A bidirectional corneoconjunctival transposition for the treatment of feline corneal sequestrum

A case is presented of a 1‐year‐old Persian cat with a corneal sequestrum treated with a bidirectional corneoconjunctival transposition. The size of this lesion precluded use of a traditional corneoconjunctival transposition. At the time of writing, the patient maintained a clear visual axis with minimal scarring and no recurrence 6 months post‐operatively. This report describes a novel surgical technique used to successfully treat a large feline corneal sequestrum.     

Amniotic membrane transplantation for the treatment of feline corneal sequestrum: pilot study

Objectives To describe and evaluate the use of equine amniotic membrane trans‐plantation after lamellar keratectomy for the treatment of corneal sequestrum in cats. Methods Six cats (seven eyes) of various breed and ages with corneal sequestra were treated surgically with lamellar keratectomy and amniotic membrane transplantation. All the sequestra and a small piece of the amniotic membranes used for each surgery were submitted for histopathologic examination. Results Five of the seven eyes showed minimal level of scarring in the cornea and good transparency. No recurrences of the sequestra have been noted during the follow‐up period (3–9 months). One eye had necrosis of the amniotic membrane 2 weeks after the surgery. The sequestrum of this eye showed a high level of bacterial contamination on histopathology. Three months later the same cat developed a descemetocele in the area where the necrotic amniotic membrane was rejected. A second eye developed a perforation under the amniotic membrane two weeks after the surgery. The sequestrum of this eye was deep and without vascularization. Conclusion Amniotic membrane transplantation after lamellar keratectomy was a valid procedure for surgical treatment of corneal sequestrum in cats. The procedure resulted in excellent cosmesis and functional vision in five of seven eyes; although case selection is important, particularly to exclude the very deep and non‐vascularized sequestra.     

Heterologous penetrating keratoplasty for treatment of a corneal sequestrum in a cat

A corneal sequestrum was diagnosed in an 8-year-old, neutered male Burmese cat. A heterologous penetrating keratoplasty (PK) (fresh canine corneal tissue) was performed to restore a clear visual axis. A heterograft was selected in order to decrease the risk of viral transmission as a screened donor was not available. One month postoperatively the graft was vascularized and opaque. The owner failed to return for recheck examinations until 16 months postoperatively at which time only a faint central nebula remained.     

Lamellar keratoplasty with a graft of lyophilized acellular porcine corneal stroma in the rabbit

Objective To evaluate the efficacy of lamellar keratoplasty in the rabbit using a graft of lyophilized acellular porcine corneal stroma (APCS). Animal studied Twelve adult 2–2.5 kg Zealand white rabbits were studied. Procedure The cell components of the porcine cornea were removed by the means of enzymatic digestion, freezing, and thawing and then APCS was lyophilized. The 6.5 mm diameter APCS was implanted on a 6.0‐mm diameter keratectomy wound each of 12 rabbits. The postoperative clinical and histological evaluations were performed in the early, intermediate, and late periods. Results All corneal wounds healed. Ten of the 12 grafts of APCS were integrated completely with the receptive cornea except two grafts scraped partially off by the eyelid. The blepharospasm, ocular discharge, and edema of the cornea were marked 1 week after transplantation. New vessels invaded the graft after week 2 and regressed after week 8. The cornea became transparent gradually. The histological evaluation showed that the epithelium on the graft stratified normally post surgery. The keratocytes of the recipient grew into the graft and were proliferative at week 4. The inflammatory cells and new vessels were observed before week 8. The fibrosis in the graft was revealed at week 4 and lessened at week 8. The histological structure of the cornea after surgery was similar to the normal cornea at week 32. Conclusions APCS can recover the integrity of the rabbit's cornea and become transparent in vivo. APCS is an effective graft for lamellar keratoplasty in the rabbit.     

The use of porcine small intestinal submucosa in ten cases of feline corneal disease

Porcine small intestinal submucosa (SIS) was used as a novel graft material in the management of 10 cases of feline corneal disease. Five cases had stromal ulceration associated with trauma, ocular foreign body and/or suspected infection and required a grafting procedure. Five cases had feline sequestra that were managed by a keratectomy prior to placement of SIS as a graft material. Eight eyes healed with minimal corneal scarring with a very good cosmetic and visual result. One eye with continued aqueous leakage in the immediate postoperative period required a conjunctival pedicle graft to reinforce the SIS graft site. One eye required enucleation 48 h following grafting due to progressive keratomalacia but the SIS material remained intact.     

