At a Glance:
- Dry eyes is a common condition typifies by blurry, dry, irritated, itchy, red or watery eyes
- In a healthy eye, tears have numerous roles, including maintaining clear vision, and lubricating and protecting the eye
- Tears are made up of two key parts, an oily layer that is exposed to the air and helps keep the eyelid lubricated and stops the tears from evaporating, as well as deeper watery and mucus layer that helps the tears stick to the eye
- If there is an imbalance between these two parts, then the tears may not be able to adequately protect the eyes, leading to dry eyes
- Some glaucoma treatments, including eye drops and surgery may significantly increase your risk of developing dry eyes
What are Tears?
The eyes are one of the most exposed parts of the human body. The eyes have a layer of protective tears that reduce friction in the eyes during blinking, flush away irritants and fight infection. The tears also help the eyes to see, by maintaining a smooth eye surface to focus light properly.Tears may appear to be little more than water, but they are actually an incredibly complex chemical solution containing more than 2000 components. Tears feature three layers, an oily, surface layer (the part of the tear exposed to the air), a middle watery layer and a deep mucous layer that faces the eye.
The oily tear layer is created by special glands in the eyelid. These meibomian glands line the edges of the eyelids closest to the lashes. The oily layer helps keep surface tension on the tear layer and stops them from evaporating easily. If the meibomian glands are blocked or secrete substandard oil, the tears can dry out easily, leading to dry eyes.The watery/mucus layer of the tears is produced by the lacrimal glands and the conjunctiva. The lacrimal glands are situated above the outer corner of the eye on each side and produce lacrimal fluid, which contribute to the bulk of the watery layer. The lacrimal glands are also responsible for the production of tears when crying.
The conjunctiva is a thin, clear membrane that covers both a section of the surface of the eye as well as the inner surface of the eyelid. This membrane helps keep the surface of the eye and the inner surface of the eyelid lubricated.
If there is an imbalance between these two major parts, the tears may not be able to properly lubricate, nourish and moisten the eyes, leading to dry eyes.
If you have glaucoma or ocular hypertension and are concerned about developing dry eyes, schedule an appointment to see your optometrist or ophthalmologist to discuss possible treatment options that could save you the irritation whilst still lowering the pressure in your eyes. If you need to schedule a consultation, the fastest and easiest way to search for and book, the fastest and easiest way to book an appointment with an eye care specialist online is through MyHealth1st.
Glaucoma Treatments and Dry Eyes
Glaucoma is a group of optic neuropathies - conditions that cause damage to the optic nerve - that lead to progressive loss of vision. Around 300,000 Australians currently live with glaucoma. Thanks to a number of different treatments, while glaucoma can’t be cured, the progression of the disease can be managed and slowed.
Unfortunately, a number of these treatments may increase the risk of developing dry eyes. Dr. Leigh Plowman is an optometrist and authority on dry eyes. His website, Dry Eye Directory is dedicated to helping people with dry eyes find the help they need.
“The most common form of glaucoma treatment in the early stages is an eye drop”, says Dr Plowman. “The most common drops tend to be preserved to try and keep the bottle lasting longer. Those preservatives do help to increase the penetration of the medication as well. So it helps when you put the drops in and it helps to get it into the eyes to help reduce pressure.”
“The downside of those preservatives, especially things like benzalkonium chloride is that it affects the things like the conjunctiva and specifically the goblet cells. Those are the cells in the conjunctiva that produce mucus. Mucus is the bottom layer of the tears, so it's the part that anchors the normal tears to the cornea underneath. If there's not enough mucus to hold the tears on, then you've got an unstable tear film, and you can get sore eyes, red eyes and filmy vision as well”.
Benzalkonium chloride can affect the meibomian glands as well. Preservatives in eyedrops can have a significant impact on the glands. According to Dr Plowman, “it’s really kind of a double whammy as it affects mucous formation and the glands that create the oil as well”.
If you do have dry eyes and you have borderline pressures, ocular hypertension, or you've got glaucoma, switching to preservative free drops may be a good option. Preservative free eye drops relieve the burden of having to use something that irritates your eyes every time you use it, but it also gives that pressure lowering impact.
Unfortunately, preservative free eye drops don’t appear to have as much of a lowering impact as those with preservatives. That said, an optometrist or ophthalmologist can observe the pressure in the eye over time and help ensure that preservative free eye drops are providing adequate pressure lowering so that the progression of the glaucoma is slowed.
The major test used to assess the drainage angles of the eye (whether the natural drainage in the eye is open, narrowed or obstructed) is referred to as a gonioscopy. This test utilises a specialised contact lens for visualisation.
During this examination, anaesthetics containing preservatives such as benzalkonium chloride may be used. While these preservatives may cause issues with mucous or oil production, the risk is far lower, as the testing is a one off event rather than regular exposure, such as everyday use of eye drops for glaucoma treatment.
A number of different surgical techniques may be used in the treatment of glaucoma. These techniques can be classified in two different categories - conventional surgery and MIGS (Minimally or Micro-Invasive Glaucoma Surgery).Conventional surgical techniques typically either involve surgically creating a drainage channel (trabeculectomy) or implanting a specialised glaucoma drainage device (GDD). While both of these surgical techniques have proven to be successful in lowering pressure in the eye and significantly aiding in the treatment of glaucoma, they may significantly increase the risk of dry eye.
According to Dr Plowman, during a trabeculectomy, “you are wiping out some of those mucous producing cells. That is always going to weaken like the mucosal layer, and if you've had maybe any sun damage, you've got some little sun spots on your eyes as well, adding that glaucoma surgery to the sun spots, and then you really starting to deplete mucous production quite quickly”.
In recent years, a new form of surgical glaucoma treatment has risen to prominence. Minimally or Micro-Invasive Glaucoma Surgery (MIGS) aims to provide pressure relief in the least invasive manner. This typically involves the implantation of tiny stents in the eye to allow for aqueous humour to drain properly.
Depending on the type of the stent, they may create a new drainage channel or open up a compromised or blocked natural drainage channel. Most importantly, the implantation of MIGS devices typically does not disturb the conjunctiva, therefore preserving the cells that create mucous.