Superficial Keratectomy and Conjunctival Advancement Hood Flap (SKCAHF) for the Management of Bullous Keratopathy: Validation in Dogs With Spontaneous Disease

Partial incision blunt scissors lamellar keratectomy under topical anesthesia for the treatment of presumed calcific corneal degeneration in dogs

OBJECTIVE

The aim of the study was to investigate clinical features of lamellar keratectomy for presumed calcific corneal degeneration in a population of geriatric dogs using blunt scissors dissection under topical anesthesia.

ANIMALS STUDIED AND PROCEDURES

Retrospective analysis of dogs with clinically diagnosed calcific degeneration treated by keratectomy under topical anesthesia between 2015 and 2021 at two veterinary ophthalmology practices was performed. Descriptive data regarding signalment, concurrent systemic and ocular disease, complications, healing time, and recurrence were collected. Kaplan-Meier survival analysis was performed to calculate 1-year recurrence probability.

RESULTS

Sixty-five eyes in 57 dogs met inclusion criteria. All 54 eyes with follow-up healed within a median of 14 days (7-74), including 17 with complicating factors of infection or deep stromal ulceration. Globe rupture occurred intraoperatively in three eyes (4.6%), for which subsequent conjunctival graft was performed. Calculated 1-year recurrence probability from 47 eyes followed long term was 25%. Multivariate Cox proportional hazard modeling showed a significant association between documented systemic disease and time to recurrence (p = .035), irrespective of topical EDTA use (p = .432). Median follow-up time available for all cases was 249 days.

CONCLUSIONS

Blunt lamellar dissection with corneal scissors can be performed in dogs under topical anesthesia, yielding healing times and recurrence comparable to previously reported treatments for calcific corneal degeneration. Globe rupture is an inherent risk of both the disease and procedure and occurred in 4.6% of treated eyes. This approach expands non-anesthetic treatment options for affected patients but should only be performed with advanced microsurgical training and client counseling on individual risk and benefit.

Topical netarsudil for the treatment of primary corneal endothelial degeneration in dogs

This study evaluated the tolerability and efficacy of the topical rho-kinase inhibitor netarsudil for canine primary corneal endothelial degeneration (PCED). Twenty-six eyes of 21 client-owned dogs with PCED were enrolled in a prospective, randomized, vehicle control clinical trial and received topical netarsudil 0.02% (Rhopressa®) or vehicle control twice daily (BID) for the first 4 months. Then, all patients received netarsudil for the next 4 or 8 months. Complete ophthalmic examination, ultrasonic pachymetry, Fourier-domain optical coherence tomography, and in vivo confocal microscopy were performed at baseline and 1, 2, 4, 6, 8 and 12 months. Effect of netarsudil on central corneal thickness (CCT), percentage of cornea with edema, and endothelial cell density (ECD) were evaluated by repeated measures ANOVA. Kaplan-Meier curves and log-rank test were used to compare corneal edema and clinical progression of eyes in netarsudil versus vehicle control groups. All dogs developed conjunctival hyperemia in at least one eye while receiving netarsudil. Unilateral transient reticulated intraepithelial bullae and stromal hemorrhage were observed respectively in 2 dogs in the netarsudil group. Two dogs showed persistently decreased tear production while receiving netarsudil, requiring topical immunomodulatory treatment. No significant differences in CCT, ECD, corneal edema or clinical progression were observed between netarsudil or vehicle treated eyes. When comparing efficacy of topical netarsudil BID and topical ripasudil 0.4% administered four times daily from our previous study, dogs receiving ripasudil had significantly less progression than those receiving netarsudil.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

Canine Descemet Stripping Endothelial Keratoplasty with a Tissue Insertion Device: Technique and Long-Term Outcome

