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The Science Behind Dry Eyes

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woman removing her glasses to rub her dry eyes

Everyone has likely experienced dry eyes at some point in their life. Everyday factors like a long day of work or windy weather can leave our eyes feeling less than ideal, but this feeling should be temporary. Chronic dry eye, however, is a condition that affects your eyes constantly. While constant dry eye is frustrating, it can be treated provided you get the proper diagnosis from your optometrist. 

Understanding Dry Eye

What is Dry Eye?

Dry eye covers a number of conditions that lead to insufficient eye lubrication and ultimately, discomfort. It’s important to treat dry eye as soon as possible, not only to relieve discomfort, but to prevent damage to your eyes.

Chronic dry eye can increase your eye’s risk of infection because your tears naturally protect your eyes from bacteria and viruses. If left untreated, chronic dry eye can eventually lead to eye damage including inflammation, corneal abrasions, and corneal ulcers. Even without these issues, constant dry eyes can cause decreased quality of life from consistent discomfort.

Symptoms of Dry Eye

You probably have a pretty good idea of whether you have dry eyes. Itchy, red eyes are very common symptoms, and you may get temporary relief from over-the-counter eye drops. Some additional, common symptoms include:

  • Stinging or burning feeling in your eyes
  • Mucus in or around your eyes
  • Light sensitivity
  • Feeling like something is in your eyes
  • Difficulty wearing contact lenses
  • Difficulty with nighttime driving
  • Excessive or constant watery eyes
  • Blurred vision
  • Eye fatigue

Now that you have an idea of the symptoms, it’s important to gain an understanding of the categories of dry eye. 

Categorizing Dry Eye

There are 2 main categories of dry eye: dry eye due to poor quality tears and dry eye due to insufficient tear production. That said, there are a variety of other underlying conditions that could be causing your dry eye symptoms.

Poor Quality Tears

Meibomian gland dysfunction is thought to be the leading cause of dry eye. It causes poor quality tears, leading to the discomfort of dry eye. Meibomian glands are glands located throughout the eyelid that secrete oil, known as meibum, onto the surface of the eye. Meibum prevents tears from evaporating too quickly, keeping your eyes lubricated and hydrated. 

When there is an issue with meibum levels, tears evaporate more quickly than they should, which can lead to dry eye. Meibomian gland dysfunction can happen when the meibum glands are blocked or not functioning properly. It can also be linked to blepharitis, a condition that causes inflammation of the eyelids. 

Insufficient Tear Production

Lacrimal glands are responsible for producing the watery portion of your tears. When there is a problem with the lacrimal glands, it results in insufficient dry quantity. When there isn’t enough watery fluid, known as aqueous fluid, to keep the eyes moist, you can end up with a condition known as aqueous deficiency dry eye

Secondary Causes

There is dry eye disease, which is caused by poor tear quality or insufficient tear production. There are also a number of other conditions that cause dry eye symptoms, but often need to be treated separately in order to provide relief. Some conditions that cause dry eye symptoms include:

  • Blepharitis
  • Eyelid problems, such as out-turning of the lids (ectropion) and in-turning of the lids (entropion)
  • Certain medical conditions, including diabetes, rheumatoid arthritis, lupus, scleroderma, Sjogren’s syndrome, thyroid disorders and vitamin A deficiency
  • Certain medications, including allergy medication, decongestants, hormone replacement therapy, antidepressants, and drugs for high blood pressure, acne, birth control and Parkinson’s disease
  • Certain tasks, especially visually-demanding tasks that require high focus and cause less frequent blinking
    • Computer work
    • Driving
  • Laser eye surgery, though dry eye symptoms from refractive surgery are usually temporary

Quantitatively Measuring Dry Eye

Because there are so many underlying causes of dry eye, it’s crucial to get a comprehensive exam and diagnosis for your dry eye before starting treatment. A proper diagnosis should include your medical history, a discussion of your symptoms, and quantitative testing.

Many patients with dry eyes don’t have typical dry eye, but instead, have other issues that need to be addressed in order to relieve their symptoms. For example, 24% of patients with dry eye symptoms had allergic conjunctivitis and another 24% of patients had blepharitis, rather than conventional dry eye or an issue with their tear composition. 

Quantitative testing combined with qualitative analysis of your symptoms by an optometrist is the best way to effectively diagnose your dry eye. 

Osmolarity Testing

An osmolarity test is a quantitative way to measure dry eye. It indicates the health of the surface of your eye by measuring the osmolarity of your tears. Tear osmolarity measures the concentration of salt in your tears, which can indicate if there is an imbalance in your tear composition. If your glands aren’t producing enough tears or they are producing poor quality tears, this will likely affect your tears’ osmolarity.  

The test works by inserting a small instrument on to the tear film, just above the lower lash line. The instrument collects a small tear sample from both eyes, smaller than a period on your screen. From there, your tears will be analyzed. 

An osmolarity greater than 300 mOsm/L indicates a problem with your tears. Your optometrist will also analyze the difference in osmolarity between your eyes, as a difference in osmolarity greater than 8 mOsm/L could indicate you have an unstable tear film, or issues maintaining tears. 

Combined with a thorough discussion of your symptoms and your history, tear osmolarity testing provides insight into your dry eye. You may have symptoms of dry eye but have normal tear osmolarity. This means you might have a secondary problem causing your dry eye, like blepharitis or allergies. It’s important to understand the cause in order to get the most effective treatment. 

When to See an Optometrist for Dry Eye Testing

Dry eye is one of the most under-diagnosed ocular diseases. You should see your optometrist about your dry eye if you have had prolonged symptoms of dry eye with no relief. Your optometrist will be able to assess your dry eye and provide the appropriate treatment. 

Eye Rx is an accredited TearLab Dry Eye Center, with a fully-certified tear testing laboratory. We can quickly and easily perform osmolarity tests to measure the quality and quantity of your tears, giving us insight into the most appropriate way to treat your specific case of dry eye. Contact us to book your dry eye consultation and get the dry eye treatment that’s right for you. 

Written by Benjamin Teller

Dr. Teller earned his doctorate in optometry from the Pennsylvania College of Optometry in 1996 and has been helping local residents see clearly ever since. After graduation, Dr. Teller completed an internship with the Hopewell Valley Eye Associates, as well as several externships with the National Naval Medical Center and Katzen Eye Group.

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