Why dry eye means poor vision

April 10, 2015

There are lots of parameters to choose from when looking for dry eye disease.

There are lots of parameters to choose from when looking for dry eye disease. Despite many studies that show poor correlation between signs and symptoms, and poor correlation with positive tests results with a dry eye diagnosis, we need to persist.1

In establishing my dry eye protocol, I have used many of these tools. After a few years, I distilled it down to what was most meaningful to me. 

More from Dr. Schachter: Evaporative dry eye vs. aqueous tear deficiency

The parameters that I have found most salient are:

• History

• Tear volume and composition

• Corneal staining

• Tear film break-up time (TFBUT)

In looking at history, it is important to remember that signs and symptoms do not always match. When I first started actively screening for dry eye, I was often finding clinical signs, but minimal subjective symptoms. I reached out to ocular surface guru Kelly Nichols, OD, MPH, PhD, for advice. I asked her if she treats signs or symptoms, and she replied, “I treat both, but I don’t think there is such a thing as an asymptomatic dry eye patient-I think you are not asking the right questions.” That sage advice stays with me to this day.

Next: A new approach   

 

A new approach

I changed my questions to ask more than, “Are your eyes dry, sandy, watery, gritty, etc.?” to include questions like:

• What is your vision like at the end of the day?

• Can you read at night as long as you like?

• Are your contact lenses “ready” to come out at night, or do you have to remember to take them out? 

Related: Creating a dry eye protocol

I ask about stability of vision, especially in toric and multifocal wearers. 

I also changed the way that I ask the questions. In the past, I think I came off to patients like “Your eyes don’t bug you, right?” Now, I show more concern and sincerity. That seems to make a difference in how patients respond. 

Next: The tear film, inflammation and vision

 

The tear film, inflammation and vision

The tear layer is complicated, and it needs to be present in not only the right quantity, but quality as well. A poor lipid layer can cause the tear film to break up too fast. A watery eye can cause vision to fluctuate. If the mucoid-aqueous layer is insufficient, the tear film will not spread evenly.

A decrease in aqueous production can increase osmolarity, which can trigger inflammation. It is thought that uneven tear film distribution can cause higher-order aberrations, and this has indeed been my own experience in my practice. Excessive matrix metallopeptidase 9 (MMP-9) proteins indicate inflammation in the tear layer.

These are all important factors when diagnosing and treating dry eye.

For example, if tear volume is low, and the plan is to use punctal occlusion, it is critical to know whether the tear film is inflamed. Preserving a tear layer that has inflammation can cause harm to the cornea, as MMP-9s are collagenases. 

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In order to see optimally, the cornea must be intact and have a smooth tear film overlying it.2 Corneal staining not only triggers inflammation,3 it distorts vision. I tell patients that it is like looking through scratched glass. Optimal vision requires optimal optical surface.

When thinking about dry eye, its impact on vision is what made it so important to me. Therefore, TFBUT is critical in my mind. Remember, each blink forms a tear film, and this is what allows our patients to see clearly. If the tear layer breaks up quickly, vision suffers, and the patient is at risk of superficial corneal staining, which in turn can trigger inflammation, exacerbating the condition.

This also occurs when blink rates are reduced, which is more and more common with increased use of electronic devices.4

Next time I will discuss my favorite tools to get this information.

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References:

1. Bjerrum KB. Test and symptoms in keratoconjunctivitis sicca and their correlation. Acta Ophthalmol Scand. 1996 Oct;74(5):436-41.
2. Goto E, Yagi Y, Matsumoto Y, et al. Impaired functional visual acuity of dry eye patients. Am J Ophthalmol. 2002;133:181-6.

3. Stevenson W, Chauhan SK, Dana R. Dry Eye Disease: An Immune-Mediated Ocular Surface Disorder. Arch Ophthalmol. 2012;130(1):90-100.

4. Bentivoglio AR, Bressman SB, Cassetta E, et al. Analysis of blink rate patterns in normal subjects. Mov Disord. 1997 Nov;12(6):1028-34.