Reconstruction of deep and perforating corneal defects in dogs-A review (Part II/III): Biomaterials and keratoprosthesis.

The surgical reconstruction of severe corneal ulcers is a common and crucial component of the clinical practice of veterinary ophthalmology. Numerous surgical techniques are used in dogs for corneal reconstruction, and these techniques may be categorized by the material used to repair the corneal lesion. The first part of the present review described procedures that utilize autogenous ocular tissues, homologous donor tissues, and heterologous donor tissues. In this second part of the review, the categories of biomaterials and keratoprosthetics will be summarized. Biomaterials that are reported for use in dogs include amniotic membrane, porcine urinary bladder acellular matrix, porcine small intestinal submucosa, acellular porcine corneal stroma, and other miscellaneous soft tissue and cartilage grafts (e.g., preserved equine renal capsule, autologous omentum, autologous buccal mucosa membrane, bovine pericardium, and homologous peritoneum). Descriptions of keratoprosthesis surgery in dogs are currently limited, but the use of artificial corneal transplants hold promise for dogs with severe, vision-compromising corneal disease that is not amenable to other reconstruction techniques. This review describes the results of experimental studies evaluating these graft materials in dogs, and it will summarize the findings and outcomes of the clinical articles published in each material category. Reporting inconsistencies and areas where additional research is required will be highlighted to help guide future studies in this area. A major aim of this review is to help identify potential subjects that could be evaluated in future investigations and that might lead to refinements in clinical practice.

Reconstruction of deep and perforating corneal defects in dogs-A review (Part I/III): Autogenous ocular tissues, donor tissues, and corneal clarity scoring.

Corneal reconstruction is a key part of veterinary ophthalmic practice and numerous reconstructive techniques have been described for use in small animals in the peer-reviewed veterinary literature written in English. Despite the evidence accrued over the last six decades in over 40 clinical articles and numerous other publications on ocular surface health, several key areas require further study. The comparison between studies is difficult due to elements that go beyond common factors, such as the indication for surgery, the reconstructive technique preferred by the surgeon or the availability of reconstructive materials. However, the differences in reporting style adopted by different authors between similar studies and the lack of data found in retrospective studies add to this complexity. The present review is divided into three parts. One covers the use of autologous materials for reconstruction and corneal transplants, as well as corneal clarity. A second part focuses on biomaterials and keratoprosthetics, while the third part focuses on the use of corneal sutures and report of ocular discomfort/pain in the veterinary literature. The review focuses on the main findings of each reconstruction technique. It aims to identify areas where key information about common procedures is missing so that general guidelines may be provided for the planning of patient record keeping and future retrospective or prospective studies, while it also aims to highlight the presence of knowledge gaps that deserve further attention.

The pandemic of ocular surface disease in brachycephalic dogs: The brachycephalic ocular syndrome.

Brachycephalic dog breeds are popular around the world, yet many brachycephalic dogs are affected by numerous health problems, including several head-related diseases that are directly linked to their conformation. In addition to the well-recognized disorders associated with the respiratory system (brachycephalic obstructive airway syndrome, i.e., BOAS), brachycephalic dogs have a concerningly high prevalence of ocular surface disorders that can cause chronic discomfort, loss of the globe, and/or require long-term, daily therapy. This review offers a summary of the physiological and anatomical features of brachycephalic ocular syndrome (BOS) that predispose brachycephalic dogs to develop ocular surface disease, followed by a concise description of common ocular diseases associated with BOS. It ends with an overview of evidence-based guidelines and animal welfare legislation that some in the veterinary community have already implemented but that requires a wider, international effort in order to reduce the prevalence of BOS-associated disorders and improve the ocular health of affected dogs.

Corneo-limbo-conjunctival transposition to treat deep and perforating corneal ulcers in dogs: A review of 418 eyes and corneal clarity scoring in 111 eyes.

