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

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.

Topical Ripasudil for the Treatment of Primary Corneal Endothelial Degeneration in Dogs

Purpose

The purpose of this study was to evaluate the tolerability and efficacy of topical rho-kinase inhibitor ripasudil in the treatment of primary corneal endothelial degeneration (PCED) in dogs.

Methods

Twenty-one eyes of 12 client-owned, PCED-affected dogs received topical ripasudil 4 times daily. Ophthalmic examination, ultrasonic pachymetry (USP), Fourier-domain optical coherence tomography (FD-OCT), and in vivo confocal microscopy were performed at baseline and 1, 3, 6, and 12 months. Effects of treatment on corneal thickness, corneal edema extent, and endothelial cell density (ECD) were evaluated by repeated-measures ANOVA or Friedman test. Individual eyes were classified as improved, progressed, or stable at 12 months using clinical response criteria. Kaplan-Meier curves and log-rank test were used to compare ripasudil-treated eyes to age-, breed/size-, and disease stage-matched historical controls.

Results

During treatment, 12 dogs developed conjunctival hyperemia, 4 demonstrated reticular bullous epithelial edema, and 2 developed corneal stromal hemorrhage. No adverse event necessitated permanent cessation of ripasudil. Central corneal thickness measured by USP significantly progressed from baseline to 12 months. Corneal thickness by FD-OCT, ECD, and edema extent did not differ over time. Considered individually, 5 eyes improved, 8 remained stable, and 8 progressed. The log-rank test found less edema progression in ripasudil-treated eyes compared to historical controls.

Conclusions

Ripasudil was well-tolerated in PCED-affected dogs. Response to therapy varied; 62% of eyes showed improved or stable disease whereas 38% progressed. Ripasudil-treated eyes progressed more slowly than historical controls.

Translational Relevance

Topical ripasudil offered a therapeutic benefit in a subset of patients using a canine model of endothelial degeneration, which may guide future trials in humans.

A multicenter retrospective evaluation of the prevalence of known and presumed hereditary eye diseases in Lagotto Romagnolo dog breed within a referral population in Italy (2012-2020)

OBJECTIVE

To describe the ophthalmological findings of Lagotto Romagnolo dog breed and to report the prevalence of Known and Presumed Hereditary Eye Diseases (KP-HED).

ANIMALS STUDIED

Two hundred sixteen dogs were examined and included in this retrospective study.

PROCEDURES

Medical records of Lagotto Romagnolo dogs between 2012 and 2020 were included. Data about the ocular status were collected through ocular screening examinations (OSE) or clinical ophthalmic examinations (COE). The prevalence of each KP-HED was expressed as a function of the total number of the KP-HED in this referral population.

RESULTS

A total of 85 dogs (39.35%) were ophthalmologically healthy, ocular diseases presumably not hereditary were found in 43 dogs (19.91%), and 88 dogs (40.74%) were affected by one KP-HED. The most common KP-HEDs diagnosed were cataract (28/88; 31.82%), corneal endothelial dystrophy (17/88; 19.32%), retinal dysplasia (9/88; 10.23%), lens instability (7/88; 7.95%), progressive retinal atrophy (6/88, 6.82%), and keratoconjunctivitis sicca (6/88, 6.82%). Most of dogs with a KP-HED (77.27%, 68/88) were identified within COE group.

CONCLUSIONS

To the authors' knowledge, this is the first report of the prevalence of ocular disease in the Lagotto Romagnolo dog breed within a referral population in Italy. This study suggests a relatively high prevalence of KP-HED, with a characteristic late-onset presentation in some diseases. Many of these KP-HED's, lead to ocular pain and irreversible blindness, for this reason, the authors highlight the importance of aiming for an early diagnosis. Breeder's efforts and breeding programs should be directed at limiting such disorders.

Multimodal ocular imaging of known and novel corneal stromal disorders in dogs

Background

Imaging features obtained with Fourier-domain optical coherence tomography (FD-OCT) and in vivo confocal microscopy (IVCM) for corneal stromal disorders have been sparsely reported in dogs. This case report is a compilation of imaging features for three cases of different stromal disorders of the canine cornea which have not yet been reported elsewhere.