Comparison of the pig and feline models for full thickness corneal transplantation

Purpose The goal of this study was to report on the advantages and limitations of the pig and feline models for experimental in vivo corneal transplantation. Methods Ten healthy domestic pigs and ten healthy cats were used. Full thickness penetrating keratoplasty was performed using autologous (eight cases), allogeneic (seven cases) or human xenogeneic (three cases) tissue. In two other cases, the inflammatory response to partial thickness trephination (without transplantation) was evaluated. Eyes were assessed daily before and after surgery by slit‐lamp, pachymetry, and tonometry. A transparency score ranging from 0 (opaque graft) to 4 (clear graft) was used, based on the slit‐lamp examination. Optical coherence tomography, histology, and electron microscopy were performed postmortem. Results In the pig, the mean (±SD) transparency score for the eight full thickness grafts was 0.88 ± 0.99, ranging from 0 to 3. In the feline model, the mean transparency score for the seven uncomplicated grafts was 3.93 ± 0.19, ranging from 3.5 to 4. Both negative controls without endothelium remained opaque at all time. Intraoperative tendency for iris incarceration into the wound, rapid corneal swelling, suture cheese wiring, and postoperative intraocular inflammation were the main factors jeopardizing the functional success of the corneal transplant in the pig model. Conclusion Suboptimal functional results were obtained after full thickness corneal transplantation in the pig model, while in the feline model, the same protocol yielded uneventful surgeries and clear transplants, with functional results similar to those achieved in human subjects.     

Ultrastructural findings in feline corneal sequestra

OBJECTIVES: (1) To describe the ultrastructural features of corneal sequestra in cats; and (2) to enhance our understanding regarding the pathogenesis of feline corneal sequestration. METHODS: Nine corneal sequestra were harvested via keratectomy from globes of nine cats. The sequestra were routinely fixed then postfixed for high resolution light and transmission electron microscopy (HR-LM and TEM, respectively). The tissues were embedded in Epon/Araldite. Sections of 0.5-microm thickness were cut and stained with 1% toluidine blue in 1% sodium tetraborate solution for HR-LM. Ultrathin sections were collected on copper grids and stained with uranyl acetate and Sato's lead stain for TEM. Ultrathin sections were examined and the images were captured on an Advantage HR CCD camera using a Hitachi 7500 electron microscope operated at 80 kV. Two healthy corneas from two cats were harvested immediately following euthanasia. These corneal tissues (control samples) were processed in the same manner as the corneal sequestra for HR-LM and TEM. A portion of each sequestrum was also submitted for polymerase chain reaction (PCR) testing for infectious agents including feline herpesvirus-1 (FHV-1), Toxoplasma gondii, Chlamydophila felis and Mycoplasma spp. RESULTS: Ultrastructure of healthy corneal tissues revealed basal corneal epithelial cells aligned adjacent to a thin acellular layer similar to Bowman's layer with underlying tightly packed, regularly arranged, collagen fibrils oriented in different planes. Keratocytes were elongated and had long and irregularly shaped nuclei, and cytoplasm contained rough endoplasmic reticulum and abundant membrane-bound vesicles. In contrast, corneal sequestra contained varying amounts of an amorphous, electron-dense substance, continuous with intact basal epithelial basement membranes peripherally, and overlying corneal ulceration and loosely packed collagen fibrils. Remnants of necrotic keratocytes were seen in spaces between disarranged collagen layers. In all samples, occasional keratocytes exhibited morphology indicative of apoptosis including clumping and margination of chromatin, and shrunken cytoplasm. Varying degrees of inflammation were noted on HR-LM and TEM of affected corneas including peri- and intralesional neutrophils, lymphocytes, plasma cells, and macrophages. Corneal sequestra were FHV-1-positive (n = 3), FHV-1- and T. gondii-positive (n = 1), T. gondii-positive (n = 3), or negative for DNA of these infectious agents (n = 2) using PCR. All corneal sequestra were negative for DNA of Chlamydophila felis and Mycoplasma spp. using PCR. CONCLUSIONS: Apoptosis may play a role in the pathogenesis of feline corneal sequestration independent of the presence of DNA of these infectious organisms. Prospective clinical studies are warranted to further understand the significance of T. gondii in relation to feline corneal sequestration.     

Feline corneal sequestrum: laboratory analysis of ocular samples from 12 cats

Feline corneal sequestrum is a common ocular condition typified by brown to black discoloration of the cornea. The nature of the discoloration has not been identified. The purpose of this study was to perform a laboratory investigation of ocular samples from 12 clinical cases of feline corneal sequestrum in an attempt to characterize the nature of the discoloration. The 12 cases were referred to the Ophthalmology Unit at the Animal Health Trust between April and September 2000, and were also part of a clinical review of 64 cases of feline corneal sequestrum described separately. Five laboratory techniques that are routinely performed at the Biomaterials Unit, Aston University were employed for analysis of the ocular samples. Ocular material included corneal sequestrum, tear samples, meibomian gland secretions, and bandage contact lenses from the 12 clinical cases. High-performance liquid chromatography data showed that total tear lipid in affected eyes was significantly lower than in control eyes (P = 0.016); total tear lipid in affected eyes was lower than in the unaffected, contralateral eyes of the same cat but the difference was not significant (P = 0.29). The presence of an unknown lipid class was observed in tears and meibomian secretions of affected, contralateral and control eyes. Scanning electron microscopy showed that the discoloration in affected corneas was not due to the presence of iron. Fluorescence spectroscopic analysis of sequestra, unaffected corneas and contact lenses (from affected and contralateral/unaffected eyes) showed that lipid and protein were present but did not play an important role in sequestra. Ultraviolet-visible light absorbance spectroscopy revealed a peak at 385 nm in unaffected corneas that was absent in sequestra and the difference was significant (P < 0.0001); this peak may be a characteristic feature of the normal feline cornea. The absorbance spectra displayed a peak at 280 nm in two sequestra suggesting that chromophore groups (e.g. melanin) were present. Optical microscopy performed on 10 sequestra revealed the presence of particles, which were consistent with the appearance of melanin particles, providing laboratory evidence that characterized the nature of the discoloration as melanin for the first time.     

