Results of grid keratotomy, superficial keratectomy and debridement for the management of persistent corneal erosions in 92 dogs

Ninety-two cases of persistent corneal erosions in dogs were analyzed for breed, gender, age and which eye was affected. The results of the treatment of 92 persistent corneal erosions in dogs by superficial keratectomy (SK), grid keratotomy (GK), or debridement with a sterile dry cotton swab are presented. These techniques gave better rates of healing than have been previously reported. All cases of persistent corneal erosions healed in this study. However, it must be noted that three cases treated with debridement only failed to heal after several treatments and were eventually treated with SK. After one procedure 80 out of 92 (87%) had healed. After one procedure, 63% of cases treated with debridement healed, 100% of cases treated with SK healed, and 85% of cases treated with GK healed. At the first postoperative visit, 88% (21/24 cases) of ulcers treated by SK had healed, and 75% (39/52 cases) of ulcers treated by GK had healed. Only 25% of the persistent corneal erosions had healed at the first visit after debridement. All 24 cases of persistent corneal erosions treated with SK healed after one treatment in a mean +/- SD of 9.3 +/- 3.9 days (median of 7 days). Fifty-two cases were managed with GK; 44 (83%) of these healed with one procedure and eight cases required a second GK procedure to resolve. A mean +/- SD of 13.4 +/- 5.1 days (median of 11.5 days) following GK was required for the persistent corneal erosions to heal. Nineteen cases were initially managed by debridement with a dry cotton swab under local anesthesia. Sixteen out of these 19 debridement cases healed (giving an overall healing rate of 84%) in a mean +/- SD time of 23.4 +/- 11.1 days (median 21.5). There were three cases that did not heal with debridement. These cases were debrided at 10-20 day intervals for 30-60 days, and were then treated with SK. Two of these cases healed within 7 days, the other case required 18 days to heal. Sixty-three per cent of persistent corneal erosions treated with debridement healed after one procedure; however, only four out of 19 cases (21%) were healed at the first revisit. Complications were rare: corneal edema occurred in two cases following multiple GK, and excessive granulation tissue in one case was managed with a SK. There was the occurrence of an ulcer adjacent to the surgery site in four cases, two cases following GK and two cases following SK.     

Histologic evaluation of the immediate effects of diamond burr debridement in experimental superficial corneal wounds in dogs

Purpose To evaluate the corneal changes immediately after diamond burr debridement of superficial corneal wounds in dogs. Spontaneous chronic corneal epithelial defects (SCCEDs) are the most common form of canine recurrent corneal ulcers. The diamond burr has been used in the management of corneal lesions in humans since 1983. Recently, it has been successfully used in the treatment of SCCEDs in dogs; however, little has been documented as to its mechanism of action. Methods Five adult female research dogs euthanized for reasons unrelated to the study were included, providing 10 normal eyes. An excimer laser spatula was used for epithelial removal after delineation with an 8 mm punch biopsy trephine. Diamond burr debridement was performed for 30 and 45 s in five eyes each (groups 1 and 2 respectively). The procedure was performed on the ventral half of the experimental defect as well as ventral normal cornea, immediately after euthanasia, and prior to enucleation. Samples were processed routinely for histologic evaluation and stained with periodic acid–Schiff. Results No stromal defects could be identified under light microscopy. In experimental corneal wounds, multi‐focal areas remained covered by the epithelial basement membrane (BM) after diamond burr treatment in both groups (group 1 = 48%±16SD, group 2 = 26%±12SD). Removal of BM on group 2 was significantly higher than group 1 (P < 0.05). Conclusions The diamond burr allows a safe method of debridement and does not create defects beyond the epithelial BM in corneal wounds in normal dogs. Evaluation of the diamond burr debridement in cases of SCCEDs is warranted.     

