The Ocular Surface and Tear Center at the University of Minnesota is one of the premier centers committed to better understanding and more effective treatment of ocular surface and tear disorders. Many patients with unresolved or unidentified ocular surface problems come to us for assistance in the diagnosis and management of their ocular irritation.
Many people suffer from the discomfort of this condition and spend a lot of money on eyedrops and treatment, which frequently provide only limited relief. Low patient satisfaction occurs primarily because of inaccurate diagnosis and a limited number of available treatments. Why are accurate diagnosis and effective treatment for these conditions so elusive? Understanding the delicate balance maintained on the surface of the eye will help answer this question.
The ocular surface is comprised of the cornea (the clear window of the eye), and conjunctiva (a thin membrane in front of the white part of the eye). This integral surface depends on the presence of a protective tear film to ensure clarity of vision, function and comfort. Our natural tear film is comprised of three layers: a lubricating, mucous substance produced in the cells of the conjunctiva; a nourishing and cleansing watery middle substance produced in the tear (lacrimal) glands of the eye; and a superficial oily substance produced by oil glands in the eyelids to prevent water evaporation. These three elements have to be in perfect balance in order to spread evenly over the surface of the eye. The tear film acts like windshield cleaning fluid. The blinking of the eyelids is similar to the action of a windshield wiper distributing washer fluid (tear film) over the windshield.
Because this protecting and lubricating mechanism depends on highly orchestrated cooperation among the cells and glands, it is important for physicians to investigate every component to identify each patient’s ocular surface dysfunction and the abnormalities involved before making a definitive diagnosis or prescribing treatment. Disruption of the delicate balance between the ocular surface and tear film can cause severe ocular surface morbidities. The discomfort can range from constant annoyance to blurred vision, eye fatigue, and difficulty in reading, watching TV, sewing, or driving. Many patients suffer not only eye irritation but also diminished quality of vision and life.
At the Ocular Surface and Tear Center at the University of Minnesota, we use a series of clinical tests to detect and dissect the complexity of the ocular surface and tear film. Via these special diagnostic tests and careful analysis, our specialists have been able to provide much better insight and understanding of the patients' symptoms, thereby prescribing or providing better and more effective treatments for these frustrating conditions. Our specialists continue to conduct clinical and laboratory research to explore and resolve the important issues related to ocular surface disorders and related treatments.
Among the many different reasons for eye discomfort, dry eye is by far the most common. This condition is characterized by an unstable tear film due to the breakdown of one or more of the three tear components. Because of the complexity of the tear film, using commercial preparations of artificial tears to replace the quantity of the water in the tear film is usually not sufficient. For example, it was previously assumed that irritation suffered by dry eye patients was due to the lack of tears (a deficiency in quantity). However, with better understanding of the tear film by our specialists, we now know that eye comfort depends not only on the quantity of tears but also on the quality of the tears, especially on the lubricating mucous layer of tears produced by the conjunctival cells. Many dry eye patients suffer from significant damage of these cells, a condition known as keratoconjunctivitis sicca. It is also known that there is a strong correlation between lacrimal gland dysfunction (loss of watery tears) and the loss of mucous-producing cells in the conjunctiva of the patients with keratoconjunctivitis sicca. Furthermore, when deprived of tears the ocular surface cells begin producing inflammatory proteins which results in abnormal growth and turns off mucous production. To provide a better quality of the lubricating tears, our specialists have been developing several bioactive eye drops to provide better lubrication, better tear film stability, and more effective suppression of inflammation on the ocular surface.
Tears: The Eye’s First Line of Defense
As the eye's first line of defense, the tear film can be compromised by many conditions and diseases.
Contact lens use:
The comfort and improved vision afforded by contact lenses relies on an ample amount of tears. Many patients cannot tolerate contact lenses because of an underlying dry eye condition. Furthermore, many patients can incur contact lens-related trauma or infection secondary to inadequate lubrication by natural tears.
Ocular surgeries:
Many ocular surgeries, such as cataract surgery, glaucoma surgery, and retina procedures, can violate the integrity of the ocular surface by creating surgical wounds. In general, these surgical wounds heal without complications; however, problems may develop as a result of insufficient or excessive healing, especially for those patients with pre-existing tear film or ocular surface abnormalities. Many patients with pre-existing ocular surface conditions or tear deficiency develop severe ocular irritation after ocular surgeries. Even though dry eye is known to be prevalent in patients of middle ages, severe dry eye conditions can also develop after the popular keratorefractive surgeries because by creation of the flap during LASIK the corneal nerves are severed and corneal sensation is decreased. As a result of the decreased nerve impulse, the lacrimal gland produces less reflex tears and causes inadequate lubrication of the ocular surface after the surgery.
