In vivoconfocal microscopy of the normal equine cornea and limbus

A new perspective on the corneo-scleral junction with three types of microscopy techniques

The conjunctions of the cornea and sclera in the eyes of donkeys, cattle, dogs, sheep, pigs and rabbits, regardless of gender, were examined in this study. No animals were specifically sacrificed for this investigation. Scanning electron microscopy, light microscopy, and dissecting microscopy were used in this research. In the limbus of all the animals investigated, the cornea and sclera fused in accordance with a pattern. At the corneo-scleral junction, the sclera was situated anteriorly and the cornea posteriorly in the dorsal and ventral sections of the bulbus oculi. In the medial and lateral parts of the eyeball, the cornea and sclera were facing each other and interlaced. Pigmentation and the sulcus scleralis externus could be used to identify the macro-and micro-anatomical boundaries of the limbus. In addition, the cytoplasm of basal epithelial cells shrank, signaling the end of the corneal epithelium and the start of the conjunctival epithelium. The presence of Bowman's membrane in cattle and sheep eyes was definitely determined in histological examinations. Bowman's membrane in these animals came to an end at the limbus, which is where the conjunctival epithelium starts and the corneal epithelium ends. In all areas of the cornea, Bowman's membrane revealed irregular, abrupt thickening and thinning. The corneal epithelium was thick in the vertex and thinner towards the limbus, whereas Descemet's membrane was thin in the center (vertex) and thick in the periphery (near the limbus). In this study, pictures and diagrams were used to illustrate the general anatomical, histological, and morphometric characteristics of the limbus in the species under investigation. The data from our study showed that the limbus region of the bulbus oculi was narrow in the lateral and medial parts and wide in the dorsal and ventral parts. This was confirmed in the studied animals as a general rule. The width value will undoubtedly affect the number of cells covered by the regions. It is conceivable that these cells will play a significant role in the decision of where to perform surgical procedures in order to promote wound healing, giving doctors an advantage. In this circumstances, we think that the limbus should be studied in terms of clinical methods because it has different shapes depending on the species and the position of the bulbus.

Comparative Histology of the Cornea and Palisades of Vogt in the Different Wild Ruminants (Bovidae, Camelidae, Cervidae, Giraffidae, Tragulidae)

In the study, we data concerning the histological and morphometrical examination of the cornea and palisades of Vogt in the different species of ruminants from the families Bovidae, Camelidae, Cervidae, Giraffidae and Tragulidae, coming from the Warsaw Zoological Garden, the Wroclaw Zoological Garden and the Division of Animal Anatomy. The following ruminant species were investigated: common wildebeest, Kirk's dik-dik, Natal red duiker, scimitar oryx, sitatunga, Philippine spotted deer, Père David's deer, moose, reindeer, reticulated giraffe, okapi, Balabac mouse-deer and alpaca. The cornea of ruminant species such as the common wildebeest, Kirk's dik-dik, Natal red duiker, scimitar oryx, reindeer and Balabac mouse-deer consisted of four layers (not found in the Bowman's layer): the anterior corneal epithelium, the proper substance of the cornea, the posterior limiting membrane (Descemet's membrane) and the posterior corneal epithelium (endothelium). The anterior corneal epithelium was composed of a multilayer keratinizing squamous epithelium, which was characterized in the studied ruminants with a variable number of cell layers but also with a different thickness both in the central epithelium part and in the peripheral part. Moreover, the proper substance of cornea was thinnest in Balabac mouse-deer, Kirk's dik-dik, Natal red duiker, scimitar oryx, Philippine spotted deer, alpaca, reindeer and sitatunga and was thickest in the reticulated giraffe. The thickest Descemet's membrane was observed in the Père David's deer. The corneal limbus is characterized by a large number of pigment cell clusters in Kirk's dik-dik, scimitar oryx, moose, Balabac mouse-deer and alpaca. In the common wildebeest, Père David's deer, moose, reticulated giraffe, okapi and alpaca, the palisades of Vogt were marked in the form of a crypt-like structure. The corneal limbus epithelium in the examined ruminants was characterized by a variable number of cell layers but also a variable number of melanocytes located in different layers of this epithelium. The detailed knowledge of the corneal structure of domestic and wild animals can contribute to the even better development of methods for treating eye diseases in veterinary medicine.

