Dry eye syndrome is incredibly common and millions of people in this country suffer from it. In many cases, however, people simply get on with it and don’t even think about what the cause could be. This can be a mistake because dry eye syndrome can also be symptomatic if an underlying condition. Furthermore, it is incredibly uncomfortable and people should not have to live with constant discomfort.
People with dry eye syndrome usually find that their vision is blurred towards the end of the day. They also find that their eyes are often irritated, with redness and stinging and burning sensations. Additionally, many feel like there is a foreign object in their eyes. Interestingly, many people with dry eye syndrome also experience excessive tearing.
Dry eye is actually a very complex condition. It is important, therefore, that you have a medical professional such as an ophthalmologist look into what is actually going on with your eye. It may simply be that your tear production is slightly off balance, but you may also have an infection, an autoimmune disorder, an allergy, trauma to the eye and more.
What Causes Dry Eye?
Dry eye happens when either the quantity or the quality of your tears isn’t right. This leads to your eyes being more susceptible to irritation as well. When you do not produce enough tears, your eyes will feel dry. This can be caused by:
- Medical condition
- Tear gland problems
- Eye surgery
It is also possible the quality of your tears is not good enough. This can happen in any of the three layers of your tears (water, oil, mucus), as explained in the table below. When there is a problem in any of those areas, your eye can become irritated.
|Outer Layer||Middle Layer||Inner Layer|
|Made up of lipids (oils)||Made up of aqueous substance (water)||Made up of mucus|
|Stops the tears from evaporating too quickly||Gives your eyes salt and nutrients. Helps to clean your eyes. Provides the ocular tissue with oxygen.
Most common cause of dry eye syndrome or keratoconjunctivitis sicca.
|Designed to make sure tears are evenly spread across the eye ball. Stabilizes the entire tear film.|
If you do have dry eye, a number of tests can be performed in order to see what is really going on.
There are various osmolarity instruments, which can test anything such as cell culture media, milk, bilirubin, urine, plasma, blood, serum and more. Osmolarity testing can be used to test the quality of tears in three different ways.
- Freezing point depression. This method has been used for around 50 years. It is beneficial because only a tiny amount of tear is required and it is one of the most accurate testing methods. However, it can only be performed in specialized laboratories.
- Vapor pressure. This is a very simple method of measuring the osmolarity of tears. As a result, it is generally a preferred method for many ophthalmologists. They insert a sample of tear into a chamber to measure at which point dew starts to form. It is a quick and reliable method, but quite a large tear sample is required in order to perform it. Unfortunately, most people with dry eye syndrome do not have enough tear fluid for this particular test. It is classed as a secondary diagnostic test because of this.
- Electrical impedance. This measures the ionic content in the tear fluid. Only a relatively small sample of tear fluid is needed in order to perform this test. A handheld device is used by a clinician to collect some of the tear, which is then placed on a microchip for testing in a stationary reader. Interestingly, this test is believed to be as effective as the freezing point depression, and many clinicians are now using it. It is a quick and easy to administer test and can be reimbursed under Medicare, which makes it even more popular. However, the instrument that is needed for this test is very expensive, resulting in few ophthalmologists investing in it.
The Schirmer’s test is the most commonly used test to determine whether or not dry eye syndrome is present. A patient will first be given some numbing drops, so that they don’t react to the presence of eye strips. These drops may cause some stinging or irritation, however. Once they work, an ophthalmologist pulls the patient’s bottom eyelid down, placing a strip of paper beneath it. Patients then have to close their eyes, without squeezing, keeping them closed for around five minutes. They may not touch their eyes during this period. The strips are then removed and the amount of moisture is measured. If insufficient moisture is present, dry eye syndrome can be diagnosed.
Red Thread Test
The red threat test is very similar to the Schirmer’s test. The only difference is that, rather than using a paper strip, a red thread is used underneath the eye. This can be more beneficial to people who have a fear of having something inserted in the eye, or who have small lower eyelids, for instance.
Resources and References:
Methodologies to Diagnose and Monitor Dry Eye Disease: Report of the Diagnostics Subcommittee of the International Dry Eye Workshop – Methods to diagnose and monitor dry eye. (Tear Film and Ocular Surface Society)
Dry Eye Syndrome Tests – Tests for dry eye syndrome. (Kellog Eye Center)