Introduction. We describe a case of canine Descemet's stripping endothelial keratoplasty (DSEK) using an open-source canine tissue delivery device. Case Presentation. We follow the four-year outcomes of a 1.5-year-old Tibetan Terrier who presented with difficulty seeing, diffuse corneal edema, and central corneal thickness of 1400 microns in the left eye. To perform DSEK, a polycarbonate carrier and insertion device was designed for canine corneas that measure up to 15 mm in diameter. The tissue was loaded into the inserter prior to surgery with the endothelium facing inwards and the stroma facing the cartridge wall. From the cartridge, the graft was pulled into the eye using microforceps and an anterior chamber maintainer. We assessed preoperative endothelial cell count, postoperative corneal clearance, and graft adhesion. The donor was a two-year-old Airedale Terrier who died one day prior to surgery, with endothelial cell density of 3149 cells/mm2. One week after DSEK, the cornea began to clear, and pachymetry of the donor and graft total was 1410 microns. This improved to 800 microns at 4 months and continued improving in its clarity at the last postoperative visit 4 years after surgery. Discussion. We demonstrate the feasibility of conducting canine endothelial keratoplasty with a specially designed tissue delivery device and the potential of long-term corneal clearance after DSEK in canine eyes.

Application of a modified nictitating membrane flap in a fledgling feral pigeon (Columba livia domestica) with bullous keratopathy

A fledgling feral pigeon with systemic protozoal infection was referred with corneal protrusion in the right eye after being treated for a corneal ulcer for 12 days. Ophthalmic examination revealed a corneal bulla covering almost the entire central cornea and preventing the eyelids from closing. Gelatinous corneal stroma with numerous heterophils surrounding the corneal bulla was also detected on cytologic examination. Bullous keratopathy and melting keratitis in the right eye were diagnosed. Temporary tarsorrhaphy with topical eye drops was prescribed for a week; however, the bulla persisted. A modified nictitating membrane flap was created under general anesthesia and maintained for 2 weeks. The corneal bulla resolved, and corneal thickness was restored. The pigeon was presented again with recurrence of the corneal bulla in the right eye after 45 days. Alternative surgical options were recommended; however, the pigeon was euthanized because the protozoa-induced intra-oral and intra-aural masses caused malformation of the beaks, which made voluntary feeding impossible.

Animal models of corneal endothelial dysfunction to facilitate development of novel therapies

Progressive corneal endothelial disease eventually leads to corneal edema and vision loss due to the limited regenerative capacity of the corneal endothelium in vivo and is a major indication for corneal transplantation. Despite the relatively high success rate of corneal transplantation, there remains a pressing global clinical need to identify improved therapeutic strategies to address this debilitating condition. To evaluate the safety and efficacy of novel therapeutics, there is a growing demand for pre-clinical animal models of corneal endothelial dysfunction. In this review, experimentally induced, spontaneously occurring and genetically modified animal models of corneal endothelial dysfunction are described to assist researchers in making informed decisions regarding the selection of the most appropriate animal models to meet their research goals.

A Retrospective Study of Corneal Endothelial Dystrophy in Dogs (1991-2014)

PURPOSE

To retrospectively evaluate the clinical data, diagnostic tests, treatments, and outcomes for dogs with corneal endothelial dystrophy (CED) and determine risk factors for CED when compared with a canine reference population.

METHODS

Medical records of 99 dogs (1991-2014) diagnosed with CED at the University of California Davis Veterinary Medical Teaching Hospital were reviewed and compared with 458,680 dogs comprising the general hospital population during the study period. Retrieved data included signalment, examination findings, diagnoses, treatments, and outcomes associated with CED. The exact Pearson χ2 test or exact Kruskal-Wallis test was used to compare parameters between the groups. Progression of corneal edema was assessed using 3 independent Kaplan-Meier curves, identifying clinically significant changes in corneal opacity.