Applications of in vivo confocal microscopy in the management of infectious keratitis in veterinary ophthalmology

In vivo confocal microscopy (IVCM) is a relatively new ocular imaging technique that permits morphological and quantitative assessment of the living cornea on the cellular level. The applications for IVCM in clinical ophthalmology are numerous and diverse. There are several advantages inherent to IVCM over standard diagnostic techniques currently used to confirm a diagnosis of infectious keratitis in veterinary ophthalmology. With IVCM, images can be viewed in real-time providing immediate diagnostic information. Traumatic corneal sampling techniques are avoided, and the procedure can be repeated as frequently as is clinically indicated without risk of corneal tissue damage. Both superficial and deep corneal lesions can be evaluated by IVCM in an atraumatic fashion. Microorganism viability is not required for their detection and specialized diagnostic laboratory assay procedures are not necessary. Many larger infectious agents can be directly identified within corneal lesions by IVCM, including fungi and parasites such as Acanthamoeba spp. In other situations, such as bacterial infectious crystalline keratopathy, the biological systems associated with the microorganism can be detected within the cornea. The current resolution of IVCM is inadequate to directly visualize some corneal infectious agents, such as herpesviruses, but host responses and virus-infected epithelial cells can be identified. This review summarizes the current knowledge and applications of IVCM in the management of infectious keratitis in veterinary ophthalmology, including its use in animals with bacterial, fungal, parasitic, and viral keratitis.

Evaluation of equine corneal disease using ultrasound biomicroscopy

OBJECTIVE

To describe the clinical use of ultrasound biomicroscopy (UBM) to evaluate equine corneal disease.

METHODS

Images were obtained using a 50-MHz probe ultrasound biomicroscopy system (Quantel Aviso) and Clear Scan® probe cover. Six horses with corneal disease were evaluated via UBM for lesion size, lesion depth, and continuity of Descemet's membrane. Horses were sedated and received auriculopalpebral nerve blocks and application of topical anesthetic prior to UBM.

RESULTS

Ultrasound biomicroscopy was easily performed in all cases. UBM evaluation of three cases of corneo-limbal squamous cell carcinoma yielded information regarding lesion depth for planning of keratectomies using fixed-depth keratomes and subsequent β-radiation therapy. Corneal depth and continuity of Descemet's membrane were determined in two horses with stromal abscesses and allowed for planning of therapeutic options. In one horse with a corneal foreign body, UBM contributed to accurate assessment of the foreign body's stromal depth, which could not be assessed during ophthalmic examination due to extensive corneal cellular infiltrate. The information regarding corneal depth allowed for more accurate pre-surgical planning in patients with opaque corneal lesions.

CONCLUSIONS

Ultrasound biomicroscopy was easily performed and provided useful information regarding lesion depth and continuity of Descemet's membrane for patients with corneo-limbal squamous cell carcinoma, stromal abscesses, and a corneal foreign body, allowing for increased precision in pre-surgical planning and development of therapeutic protocols.

Optimizing corneal riboflavin administration in ex vivo horse, dog, rabbit, and pig samples for use in corneal collagen cross-linking

PURPOSE

Determine optimal iontophoresis times for riboflavin delivery to the corneal stroma across different species and compare these to corneal injection.

METHODS

Ex vivo horse, dog, rabbit, and pig globes were treated with riboflavin administered with either iontophoresis for 2.5-20 minutes with or without corneal epithelium; or with purpose-designed precise corneal injection (PCI) application with intact epithelium. Immediately following riboflavin administration, samples were harvested, frozen, and sectioned. Riboflavin penetration was imaged using fluorescence microscopy.

RESULTS

Horse samples processed with iontophoresis without epithelium for 2.5, 5, and 7.5 minutes, and processed with intact epithelium for 20 minutes, had mean percent stromal penetration (%SP_mean ) of 63.4%, 93.8%, 100.0%, and 0.0% (respectively). Dog samples processed with iontophoresis without epithelium for 2.5 and 5 minutes, had %SP_mean of 60.7% and 82.1% (respectively). Pig samples processed with iontophoresis for 5 minutes without and with epithelium had %SP_mean of 63.3% and 35.1% (respectively). Rabbit samples processed with iontophoresis without epithelium for 2.5 and 5 minutes, had %SP_mean of 81.8% and 100.0% (respectively). For all injected volumes, riboflavin was observed spanning throughout the corneal stroma, and lamellar separation was noted surrounding all sites of injection.

CONCLUSIONS

Both iontophoresis and injection via PCI needles provide efficient and effective means of riboflavin administration in ex vivo horse, dog, rabbit, and pig corneas. Epithelial debridement is required for stromal delivery of riboflavin using iontophoresis in horses. Following epithelial removal, riboflavin penetrated through the horse corneal stroma faster than all other species tested.

