In vivo measurement of central corneal thickness in normal chicks (Gallus gallus domesticus) with the optical low-coherence reflectometer

Objective To determine the practicability and accuracy of central corneal thickness (CCT) measurements in living chicks utilizing a noncontact, high‐speed optical low‐coherence reflectometer (OLCR) mounted on a slit lamp. Animals studied Twelve male chicks (Gallus gallus domesticus). Procedures Measurements of CCT were obtained in triplicate in 24 eyes of twelve 1‐day‐old anaesthetized chicks using OLCR. Every single measurement taken by OLCR consisted of the average result of 20 scans obtained within seconds. Additionally, corneal thickness was determined histologically after immersion fixation in Karnovsky’s solution alone (20 eyes) or with a previous injection of the fixative into the anterior chamber before enucleation (4 eyes). Results Central corneal thickness measurements using OLCR in 1‐day‐old living chicks provide a rapid and feasible examination technique. Mean CCT measured with OLCR (189.7 ± 3.34 μm) was significantly lower than histological measurements (242.1 ± 47.27 μm) in eyes with fixation in Karnovsky’s solution (P = 0.0005). In eyes with additional injection of Karnovsky’s fixative into the anterior chamber, mean histologically determined CCT was 195.2 ± 8.25 μm vs. 191.9 ± 8.90 μm with OLCR. A trend for a lower variance was found compared to the eyes that had only been immersion fixed. Conclusion Optical low‐coherence reflectometry is an accurate examination technique to measure in vivo CCT in the eye of newborn chicks. The knowledge of the thickness of the chick cornea and the ability to obtain noninvasive, noncontact measurements of CCT in the living animal may be of interest for research and development of eye diseases in chick models.     

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.     

Morphology of the pig cornea in normal conditions and after incubation in a perfusion apparatus

The fine structure of the pig cornea in normal conditions and after being used in a perfusion apparatus, for 4 h, is described. Earlier reports on the normal morphology of the pig cornea were partly not confirmed. Thus the number of cell layers in the epithelium was found to be 19-23 (a basal cell layer, 4–5 polyhedral cell layers and 14–17 squamous cell layers) compared to earlier reported 6–9 layers.The mean thickness of normal and perfused corneas were 722 μm and 752 μm respectively. Normal corneas had a hydration level of 77.2 % and after perfusion 78.5 %. The normal morphology and morphological changes due to exposure to perfusion were studied by light and electron microscopy. The differences observed between normal and perfused corneas have to be considered limited, and restricted mainly to the anterior squamous epithelium and the endothelium.Taken together our results indicate that the corneas used in the apparatus still had functional integrity.     

Ultrasound biomicroscopic findings of the iridocorneal angle in live healthy and glaucomatous dogs

By using ultrasound biomicroscopy (UBM), the cross-sectional structures of the entire iridocorneal angle (ICA) which are unable to assess with gonioscopic examination were evaluated objectively and quantitatively in live healthy and glaucomatous dogs. The ICAs of normotensive eyes in healthy dogs with normal open angle (NOR), a predisposition to primary closed angle glaucoma (PCAG) (PREDIS) and suffering from unilateral PCAG (UNI), as well as the ICAs of hypertensive eyes with acute and chronic PCAG (ACG and CRG), were assessed. The opening of the ciliary cleft in PREDIS was smaller than that in NOR. In UNI, the opening and area of the ciliary cleft were significantly decreased compared with those of NOR and PREDIS. ACG had widespread structural abnormalities including marked decrease in the ciliary cleft and scleral venous plexus, and a thinner sclera than those in normotensive eyes, whereas the ICA collapsed in CRG with the thinnest sclera. Medical therapy-responsive glaucomatous cases had wider ciliary cleft and scleral venous plexus than unresponsive ones. These findings suggest that the ciliary cleft and scleral venous plexus of the ICA are key structures contributing to not only the pathophysiology of canine glaucoma but also the responsiveness to medical therapy in glaucomatous eyes, and cross-sectional entire structures of the ICA should be evaluated quantitatively with UBM when diagnosing and managing canine glaucoma.     

Establishing and functional testing of a canine corneal construct

Purpose  To provide a model to be used for in vitro studies on drug effects in dogs, this study was conducted to establish a protocol for the construction of a three-dimensional corneal construct. Primary canine corneal cells and a rabbit corneal epithelial (RCE) cell line were used in comparison.
Methods  The corneal construct was assembled step by step in membrane inserts of a six-well plate over a total of 5 weeks, including culture at the air–liquid interface to allow a differentiation of the epithelial cells. The constructs were studied histologically.
Single cell cultures of canine corneal cells as well as RCE cells were stimulated with lipopolysaccharides (LPS) and sodium dodecyl sulfate (SDS). Treatment with different concentrations of dexamethasone was used to test its effects on the cellular prostaglandin E₂ (PGE₂) production. The same experiments were repeated with the corneal constructs and the reactions compared. Expression of the glucocorticoid receptor (GR) in the constructs was studied using immunohistochemistry.
Results  A protocol for the construction of a vital corneal construct was established and the morphological similarity to the canine cornea in vivo shown. The GR protein was detected in all three cell types of the constructs. Stimulation with LPS and SDS led only in the corneal constructs to a significantly increased PGE₂ production, which could be reduced by dexamethasone.
Conclusions  The corneal construct is an interesting system to test drug effects on corneal cells. It allows studies on a cornea-like system including all three major cell types.