Corneal damage:
The ocular surface can be damaged by many conditions including:
Chemical/thermal injuries.
Conjunctival scarring conditions such as Stevens-Johnson syndrome and ocular cicatricial pemphigoid.
Chronic infections or inflammation of normal tissue growth on the conjunctiva such as pterygium or tumors.
Damage to the sensory nerves of the cornea such as dysautonomia or Riley-Day syndrome.
Rare hereditary conditions such as aniridia or congenital anomalies.
These problems usually result in extensive damage to the ocular surface and lead to abnormal proliferation of the conjunctival cells on the corneal surface and abnormal blood vessel formation with scarring. Severe damage of the ocular surface usually leads to profound loss of vision. Our specialists at the Ocular Surface and Tear Center are developing new strategies to use bioactive tears and to promote ocular surface wound healing to facilitate visual recovery and ensure patients' comfort after a variety of ocular surgeries.
New Bioactive Tear Therapies:
With a better understanding of the tear composition and its physiological roles, the research team at the Ocular Surface and Tear Center is actively involved in studies to use biologically essential components of tears, which promote a healthy ocular surface. These formulated bioactive eye drops may mimic the action of normal tears. This treatment can potentially be more effective than either the use of artificial tears which only act as replacement of the quantity of tears or punctal occlusion, a procedure to close the tear duct to conserve the amount of naturally produced tears.
Reconstructive Therapies:
Recent advances of stem cell research have created a flurry of activities in many scientific laboratories, including ours at the Ocular Surface and Tear Center. Our researchers are working to understand the gross process of these master mother cells and their potential to repair diseased tissues. The first major breakthrough for this research came when scientists identified stem cells or reproductive mother cells located at the edge of the cornea, known as the limbus. Our clinicians have found that transplanting these limbal stem cells can often repair the damaged ocular surface. Many patients with corneal damage in one eye can use their own stem cells, harvested from the other healthy eye. With close collaboration with the Minnesota Lions Eye Bank, our surgeons have also perfected the technique of transplanting cells from preserved donor eyes. The donor limbal tissue can be extended to the patient with corneal damage in both eyes. Our researchers continue to investigate the mechanism of regulating stem cell function and the possibility of increasing these precious stem cells in tissue culture for future use.
In addition, our scientists are also researching ways to encourage the conjunctival cells located in the tissue on the white part of the eye to transform into corneal stem cells to improve the quality of the cornea. They are also studying the naturally occurring death of cells in the cornea to improve upon techniques for corneal preservation, corneal transplantation, and ocular surface reconstruction. In many situations, the damage to the ocular surface is not limited only to the superficial cells. A deeper layer of tissue, known as the stroma, is also damaged. With better understanding of the ocular surface, our specialists are using preserved amniotic membrane (the membrane from the inner surface of the placenta) to reconstruct the surface of the damaged eyes and eyelids. Research has shown that the inflammation and vascularization of abnormal ocular surface wound healing has been decreased with use of this membrane, which has also been shown to prevent graft rejection.
New Light Therapy
Abnormal blood vessel formation can occur on the ocular surface after extensive damage. In general, new blood vessels are one of the body's normal healing mechanisms. However, when they form in the cornea of the eye they not only obstruct the vision but increase the chance of graft rejection in the event of corneal transplantation. In the past, clinicians have been trying to remove the blood vessels by conventional lasers. However, that therapy is not a permanent solution because the intensity of conventional laser can produce additional inflammation and further regrowth.
A novel therapeutic modality to destroy new and abnormal blood vessels on the surface of the eye has been developed by our specialists at the Ocular Surface and Tear Center. It is called the photothrombosis technique, and is very similar to the photodynamic therapy used in treating patients with age-related macular degeneration. The photothrombosis technique employs a photosensitizer, which increases the light available without increasing its heat intensity. This makes it possible to use 10-20 times less energy and achieve the destruction of the blood vessels without further damage to the cornea. The technique is based on the blood vessels’ response to the interaction of laser light and injected rose Bengal dye. The combination not only obliterates the blood vessel, but also creates a long-lasting blood clot, making the procedure an ideal therapy for patients with severe ocular surface disease. By eliminating these corneal vessels, vision can also be improved. Should these patients be found to need corneal transplantation, the risk of tissue rejection is certainly reduced.
With their unique perspective on understanding and management of ocular surface diseases, our specialists at the Ocular Surface and Tear Center are committed to a program of innovative patient care aimed at relieving and ultimately solving the agony of ocular surface disease and associated visual difficulties.
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