Comparative Anatomy of the Mammalian Corneal Subbasal Nerve Plexus

Purpose

The subbasal nerve plexus (SNP) is the densest and most recognizable component of the mammalian corneal innervation; however, the anatomical configuration of the SNP in most animal models remains incompletely described. The purpose of the current study is to describe in detail the SNP architecture in eight different mammals, including several popular animal models used in cornea research.

Methods

Corneal nerves in mouse, rat, guinea pig, rabbit, dog, macaque, domestic pig, and cow eyes were stained immunohistochemically with antiserum directed against neurotubulin. SNP architecture was documented by digital photomicrography and large-scale reconstructions, that is, corneal nerve maps, using a drawing tube attached to a light microscope.

Results

Subbasal nerve fibers (SNFs) in mice, rats, guinea pigs, dogs, and macaques radiated centrally from the corneoscleral limbus toward the corneal apex in a whorl-like or spiraling pattern. SNFs in rabbit and bovine corneas swept horizontally across the ocular surface in a temporal-to-nasal direction and converged on the inferonasal limbus without forming a spiral. SNFs in the pig cornea radiated centrifugally in all directions, like a starburst, from a focal point located equidistant between the corneal apex and the superior pole.

Conclusions

The results of the present study have demonstrated for the first time substantial interspecies differences in the architectural organization of the mammalian SNP. The physiological significance of these different patterns and the mechanisms that regulate SNP pattern formation in the mammalian cornea remain incompletely understood and warrant additional investigation.

In vivo confocal microscopy features and clinicohistological correlation of limbal nerve corpuscles

Aims

To describe the in vivo confocal microscopy (IVCM) features of human limbal nerve corpuscles (LNCs) and correlate these with the histological features.

Methods

We examined 40 eyes of 29 healthy living subjects (17 female, 12 male; mean age=47.6) by IVCM. Four limbal quadrants were scanned through all epithelial layers and stroma to identify the LNCs and associated nerves. Ten fresh normal human corneoscleral discs from five deceased patients with a mean age of 67 years and 17 eye-bank corneoscleral rims with a mean age of 57.6 years were stained as whole mounts by the acetylcholinesterase (AChE) method to demonstrate LNCs and corneal nerves. Stained tissue was scanned in multiple layers with the NanoZoomer digital pathology microscope. The in vivo results were correlated to the histological findings.

Results

On IVCM, LNCs were identified in 65% of the eyes studied and were mainly (84%) located in the inferior or superior limbal regions. They appeared either as bright (hyper-reflective) round or oval single structures within the hyporeflective, relatively acellular fibrous core of the palisades or were clustered in groups, often located anterior to the palisades of Vogt. They measured 36 µm in largest diameter (range 20–56 µm). The in vivo features were consistent with the histology, which showed LNCs as strongly AChE positive round or oval structures.

Conclusion

The strong correlation with histology will enable use of IVCM to study LNCs in normal and disease conditions.

Evaluation of equine corneal endothelium after exposure to 0.05% brilliant blue - an in vitro study

ABSTRACT The aim of this study was to evaluate the immediate effects of 0.05% brilliant blue on corneal endothelium of horses. Thirty-eight corneas of 19 horses, male or female, of different ages were studied. Corneas were randomly divided into two groups. Group 1: Corneal endothelium was covered with 0.3mL of brilliant blue 0.05% for 60 seconds followed by rinsing with a balanced salt solution. Group 2: Corneal endothelium was covered with BSS for 60 seconds. The corneas were excised with an 8mm trephine and prepared to analyze posterior endothelial surface using a light microscope (24 corneas) and a scanning electron microscope (14 corneas). The equine posterior corneal endothelium surface observed by optical microscopy and scanning electron microscopy revealed a continuous layer of polygonal cells of uniform size and shape in both the control and treatment groups. Due to non-normal residuals at ANOVA mean comparison, a generalized linear model was utilized at 5% level of significance. The chi-square test stated that treatment and control group were not different statistically. The 0.05% brilliant blue did not cause damage to equine corneal endothelium.

Laser scanning in vivo confocal microscopic characterization of equine immune-mediated keratitis

OBJECTIVE

To describe the corneal in vivo confocal microscopy (IVCM) findings in horses with putative immune-mediated keratitis (IMMK).

