Corneal collagen cross-linking as treatment for infectious and noninfectious corneal melting in cats and dogs: results of a prospective, nonrandomized, controlled trial

Evaluation of photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) in feline infectious keratitis-patient demographics, treatment protocols, risk factors, and treatment outcome: a retrospective study

OBJECTIVES

To describe patient demographics and treatment protocols in a population of feline patients undergoing photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) as an adjunctive treatment for infectious keratitis. Furthermore, to determine the proportion of PACK-CXL treatment success in the population studied, explore risk factors for treatment failure, and provide recommendations for future PACK-CXL clinical studies.

MATERIALS AND METHODS

Records from four veterinary ophthalmology practices were reviewed to identify eligible patients and extract data. Recorded variables included patient-related factors, ocular examination findings, PACK-CXL protocol parameters, and treatment outcome.

RESULTS

Records for 153 cats (154 eyes) were included. Median age in the treatment success group was 8 years (interquartile range (IQR) 4-12), with a median ulcer depth of 30% (IQR 30-40). Median age in the treatment failure group was 10.5 years (IQR 4.75-12) with a median ulcer depth of 45.9% (IQR 30-75). Persian cats were the most represented brachycephalic breed (52 out of 64 cats). Modified PACK-CXL protocols were used, including fast energy delivery (134 eyes), and increased fluence (52 eyes). The overall proportion of success was 88% (95% CI 84-93), which was variable between clinics. Eighty-two of 89 mesocephalic cat eyes (92%), and 54 of 65 brachycephalic cat eyes (83%) were classified as treatment successes.

CONCLUSIONS

PACK-CXL appeared to be a useful, adjunctive therapeutic modality for the treatment of infectious keratitis in the feline patient population presented here. Brachycephalic cats, older cats, and those with deeper ulcers may be at increased risk for treatment failure.

How does atmospheric pressure cold helium plasma affect the biomechanical behaviour on alkali-lesioned corneas?

BACKGROUND

Melting corneal ulcers are a serious condition that affects a great number of animals and people around the world and it is characterised by a progressive weakening of the tissue leading to possible severe ophthalmic complications, such as visual impairment or blindness. This disease is routinely treated with medical therapy and keratoplasty, and recently also with alternative regenerative therapies, such as cross-linking, amniotic membrane transplant, and laser. Plasma medicine is another recent example of regenerative treatment that showed promising results in reducing the microbial load of corneal tissue together with maintaining its cellular vitality. Since the effect of helium plasma application on corneal mechanical viscoelasticity has not yet been investigated, the aim of this study is first to evaluate it on ex vivo porcine corneas for different exposition times and then to compare the results with previous data on cross-linking treatment.

RESULTS

94 ex vivo porcine corneas divided into 16 populations (healthy or injured, fresh or cultured and treated or not with plasma or cross-linking) were analysed. For each population, a biomechanical analysis was performed by uniaxial stress-relaxation tests, and a statistical analysis was carried out considering the characteristic mechanical parameters. In terms of equilibrium normalised stress, no statistically significant difference resulted when the healthy corneas were compared with lesioned plasma-treated ones, independently of treatment time, contrary to what was obtained about the cross-linking treated corneas which exhibited more intense relaxation phenomena.

CONCLUSIONS

In this study, the influence of the Helium plasma treatment was observed on the viscoelasticity of porcine corneas ex vivo, by restoring in lesioned tissue a degree of relaxation similar to the one of the native tissue, even after only 2 min of application. Therefore, the obtained results suggest that plasma treatment is a promising new regenerative ophthalmic therapy for melting corneal ulcers, laying the groundwork for further studies to correlate the mechanical findings with corneal histology and ultrastructural anatomy after plasma treatment.

Risk factors for corneal conjunctival grafting failure in dogs at four referral centers in the southern United States (203 patients): 2015-2021

OBJECTIVE

To report risk factors associated with conjunctival graft failure in dogs at four referral specialty centers.

PROCEDURES

Records of 203 dogs (229 eyes) undergoing conjunctival graft repair of ulcerative keratitis at four hospitals from 2015 to 2021 were reviewed. Success was defined as full graft integration with globe retention at the last postoperative evaluation; vision status was reported separately. Factors assessed included patient signalment, ophthalmic examination findings, surgical factors, and follow-up information.

RESULTS

Conjunctival graft failure occurred in 11% (25/229) of eyes and was significantly associated with ulcer depth, with corneal perforations having increased odds of graft failure compared with descemetoceles (odds ratio [OR] = 3.22, 95% confidence interval [CI] 1.11-9.32; p = .03) and stromal ulcers (OR = 10.89 [95% CI 1.38-86.18], p = .02). Brachycephalic dogs were significantly more likely than non-brachycephalic dogs to experience graft failure (OR = 5.02 [95% CI 1.42-17.74], p < .01). Surgery on the opposite eye relative to surgeon handedness was significantly associated with an increased risk of graft failure (OR 4.28 [95% CI 1.53-11.94], p < .01). The use of 7-0 and 8-0 suture versus 9-0 (p = .03) and the use of a combined simple continuous and interrupted pattern (p = .03) were significantly associated with an increased risk of graft failure. At the last follow-up, (median 61.5 days), 87% of dogs were visual.