PURPOSE: To report surgical and corneal clarity scores (CCSs) of corneo-limbo-conjunctival transpositions (CLCTs) in a large number of canine cases. METHODS: Retrospective review of records that underwent CLCT to repair deep ulcers or perforations between 2002 and 2018. Signalment, concurrent eye disease, additional procedures, pathogenesis, medication, graft orientation, follow-up, and CCSs were recorded. RESULTS: 418 eyes of 399 dogs were included. Brachycephalics were most commonly affected, comprising 325/418 (77.75%) of the eyes. The most commonly affected breeds were Pugs, Shih Tzus, Cavalier King Charles Spaniels, and French Bulldogs, with 116/418 (27.75%), 64/418 (15.31%), 34/418 (8.13%), and 34/418 (8.13%) ulcerated eyes, respectively. Mean age at surgery was 5.5 years (range 59 days-17.7 years), and median follow-up time was 100 days (range 3 days-7.64 years). The most common etiopathogenesis was spontaneous ulceration in 205/418 eyes (49.04%) of which 191 (93.17%) occurred in brachycephalics. Primary keratoconjunctivitis sicca affected 122/418 eyes (29.19%) and injury 39/418 eyes (9.33%). Mean ulcer width was 3.5 mm (0.5-10 mm). Success rate was 97.13% (406/418 eyes). Failure end points recorded included no menace response, secondary glaucoma, and endophthalmitis. Pre-existing perforation was found in 101/418 (24.16%) of the eyes and significantly increased failure rate (P < .001). The median CCS was G3 (G0-G4), which was lower for Pugs (G2). Graft orientation affected CCS, but did not reach statistical significance. CONCLUSION: The high success rate and CCS for CLCT in dogs make it a good technique to treat deep ulcers but a less desirable outcome is anticipated when treating perforations and Pugs.

Progressive retrocorneal pigmentation in dogs: A clinical report of 34 cases.

OBJECTIVES: To describe the signalment, ophthalmic examination findings, and follow-up of dogs affected with a previously unreported retrocorneal pigmentary lesion. MATERIALS AND METHODS: Retrospective record evaluation spanning 2009-2019. RESULTS: Retrocorneal pigmentary lesions were described in 34 patients (46 eyes). German Shepherds (n = 7), Jack Russel terriers (n = 5), and terrier crosses (n = 4) made up 16/34 (47.1%) of the cases. The mean age was 13.5 years (range 1.4-14.2 years), and 16/30 (53.3%) dogs were female. Most dogs were affected unilaterally (22/34 (64.7%)), the others bilaterally, and 5/34 (14.7%) were referred for it while the others were incidentally diagnosed. The lesions affected the ventral, peripheral, inner cornea and had a round/undulated leading edge. The number of corneal clock hours affected was known for 41/46 (89.1%) eyes and involved 1-3 clock hours in 32/41 (78.1%) eyes, 4-6 in 6/41 (14.6%), 7-9 in 2/41 (4.9%), and 10 in 1/41 (2.4%). The central cornea was affected in 9/46 (19.6%) eyes, and in 5/9 (55.6%), the median corneal clarity score was G2 (scale: G0-G4). The commonest additional findings included free-floating uveal cysts (11/34 dogs, 32.4%), cataracts (6/34 dogs, 17.6%), and primary glaucoma (5/34 dogs, 14.7%). Gonioscopy was available in 16/34 (47.1%) dogs and was normal except in primary glaucoma cases. Follow-up was documented in 13/34 (38.2%) dogs with a mean follow-up of 17 months (range: 5-26 months). Lesion progression was documented in 6/13 (46.2%) dogs. CONCLUSIONS: Retrocorneal pigmentation occurs as a slowly progressive lesion of older dogs that could impact vision. Histological studies of affected eyes are warranted.

Effect of Insulin and Fasting Regimen on Blood Glucose Concentrations of Diabetic Dogs During Phacoemulsification.

This study aimed to compare four protocols for preanesthetic insulin administration and fasting time with respect to the variation of intraoperative blood glucose (BG) concentrations versus preanesthetic values (baseline). The patient records of dogs undergoing cataract surgery were included. Data on anesthetic protocols, comorbidities, and intraoperative complications (hyper- and hypoglycemia, hypotension, hypothermia, and bradycardia) were analyzed. The insulin/fasting protocols included (A) 12 hr fasting and half insulin dose, (B) 6 hr fasting and half insulin dose, (C) 12 hr fasting and full insulin dose, and (D) 12 hr fasting and no insulin. Forty-eight dogs were included (14 in A, 10 in B, 13 in C, and 11 in D). Protocol D resulted in a significant increase of intraoperative BG concentrations compared with baseline (P = .001), whereas in the remaining groups, the baseline BG did not differ from intraoperative values. There were no statistically significant associations between the treatment group and the occurrence of intraoperative complications or the presence of diagnosed comorbidities. In conclusion, different insulin and fasting regimen protocols may be used for diabetic patients with no apparent benefit or risk from one protocol versus another. The use of insulin before surgery results in lesser increase of BG intraoperatively as compared with preanesthetic values. However, whether this should be interpreted as better perioperative control of glycemia remains debatable.

