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0:00
Welcome to this lecture on dry eyes. My name is Professor James Wolffsohn. I'm an Associate Pro-Vice Chancellor at Aston University in Birmingham, and I've been a technician involved in dry eye and filming management for over 20 years, with recent experience of chairing the sub-committee of the Tear Film and Ocular Surface disease workshop on dry eye.
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Despite being thinner than a human hair, a tear film has multiple important properties. First of all, it has optical properties. It gives a smooth optical surface to the front of the eye, giving high-quality vision. It provides nutrition, particularly to the cornea, the window of the eye, the clear tissue beneath it. It also removes the waste products particularly cells from the epithelial surface. It maintains the transparency of the cornea, preventing it from breaking up, which is called desiccation. It also has mechanical properties to flush away any debris and lubricates, and it also has antibacterial properties, with components such as lysozyme, lactoferin and immunoglobulins, which help to prevent eye infection.
1:18
In terms of components, we can see it's a complex system. We have various glands producing the various components of the tear film. Principally, the top layer, the lipid or oily layer, which largely prevents evaporation and stabilizes the tear film, comes from our meibomian glands along the lid margins, but also the glands of Zeis and Moll. The bulk of the tear film is the aqueous, the watery part, and this mainly comes from the lacrimal gland, but also from the accessory glands of Krause and Wolfring. Then, our mucus phase, what sticks the tear film to the ocular surface, comes from the conjunctiva tissue. The loose tissue over this area. The white of the eye from the goblet cells and this is, therefore, the final layer of the tear film. As well as the production of the tear film, we have the distribution of the tear film over the ocular surface with each blink, and then the drainage of the tear film through the tear menisci, mainly along the lower lid, but also along the upper lid towards the nose, and then the canaliculi, and the puncta, down through the nasolacrimal canal into your nose.

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