performed.ResultsImmunohistochemical staining showed the retention of 44-mer in the corneal stroma for at least 7 days after a single dose of corneal intrastromal injection and promoted corneal nerve regeneration revealed by in vivo confocal microscopy. Corneal esthesiometer demonstrated gradual recovery of the corneal sensation in 44-mer-treated eyes with a lower corneal touch threshold than wounded vehicles and closer to baseline at 3 weeks after corneal injury (P < 0.001). In vitro studies showed a dose-dependent neurotrophic effect of 44-mer in cultivated trigeminal neuron cells.ConclusionsThe 44-mer showed in vivo and in vitro corneal neurotrophic abilities. Our results suggest that intrastromal injection of 44-mer into the corneal stroma may have a potential role in treating diseases related to corneal nerve damage.

Effects of Intravenous Flunixin Meglumine, Phenylbutazone, and Acupuncture on Ocular Pain Scores in the Horse: A Pilot Study

In this controlled, blinded, randomized block pilot study, the main objective was to evaluate the effectiveness of intravenous flunixin meglumine, phenylbutazone, and acupuncture on ocular pain relief using a multifactorial pain scale in the horse. Four experimental horses underwent corneal epithelial debridement in four sessions, when a randomly selected treatment or a control was used. All horses were pain scored before corneal wounding, then at 18 time points, when 11 parameters were allocated. Differences in the area under the curve of pain scores between the treatment groups were analyzed using a paired t-test. Corneal pain was significantly reduced by the third postoperative day (P = .03) when all 11 parameters were considered. Five ocular signs showed significant differences between treatments and proved to be good indicators of ocular pain. The other parameters (heart rate, corneal touch threshold, respond to palpation, and three behavioral parameters) were determined to be irrelevant when evaluating the degree of pain. When considering the five ocular signs, the lowest pain score was attributed to the flunixin meglumine group (1114), followed by the electroacupuncture group (1356), the phenylbutazone group (1397), and the control group (1580). There were significantly lower pain scores (P = .01) in the flunixin meglumine group when compared with those recorded in the control group during the first 46 hours. Flunixin meglumine was the most effective treatment at reducing ocular pain in the horse. In the future, a reduction in the number of pain score parameters and more precisely defined image evaluation criteria could be used.

Effects of orally administered gabapentin, tramadol, and meloxicam on ocular variables in healthy dogs.

To determine the effects of gabapentin, tramadol, and meloxicam on tear production, intraocular pressure (IOP), pupillary diameter, tear break-up time, and corneal touch threshold in healthy dogs when given orally for 3 days. 9 healthy research Beagles. A randomized, blinded, case-crossover study with a 6-sequence, 3-treatment, and 3-period design was performed. A 7-day acclimation period was followed by 3 treatment phases, each with a 3-day treatment period followed by a 7-day washout period for 3 different drugs. Block randomization was used to group dogs for treatments with drug A (gabapentin), B (tramadol), or C (meloxicam). Measurements of tear production, IOP, pupillary diameter, tear break-up time, and corneal touch threshold were performed on a schedule. A generalized mixed-effects linear regression model was created for each ocular variable, accounting for repeated measures within individuals. Intraocular pressure was the only variable to have differed substantially between the first 5 and last 2 days of the acclimation period. When treatment phase, day, time of day, dog identification, baseline value, and eye were accounted for, the mean IOP was lower for dogs during treatment phases with gabapentin or tramadol, compared with meloxicam, but this difference was not considered clinically meaningful. Results indicated that a minimum 5-day acclimation period is necessary for IOP measurements to return to baseline in dogs. The statistically identified effect of gabapentin and tramadol on IOP in dogs of the present study warrants further investigation. It is possible that at higher dosages, or in dogs with glaucoma, this effect may become clinically significant.

Effects of topical application of 0.4% oxybuprocaine hydrochloride ophthalmic solution and 1% ropivacaine hydrochloride on corneal sensitivity in rats

The aim of the present study was to determine and compare the degree and duration of corneal anesthesia following topical application of 0.4% oxybuprocaine hydrochloride ophthalmic solution and 1% ropivacaine hydrochloride treatment in healthy rats. A randomized, blinded, crossover study was conducted on 20 healthy adult Wistar rats, following complete physical and ophthalmological examination. Baseline corneal touch threshold (CTT) was determined in the central corneal area of both eyes with a Cochet–Bonnet aesthesiometer, in mm filament length. Oxybuprocaine was randomly applied to one eye and 0.9% sterile sodium chloride solution was instilled into the contralateral eye. Subsequent CTT measurements were performed in both eyes 5 minutes after topical application and at 5-minute intervals thereafter for 75-minutes in the anesthetized eye. Following a 2-week washout period, this protocol was repeated with ropivacaine. Quantitative data were summarized as mean ± standard deviation, median and inter-quartile range (Q1–Q3). Repeated measures data were analyzed over time and between treatments using Friedman test and Wilcoxon signed-rank test with Bonferroni adjustment (p < 0.05). Baseline CTT values were 60 mm in all eyes. With oxybuprocaine, CTT values decreased significantly for 65 minutes (0–55 mm; p = 0.002) when compared with baseline; the maximal anesthetic effect (no blink response at 5 mm filament length) was maintained for up to 15 minutes (p < 0.0001). With ropivacaine, CTT values were significantly lower than baseline for 30 minutes (0–55 mm; p = 0.002), with a maximal anesthetic effect recorded at 5 minutes in 18 eyes (p < 0.0001). Oxybuprocaine induced a significantly lower CTT than ropivacaine (p = 0.002) from 10 to 65 minutes following topical application. Both anesthetic agents induced significant corneal anesthesia; however, oxybuprocaine provided a greater and longer anesthetic effect, making it more suitable for potentially painful ophthalmologic procedures.

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

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. 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 75min. The topical protocol involved 3 treatment conditions, separated by a 2-week washout period: proparacaine, tramadol alone, and tramadol in combination with dexmedetomidine. 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 1-5min in 18 eyes and ranged from 5 to 25min. Co-administration of dexmedetomidine to tramadol resulted in significantly increased CTT values from 5 to 20min following topical application, compared to tramadol alone (p < 0.0083), and complete corneal anesthesia was achieved in only 14 out of 20 treated eyes. 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.