Rabbits with naturally occurring cataracts referred for phacoemulsification and intraocular lens implantation: a preliminary study of 12 cases.

OBJECTIVE: To describe the presentation of 15 rabbits with naturally occurring cataracts referred for phacoemulsification surgery, the procedure in 13 cases and the follow-up in 12. ANIMALS INCLUDED: Fifteen rabbits (30 eyes), nine of which stopped following visual cues in association with cataract progression. MATERIALS AND METHODS: Rabbits underwent preoperative ophthalmic and ocular ultrasound examination. RESULTS: Thirteen rabbits (22 eyes) had mature cataracts. Ten were bilateral and three unilateral. Two rabbits had an anterior chamber abscess. The cataract in one of these was incipient. One rabbit had bilateral immature cataracts. One rabbit had a subluxated lens, and one had a retinal detachment. Thirteen rabbits (22 eyes) underwent phacoemulsification. Eighteen, 13.5-mm capsular tension rings (CTRs) and seventeen, 13-mm IOLs (Acrivet® , Berlin, Germany) were fitted including one 41D 60V-model, and three 49D and thirteen 58D 20S-models. Intraoperative complications included one unilateral posterior-capsular tear, one lens subluxation, and one expulsive choroidal hemorrhage. One rabbit died during anesthetic recovery. Nine cases were PCR-tested for Encephalitozoon cuniculi, and only three were positive. The median follow-up time was 12 months (4-24 months). Rabbits that were not following visual cues preoperatively did so postoperatively, and surgery resulted in a clear visual axis for the follow-up period in every case except in two, due to reasons other than the surgery. CONCLUSIONS: Phacoemulsification with CTR and IOL implantation offers good long-term results and can improve the quality of life of pet rabbits. Retinal detachment, lens luxation, expulsive choroidal hemorrhage, and anesthetic death are potential complications.

Calculation of posterior chamber intraocular lens (IOL) size and dioptric power for use in pet rabbits undergoing phacoemulsification.

OBJECTIVES: To calculate the size and dioptric power of a posterior chamber intraocular lens (IOL) to achieve emmetropia in adult rabbits and to compare the dioptric power calculation results using a proprietary predictive formula to a retinoscopy-based method. ANIMALS STUDIED: Three wild rabbit cadavers, seven pet rabbits with cataracts and ten healthy pet rabbits. MATERIALS AND METHODS: Implant size was calculated using a capsular tension ring (CTR) (Acrivet® , Berlin, Germany). Published and cadaveric biometric data were used in the predictive formula. An IOL power-escalation study compared the predicted values to the refraction results of one pet rabbit (P1) fitted with a + 41D canine IOL (Acrivet® ) and six pet rabbits (P2-P7) fitted with prototype IOLs (Acrivet® ). Retinoscopy of 10 healthy pet rabbits served as controls. RESULTS: A 13.5 mm CTR fitted in all rabbits and permitted the use of a 13 mm IOL. The predicted IOL power ranged between +24D and +25D. The +41D IOL resulted in a refraction error of +8D. Progressive recalculation through a calibration formula led to the insertion of three +49D IOLs in two pet rabbits and a refraction of +6D to +8D, followed by seven +58D IOLs in four pet rabbits and a refraction median of 0D (range: -1.5D to +1D). CONCLUSIONS: A 13 mm prototype IOL of +58D achieves emmetropia and is of adequate size for rabbits. The combined use of a CTR and retinoscopy is a useful method to calculate the size and refractive power of a new, species-specific, veterinary IOL.

The effect of repeated eye examinations and breeding advice on the prevalence and incidence of cataracts and progressive retinal atrophy in German dachshunds over a 13-year period.