ANIMALS

Sixty five horses with IMMK.

PROCEDURES

Horses diagnosed with IMMK were examined with a modified Heidelberg Retina Tomograph II and Rostock Cornea Module. The findings from the IVCM examinations were correlated with clinical details from ophthalmic examination and diagnostic test results.

RESULTS

Eighty eyes from 65 horses were examined. Clinical IMMK lesions were categorized as epithelial (n = 17 eyes), superficial stromal (n = 38), midstromal (n = 18), and endothelial (n = 7). Epithelial, superficial stromal, and midstromal lesions were characterized with IVCM by variable corneal leukocyte infiltrates and vascularization of the approximate corneal anatomic region that was clinically affected as determined by biomicroscopy. In addition, all horses displayed a dense network of dendritic cells in the epithelial basement membrane and immediate subepithelial stroma. Less consistent IVCM findings included epithelial disorganization, corneal edema, mineral deposition, stromal fibrosis, and epithelial pigment granules. Endothelial IMMK was distinct from the other forms of IMMK and characterized with IVCM by stromal edema, endothelium disorganization, endothelial cell loss, and multifocal accumulations of highly reflective material within the endothelium.

CONCLUSIONS AND CLINICAL RELEVANCE

The distinguishing feature of epithelial and stromal forms of IMMK is a dense accumulation of dendritic cells in the epithelial basement membrane and immediate subepithelial stroma. Cellular changes in endothelial IMMK were largely confined to the endothelium and distinct from the other forms of IMMK evaluated.

Characterisation of corneal impression cytology in dogs and its application in the diagnosis of keratoconjunctivitis sicca

OBJECTIVE

Determine morphological and morphometric parameters of corneal epithelium in dogs, and determine the cellular alterations that occur in canine keratoconjunctivitis sicca (KCS) using impression cytology.

STUDY ANIMALS

60 dogs divided into two groups: dogs with Schirmer tear test (STT) at least 15 mm/minute and absence of ocular disease, and dogs with STT less than 15 mm/minute and clinical signs of KCS.

PROCEDURES

Impression cytology was used to collect corneal samples. The percentage of eyes with cell changes, the number of such cells and the percentage of cells with structural alterations in each group were determined. The possible correlation between corneal epithelium alterations and decreased tear production was evaluated.

RESULTS

A significant positive correlation existed between STT and the area of the cytoplasm and nucleus of corneal cells. A significant negative correlation was found between STT ​​and the nucleus/cytoplasm ratio, and the presence of cellular changes. A significant difference existed between the numbers of pyknotic nuclei, being higher among animals with all stages of KCS.

CONCLUSION

Corneal impression cytology can be used to assess the corneal epithelium in healthy eyes and eyes with KCS, demonstrating its usefulness as a diagnostic tool especially in mild and early cases.

Morphological and immunohistochemical characteristics of the equine corneal epithelium

Objective

The morphology of the corneal epithelium in two age groups of horses is described. Distribution patterns of proliferation‐, differentiation‐, stem cell‐associated markers and cell junction proteins were assessed.

Methods

Corneal samples from 12 horses (six foals and six adult horses) were analyzed after H&E staining and immunohistochemistry using the following antibodies: E‐cadherin, β‐catenin, Connexin 43 (Cx43), tight junction protein 1 (TJP1), cytokeratin (CK) 14, CK 19, CK 3, CK 10, vimentin, Ki67, p63, nerve growth factor (NGF), ABCG2, and epithelial growth factor receptor. Semiquantitative analysis of crypt, limbal, peripheral, and central zone was performed. Semithin and ultrathin sections were used for ultrastructural evaluation of the epithelium.

Results

The height of the epithelium varied between age groups and crypts were consistently present. In the peripheral and central epithelium, three types of basal cells resembling a pseudostratified epithelium were characterized. Potential stem cell markers (CK 14, p63, NGF, and ABCG2) were present in all zones with decreasing frequency toward the center. Cornea‐specific differentiation marker CK 3 was not expressed in the most basal cell layer of the limbal epithelium. E‐cadherin, β‐catenin, and Cx43 revealed a similar apico‐lateral signal pattern throughout the entire epithelium; only TJP1 was additionally seen at the basal surface.

Conclusions

This study presents a systematic semiquantitative evaluation of the equine corneal epithelium, showing the presence of crypts as potential stem cell niche with CK 14, p63, NGF, and ABCG2 as relevant markers for cells with regenerative capacity. The pseudostratified arrangement of the basal layer was a unique finding.