Posterior lamellar keratoplasty for treatment of deep stromal absesses in nine horses

OBJECTIVE: To describe and evaluate the use of posterior lamellar keratoplasty as a surgical treatment for deep corneal stromal abscesses in horses. Animals studied Nine horses of various breeds and ages that presented with corneal stromal abscesses located in the posterior one-third of the cornea. Procedure Retrospective medical record study. RESULTS: Nine horses had deep corneal stromal abscesses that were treated with posterior lamellar keratoplasty. Median patient age was 3 years. Six patients were females and three were geldings. Medical therapy alone had been attempted prior to surgery in all nine animals. Corneal abscess culture and histopathology were performed in 8/9 horses. Cultures were positive for an infectious etiology in 4/8 (50%). Histopathology was positive for an infectious etiology in 5/8 (62.5%). Mean surgical time was 71.0 +/- 18.8 min and the average healing time was 23.7 +/- 5.2 days. Visual outcome was positive in 8/9 cases. Conclusion Posterior lamellar keratoplasty is a promising procedure for treatment of deep corneal stromal abscesses in horses. The procedure resulted in considerable shorter surgery time and healing time than had been observed with full-thickness penetrating keratoplasty. Scar formation with this procedure was not significantly different than with penetrating keratoplasty.     

Deep lamellar endothelial keratoplasty in 10 horses

Objective  To describe and evaluate a surgical technique utilized for the therapy of deep corneal stromal abscesses (DSA) in horses. The DSA is excised and replaced with a partial thickness corneal lamellar allograft.
Methods  A retrospective clinical study describing the indications for the surgical technique utilized and the outcomes of this procedure in 10 eyes of 10 horses.
Results  Each affected eye had a discrete DSA within the posterior stroma. An initial partial thickness semicircular corneal incision was made at the limbus, followed by anterior stromal lamellar dissection over the lesion. After excision of the DSA and replacement with a larger diameter split-thickness donor button, the anterior stroma was replaced into its original position and the initial corneal incision was repaired. All of the animals that underwent deep lamellar endothelial keratoplasty (DLEK) procedure healed appropriately and with subjectively less postoperative scarring and complications than previously described surgical approaches to DSA.
Conclusions  This procedure is an effective technique for surgical removal of DSA in horses and, in most cases, results in a visual and cosmetically acceptable globe. The advantages of this technique compared to other surgical approaches to DSA are the peripheral location of the incision, shortened anesthesia times, the resultant minimal scarring and shorter healing times associated with DLEK.     

Outcome following treatment of feline gastrointestinal mast cell tumours

Prognosis of feline gastrointestinal mast cell tumours (FGIMCT), based on limited available literature, is described as guarded to poor, which may influence treatment recommendations and patient outcome. The purpose of this study is to describe the clinical findings, treatment response, and outcome of FGIMCT. Medical records of 31 cats diagnosed with and treated for FGIMCT were retrospectively reviewed. Data collected included signalment, method of diagnosis, tumour location (including metastatic sites), treatment type, cause of death and survival time. Mean age was 12.9 y. Diagnosis was made via cytology (n = 15), histopathology (n = 13) or both (n = 3). Metastatic sites included abdominal lymph node (n = 10), abdominal viscera (n = 4) and both (n = 2). Therapeutic approaches included chemotherapy alone (n = 15), surgery and chemotherapy (n = 7), glucocorticoid only (n = 6) and surgery and glucocorticoid (n = 3). Lomustine (n = 15) and chlorambucil (n = 12) were the most commonly used chemotherapy drugs. Overall median survival time was 531 d (95% confidence interval 334, 982). Gastrointestinal location, diagnosis of additional cancers, and treatment type did not significantly affect survival time. Cause of death was tumour‐related or unknown (n = 12) and unrelated (n = 8) in the 20 cats dead at the time of analysis. The prognosis for cats with FGIMCT may be better than previously reported, with 26% of cats deceased from an unrelated cause. Surgical and medical treatments (including prednisolone alone) were both associated with prolonged survival times. Treatment other than prednisolone may not be necessary in some cats. Continued research into prognostic factors and most effective treatment strategies are needed.