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Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic or therapeutic reasons. In 2010, the worldwide market for contact lenses was estimated at $6.1 billion, while the US soft lens market was estimated at $2.1 billion. Multiple analysts estimated that the global market for contact lenses would reach $11.7 billion by 2015. As of 2010, the average age of contact lens wearers globally was 31 years old, and two-thirds of wearers were female.
Tears are a clear liquid secreted by the lacrimal glands found in the eyes of all land mammals. Their functions include lubricating the eyes, removing irritants, and aiding the immune system. Tears also occur as a part of the body's natural pain response. Humans are the only mammals known to produce tears as part of an emotional response, such as out of joy or grief. Tears have symbolic significance among humans. Emotional secretion of tears may serve a biological function by excreting stress-inducing hormones built up through times of emotional distress. Tears are made up of water, electrolytes, proteins, lipids, and mucins that form layers on the surface of eyes. The different types of tears—basal, reflex, and emotional—vary significantly in composition.
Blepharitis is one of the most common ocular conditions characterized by inflammation, scaling, reddening, and crusting of the eyelid. This condition may also cause burning, itching, or a grainy sensation when introducing foreign objects or substances to the eye. Although blepharitis is not sight-threatening, it can lead to permanent alterations of the eyelid margin. The overall etiology is a result of bacteria and inflammation from congested meibomian oil glands at the base of each eyelash. Other conditions may give rise to blepharitis, whether they be infectious or noninfectious, including, but not limited to, bacterial infections or allergies.
Dry eye syndrome (DES), also known as keratoconjunctivitis sicca (KCS), is the condition of having dry eyes. Other associated symptoms include irritation, redness, discharge, and easily fatigued eyes. Blurred vision may also occur. Symptoms range from mild and occasional to severe and continuous. Scarring of the cornea may occur in untreated cases.
Chalazion is a cyst in the eyelid usually due to a blocked meibomian gland, typically in the middle of the eyelid, red, and not painful. They tend to come on gradually over a few weeks.
The human eye is a sense organ that reacts to light and allows vision. Rod and cone cells in the retina are photoreceptive cells which are able to detect visible light and convey this information to the brain. Eyes signal information which is used by the brain to elicit the perception of colour, shape, depth, movement, and other features. The eye is part of the sensory nervous system.
Meibomian glands are holocrine type exocrine glands, along the rims of the eyelid inside the tarsal plate. They produce meibum, an oily substance that prevents evaporation of the eye's tear film. Meibum prevents tears from spilling onto the cheek, traps them between the oiled edge and the eyeball, and makes the closed lids airtight. There are about 25 such glands on the upper eyelid, and 20 on the lower eyelid.
Artificial tears are lubricating eye drops used to relieve dryness and irritation of the ocular surface. Dry eye syndrome is a common ocular surface disorder and is characterized by disruption of the tear film and increased inflammation.
A scleral lens, also known as a scleral contact lens, is a large contact lens that rests on the sclera and creates a tear-filled vault over the cornea. Scleral lenses are designed to treat a variety of eye conditions, many of which do not respond to other forms of treatment.
Lacritin is a 12.3 kDa glycoprotein encoded in humans by the LACRT gene. Lacritin's discovery emerged from a screen for factors that stimulate tear protein secretion. Lacritin is a secreted protein found in tears and saliva. Lacritin also promotes tear secretion, the proliferation and survival of epithelial cells, and corneal wound healing Lacritin is thus a multifunctional prosecretory mitogen with cell survival activity. Natural or bacterial cleavage of lacritin releases a C-terminal fragment that is bactericidal.
A pinguecula is a common type of conjunctival stromal degeneration in the eye. It appear as an elevated yellow-white plaque in the bulbar conjunctiva near to limbus. Calcification may also seen occasionally.
Conjunctivochalasis is a common eye surface condition characterized by the presence of excess folds of the conjunctiva located between the globe of the eye and the eyelid margin.
Gerd Geerling is a German consultant ophthalmic surgeon, Professor of Ophthalmology and since 2011 head of the Universitäts-Augenklinik Düsseldorf of the University of Düsseldorf, Germany.
Meibomian gland dysfunction is an inflammation of the meibomian glands that causes the glands to be obstructed by thick, cloudy-to-yellow, more opaque and viscous-like, oily and waxy secretions, a change from the glands' normal clear secretions. Besides leading to dry eyes, the obstructions can be degraded by bacterial lipases, resulting in the formation of free fatty acids, which irritate the eyes and sometimes cause punctate keratopathy.
TearScience is an American company founded in 2005 that develops, manufactures and markets ophthalmic medical devices aiding in the identification and treatment of meibomian gland dysfunction, also known as dry eye disease, which is a condition that affect as many as 25 million Americans. The company's Lipiflow System was FDA cleared in June 2011 for treating meibomian gland dysfunction and is currently installed in over 250 locations across the globe. The company is headquartered in Morrisville, North Carolina.
Heiko Pult is a leading expert for Dry Eye, Contact Lenses, Tear Film and Vision. He is CEO at Horst Riede GmbH in Weinheim and also owns his own research group named Dr Heiko Pult - Optometry and Vision Research, Weinheim, Germany. He is lecturer and an independent investigator of several research groups, companies and schools and author of numerous papers, articles and books. ResearcherID: I-3596-2015
Tear break-up time (TBUT) also known as tear film break-up time (TFBUT) is the time taken to appear first dry spot on cornea after a complete blinking. TFBUT measurement is an easy and fast method used to assess the stability of tear film. It is a standard diagnostic procedure in the dry eye clinics. The volume of tear in the eye depends on two factors, drainage through the lacrimal passages and evaporation. Factors like decreased tear production, increased evaporation rate, tearfilm instability, tear hyperosmolarity, inflammations, ocular surface damages etc. can cause dryness to the eyes.
Exposure keratopathy is medical condition affecting the cornea of eyes. It can lead to corneal ulceration and permanent loss of vision due to corneal opacity.
Michel Guillon is a British optometrist and researcher. Guillon is mainly known for his research and advances in optometry and ophthalmology.
Evaporimetry is medical test to measure the rate of the evaporation of the eye. Individuals with meibomian gland dysfunction will have an increased rate of evaporation because the glands release lower quality meibum. This impacts the tear film increasing the evaporation rate and can cause dry eye. The device used to perform an evaporimetry is called evaporimeter.
References
- ↑ "Tear Film and Ocular Surface Society (TFOS) | National Eye Institute".
- ↑ "TFOS".
- ↑ "The Tear Film and Ocular Surface Society: A Mission to Advance Understanding of the Ocular Surface". The Ocular Surface. 2 (3): 218–220. 1 July 2004. doi:10.1016/S1542-0124(12)70065-4. PMID 17216095.