Investigations of the corneal epithelium in Veterinary Medicine: State of the art on corneal stem cells found in different mammalian species and their putative application

The existence of progenitor cells that can readily differentiate into a specific cell type is a common cellular strategy for physiological tissue growth and repair mechanisms. In the mammalian cornea, many aspects regarding the nature and location of these cells are still unclear. In the human limbus (peripheral area of the cornea) progenitor cells have been found and characterized but in non-human mammals, the picture is not so clear. In this review, we examine current knowledge about the morphology of limbus and the localization of corneal epithelial stem cells in all species studied so far, comparing data with humans. We have also explored different research directions in the veterinary field in order to discuss the: i) currently used protocols and ii) best range of treatments for ocular pathologies in which corneal stem cells are involved.

Relationship between corneal sensitivity, corneal thickness, corneal diameter, and intraocular pressure in normal cats and cats with congenital glaucoma

OBJECTIVE

To determine the effect of feline congenital glaucoma (FCG) on corneal sensitivity, and relationships between corneal sensitivity, central corneal thickness (CT), and corneal diameter (CD).

ANIMALS AND PROCEDURES

Corneal sensitivity (estimated by corneal touch threshold [CTT] using Cochet-Bonnet esthesiometry); CT using ultrasonic pachymetry; intraocular pressure (IOP) using rebound tonometry; and maximal horizontal CD were measured in 16 normal and 14 FCG cats, both males and females, aged 7 months-3.5 years. All procedures complied with an Institutional Animal Care and Use Committee-approved protocol. Data were analyzed by linear regression: paired Student's t tests for between-eye comparisons, and unpaired Student's t tests for comparisons between groups. Relationships between parameters were evaluated by Pearson correlation coefficients and linear mixed effects modeling. For statistical tests, with the exception of values that were Benjamini-Hochberg adjusted for multiple comparisons, P-values < 0.05 were considered significant.

RESULTS

Mean CTT and CT values were lower in FCG eyes relative to normal eyes, but differences were not statistically significant. Mean CD was significantly larger in FCG eyes relative to normal eyes, and there was a significant negative correlation between CD and CTT in FCG (r = -0.8564, corrected P = 0.005). These associations were confirmed in linear mixed effects models.

CONCLUSIONS

Eyes with FCG have significantly larger CDs when compared with normal eyes, and larger CDs correlated with decreased corneal sensitivity in this group. Further studies are warranted to explore the effect of buphthalmos and corneal enlargement on corneal sensitivity and innervation in feline subjects with chronic glaucoma.

Advanced Imaging of the Equine Eye

This article reviews the literature for studies describing advanced imaging of the equine eye as a reference for practitioners to help in the selection of image modalities, describe how to use the instruments, and help interpret the image findings. Indications for, technique of, and image interpretation of advanced image modalities such as ultrasound, computed tomography, MRI, optical coherence tomography, confocal microscopy, and angiography are reviewed. The article is organized anatomically, not by instrument, so that the reader will be able to quickly research ways to image specific disease entities or anatomic locations that are affecting their equine patients.

Corneal Surface and Superficial Cells as Viewed by Scanning Electron Microscopy and Impression Cytology Sampling

PURPOSE

To objectively compare sizes of corneal epithelial surface cells visualized by scanning electron microscopy (SEM) or collected by impression cytology (IC).

METHODS

Corneas of recent postmortem sheep eyes were either glutaraldehyde fixed for SEM or IC samples taken, glutaraldehyde fixed, and then stained with Giemsa. The corneal epithelial surface was examined at ×200, with the borders of all cells marked and dimensions and areas measured. For SEM, the cells were classified as having light, medium, or dark electron reflex and by the number of cell sides.

RESULTS

SEM revealed a mosaic of polygonal features with different electron reflexes according to the density of cell surface microplicae. The cell area and longest dimension were predictably dependent on the number of cell sides. Compared with the overall average cell area of 1598 μm(2) (range 200-3900 μm(2)), the dark reflex cells were predominantly the largest, with an average area of 2435 μm(2) and having the average longest dimension of 59.9 μm(2). Cells collected by IC had a range of areas from 1150 to 4800 μm(2) but were predominantly large and had an average area of 2802 μm(2) with the average cell longest dimension averaging 64.4 μm(2). IC-sampled cells had nucleocytoplasmic ratio values consistent with their having a squamous phenotype.