CONCLUSIONS

Corneal perforations, surgery on the opposite eye relative to surgeon handedness, suture size and pattern, and brachycephalic conformation were significantly associated with an increased risk of graft failure in this study. These characteristics can be considered when determining prognosis for ulcerative keratitis requiring surgical intervention.

Evaluation of risk factors for treatment failure in canine patients undergoing photoactivated chromophore for keratitis - corneal cross-linking (PACK-CXL): a retrospective study using additive bayesian network analysis

BACKGROUND

Infectious keratitis is a common ophthalmic condition in canine patients. Sequelae can include keratomalacia and corneal perforation, a vision threatening outcome. Photoactivated chromophore for keratitis - corneal cross-linking (PACK-CXL) is a non-surgical, adjunctive treatment method for infectious keratitis. The goal of this retrospective, multicenter study was to determine risk factors for treatment failure following PACK-CXL in canine patients suffering from suspected infectious keratitis. Medical records from four veterinary ophthalmology services were reviewed, and information related to patient demographics, ophthalmic findings, the PACK-CXL protocol used, and epithelialization time was collected and analyzed. Due to the potential for intervariable relationships, an additive Bayesian network (ABN) analysis was performed to evaluate these complex relationships.

RESULTS

Records for 671 eyes (668 dogs) were included in the analysis. Based on the ABN, in the population included here, patients who underwent an accelerated PACK-CXL protocol were less likely to experience treatment failure versus patients treated with a slow protocol. Mutual dependencies between exposure variables were identified by ABN, which would have been overlooked using classical regression. Corneal re-epithelialization time was shortened following PACK-CXL combined with topical medical therapy compared to PACK-CXL alone.

CONCLUSIONS

No risk factors associated with treatment failure were identified in the population included in the present study. Canine patients may benefit from the use of accelerated PACK-CXL protocols, especially when combined with topical antibiotics and anti-collagenolytic therapy. The reasons for this apparent positive impact on treatment outcome remain unclear.

Multidirectional corneoconjunctival transposition in the treatment of large keratomalacia in 7 dogs and 5 cats

OBJECTIVE

To describe the use of multidirectional corneoconjunctival transposition (CCT) as a surgical treatment for large keratomalacia.

METHOD

A prospective study including dogs and cats initially presenting with keratomalacia larger than 6 × 6 mm and affecting more than half of the corneal thickness. Signalment, concurrent eye diseases, ulcer size, bacterial culture and susceptibility testing results, follow-up, and outcome were recorded. The surgery consisted of harvesting of two or three opposite corneoconjunctival grafts, after removal of the malacic tissue using a square-edge keratectomy. The medical treatment consisted of administration of topical and systemic antibiotics, topical atropine, and N-acetylcysteine. Follow-up examinations were performed at D7, D14, D21, and D28, and then at various time points. The corneal clarity score (CCS) was recorded upon completion of the follow-up period.

RESULTS

Seven dogs and five cats were included. Brachycephalic dogs were overrepresented, with no breed predisposition in cats. Concurrent eye diseases were corneal pigmentation in three dogs, hypopyon in two dogs, nictitating membrane wound in one dog, and corneal perforation in one cat. The size of the keratomalacia ranged from 6 × 6 to 9.5 × 11.5 mm. The short-term complications were suture dehiscence (two of 12) and progression of the keratomalacia (one of 12). The long-term complications were corneal pigmentation (10 of 12), corneal epithelial inclusion cyst (two of 12), and marginal synechiae (one of 12). All animals were sighted at the last follow-up. The median CCS was G3 (range G2-G4).

CONCLUSION

Multidirectional CCT is an effective surgical treatment for large keratomalacia in dogs and cats.

The bactericidal effect of two photoactivated chromophore for keratitis-corneal crosslinking protocols (standard vs. accelerated) on bacterial isolates associated with infectious keratitis in companion animals

Background

Bacterial corneal infections are common and potentially blinding diseases in all species. As antibiotic resistance is a growing concern, alternative treatment methods are an important focus of research. Photoactivated chromophore for keratitis-corneal crosslinking (PACK-CXL) is a promising oxygen radical-mediated alternative to antibiotic treatment. The main goal of this study was to assess the anti-bactericidal efficacy on clinical bacterial isolates of the current standard and an accelerated PACK-CXL treatment protocol delivering the same energy dose (5.4 J/cm²).

Methods

Clinical bacterial isolates from 11 dogs, five horses, one cat and one guinea pig were cultured, brought into suspension with 0.1% riboflavin and subsequently irradiated. Irradiation was performed with a 365 nm UVA light source for 30 min at 3mW/cm² (standard protocol) or for 5 min at 18mW/cm² (accelerated protocol), respectively. After treatment, the samples were cultured and colony forming units (CFU’s) were counted and the weighted average mean of CFU’s per μl was calculated. Results were statistically compared between treated and control samples using a linear mixed effects model.

Results

Both PACK-CXL protocols demonstrated a significant bactericidal effect on all tested isolates when compared to untreated controls. No efficacy difference between the two PACK-CXL protocols was observed.