RESULTS

Boston terriers, German wirehaired pointers, and Dachshunds were overrepresented in the CED-affected group, whereas Labradors were underrepresented. Dogs older than 11 years were overrepresented in the CED-affected group, whereas intact dogs were underrepresented. Surgical intervention was performed (n = 11) based on the severity of disease and secondary complications from CED. Median time to progression of corneal edema was 1) 368 days when an at-risk eye initially without edema developed edema at a subsequent visit, 2) 701 days when there was progression from mild to marked corneal edema, and 3) 340 days when there was progression from focal to diffuse corneal edema.

CONCLUSIONS

Many CED-affected dogs progress over months to years without surgical intervention, making dogs with CED a useful model for studying genetic predispositions and development of novel therapeutics for Fuchs endothelial corneal dystrophy.

A modified technique of keratoleptynsis ("letter-box") for treatment of canine corneal edema associated with endothelial dysfunction

PURPOSE

To describe a modified keratoleptynsis procedure, as a method of preserving central corneal function, and evaluate the outcome in vision, reduction of corneal thickness and treatment of epithelial corneal ulcers in cases with endothelial cell dysfunction.

METHODS

Forty-four dogs (72 eyes) were affected by progressive corneal edema, with or without ulcerative keratitis. All patients were treated with a dorsal and ventral superficial keratectomy followed by conjunctival flaps, maintaining a clear central cornea. Corneal thickness measurements were obtained via ultrasound biomicroscopy.

RESULTS

All eyes showed resolution of ocular discomfort postoperatively, with a median time to resolution of 35 days. Two years post-surgery, vision had been lost in 2 of 29 eyes (7%). From the initial population, 23 dogs (39 eyes) had follow-up evaluations of corneal thickness. The mean central corneal thickness was 1359 ± 251 μm prior to surgery. Thickening of the central cornea was observed one week after surgery to 1559 ± 263 μm. Decreased corneal thickness was reported, at 1 month, 4 months, 10 months and 2 years postoperatively (1285 ± 267 μm, 1102 ± 150 μm, 1121 ± 288 μm, 1193 ± 283 μm, respectively). All eyes showed a similar trend of increasing and then decreasing corneal thickness.

CONCLUSIONS

This surgical technique provided statistically significant reduction in central corneal thickness and sustained relief of ocular pain. Reduction in corneal thickness appeared to be maintained 2 years post-surgery, and all patients remained comfortable. Superficial corneal pigmentation and fibrosis resulted in vision loss in two eyes.

Descemet's membrane detachments, ruptures, and separations in ten adult horses: Clinical signs, diagnostics, treatment options, and preliminary results

OBJECTIVE

To describe the clinical presentation, diagnostic imaging results, and treatment outcomes of a series of presumed spontaneous Descemet's membrane detachments (DMD), ruptures, or separations (DMRS) in the adult horse.

ANIMALS STUDIED

Ten adult horses of various breeds with DMD or DMRS.

PROCEDURES

Descemet's membrane detachments/DMRS were diagnosed via slit lamp biomicroscopy, ultrasound biomicroscopy (UBM), and/or optical coherence tomography (OCT). Penetrating keratoplasty (PK) with heterologous corneal donor tissue (n = 1), superficial lamellar keratectomy, and Gundersen inlay flaps alone (GF, n = 1) or with subsequent intracamerally assisted corneal tissue welding (CTW, n = 2), or CTW alone (n = 5) were performed in 9/10 horses. One horse underwent spontaneous resolution (n = 1).

RESULTS

Ten horses were diagnosed with either unilateral DMD (n = 4) or DMRS (n = 6). Seven of ten eyes remained visual during the follow-up period (8.16 ± 6.57 months). Graft transparency was good for the eye treated with PK. The horse that underwent GF alone was functionally blind due to persistent corneal edema. The clinical signs resolved in 3/5 horses that underwent CTW alone, but 2/5 eyes were enucleated due to corneal perforation. Both eyes treated with combined GF/CTW had significant corneal clearing with one having evidence of reattachment on UBM and OCT.

