Harriet J. Davidson

The tear film and ocular mucins

Abstract The trilaminar tear film, composed of the lipid, aqueous and mucin layers, has many functions including defending the ocular surface. The aqueous layer has several soluble antimicrobial factors that protect the ocular surface. Ocular mucins have recently been studied with regard to their role in the defense of the eye as well as in dry eye syndromes. To date, 15 mucin genes have been identified, and six of these mucin genes are localized to or secreted by ocular glands or epithelia. Understanding the production, secretion and function of ocular mucins will aid in the treatment of dry eye syndromes and ocular surface microbial infections.

Normal conjunctival flora in the North American opossum (Didelphis virginiana) and raccoon (Procyon lotor).

We documented the normal conjunctival bacterial flora from 17 opossums (Didelphis virginiana) and 10 raccoons (Procyon lotor) trapped in Manhattan, Kansas (USA) from November 1999 to January 2000. Both raccoons and opossums were free of apparent ocular disease. The inferior conjunctival sacs of each animal were swabbed for aerobic bacterial and Mycoplasma culture and polymerase chain reaction (PCR) for Mycoplasma and Chlamydia detection. All conjunctival samples were positive for one or more species of aerobic bacteria. The most common isolate from opossums was Staphylococcus spp. Other isolates included Streptococcus spp., Bacillus spp., Corynebacterium spp., and Enterococcus faecalis. The most common isolate in raccoons was Bacillus spp. Other isolates included Streptococcus spp., Staphylococcus spp., non-hemolytic Escherichia coli, and Enterococcus faecalis. Mycoplasma culture was negative in samples from opossums and raccoons. Evidence of Mycoplasma and Chlamydia presence was detected by PCR.

NC-1059: A Channel-Forming Peptide That Modulates Drug Delivery across In Vitro Corneal Epithelium

PURPOSE The goal of this study was to determine whether a synthetic peptide, NC-1059, can modulate the corneal epithelium to increase the permeation of therapeutic agents across this barrier. METHODS An in vitro system employing transformed human corneal epithelial (THCE) cells was optimized for this study. Culture conditions were identified to promote formation of a confluent monolayer that rapidly develops a substantial transepithelial electrical resistance. Electrical parameters were measured with a modified Ussing flux chamber, and solute flux was quantified with fluorescently labeled compounds. RESULTS NC-1059 causes a concentration-dependent increase in short-circuit current and an increase in transepithelial electrical conductance when assessed in modified Ussing chambers. The effect of NC-1059 on transepithelial electrical resistance was reversible. To test for paracellular permeability and size exclusion, FITC-labeled dextran ranging in size from 10 to 70 kDa was used. Dextran permeated the corneal cell monolayer in the presence, but not the absence, of NC-1059. Fluorescein sodium and carboxyfluorescein were then used as low molecular weight markers with similar NC-1059-modulated kinetics being observed. Maximum permeation for the fluorescein derivatives occurred 30 to 90 minutes after a 5-minute NC-1059 exposure. A prototypical drug, methotrexate, also exhibited increased permeation in the presence of NC-1059. CONCLUSIONS NC-1059 enhances drug permeation across cultured corneal epithelial cell monolayers by transiently affecting the paracellular pathway. Thus, NC-1059 is a lead compound for development of cotherapeutic agents to enhance access and effectiveness of ophthalmic compounds.

Comparisons of Tear Proteins in the Cow, Horse, Dog and Rabbit

Tear proteins play a major role in normal corneal health.1 Several changes in tear proteins have been shown to be related to direct corneal irritation.2 In veterinary medicine, differences between species often occurs in the clinical response to corneal irritation and external ocular disease. These differences may be a reflection of various factors including tear proteins. There is little information available on tear film properties in veterinary species. Some studies have evaluated the protein concentration for selected species; with little information on the molecular weight distribution of the proteins.3–7 This project was undertaken to determine normal protein concentration and molecular weight distribution of tear proteins in the cow, the horse, the rabbit and the dog.

Loss of Protein Kinase Cγ in Knockout Mice and Increased Retinal Sensitivity to Hyperbaric Oxygen

OBJECTIVE To determine if loss of protein kinase Cgamma (PKCgamma) results in increased structural damage to the retina by hyperbaric oxygen (HBO), a treatment used for several ocular disorders. METHODS Six-week-old mice were exposed in vivo to 100% HBO 3 times a week for 8 weeks. Eyes were dissected, fixed, embedded in Epon, sectioned, stained with toluidine blue O, and examined by light microscopy. RESULTS The thicknesses of the inner nuclear and ganglion cell layers were increased. Destruction of the outer plexiform layer was observed in the retinas of the PKCgamma-knockout mice relative to control mice. Exposure to HBO caused significant degradation of the retina in knockout mice compared with control mice. Damage to the outer segments of the photoreceptor layer and ganglion cell layer was apparent in central retinas of HBO-treated knockout mice. CONCLUSIONS Protein kinase Cgamma-knockout mice had increased retinal sensitivity to HBO. Results demonstrate that PKCgamma protects retinas from HBO damage. CLINICAL RELEVANCE Care should be taken in treating patients with HBO, particularly if they have a genetic disease, such as spinocerebellar ataxia type 14, a condition in which the PKCgamma is mutated and nonfunctional.

Surgical correction of periocular fat pads and entropion in a potbellied pig (Sus scrofa)

A 16-year-old Vietnamese potbellied pig was examined because of recurrent ocular discharge and reduced visual ability. Bilateral upper eyelid entropion and impaired vision secondary to periocular fat deposition were diagnosed. Surgical correction with excision of subdermal fat and redundant skin was performed to address both issues. Surgery restored vision and resolved ocular irritation. More than 1 year following surgical therapy the pig is visual and comfortable with no evidence of recurrent fat deposition or entropion.