Conclusion

The accelerated PACK-CXL protocol can be recommended for empirical use in the treatment of bacterial corneal infections in veterinary patients while awaiting culture results. This will facilitate immediate treatment, the delivery of higher fluence PACK-CXL treatment within a reasonable time, and minimize the required anesthetic time or even obviate the need for general anesthesia.

In vitro susceptibility of canine corneal bacterial pathogens to three cross-linking protocols

OBJECTIVE

To assess in vitro antibacterial efficacy of three cross-linking (XL) protocols on bacteria associated with canine ulcerative keratitis.

METHODS

Three XL protocols: UVA 3 mW/cm² for 60 min, UVA 3 mW/cm² for 30 min, and UVA 30 mW/cm² for 3 min with and without application of riboflavin and a riboflavin-only protocol were performed in vitro on the four most common bacterial genera isolated from cases of canine ulcerative keratitis treated at Dick White Referrals, UK. Zones of bacterial growth inhibition (GIZ) associated with treatment were measured and compared.

RESULTS

The four most common isolates were Pseudomonas aeruginosa (PA) (48/140, 34.3%), Streptococcus spp. (32/140, 22.9%), Staphylococcus spp. (24/140, 17.1%) and Escherichia coli (EC) (11/140, 7.9%). PA, EC, Streptococcus canis (SC), and Staphylococcus pseudintermedius (SP), isolated from canine corneas, were selected for testing. EC and SC demonstrated growth inhibition following all UVA/riboflavin protocols. PA and SP only displayed growth inhibition following the 60 min UVA/riboflavin protocol. GIZ areas for 60 min UVA/riboflavin protocols were significantly greater than 30 and 3 min UVA/riboflavin protocols (p < .01) and there was no significant difference between 30 and 3 min UVA/riboflavin protocols. In respect to GIZ areas, EC was significantly more susceptible to XL than SP (p = <.01).

CONCLUSIONS

All UVA/riboflavin XL protocols caused growth inhibition of EC and SC in vitro. PA and SP did not show clear growth inhibition in vitro following exposure to XL protocol settings of UVA 3 mW/cm² for 30 min and UVA 30 mW/cm² for 3 min.

Riboflavin/UV-A corneal phototherapy as stand-alone management of ulcerative keratitis in dogs

Corneal ulcers are one of the most common ocular disorders in veterinary ophthalmology and several factors can negatively influence the efficacy of the currently available therapeutic options, leading to a loss of corneal transparency and, thus, vision. Twenty-five dogs with clinical signs of corneal ulcers were randomised to receive either corneal phototherapy (16 dogs; study group) or topical standard medical therapy (9 dogs; control group). The riboflavin/UV-A corneal phototherapy (PACK-CXL) consisted in the application of a riboflavin ophthalmic solution (Visioflavin®; Vision Engineering Italy srl, Rome, Italy) onto the cornea for 20 min followed by 30 mW/cm2 UV-A irradiance for 3 min using a point-of-care UV-A device (Vetuvir®; Vision Engineering Italy srl, Rome, Italy). The complete healing of the ulcerative lesion was defined as the complete restoration of the corneal epithelial integrity with negative fluorescein staining. The corneal phototherapy achieved complete corneal healing in all the dogs by 20.5 ± 7.8 days. In the control group, only two dogs achieved complete healing by 21.5 ± 15.6 days. This intervention may represent a valid option to hasten corneal wound healing and a clinical resolution of ulcerative keratitis in dogs.

Albumin in Tears Modulates Bacterial Susceptibility to Topical Antibiotics in Ophthalmology

Bacterial keratitis is a serious and vision-threatening condition in veterinary and human patients, one that often requires culture and susceptibility testing to adjust therapy and improve clinical outcomes. The present study challenges the antimicrobial susceptibility testing (AST) paradigm in ophthalmology, enabling more accurate in vitro-to-in vivo translation by incorporating factors normally present during host-pathogen interactions in clinical patients. Thirty bacteria (10 Staphylococcus pseudintermedius, 10 Streptococcus canis, 10 Pseudomonas aeruginosa) were isolated from canine patients with infectious keratitis. For each isolate, commercial plates (Sensititre™ JOEYE2) were used to assess the minimal inhibitory concentration (MIC) of 17 different antibiotics in the absence (0% albumin, control) or presence of canine albumin (0.01–2%). For Staphylococcus pseudintermedius, the experiment was repeated with actual tear fluid collected from canine eyes with ocular surface inflammation. Kruskal-Wallis, Wilcoxon signed rank test and Spearman's correlation tests were used for statistical analysis. Clinical outcomes were unfavorable in selected canine patients with bacterial keratitis (e.g., globe perforation, graft dehiscence) despite standard AST (i.e., 0% albumin in test medium) confirming that most corneal infections (93%) were susceptible to ≥1 topical antibiotics used at the initial visit. Albumin levels ≥0.05% increased MICs in a dose-dependent, bacteria-specific, and antibiotic-specific manner. No significant differences (P = 1.000) were noted in MICs of any antibiotic whether albumin or tear fluid was added to the Mueller-Hinton broth. Percent protein binding inherent to each antibiotic was associated with clinical interpretations (Spearman's rho = −0.53, P = 0.034) but not changes in MICs. Albumin in tears impacted the efficacy of selected ophthalmic antibiotics as only the unbound portion of an antibiotic is microbiologically active. The present findings could improve decision making of clinicians managing bacterial keratitis, reduce development of antimicrobial resistance, influence current guidelines set by the Clinical and Laboratory Standards Institute, and serve as a reference for bacteriological evaluations across medical fields and across species.