CONCLUSIONS

Descemet's membrane detachments separations presents differently than typical DMD and advanced corneal imaging modalities may aid in their diagnosis. Corneal tissue welding using infraCG as the photosensitive agent, or in combination with Gundersen inlay flaps, represents a feasible treatment option for management of equine DMD/DMRS as described in the present case series.

Endothelial keratoplasty for corneal endothelial dystrophy in a dog

OBJECTIVE

To assess the efficacy of an endothelial keratoplasty procedure at defined intervals to 1 year postoperatively for the treatment of corneal endothelial dystrophy (CED) in a canine patient.

PROCEDURE

A dog diagnosed with CED with progressive corneal edema underwent an endothelial keratoplasty. The patient was examined pre- and postoperatively with slit lamp biomicroscopy and ultrasonic pachymetry.

RESULTS

Mean central corneal thickness (CCT) measured with pachymetry was >1400 μm preoperatively and decreased postoperatively to 725 μm. The transplanted donor tissue became transparent 2 weeks postoperatively and incorporated with the recipient cornea. The graft remained transparent throughout the duration of the postoperative period evaluated in this study (2 weeks postoperatively to 1 year). The canine patient was comfortable pre- and postoperatively.

CONCLUSIONS

Endothelial keratoplasty is a potential therapeutic option for canine cases with progressive corneal thickening due to CED. As this is a single case study, further investigation into the use of endothelial keratoplasty to treat CED is warranted. Moreover, canine patients with CED might serve as a surgical model for human patients with Fuchs' Endothelial Corneal Dystrophy.

Comparison of automated vs manual analysis of corneal endothelial cell density and morphology in normal and corneal endothelial dystrophy-affected dogs

OBJECTIVE

To determine the efficacy of automated imaging software of the Nidek ConfoScan 4 confocal biomicroscope at analyzing canine corneal endothelial cell density and morphology in health and disease, by comparing to a manual analysis method.

ANIMAL STUDIED

Nineteen eyes of 10 dogs were evaluated and include three Beagles, three Jack Russell Terriers, and four miscellaneous breeds. Twelve clinically normal and seven eyes affected with corneal endothelial dystrophy (CED) were scanned and analyzed.

PROCEDURES

Endothelial cell density (ECD), mean and standard deviation (SD) of cell area, percent polymegathism, mean and SD of the number of cell sides, and percent pleomorphism were calculated using automated and manual methods for each scan.

RESULTS

The automated analysis showed significantly greater ECD in comparison with the manual frame method due to misidentification of cell domains in CED-affected dogs. No significant differences in ECD were observed between normal and CED-affected dogs in automated analysis, while CED-affected dogs showed significantly lower ECD in manual frame method and planimetry. Using both automated and manual methods, CED-affected dogs showed greater variability of cell area or the number of cell sides than normal dogs.

CONCLUSION

The automated imaging software is unable to accurately identify cell borders in CED-affected dogs resulting in inaccurate estimates of ECD. Thus, manual analysis is recommended for use in clinical trials assessing adverse events associated with novel medical treatments and/or surgical procedures.

Early postoperative results of Descemet's stripping endothelial keratoplasty in six dogs with corneal endothelial dystrophy

OBJECTIVE

To describe and assess the clinical outcome and intraoperative and postoperative complications of Descemet's stripping endothelial keratoplasty (DSEK) in the treatment of canine corneal endothelial dystrophy.

ANIMALS STUDIED

Six dogs (six eyes) diagnosed with progressive corneal edema resulting from abnormal dystrophic endothelial cells underwent Descemet's stripping endothelial keratoplasty.

PROCEDURES

Six patients underwent Descemet's stripping endothelial keratoplasty (DSEK). The patients were examined preoperatively and postoperatively at 24 hours, 7 days, 1, 2, and 3 months after surgery. Corneal edema and ultrasonic pachymetry were evaluated preoperatively and postoperatively. The positions of DSEK grafts were evaluated 3 months after surgery using optical coherence tomography. Intraoperative and postoperative complications were noted.