OBJECTIVE: To analyze the change in prevalence and incidence of hereditary eye diseases (HED) in dachshunds due to breeding regulations based on biennial examinations performed by the German panel of veterinary ophthalmologists (DOK) from 1998 to 2011. ANIMALS INCLUDED: A total of 12 242 dachshunds examined by the DOK and pedigree data of 318 852 dachshunds provided by the German Dachshund Club (DTK). PROCEDURES: The prevalence of congenital cataract (CC), distichiasis (DIST), hereditary cataract (HC), persistent pupillary membranes (PPMs), persistent hyperplastic tunica vasculosa lentis / persistent hyperplastic primary vitreous (PHTVL/PHPV), progressive retinal atrophy (PRA), retinal dysplasia (RD), and findings such as fiberglass-like cataract (FGC) and prominent suture lines (PSLs) was analyzed. The significance (P), confidence interval (CI), odds ratio (OR), relative risk (RR) and inbreeding coefficients (F) were calculated and P < 0.05 was considered significant. The incidence was evaluated based on affected dogs within birth cohorts from 1993 to 2006. RESULTS: The prevalent conditions studied were as follows: CC 0.5%, DIST 6.7%, HC 3.9%, PPMs 8.4%, PHTVL/PHPV 0.4%, PRA 1.5%, RD 0.2%, FGC 2.2%, and PSL 1.5%. The incidence of PRA decreased significantly from 6.0% to 0.6% for dogs born from 1993 to 2006, while HC showed a decreasing trend from 8.7% to 3.1%. More males than females were diagnosed with HC and PRA. Dachshunds with HEDs had an F that was not significantly higher than that of healthy dachshunds. CONCLUSIONS: The decreasing incidence of PRA and HC in dachshunds supports the use of frequent HED examinations in combination with breeding control.

Immediate effects of diamond burr debridement in patients with spontaneous chronic corneal epithelial defects, light and electron microscopic evaluation.

PURPOSE: To evaluate immediate effects of diamond burr debridement (DBD) on the cornea of canine patients diagnosed with spontaneous chronic corneal epithelial defects (SCCEDs). ANIMALS STUDIED: Eight client owned dogs with SCCEDs. METHODS: Nine eyes from eight dogs with SCCEDs underwent superficial keratectomy (SK). The ulcerated area was divided into quadrants with a 300-micron restricted depth knife. Two of four quadrants underwent DBD for 40-60 s. A SK followed immediately. One burred section and one nonburred section were fixed with formaldehyde 10% and underwent light microscopy (LM). The remaining quadrants from five eyes were fixed with glutaraldehyde 2.5% and underwent transmission electron microscopy (TEM). Masked pathologists evaluated the samples. A student's paired t-test was used to analyze the data. RESULTS: With LM all nonburred samples had a superficial stromal hyaline acellular zone (HAZ), seven of the burred samples had an intermittent HAZ and in two burred samples this zone was absent. The HAZ thickness of burred samples (1.062 ± 0.664 µm) was significantly thinner than that of the nonburred samples (4.309 ± 1.348 µm) (P < 0.0001). Transmission electron microscopy showed an absence of basement membrane and the presence of an amorphous, fine fibrillar material in the superficial stroma in nonburred samples. This material was intermittent or absent in burred samples. CONCLUSION: DBD significantly reduces the superficial stromal HAZ in SCCEDs. A reduction of its thickness may be responsible for the healing rates reported with DBD.

A prospective study of the prevalence of corneal surface disease in dogs receiving prophylactic topical lubrication under general anesthesia.

OBJECTIVE: To identify the prevalence of corneal ulceration in dogs receiving prophylactic gel lubrication under general anesthesia (GA). MATERIALS AND METHODS: An ophthalmic examination was performed before premedication and 24 h after GA in 100 dogs (199 eyes) undergoing nonophthalmic procedures. Individuals with known pre-existing ocular surface conditions were excluded. An ocular lubricating gel containing carmellose sodium was applied by the anesthetist at induction and every 2-4 h until extubation. Logistic regression analysis was used to calculate risk factors for ulcerative disease, including signalment, length of GA, patient position, procedure performed, pre-, and post-GA ophthalmic examination findings and admitting service. A Wilcoxon rank sum test compared pre- and post-GA Schirmer tear test-1 (STT-1) values. RESULTS: One dog (0.5% of total eyes) developed fluorescein stain uptake consistent with superficial corneal ulceration that resolved within 48 h with supportive treatment. Twenty-five (18.6% of total eyes) developed a faint, patchy corneal uptake of stain in the axial cornea that was consistent with epithelial erosion. All erosions resolved with lubrication 24 h later. The decrease in STT-1 readings at 24 h post-GA was statistically significant from those pre-GA (P < 0.001). No significant risk factors for corneal erosion/ulceration were identified. CONCLUSIONS: The results of this study show that a basic protocol of prophylactic lubrication during GA was associated with a low prevalence of corneal ulceration but a higher prevalence of epithelial erosion. In addition, the study supports the need for post-GA corneal examination.