Mechanical behaviour of healthy versus alkali-lesioned corneas by a porcine organ culture model

BACKGROUND

Cornea is a composite tissue exhibiting nonlinear and time-dependent mechanical properties. Corneal ulcers are one of the main pathologies that affect this tissue, disrupting its structural integrity and leading to impaired functions. In this study, uniaxial tensile and stress-relaxation tests are developed to evaluate stress-strain and time-dependent mechanical behaviour of porcine corneas.

RESULTS

The samples are split in two groups: some corneas are analysed in an unaltered state (healthy samples), while others are injured with alkaline solution to create an experimental ulcer (lesioned samples). Furthermore, within each group, corneas are examined in two conditions: few hours after the enucleation (fresh samples) or after 7 days in a specific culture medium for the tissue (cultured samples). Finally, another condition is added: corneas from all the groups undergo or not a cross-linking treatment. In both stress-strain and stress-relaxation tests, a weakening of the tissue is observed due to the imposed conditions (lesion, culture and treatment), represented by a lower stiffness and increased stress-relaxation.

CONCLUSIONS

Alkali-induced corneal stromal melting determines changes in the mechanical response that can be related to a damage at microstructural level. The results of the present study represent the basis for the investigation of traditional and innovative corneal therapies.

Surgical treatment of canine and feline descemetoceles, deep and perforated corneal ulcers with autologous buccal mucous membrane grafts

Objectives

To report the surgical technique and postoperative outcome of corneal repair with autologous buccal mucous membrane grafts in dogs and cats with descemetoceles, deep corneal ulcers, and perforated corneal ulcers with or without iris prolapse.

Animal studied

Twelve cats (13 eyes) and fourteen dogs (14 eyes) were treated.

Procedures

Grafts were harvested from the unpigmented superior labial mucosa using a biopsy punch. The corneal lesion was carefully debrided and cleaned. The graft was secured to the healthy cornea with a combination of simple interrupted and continuous 9–0 polyglycolic acid sutures. In 25/27 treated eyes, an overlying pedicle conjunctival graft was also performed. A temporary nictitating membrane flap was used in all cases. The pedicle conjunctival graft was trimmed about 10–20 days postoperatively. The median follow‐up period was 549.2 days (range 14–2691 days).

Results

No surgical intra‐operative complications were observed. The ulcers healed and the integrity of the globe was restored in 24/27 treated eyes. Different grades of corneal fibrosis and/or vascularization and/or pigmentation were observed in all cases at the long‐term follow‐up. In two cases, enucleation was performed due to postoperative complications and one animal developed phthisis bulbi. A total of 22/27 treated eyes appeared to have regained effective visual function at the last clinical evaluation.

Conclusions

Autologous buccal mucous membrane grafts appear to successfully manage severe corneal ulcers in dogs and cats, providing a useful and economical alternative to other corneal grafts.

Outcomes of treatments for keratomalacia in dogs and cats: a systematic review of the published literature including non-randomised controlled and non-controlled studies

OBJECTIVES

The aim of this review was to interrogate the evidence base for treatment of keratomalacia in dogs and cats, through examination of the applicable literature.

MATERIALS AND METHODS

Studies were screened for evidence to answer the following question Which of the treatment options for keratomalacia in dogs and cats offers the best chance of globe survival, the fastest time to resolution with globe survival, and the best visual outcome. The search utilised the PubMed (http://www.pubmed.gov/) and ISI Web of Science (http://wok.mimas.ac.uk/) databases. Databases were searched using the following terms: (keratomalacia OR corneal melt OR corneal malacia) AND (dog OR canine OR canid OR cat OR feline OR felid) AND (treatment OR outcome OR morbidity OR complications). Studies were assessed by one author (CH) and excluded if they related to less than three keratomalacia cases, experimental treatments, in vitro studies, or did not provide information regarding outcome. Studies were classified to a level of evidence according to the system described by the Oxford Centre for EvidenceBased Medicine.

RESULTS

Eighteen (18) studies were identified as providing information to answer the proposed question, one as level 3, 10 as level 4 and seven as level 5 evidence. Only one study compared two treatments, the remaining were prospective or retrospective case series of a single treatment intervention. Study design was highly variable with respect to population size, followup and outcome assessment, making direct comparison difficult, and metaanalysis was not applied.

CLINICAL SIGNIFICANCE

Overall, the evidence for improved outcome of one proposed treatment over another proposed treatment for keratomalacia in dogs and/or cats is very weak.

Melting corneal ulcers (keratomalacia) in dogs: A 5-year clinical and microbiological study (2014-2018)

OBJECTIVES

To identify bacterial microorganisms associated with canine keratomalacia, review their antimicrobial sensitivity, and evaluate clinical outcomes compared to results of microbial culture.