CONCLUSIONS

Cells sampled by IC from the corneal epithelial surface are predominantly those that are enlarged (and flattened out) in preparation for desquamation, a feature also attributed to the dark reflex cells seen in SEM.

Listeria monocytogenes associated kerato-conjunctivitis in four horses in Norway

Listeria monocytogenes has been reported to cause various infectious diseases in both humans and animals. More rarely, ocular infections have been reported. To our knowledge, only two cases of Listeria keratitis have been described in horses. We report kerato-conjunctivitis in four Norwegian horses associated with L. monocytogenes. Clinically, all cases were presented with recurrent unilateral kerato-conjunctivitis. L. monocytogenes bacteria were isolated from swab samples from all cases, and cytology carried out in 3 cases was indicative of L. monocytogenes infection. The present report describes the first known cases in which L. monocytogenes has been isolated from keratitic lesions in horses in Norway. A potential risk factor may be feeding of silage or haylage, but other sources of infection cannot be ruled out. The phenotypic features including antimicrobial susceptibility and serotype of the isolates are described. Laboratory detection of L. monocytogenes demands extra caution since only low numbers of bacteria were detected in the eye-swabs, probably due to the low volume of sample material and the intracellular niche of the bacterium. A general poor response to treatment in all these cases indicates that clinicians should pay extra attention to intensity and duration of treatment if L. monocytogenes is identified in connection with equine kerato-conjunctivitis.

Comparative morphological evaluation of domestic animal cornea

OBJECTIVE

This study described corneal morphology in different domestic animals using histological and immunohistochemical methods. Specifically, we evaluated the species-specific distribution pattern of cytokeratins (CKs) and aquaporins (AQPs) to assess their contribution to the strength and transparency of the cornea, respectively.

PROCEDURES

Corneal sections (2 μm thick) were obtained from 28 pigs, 11 cows, two goats, six horses, four dogs, and five cats and stained with hematoxylin-eosin and periodic acid-Schiff (PAS) reaction. Immunohistochemistry was also performed using CK1 to 3 and AQP1 and 5 antibodies.

RESULTS

Domestic animal corneas were composed of corneal epithelium, stroma, Descemet's membrane, and corneal endothelium. Bowman's layer was not detected using the PAS reaction. The three-layered epithelium was thinnest in carnivores and thickest in equines and bovines. CKs were demonstrated immunohistochemically in all species examined, especially in the most superficial layer of the corneal epithelium. CKs were more widely distributed in canine and feline corneal epithelial cell layers compared to other species. The corneal monolayer endothelium was immunostained with AQP1 in all species examined, and it was also present in stromal keratocytes in a species-specific manner. In contrast, AQP5 was exclusively localized to the corneal epithelium. Epithelial staining patterns varied markedly between species, and the widest distribution of AQP5 was demonstrated in feline epithelial cell layers.

CONCLUSIONS

Differences in the distribution of CKs and AQPs in various species suggest species differences in the maintenance of structural integrity and fluid balance.

In vivo ocular imaging of the cornea of the normal female laboratory beagle using confocal microscopy

OBJECTIVE

To obtain normative data for the normal laboratory beagle cornea using high-resolution in vivo confocal microscopy (IVCM).

ANIMALS STUDIED

Sixteen eyes of eight healthy young female intact beagles.

PROCEDURES

The central cornea was imaged using IVCM. Mixed effects linear regression was used for statistical analysis.

RESULTS

in vivo confocal microscopy allowed detailed visualization and quantification of epithelial cells (superficial epithelial cell diameter: 43.25 ± 6.64 μm, basal cell diameter: 4.43 ± 0.67 μm), and nerve fibers (subepithelial nerve fiber diameter: 2.38 ± 0.69 μm, anterior stromal nerve fiber diameter: 16.93 ± 4.55 μm). Keratocyte density (anterior stroma 993.38 ± 134.24 cells/mm(2) , posterior stroma 789.38 ± 87.13 cells/mm(2) ) and endothelial cell density (2815.18 ± 212.59 cells/mm(2) ) were also measured.

CONCLUSION

High-resolution IVCM provides detailed noninvasive evaluation of the cornea in the normal laboratory beagle.

Characterization of fungal keratitis in alpacas: 11 cases (2003-2012)

OBJECTIVE

To describe clinical, microbiological, in vivo confocal microscopic, and histopathologic features of fungal keratitis in alpacas and to estimate prevalence of the disease in a population of alpacas from the northeastern United States.

DESIGN

Retrospective case series. Animals-11 alpacas.