RESULTS

The degree of corneal edema and corneal thickness improved postoperatively in all the patients (n = 6). Fibrin was encountered intraoperatively in one out of the six eyes (1/6) and postoperatively in two out of the six eyes (2/6). One out of the six DSEK grafts was partially scrolled (1/6). Secondary ocular hypertension was observed in one out of the six eyes (1/6). Corneal vascularization was encountered in four out of six patients (4/6).

CONCLUSIONS

Descemet's stripping endothelial keratoplasty is an effective surgical treatment option for corneal endothelial dystrophy in dogs. Corneal edema resolved and corneal thickness reduced significantly. The early postoperative results are encouraging. Further investigation is warranted to document any long-term complications and to study the longevity of the transplanted grafts.

Topical Rho-Associated Kinase Inhibitor, Y27632, Accelerates Corneal Endothelial Regeneration in a Canine Cryoinjury Model

PURPOSE

Corneal endothelial cell regeneration varies by species, with nonhuman primates (NHPs) and rabbits displaying low and high proliferative capacities, respectively. Recent studies report that topical application of rho-associated kinase (ROCK) inhibitors accelerates corneal endothelial wound healing in animal models and human patients with endothelial dysfunction. This study determines the regenerative capacity of canine corneal endothelial cells in vivo and their response to a topical ROCK inhibitor, Y27632, after transcorneal freezing.

METHODS

Right eyes of 6 beagles underwent transcorneal freezing; 10 mM ROCK inhibitor Y27632 or vehicle control was applied topically to both eyes at least 4 times daily for 56 days. Endothelial cell density was evaluated by in vivo confocal microscopy, and corneal thickness was measured by Fourier-domain optical coherence tomography (FD-OCT) and ultrasound pachymetry.

RESULTS

Transcorneal freezing induced severe central corneal edema in dogs, with restoration of transparency occurring within 4 weeks. Y27632 significantly decreased corneal thickness by FD-OCT and ultrasound pachymetry in the acute phase and significantly increased endothelial cell density at days 28 and 42 post-cryoinjury, suggesting faster restoration of endothelial cell recovery.

CONCLUSIONS

Canine corneal endothelial function recovers at a similar rate as NHPs but more slowly than rabbits after cryoinjury. Faster corneal endothelial wound healing was observed by in vivo confocal microscopy and FD-OCT in dogs treated with Y27632 versus vehicle controls. Thus, a canine cryoinjury model may be a useful alternative to NHPs in detecting a response to therapies directed at endothelial regeneration.

Comparison of ultrasonic pachymetry and Fourier-domain optical coherence tomography for measurement of corneal thickness in dogs with and without corneal disease

Several ultrasonic and Fourier-domain optical coherence tomography (FD-OCT) pachymeters are used to measure corneal thickness in canine patients and research subjects. This study assessed the reliability of and consistency between two ultrasonic pachymetry (USP) devices, Pachette 3 and Accupach VI, as well as automated and manual measurements obtained using FD-OCT in dogs with and without corneal disease. Corneal thickness measurements were compiled from 108 dogs and analyzed using mixed effects linear regression, with Bonferonni adjustments for post-hoc comparisons, to determine the effects of age, weight and disease state. Data are presented as predicted mean±standard error. Canine corneal disease can result in marked increases in thickness that frequently exceed the upper limits of measurement of some pachymetry devices developed for human use. In this study, the corneas of dogs with endothelial disease or injury frequently exceeded the upper limits of quantitation of 999 and 800μm for the Accupach VI and automated FD-OCT pachymeters, respectively. Using values <800μm, the Pachette 3 generated significantly greater values for central corneal thickness (CCT) than the Accupach VI, manual FD-OCT and automated FD-OCT at 625±7.0, 615±7.2, 613±7.2, and 606±7.4μm respectively (P<0.001). Of the two devices where measurements >1000μm were obtained, manual FD-OCT demonstrated less variability than the Pachette 3. Corneal thickness increased linearly with age and weight with an increase of 6.9±1.8μm/year and 1.6±0.8μm/kg body weight (P<0.005 and P=0.038, respectively).