METHODS

Retrospective analysis of clinical records of dogs diagnosed with a melting corneal ulcer presented to a referral hospital in Hertfordshire, UK between 2014 and 2018.

RESULTS

One hundred and ten melting corneal ulcers were sampled in 106 dogs. The most common pure bacterial isolate was Pseudomonas aeruginosa (n = 26) followed by β-hemolytic Streptococcus (n = 12). Melting corneal ulcers that cultured coagulase-positive Staphylococcus, coliform bacteria, Pasteurella multocida, Enterococcus, and Streptococcus viridans presented in smaller numbers and were analyzed together (n = 16). Multiple cultures were identified in nine cases (n = 9). Forty-seven cultures yielded no bacterial growth (n = 47). The susceptibility to fluoroquinolones remained high with the exception of β-hemolytic Streptococci. There was no significant difference in the ulcer severity at presentation in regard to the cultured bacteria. Overall, 63 eyes (57%) received surgical grafting in addition to medical treatment. In 14 cases (13%), the progression of corneal melting despite medical ± surgical treatment resulted in enucleation. Fifty-seven percent (8/14) of the enucleated eyes cultured pure Pseudomonas aeruginosa isolates. In contrast, all β-hemolytic Streptococcus-associated ulcers healed.

CONCLUSIONS

The most common bacterial species associated with canine keratomalacia were Pseudomonas aeruginosa and β-hemolytic Streptococcus. Because of the variation in antibacterial sensitivity between these two species, bacterial culture and sensitivity testing should be performed in all dogs presenting with keratomalacia. Melting corneal ulcers associated with pure Pseudomonas infection were significantly more likely to result in globe loss than melting corneal ulcers associated with other cultures.

Accelerated Corneal Cross-linking as an Adjunct Therapy in the Management of Presumed Bacterial Keratitis: A Cohort Study

PURPOSE

To compare the outcomes of accelerated photoactivated chromophore for keratitis corneal cross-linking (PACK-CXL) as an adjunct treatment for bacterial keratitis (PACK-CXL plus standard antibiotic therapy) for patients receiving only standard antibiotic therapy.

METHODS

Retrospective cohort study of outcomes of patients with moderate infectious presumed bacterial keratitis (ulcer diameter 2 to 7 mm and stromal depth < 300 µm) were compared before and after initiation of a new treatment protocol of PACK-CXL in addition to standard antibiotic treatment.

RESULTS

A total of 70 eyes of 70 patients were included: 39 eyes in the PACK-CXL plus antibiotic (PACK-ABX) group and 31 eyes in the antibiotic only (ABX) control group. The PACK-ABX group showed shorter times to complete reepithelialization (9.3 ± 6.0 vs 16.0 ± 12.7 days, P = .01) and did not require tectonic emergency keratoplasty (0% versus 19.4%, P = .006). The PACK-ABX group also showed a higher percentage of eyes with complete reepithelialization in 6 days or less (46.2% vs 6.5%, P < .001) and a trend for shorter hospitalizations (6.3 ± 5.0 vs 8.5 ± 4.5 days, P = .06). A multivariate analysis controlling for age showed that PACK-ABX treatment remained significantly associated with early ulcer reepithelialization (odds ratio = 0.09, 95% confidence interval = 0.02 to 0.48, P = .005).

CONCLUSIONS

This study validates previous findings regarding the use of accelerated PACK-CXL in the treatment of bacterial keratitis. Adding PACK-CXL improved clinical outcomes (reducing healing time) when compared to antibiotics alone. [J Refract Surg. 2020;36(4):258-264.].

Tissue Inhibitor of Metalloproteinase (TIMP) Peptidomimetic as an Adjunctive Therapy for Infectious Keratitis

Matrix metalloproteinase 9 (MMP-9) has a key role in many biological processes, and while it is crucial for a normal immune response, excessive release of this enzyme can lead to severe tissue damage, as evidenced by proteolytic digestion and perforation of the cornea during infectious keratitis. Current medical management strategies for keratitis mostly focus on antibacterial effects, but largely neglect the role of excess MMP activity. Here, a cyclic tissue inhibitor of metalloproteinase (TIMP) peptidomimetic, which downregulated MMP-9 expression both at the mRNA and protein levels as well as MMP-9 activity in THP-1-derived macrophages, is reported. A similar downregulating effect could also be observed on α smooth muscle actin (α-SMA) expression in fibroblasts. Furthermore, the TIMP peptidomimetic reduced Pseudomonas aeruginosa-induced MMP-9 activity in an ex vivo porcine infectious keratitis model and histological examinations demonstrated that a decrease of corneal thickness, associated with keratitis progression, was inhibited upon peptidomimetic treatment. The presented approach to reduce MMP-9 activity thus holds great potential to decrease corneal tissue damage and improve the clinical success of current treatment strategies for infectious keratitis.