Case presentation

Lipid deposition in case 1 appeared as needle-shaped hyperreflective lines along the collagen lamellae, which correlated histologically with lipid clefts. In case 2, glycosaminoglycan accumulation by mucopolysaccharidosis type 1 caused diffuse stromal hyperreflectivity and depletion of keratocytes on IVCM and was associated with secondary corneal degeneration presumed to be calcium deposition. In case 3, posterior corneal stromal opacities in the absence of ocular inflammation were identified. Hyperreflective particles were scattered in the middle and posterior corneal stroma on FD-OCT. With IVCM, hyperreflective deposits were identified within keratocytes and the number of enlarged keratocytes containing hyperreflective deposits increased towards the posterior stroma. The bilateral, non-inflammatory nature and unique appearance with IVCM is most consistent with a posterior stromal dystrophy reminiscent of pre-Descemet corneal dystrophy described in humans.

Conclusions

In vivo multimodal corneal imaging facilitated instantaneous microstructural analysis and may be valuable in the differential diagnosis of corneal stromal disorders in veterinary clinical practice. The non-specific nature of imaging findings occurs in some conditions such as mucopolysaccharidosis, thus in vivo corneal imaging should be complemented with other gold standard methods of definitive diagnosis.

Primary cell culture of canine corneal endothelial cells

OBJECTIVE

To establish a primary cell culture and clarify the characteristics of canine corneal endothelial cells in vitro.

PROCEDURES

The eyes were enucleated from dogs that were euthanized for reasons unrelated to this study. Enucleated canine eyes were dissected, and the intact corneas were isolated from the globes. Using enzymes, the corneal endothelial cells were dispersed from the cornea. The obtained canine corneal endothelial cells were cultured in a cell culture dish. Cultured corneal endothelial cells were morphologically evaluated using phase-contrast microscopy. Immunohistochemical analysis of the cultured cells, particularly of the corneal endothelial cell marker, zonula occludens-1 (ZO-1), Na⁺ /K⁺ -ATPase, and vimentin, was performed to clarify whether the cultured cells were actually corneal endothelial cells. Furthermore, the post-passage morphology of cultured cells was evaluated.

RESULTS

Canine primary cultured corneal endothelial cells showed morphologically small, cobblestone-like structures. The isolated cells had proliferative ability in vitro and demonstrated positive expression of the corneal endothelial cell markers, ZO-1, Na⁺ /K⁺ -ATPase, and vimentin. However, repeated passages resulted in larger cell sizes as assessed by phase-contrast microscopy. Repeated passages also resulted in lower cell density.

CONCLUSIONS

This study demonstrated the successful culture of canine corneal endothelial cells. This might enhance the understanding of corneal endothelial cell characteristics in dogs.

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.

Corneal Dystrophy in Dutch Belted Rabbits as a Possible Model of Thiel-Behnke Subtype of Epithelial-Stromal TGFβ-Induced Corneal Dystrophy

The International Committee for Classification of Corneal Dystrophies (IC3D) categorized corneal dystrophies in humans using anatomic, genotypic, and clinicopathologic phenotypic features. Relative to the IC3D classification, a review of the veterinary literature confirmed that corneal dystrophy is imprecisely applied to any corneal opacity and to multiple poorly characterized histologic abnormalities of the cornea in animals. True corneal dystrophy occurs in mice with targeted mutations and spontaneously in pet dogs and cats and in Dutch belted (DB) rabbits, but these instances lack complete phenotyping or genotyping. Corneal dystrophy in DB rabbits can be an important confounding finding in ocular toxicology studies but has only been described once. Therefore, the ophthalmology and pathology of corneal dystrophy in 13 DB rabbits were characterized to determine whether the findings were consistent with or a possible model of any corneal dystrophy subtypes in humans. Slit lamp and optical coherence tomography (OCT) imaging were used to characterize corneal dystrophy over 4 months in young DB rabbits. The hyperechoic OCT changes correlated with light microscopic findings in the anterior stroma, consisting of highly disordered collagen fibers and enlarged keratocytes. Histochemical stains did not reveal abnormal deposits. Small clusters of 8 to 16 nm diameter curly fibers identified by transmission electron microscopy were consistent with Thiel-Behnke (TBCD) subtype of epithelial-stromal transforming growth factor β-induced dystrophies. Sporadic corneal dystrophy in DB rabbits appears to be a potential animal model of TBCD, but genotypic characterization will be required to confirm this categorization.

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.

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.