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.

Use of atracurium and its reversal with neostigmine in 14 pet rabbits undergoing ophthalmic surgery: a retrospective study.

The objective of this retrospective study was to report the clinical use of atracurium and its reversal with neostigmine in pet rabbits. The medical records of 14 rabbits undergoing anaesthesia for ophthalmic surgery were located through a search of the hospital's database. Demographic data and data pertaining to the use of the neuromuscular blocker and its reversal were analysed. After intravenous administration of 0.44±0.4 mg/kg atracurium (total dose), 11 rabbits experienced at least one of the following cardiovascular responses: hypotension, defined as systolic arterial pressure less than 75 mmHg (n=6), hypotension with decreased heart rate (HR) (n=1), hypotension with increased HR (n=1), decreased arterial blood pressure (ABP) without hypotension (n=6), decreased ABP with decreased HR (n=1), or increased HR (n=2, ABP reading could not be taken). Two of these 11 rabbits also experienced severe intraoperative hypothermia. The neuromuscular block was monitored with a train-of-four nerve-stimulation pattern, and reversed, with intramuscular 0.01-0.045 mg/kg neostigmine and 0.01-0.02 mg/kg glycopyrronium, after the return of at least two out of four muscular twitches following nerve stimulation. Decrease in ABP and possibly hypothermia are likely intraoperative complications when clinical doses of atracurium are administered to pet rabbits. Measures should be taken to detect their occurrence in order to treat them promptly.

Corneal ulcerative disease in dogs under primary veterinary care in England: epidemiology and clinical management.

BACKGROUND: Corneal ulcerative disease (CUD) has the potential to adversely affect animal welfare by interfering with vision and causing pain. The study aimed to investigate for the first time the prevalence, breed-based risk factors and clinical management of CUD in the general population of dogs under primary veterinary care in England. RESULTS: Of 104,233 dogs attending 110 clinics participating within the VetCompass Programme from January 1st to December 31st 2013, there were 834 confirmed CUD cases (prevalence: 0.80%, 95% confidence interval (CI) 0.75-0.86). Breeds with the highest prevalence included Pug (5.42% of the breed affected), Boxer (4.98%), Shih Tzu (3.45%), Cavalier King Charles Spaniel (2.49%) and Bulldog (2.41%). Purebred dogs had 2.23 times the odds (95% CI 1.84-2.87, P < 0.001) of CUD compared with crossbreds. Brachycephalic types had 11.18 (95% CI 8.72-14.32, P < 0.001) and spaniel types had 3.13 (95% CI 2.38-4.12, P < 0.001) times the odds for CUD compared with crossbreds. Pain was recorded in 385 (46.2%) cases and analgesia was used in 455 (54.6%) of dogs. Overall, 62 (7.4%) cases were referred for advanced management and CUD contributed to the euthanasia decision for 10 dogs. CONCLUSIONS: Breeds such as the Pug and Boxer, and conformational types such as brachycephalic and spaniels, demonstrated predisposition to CUD in the general canine population. These results suggest that breeding focus on periocular conformation in predisposed breeds should be considered in order to reduce corneal disease.

Mini-Review: Limbal Stem Cells Deficiency in Companion Animals: Time to Give Something Back?

Experimental animals have been used extensively in the goal of developing sight-saving therapies for humans. One example is the development of transplantation of cultured limbal epithelial stem cells (LESC) to restore vision following ocular surface injury or disease. With clinical trials of cultured LESC therapy underway in humans and a potential companion animal population suffering from similar diseases, it is perhaps time to give something back. Comparatively to humans, what is known about the healthy limbus and corneal surface physiology of companion animals is still very little. Blinding corneal diseases in animals such as symblepharon in cats with Feline Herpes Virus-1 infections require a basic understanding of the functional companion animal limbus and corneal stem cells. Our understanding of many other vision threatening conditions such as scarring of the cornea post-inflammation with lymphocytic-plasmacytic infiltrate in dogs (aka chronic superficial keratitis) or pigment proliferation with Pigmentary Keratitis of Pugs would benefit from a better understanding of the animal cornea in health and disease. This is also vital when new therapeutic approaches are considered. This review will explore the current challenges and future research directions that will be required to increase our understanding of corneal diseases in animals and consider the potential development and delivery of cultured stem cell therapy to veterinary ocular surface patients.