PROCEDURES

Medical records of alpacas evaluated by the ophthalmology service of a veterinary teaching hospital were searched to identify animals with a clinical diagnosis of fungal keratitis and positive results for fungal culture of a corneal sample between 2003 and 2012. Signalment and historical, clinical, and microbiological details were recorded. Results of cytologic, histopathologic, and in vivo confocal microscopic corneal examinations were collected when available.

RESULTS

Fungal keratitis was diagnosed in 11 of 169 (6.5%) alpacas that underwent ophthalmologic examination by the ophthalmology service during the study period. Ten of the 11 alpacas were evaluated in the summer or fall months. Corneal lesions included stromal ulcer, stromal abscess, corneal perforation, and nonulcerative keratitis. Aspergillus fumigatus and Fusarium solani were the most frequently cultured fungi. Fungi were also identified through corneal cytologic examination, histologic examination, or in vivo confocal microscopy in 9 alpacas. Historically, 2 alpacas were evaluated following external ocular trauma and 1 following corneal foreign body removal. Nine alpacas had received topical treatment with antimicrobials and 2 had antimicrobial-corticosteroid combinations administered topically prior to referral. Nine of 10 alpacas for which follow-up information was available were successfully treated, with globe and vision retention.

CONCLUSIONS AND CLINICAL RELEVANCE

Fungal keratitis was a relatively common ocular disease in this population of alpacas and appeared to share several clinical features with keratomycosis in horses.

Manual corneal thickness measurements of healthy equine eyes using a portable spectral-domain optical coherence tomography device

REASONS FOR PERFORMING STUDY

Corneal thickness measurements of the equine globe using spectral-domain optical coherence tomography (SD-OCT) have not been reported.

OBJECTIVES

To determine corneal thickness measurements and the intra- and interoperator reliability of a portable SD-OCT device in equine eyes.

STUDY DESIGN

Prospective observational study.

METHODS

Horses free of ocular disease were used for this study. Gentle manual restraint, in combination with detomidine hydrochloride and a head stand, were employed to ensure proper animal positioning. Corneal pachymetry measurements were obtained from both eyes of each animal 3 times by 2 operators in succession. A 6 mm corneal pachymetry protocol was performed using a portable SD-OCT device. All measurements were obtained manually by one operator (C.G.P.) using the integrated calliper function. Measurements included epithelial thickness, stromal thickness, Descemet's membrane thickness and total corneal thickness. All recorded measurements were analysed to determine both intra- and interoperator reliability.

RESULTS

Thirty horses with a mean age of 10.6 ± 6.4 years were examined. Mean epithelial, stromal, Descemet's membrane and total corneal thickness values obtained were, respectively, 174.7 ± 13.6, 599.2 ± 45.4, 38.4 ± 15.3 and 812.0 ± 44.1 μm for operator A and 175.9 ± 12.9, 599.2 ± 44.9, 38.4 ± 15.0 and 812.9 ± 42.9 μm for operator B. A positive correlation was found between Descemet's membrane thickness and age, whereby Descemet's membrane thickness increased by 2 μm/year (P<0.0001). The coefficients of variation for both operators were <4% for all measurements. Intraclass correlations ranged from 0.92 to 0.98.

CONCLUSIONS

Manual corneal thickness measurement using a portable SD-OCT device provides epithelial, stromal, Descemet's membrane and total corneal thickness measurements with clinically acceptable intra- and interoperator reliability in healthy equine eyes.

The role of in vivo confocal microscopy in the diagnosis of hidden corneal foreign bodies

OBJECTIVE

To investigate in vivo confocal microscopy (IVCM) to diagnose hidden corneal foreign bodies.

METHODS

Male Kunming mice (n = 25; 12 weeks old) were anaesthetized prior to the insertion of five different materials (spiny wood, rusty iron, sharp stone, sharp glass fragment and human hair fragment) into the cornea by different traumatic processes. A separate mouse was used for each corneal foreign body. The corneas of the mice were scanned 24 h later by a laser scanning IVCM to establish the characteristics (shape, reflectivity and depth in the cornea) of each foreign body. These findings were used to help screen and identify corneal foreign bodies in patients. Corneal smears and scraping cultures were performed in cases of probable corneal infection.

RESULTS

Animal models for the five different foreign particles were established successfully, with each showing distinctive characteristics. These animal results were used to diagnose 41 patients with suspected corneal foreign bodies who were negative by slit lamp examination, but positive by IVCM (observational case series). The most prevalent type of hidden foreign body was plant material (51.2%), followed by metal (29.3%). Ten patients with corneal foreign bodies developed fungal keratitis, found using IVCM.