Feline corneal disease

The cornea is naturally transparent. Anything that interferes with the cornea's stromal architecture, contributes to blood vessel migration, increases corneal pigmentation, or predisposes to corneal edema, disrupts the corneas transparency and indicates corneal disease. The color, location, and shape and pattern of a corneal lesion can help in determining the underlying cause for the disease. Corneal disease is typically divided into congenital or acquired disorders. Congenital disorders, such as corneal dermoids are rare in cats, whereas acquired corneal disease associated with nonulcerative or ulcerative keratitis is common. Primary ocular disease, such as tear film instability, adenexal disease (medial canthal entropion, lagophthalmus, eyelid agenesis), and herpes keratitis are associated with the majority of acquired corneal disease in cats. Proliferative/eosinophilic keratitis, acute bullous keratopathy, and Florida keratopathy are common feline nonulcerative disorders. Nonprogressive ulcerative disease in cats, such as chronic corneal epithelial defects and corneal sequestration are more common than progressive corneal ulcerations.     

Management of spontaneous chronic corneal epithelial defects (SCCEDs) in dogs with diamond burr debridement and placement of a bandage contact lens

Objective To describe the outcome of canine spontaneous chronic corneal epithelial defects (SCCED) treated with diamond burr debridement (DBD) and bandage contact lens placement (BCL). Animal studied Forty eyes of 36 dogs presenting to a single private practice. Procedures A retrospective review of medical records was performed. Cases were eligible for inclusion if they were newly diagnosed with SCCED by a veterinary ophthalmologist and treated with DBD/BCL. All patients received a complete ocular examination followed by DBD using a battery‐powered, handheld motorized burr (Algerbrush^®, Alger Equipment Company, Lago Vista, TX, USA). A BCL was placed post‐debridement in all patients. Data were analyzed for sex, age, breed, duration of clinical signs prior to DBD; number of debridements required before healing was achieved; contact lens retention, complications attributed to DBD, and additional surgical interventions were required to achieve healing. Results The median time to first recheck examination was 7 days (IQR 7–9 days) with 28/40 (70%) of cases healed at this examination. The mean time to second recheck examination was 15.5 ± 5.5 days with 37/40 (92.5%) healed by this examination. The median time to final recheck examination was 19 days (IQR 18–35.5 days) with a range of 18–52 days. All cases resolved by the third and final recheck examination. A second DBD/BCL was performed in 5/40 (12.5%) of cases. The BCL retention rate was 95% over all examination time points. No case required a keratectomy or other surgical intervention to achieve healing. The only complication observed was one case of suspected bacterial keratitis post‐DBD/BCL. Conclusions Results suggest that DBD/BCL is safe and effective for treatment of canine SCCED.     

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.     

Lamellar keratoplasty for the treatment of feline corneal sequestrum

A lamellar keratoplasty was used to treat corneal sequestrum in four Persian cats (six eyes). Following a superficial keratectomy, lamellar corneal allografts (feline corneal tissue) or heterografts (canine corneal tissue) which had been preserved at –20 °C were placed in the recipient cornea. All grafts became optically transparent within 2 months following surgery and no recurrences of the sequestrum have been noted during the follow-up period (4–30 months). We conclude that feline corneal sequestrum may be successfully treated with feline or canine donor corneal tissue using this technique.     

Early postnatal development of central corneal thickness in dogs

Objective To investigate the changes in corneal thickness that occur during maturation of the canine eye over the first months of life. Animals studied Dogs of two different breeds with ages ranging from 14 days to 42 weeks of age. Procedures The central corneal thickness was measured by ultrasonic pachymetry every week for the first month after eyelid opening (around 14 days) and then every month until 42 weeks of age. Segmented regression was applied to capture the two phases observed in the central corneal thickness plotted against age. Breed, eye and gender were also included in the model. Results Mean central corneal thickness (CCT) values initially decreased following eyelid opening, with the lowest point being reached at around 6 weeks of age. Then CCT gradually increased as the dogs matured. Differences between left and right eye were not significant. Breed and gender effects were significant factors in the statistical model. Conclusions Following eyelid opening there is an initial decrease in corneal thickness until approximately 6 weeks of age, which presumably mirrors maturation of corneal endothelial cell function. After 6 weeks of age the CCT increases with age until approximately 30 weeks of age after which there was only a gradual increase over the remainder of the study period. A similar pattern of changes in corneal thickness in humans has been previously recorded.     