Effects of 5% sodium chloride ophthalmic ointment on thickness and morphology of the normal canine cornea

OBJECTIVE

To determine the effect of 5% sodium chloride ophthalmic ointment (5% NaCl) on thickness and morphology of the normal canine cornea using ultrasonic pachymetry (USP), in vivo confocal microscopy (IVCM), and Fourier-domain optical coherence tomography (FD-OCT).

METHODS

Five healthy laboratory Beagles received ophthalmic examinations including USP, IVCM, and FD-OCT prior to and at fixed intervals following treatment. The right and left eyes were treated with 5% NaCl and artificial tears ophthalmic ointment (AT), respectively, every 2 hours for 4 treatments/d (days 2-9), and then hourly for 7 treatments/d (day 10). Treatment groups were statistically compared using mixed-effects linear regression.

RESULTS

Treatment with 5% NaCl resulted in a 12 μm decrease in corneal thickness from baseline (P < .001), while there was no significant difference in corneal thickness between values obtained at baseline and following treatment with AT (P = .82). Epithelial cell density significantly increased from baseline (530 ± 52 cells/mm² ) to 577 ± 43 and 567 ± 15 cells/mm² with 5% NaCl and AT, respectively (P = .003 and .005, respectively). However, keratocyte cell density in the anterior and posterior stroma and endothelial cell density did not significantly differ following treatment with 5% NaCl or AT ointment (P > .05).

CONCLUSIONS

Short-term topical treatment with 5% NaCl decreased corneal thickness in normal dogs with no observable changes in corneal morphology or signs of ocular toxicity.

Phenotypic Characterization of Corneal Endothelial Dystrophy in German Shorthaired and Wirehaired Pointers Using In Vivo Advanced Corneal Imaging and Histopathology

PURPOSE

To evaluate corneal morphology using ultrasonic pachymetry (USP), Fourier-domain optical coherence tomography (FD-OCT), and in vivo confocal microscopy (IVCM) in 2 related canine breeds-German shorthaired pointers (GSHPs) and German wirehaired pointers (GWHPs)-with and without corneal endothelial dystrophy (CED). This condition is characterized by premature endothelial cell degeneration leading to concomitant corneal edema and is similar to Fuchs endothelial corneal dystrophy.

METHODS

Corneas of 10 CED-affected (4 GSHP and 6 GWHP) and 19 unaffected, age-matched (15 GSHP and 4 GWHP) dogs were examined using USP, FD-OCT, and IVCM. A 2-sample t test or Mann-Whitney rank-sum test was used to statistically compare parameters between both groups. Data are presented as mean ± SD or median (range).

RESULTS

Central corneal thickness determined using USP was significantly greater in CED-affected than in unaffected dogs at 1179 (953-1959) and 646 (497-737) μm, respectively (P < 0.001). Central epithelial thickness was found to be significantly decreased in CED-affected versus unaffected dogs at 47 ± 7.1 and 55 ± 7.1 μm, respectively (P = 0.011), using FD-OCT. With IVCM, corneal endothelial density was significantly less (P < 0.001) in 5 dogs with CED versus 19 unaffected controls at 499 ± 315 versus 1805 ± 298 cells/mm, respectively. CED-affected dogs exhibited endothelial pleomorphism and polymegethism, whereas CED-unaffected dogs had regular hexagonal arrangement of cells.

CONCLUSIONS

GSHPs and GWHPs with CED exhibit marked differences in corneal morphology when compared with age-matched control dogs. These 2 CED-affected breeds represent spontaneous, large animal models for human Fuchs endothelial corneal dystrophy.