Dry Eye and Tears
"Dry Eye" due to tear dysfunction occurs in between 15 to 33% of the population and is more common in females. There are many causes of "dry eye". To learn more, watch the video below or take the SPEED questionnaire and book an examination with us.
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Your Amazing Tears
The tears are not simply water but are actualy a complex structure which, in simple terms, is made up of three layers. Every time we blink, this three layer structure concertinas down as the eye closes and then stretches back out again as the eye lids open. The tears have a number of functions: (1) a refractive surface, focusing light onwards through the eye (2). a lubricant reducing friction during blinking (3) supports corneal transparency (4). contains anti-bacterial enzymes (5). contains nutrients for the corneal epithelium. The healthy tear film is therefore critical to the wellbeing and comfort of the eye and to vision enabling the cornea to act as a lens refracting light onwards through the eye, lubricating and helping to clear debris from the surface and providing both nutrients and enzymes to feed and keep the surface of the eye healthy.
There are many causes of “dry eye” are because the human tear film itself is not simply a layer of water but a wonderful complex structure. In a healthy eye with a normal tear film there is adjacent to and coating the surface (conjunctiva & cornea) of the eye, a thin layer of mucin the function of which is to enable the middle, watery (aqueous) layer to spread smoothly across the surface. On top of the aqueous layer there is a thin layer of lipid (oil) the function of which is to reduce the amount of evaporation of tears,
So, the tears are made of three components and, if one or more of them is abnormal or deficient then “dry eye” will result. If you are suffering from “dry eye” symptoms your optometrist will want to diagnose the likely cause of the dryness because the treatment and management will depend upon which part of your tears is deficient.
There are a number of types of mucin found in the tears. Some are produced by goblet cells in the conjunctiva and others by the lacrimal gland. A severe deficiency in mucins can be caused by Stevens-Johnson syndrome, Sjögren syndrome and other non- Sjögren dry eye disease.. Research is ongoing with the aim of developing medication that will treat mucin abnormalities. There is some evidence that Vitamin-A may improve goblet cell production of mucin and eye ointment with vitamin A is available.
There are many causes of aqueous layer deficiency. Treatment usually consists of the instillation of tear supplement eye drops. Another management strategy is to insert tiny “plugs” in the puncta of the eye lids. Each eye lid has a punctum which is a tiny drainage hole leading to a fine pipe called the caniliculus. The canaliculae drain into the nose which is why, if you produce normal tears, your nose runs when you cry. The tiny plugs stop the drainage of tears and allow a greater volume of tears to remain on the surface of the eye.
At Barnard Levit the optometrists usually fit temporary plugs first to allow the patient to assess the effect. The plugs dissolve over a finite period of time. If the plugs worked well and the patient perceived an improvement in comfort then more “permanent” plugs can be fitted. These either sit in the punctum themselves or are fitted into the canaliculus so that they are completely hidden (Herrick Lacrimal Plugs). The plugs can be removed if required.
Diagram showing position of "permanent" Herrick plug (blue) and tempoary dissolvable plug (purple) in the canaliculi.
The oily layer of the tear film is produced by the meibomian glands which are little oil wells lying within the eye lid margins immediately behind the eye lashes. They are similar to the sebaceous glands of the skin. The sebaceous glands produce sebum whilst the meibomian glands produce meibum. If a sebaceous gland becomes blocked the content becomes thick and solid and this is often called in layman’s terms, a “white head”. Similar blockages occur in the meibomian glands often because of a bacteria called staphylococcus. The condition is termed posterior blepharitis and this leads to meibomian gland dysfunction and dry eye.
The photograph above shows thick meibum being expressed from a dysfunctional meibomian gland
Treatment usually consists of heat compresses to the eye lids with manipulation and gentle cleaning of the lid margins. Topical antibiotics are often used and in chronic cases may require a course of oral antibiotics.
Contact lenses for dry eye
Special contact lenses may also be fitted to protect the eye.