Comparative evaluation of decellularized bovine omentum alone and in combination with mitomycin-C in the management of corneal injuries in dogs

Background and Aim:

Ulcerative corneal lesions are common ocular affections encountered in veterinary ophthalmology, having a higher incidence in dogs with brachycephalic conformation. Prompt and effective diagnosis and repair are necessary to avoid corneal perforation and restore vision. Corneal wound healing is a complex phenomenon often resulting in vision impairment as a consequence of corneal fibrosis and pigmentation. The present study investigated the efficacy of decellularized and gamma-irradiated bovine omentum as an extracellular matrix scaffold in the reconstruction of extensive and full-thickness corneal defects, and the cytotoxic effects of mitomycin-C (MMC) to prevent corneal fibrosis and pigmentation.

Materials and Methods:

Twelve injured corneas of eleven dogs irrespective of breed, age, and sex were randomly divided into Groups I and II, consisting of six corneas each. Under general anesthesia, corneal grafting with decellularized and gamma-irradiated bovine omentum was carried out in Group I, whereas Group II corneas underwent single time intra-operative application of topical MMC for 2 min before corneal grafting with the same material. Epithelialization of cornea and observations including corneal edema, neovascularization, the extent of pigmentation, corneal clarity, and scarring was recorded on days 7, 14, 21, and 60 postoperatively.

Results:

All corneas in Group I showed early epithelialization by day 7 compared to Group II where the MMC delayed epithelialization in 50% of the corneas. Visual function scores improved greatly from 0.17±0.17 in Group II on the day of presentation to 1.0±00 by the end of the observation period compared to Group I (from 0.33±0.15 to 0.88±0.11). Although epithelialization and corneal healing were delayed, 50% of the corneas recovered with undetectable corneal scar and melanosis at the end of the observation period in Group II due to the anti-fibrotic effect of MMC.

Conclusion:

From the present study, it was concluded that re-epithelialization of the cornea was enhanced by corneal grafting with decellularized bovine omentum, and application of MMC was effective in delaying corneal fibrosis and pigmentation.

Optimizing corneal riboflavin administration in ex vivo horse, dog, rabbit, and pig samples for use in corneal collagen cross-linking

PURPOSE

Determine optimal iontophoresis times for riboflavin delivery to the corneal stroma across different species and compare these to corneal injection.

METHODS

Ex vivo horse, dog, rabbit, and pig globes were treated with riboflavin administered with either iontophoresis for 2.5-20 minutes with or without corneal epithelium; or with purpose-designed precise corneal injection (PCI) application with intact epithelium. Immediately following riboflavin administration, samples were harvested, frozen, and sectioned. Riboflavin penetration was imaged using fluorescence microscopy.

RESULTS

Horse samples processed with iontophoresis without epithelium for 2.5, 5, and 7.5 minutes, and processed with intact epithelium for 20 minutes, had mean percent stromal penetration (%SP_mean ) of 63.4%, 93.8%, 100.0%, and 0.0% (respectively). Dog samples processed with iontophoresis without epithelium for 2.5 and 5 minutes, had %SP_mean of 60.7% and 82.1% (respectively). Pig samples processed with iontophoresis for 5 minutes without and with epithelium had %SP_mean of 63.3% and 35.1% (respectively). Rabbit samples processed with iontophoresis without epithelium for 2.5 and 5 minutes, had %SP_mean of 81.8% and 100.0% (respectively). For all injected volumes, riboflavin was observed spanning throughout the corneal stroma, and lamellar separation was noted surrounding all sites of injection.

CONCLUSIONS

Both iontophoresis and injection via PCI needles provide efficient and effective means of riboflavin administration in ex vivo horse, dog, rabbit, and pig corneas. Epithelial debridement is required for stromal delivery of riboflavin using iontophoresis in horses. Following epithelial removal, riboflavin penetrated through the horse corneal stroma faster than all other species tested.

An Assay System to Evaluate Riboflavin/UV-A Corneal Phototherapy Efficacy in a Porcine Corneal Organ Culture Model

Simple summary

The scope of this study is to quantitatively evaluate, with an automated digital image analysis method, the efficacy of riboflavin/UV-A corneal phototherapy on the cornea in a porcine corneal organ culture model of ulcerative melting keratitis. Riboflavin/UV-A corneal phototherapy provided a favorable outcome in the corneal wound healing process after chemical injury: the treatment restores the damaged corneas to the texture of healthy corneas. This automated image analysis method may be compared to clinical diagnostic methods, such as optical coherence tomography (OCT) imaging, for in vivo damaged ocular structural investigations. Positive results from this research could provide an opportunity for studying the effects of this method in other economically and emotionally valued species, such as dogs, cats, and horses. The relatively overall low treatment cost and the ease of performing the procedure make riboflavin/UV-A corneal phototherapy accessible to the veterinary market.

Abstract

The purpose of this study was to investigate the response of porcine corneal organ cultures to riboflavin/UV-A phototherapy in the injury healing of induced lesions. A porcine corneal organ culture model was established. Corneal alterations in the stroma were evaluated using an assay system, based on an automated image analysis method able to (i) localize the holes and gaps within the stroma and (ii) measure the brightness values in these patches. The analysis has been performed by dividing the corneal section in 24 regions of interest (ROIs) and integrating the data analysis with a “multi-aspect approach.” Three group of corneas were analyzed: healthy, injured, and injured-and-treated. Our study revealed a significant effect of the riboflavin/UV-A phototherapy in the injury healing of porcine corneas after induced lesions. The injured corneas had significant differences of brightness values in comparison to treated (p < 0.00) and healthy (p < 0.001) corneas, whereas the treated and healthy corneas showed no significant difference (p = 0.995). Riboflavin/UV-A phototherapy shows a significant effect in restoring the brightness values of damaged corneas to the values of healthy corneas, suggesting treatment restores the injury healing of corneas after lesions. Our assay system may be compared to clinical diagnostic methods, such as optical coherence tomography (OCT) imaging, for in vivo damaged ocular structure investigations.