Central corneal thickness in koi fish: effects of age, sex, body length, and corneal diameter

OBJECTIVE: To establish the central corneal thickness (CCT) of normal koi fish by ultrasonic pachymetry, and its relationship to age, sex, body length and corneal diameter. METHODS: Age, sex and body length of 33 koi fish (17 male and 16 female fish) were recorded. Horizontal and vertical corneal diameters of each eye were obtained using Jameson calipers. Central corneal thickness of all eyes was measured by ultrasonic pachymetry. Intraocular pressure (IOP) by rebound tonometry was obtained for a subgroup of nine koi (18 eyes). RESULTS: Mean central corneal thickness was 325.9 microm. Central corneal thickness of female koi was greater than CCT of male fish (P < 0.01). Central corneal thickness increased with increasing age overall and within both sexes (P < 0.01). Central corneal thickness increased with increasing body length (P < 0.001). For male and female fish, CCT increased with increasing horizontal and vertical corneal diameters (P < 0.01). Mean horizontal corneal diameter (HCD) was 8.05 mm, mean vertical corneal diameter (VCD) was 7.38 mm, and HCD was consistently greater than VCD. Mean IOP of a subgroup of these koi was 4.9 mmHg by rebound tonometry. CONCLUSIONS: Koi CCT increases with increasing age, body length and corneal diameter.     

Cultivation of corneal epithelial cell sheets on canine amniotic membrane

Objective To develop and assess canine corneal epithelial cell sheets cultivated from limbal stem cells on amniotic membrane. Procedures Canine corneal limbal segments were obtained from six beagle dogs. Cryopreserved denuded amniotic membranes (obtained from Miniature Dachshund and Cavalier King Charles Spaniel breeds) from which the epithelial cells were removed were used as scaffolds. The limbal segments were cultured on these amniotic membranes with 3T3 feeder cells for 2 weeks. The harvested corneal epithelial cell sheets were stained with H&E for histologic analysis. The harvested sheets were analyzed immunohistochemically using a corneal epithelium‐specific marker keratin 3(K3) and putative stem cell markers ABCG2, p63, and vimentin. Results Cultivated cells from the corneal limbal tissues reached confluency in 7–8 days. The cultivated cells adhered to the denuded amniotic membrane and formed a sheet. The cultivated cell sheet was transparent and consisted of five to eight layers. K3 was observed in all layers and ABCG2, p63, and vimentin were notably present in the basal layer of the cultivated canine epithelium by immunofluorescence. Conclusions Canine corneal epithelial cells were successfully cultivated on the canine amniotic membrane. The cultivated epithelial sheets contained putative stem cells in the basal layer and had a stratified epithelium.     

Postnatal development of corneal curvature and thickness in the cat

Objective To evaluate the postnatal development of central corneal curvature and thickness in the domestic cat. Animals studied Six Domestic Short‐haired (DSH) kittens starting at 9 weeks of age and 6 adult cats. Procedures Kittens were evaluated biweekly to monthly for a 12‐month period, starting at age 9 weeks. Corneal development was monitored by hand‐held keratometry and ultrasound biomicroscopy. Standard regression analysis using a nonlinear least squares method was used to generate a formula that would predict corneal curvature as a function of age. Results Mean keratometry (K) values for the 9‐week‐old cats were 54.51 (±1.02) diopters (D) and these values steeply declined over the next 3 months to 44.95 (±0.90) D. Thereafter, K‐values gradually decreased to reach a plateau by 12–15 months of age of 39.90 (±0.42) D. Because K‐values still appeared to be slightly diminishing at this point, six other > 2‐year‐old cats were evaluated by keratometry and were found to have K‐values of 38.99 (±0.81). Two to four diopters of astigmatism was common in young kittens whereas adult cats had a low mean degree of astigmatism (< 1 D). A formula that predicted keratometry values in diopters (K) as a function of age in weeks (w) was established as follows: K = 39.83 + 26.87 exp(?0.074 w). The central cornea increased in thickness primarily during the first 4 months of life with 9 week‐old kittens having values of 0.379 (±0.012) mm; 16‐week‐old kittens, 0.548 (±0.021) mm and 67 week‐old cats, 0.567 (±0.012) mm. Conclusions The maturation process of the feline cornea proceeds over the first 1–2 years of life to attain an adult status that is characterized by a roughly spherical state of approximately 39 D corneal curvature, substantially flatter than the human cornea, and a central thickness similar to the human cornea. Research studies of the refractive or optical properties of the cornea in which cats are used as experimental animals should be conducted on animals greater than 18 months of age.     

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.