CONCLUSIONS

Laser IVCM is an effective and reliable tool for the diagnosis of hidden corneal foreign bodies.

The Ophthalmic Examination as It Pertains to General Ocular Toxicology: Basic and Advanced Techniques and Species-Associated Findings

Ocular toxicology pertains to toxicologic effects of drugs administered topically, intraocularly, or systemically. It should also include evaluation of adverse effects of ophthalmic devices such as contact lenses, intraocular lenses, and glaucoma implants. The ophthalmic examination is able to provide detailed in-life information and is used in combination with clinical observations, clinical pathology, and histopathology to assess potential toxicologic effects. The ophthalmologist must be familiar with the wide range of species used in the field of toxicology, be familiar with the anatomic variations associated with these species, be able to determine what is an inherited or a breed-related finding from a study-related effect, be competent with the required ophthalmic equipment, and be capable of examining this wide range of animals.

Light microscopic evaluation and scanning electron microscopic analysis of horse eyes following deep anterior lamellar keratectomy

OBJECTIVE  To describe the technique of deep anterior lamellar keratoplasty (DALK) with Descemet's membrane (DM) exposure in horse eyes. Also, to compare the efficacy and safety of viscodissection and big-bubble techniques for DALK. ANIMALS STUDIED  Thirty-four ex vivo horse eyes. PROCEDURE  Deep anterior lamellar keratoplasty was performed in 34 ex vivo horse eyes. Two groups (Group V--viscodissection--2% sodium hyaluronate; Group A--air--big-bubble) of 17 eyes were studied. Other than the substance used, the surgical technique was similar for both groups. Nonperforated eyes were submitted for light microscopic histologic evaluation and scanning electron microscopic (SEM) analysis. RESULTS  Group V--Perforations occurred in 18% of the eyes during surgery. Light microscopy revealed exposure of DM in 28% of the eyes with mean thickness of the remaining stroma being 70.4 μm. Group A--Perforations occurred in 42% of the eyes. Light microscopy revealed exposure of DM in 60% of the eyes with mean thickness of the remaining stroma being 23.3 μm. No significant differences in safety, efficacy and thickness of the remaining stroma (including all eyes or excluding those with DM exposure) were observed. SEM of the surgical site revealed a more even surface in those eyes with DM exposure compared to eyes with thicker remaining stroma in both groups. CONCLUSIONs  We describe two DALK techniques (viscodissection and big-bubble) for use in horses. No significant differences in safety, efficacy and thickness of the remaining stroma were observed. However, a nonsignificant trend toward the big-bubble technique being more efficacious but less safe was observed.

In vivo confocal microscopy of equine fungal keratitis

OBJECTIVE

To describe in vivo corneal confocal microscopy of horses with fungal keratitis and correlate findings with clinical, histopathological, and microbiological evaluations of clinical cases and an ex vivo experimental equine fungal keratitis model.

ANIMALS STUDIED

A total of 12 horses with naturally-acquired fungal keratitis and ex vivo equine corneas experimentally infected with clinical fungal isolates.

PROCEDURES

Horses with naturally-acquired fungal keratitis were examined with a modified Heidelberg Retina Tomograph II and Rostock Cornea Module. Confocal microscopy images of clinical isolates of Aspergillus fumigatus, Fusarium solani, and Candida albicans were obtained by examination of in vitro cultures and experimentally infected ex vivo equine corneas.

RESULTS

Non-specific in vivo corneal confocal microscopic findings in horses with fungal keratitis included leukocyte infiltrates, activated keratocytes, anterior stromal dendritic cell infiltrates, and vascularization. Linear, branching, hyper-reflective structures that were 2-6 μm in width and 200 to >400 μm in length were detected in all horses with filamentous fungal keratitis. Round to oval hyper-reflective structures that were 2-8 μm in diameter were detected in a horse with yeast fungal keratitis. The in vivo confocal microscopic appearance of the organisms was consistent with fungal morphologies observed during examination of in vitro cultures and infected ex vivo equine corneas.

CONCLUSIONS

In vivo corneal confocal microscopy is a rapid and non-invasive method of diagnosing fungal keratitis in the horse. This imaging technique is useful for both ulcerative and non-ulcerative fungal keratitis, and is particularly advantageous for confirming the presence of fungi in deep corneal stromal lesions.