Corneal cross-linking as a treatment for corneal dystrophy with secondary bacterial infection in a Friesian horse

Corneal cross-linking should be considered as treatment option in Friesian horses with infectious keratitis and corneal dystrophy. Optical coherence tomography, giving information of corneal structure, can help for diagnosis and monitoring.

Outcome of medical therapy for keratomalacia in dogs

OBJECTIVES

To evaluate the clinical and visual outcomes following intensive medical therapy for keratomalacia in dogs.

MATERIALS AND METHODS

Medical records were screened to identify dogs with corneal ulcers and keratomalacia. All patients were given the same topical treatment protocol with frequent administrations of tobramycin in combination with equine serum. Surgical treatment during the first 15 days of follow-up was considered as medical treatment failure.

RESULTS

We report on 57 ulcers with keratomalacia from 53 dogs. Medical treatment was successful in 31 of 57 ulcers with a median healing time of 5 days (range 2 to 15 days). At 60 days after epithelialisation, 14/15 medically-treated eyes were visual. In one case, corneal perforation was observed 1 month after healing and required surgical stabilisation.

CLINICAL SIGNIFICANCE

Intensive medical therapy has the potential to achieve healing of some ulcers with keratomalacia. Surgical stabilisation in response to progression of stromal loss was required in less than half of the cases.

Corneal cross-linking (CXL)-A clinical study to evaluate CXL as a treatment in comparison with medical treatment for ulcerative keratitis in horses

OBJECTIVE

Compare CXL treatment with medical treatment alone in horses with stromal, ulcerative keratitis.

ANIMALS STUDIED

24 horses (24 eyes) with stromal, ulcerative keratitis were included.

PROCEDURE

12 horses were initially treated with CXL, and 12 horses were given conventional medical treatment. Topical medical treatment was added to horses in the CXL group if necessary. Parameters including cytology, microbial growth, time to fluorescein negativity, and time to inhibition of stromal melting were evaluated.

RESULTS

After the first day of treatments, a decrease in inflammatory signs and pain from the eye was observed in both groups. Stromal melting ceased within 24 hours regardless of treatment. CXL treatment alone was sufficient in 3 horses with noninfectious, superficial stromal ulcerations. Clinical signs of impaired wound healing were seen after 3-14 days in corneas with suspected or proven bacterial infection treated with CXL only, most likely because of insufficient elimination of bacteria deeper in the corneal stroma or because of re-infection from bacteria in the conjunctiva. The average decrease in stromal ulcer area per day after onset of treatment was almost identical between the groups, and no significant difference in time to fluorescein negativity was found.

CONCLUSIONS

We consider CXL a possible useful adjunct treatment of corneal stromal ulcers in horses, especially for melting ulcers and as a potential alternative to prophylactic antibiotic treatment for noninfected stromal ulcers. However, CXL should not be used alone for infected or suspected infected stromal ulcers, because topical antibiotics were required in all horses with proven infectious keratitis.

Current and Future Applications of Photoactivated Chromophore for Keratitis-Corneal Collagen Cross-Linking (PACK-CXL): An Overview of the Different Treatments Proposed

PURPOSE

To review the application of the PACK-CXL and to identify different treatment protocols according to the pathogens associated with keratitis.

METHODS

A systematic review of 21 articles. The primary outcome was the healing of a corneal ulcer, defined as epithelization, blocking corneal melting. The secondary end-point was the recovery of visual acuity.

RESULTS

We studied a total of 145 eyes. Infectious keratitis was associated with bacteria in 80 eyes (55.55%), fungus in 24 eyes (16.67%), and protozoa in 13 (8.97%). In 26 (18%), the microbiological culture was negative or not performed. The mean time of re-epithelization was 25.70±29.83days (1-180). A total of 27 patients needed corneal transplantation. The overall probability of blocking corneal melting was 84.13%. Three different protocols for each group of pathogens have been proposed.

CONCLUSION

PACK-CXL still has a limit in its spread. In the future, we hope that each pathogen will be treated with the most efficient and least invasive protocols available.

PACK-CXL: Corneal cross-linking in infectious keratitis

Background

Corneal cross-linking (CXL) using ultraviolet light-A (UV-A) and riboflavin is a technique developed in the 1990’s to treat corneal ectatic disorders such as keratoconus. It soon became the new gold standard in multiple countries around the world to halt the progression of this disorder, with good long-term outcomes in keratometry reading and visual acuity. The original Dresden treatment protocol was also later on used to stabilize iatrogenic corneal ectasia appearing after laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). CXL efficiently strengthened the cornea but was also shown to kill most of the keratocytes within the corneal stroma, later on repopulated by those cells.

Review

Ultraviolet-light has long been known for its microbicidal effect, and thus CXL postulated to be able to sterilize the cornea from infectious pathogens. This cytotoxic effect led to the first clinical trials using CXL to treat advanced infectious melting corneal keratitis. Patients treated with this technique showed, in the majority of cases, a stabilization of the melting process and were able to avoid emergent à chaud keratoplasty. Following those primary favorable results, CXL was used to treat beginning bacterial keratitis as a first-line treatment without any adjunctive antibiotics with positive results for most patients. In order to distinguish the use of CXL for infectious keratitis treatment from its use for corneal ectatic disorders, a new term was proposed at the 9th CXL congress in Dublin to rename its use in infections as photoactivated chromophore for infectious keratitis -corneal collagen cross-linking (PACK-CXL).

Conclusion

PACK-CXL is now more frequently used to treat infections from various infectious origins. The original Dresden protocol is still used for this purpose. Careful modifications of this protocol could improve the efficiency of this technique in specific clinical situations regarding certain types of pathogens.

Established and emerging ancillary techniques in management of microbial keratitis: a review

Microbial keratitis is a sight-threatening condition and an ocular emergency, because of the potential for rapid progression. Intensive topical antimicrobials are the mainstay and the gold standard of treatment for microbial keratitis. However, despite appropriate diagnosis and therapy, treatment failure is still common, and can result in significant morbidity due to corneal perforation and/or scarring. For this reason, clinicians continue to seek novel treatment techniques in order to expand the armamentarium of tools available to manage microbial keratitis, and in doing so improve clinical outcomes. In this review, we examine the evidence for some established, as well as a few emerging ancillary techniques used to manage microbial keratitis. These include topical corticosteroids, corneal collagen cross-linking, intrastromal antimicrobials, amniotic membrane transplantation and miscellaneous other techniques. Of these, collagen cross-linking shows some promise for selected cases of infectious keratitis, although more research in the area is required before it is accepted as mainstream treatment for this potentially blinding condition.

Preliminary results of a prospective study of inter- and intra-user variability of the Royal Veterinary College corneal clarity score (RVC-CCS) for use in veterinary practice

OBJECTIVE

To introduce a new corneal clarity score for use in small animals and describe its inter- and intra-user variability.

ANIMALS STUDIED

Twelve dogs and two cats with corneal abnormalities and five dogs with healthy corneas.

MATERIALS AND METHODS

Four examiners scored every patient twice and never consecutively, focusing on the central cornea. The peripheral cornea was scored separately. The following scoring system was used to describe corneal clarity: G0: no fundus reflection is visible on retroillumination (RI) using a head-mounted indirect ophthalmoscope. G1: a fundus reflection is visible with RI. G2: a 0.1-mm diameter light beam is visible on the anterior surface of the iris and/or lens. G3: gross fundic features are visible when viewed with indirect ophthalmoscopy (IO) using a head-mounted indirect ophthalmoscope and a hand-held 30D lens, although fine details are not clear. G4: fine details of the fundic features are clearly visible with IO. The minimum grades given were analyzed for inter- and intra-user variability with kappa analysis.

RESULTS

Intra- and interuser variability of the central corneal clarity ranged from 0.78 to 0.96, showing substantial to almost perfect reproducibility, and from 0.66 to 0.91, showing substantial to almost perfect reliability, respectively. Intra- and interuser variability of the peripheral cornea ranged from 0.83 to 0.95, showing almost perfect agreement, and from 0.53 to 0.91, showing moderate to almost perfect agreement.

CONCLUSIONS

The RVC-CCS is well suited to assess and monitor central corneal clarity in small animals and to compare outcomes between studies and different surgeons.

PACK-CXL: Corneal Cross-linking for Treatment of Infectious Keratitis

This article discusses corneal cross-linking (CXL) and how it transitioned from a modality for treating corneal ectatic disorders to an inventive means of treating infectious keratitis. Initially, CXL was successfully developed to halt the progression of ectatic diseases such as keratoconus, using the standard Dresden protocol. Later, indications were extended to treat iatrogenic ectasia developing after laser-assisted in situ keratomileusis (LASIK) and photo-refractive keratectomy (PRK). At the time, it had been postulated that the combination of ultraviolet light with riboflavin could not only biomechanically strengthen the cornea but also was capable of destroying living cells and organisms including keratocytes and pathogens. Thus a new and innovative concept of treatment for infectious keratitis emerged through the use of CXL technology. Initially only advanced infectious melting ulcers resisting standard microbicidal therapy were treated with CXL in addition to standard therapy. In subsequent studies CXL was also used to treat bacterial keratitis as first line therapy without the use of concomitant antibiotic therapy. With the increasing interest in CXL technology to treat infectious keratitis and to clearly separate its use from the treatment of ectatic disorders, a new term was adopted at the 9(th) CXL congress in Dublin for this specific indication: PACK-CXL (photoactivated chromophore for infectious keratitis). PACK-CXL has the potential to eventually become an interesting alternative to standard antibiotic therapy in treating infectious corneal disorders, and may help reduce the global burden of microbial resistance to antibiotics and other therapeutic agents.