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Dry eye disease is currently a very prominent topic in optometry.
Increased awareness has caused a surge in articles written on the topic and research performed in the field. However, there are still patients slipping through the cracks that are even more at risk for dry eye syndrome or dry eye disease (DED) than the general population.
Most optometrists are aware of the most common systemic conditions and other causes of dry eyes including, Sjogren’s syndrome, Rheumatoid arthritis, lupus, and thyroid-related conditions.
Diabetes and glaucoma are two conditions that should be at the top of that list and every optometrists’ mind considering the increased risk for dry eye syndrome.
While glaucoma is not as prevalent as diabetes in the United States, optometrists are the sole primary doctors responsible for treating glaucoma and are more likely to use multiple topical medications for treatment versus our ophthalmologist counterparts. The cause of dry eye disease is most likely multifactorial in nature. Glaucoma is more common in an older population where dry eye disease is also more common. In addition, multiple topical glaucoma medications, especially those containing the preservative benzalkonium chloride (BAK) and topical carbonic anhydrase inhibitors (CAI), are toxic to the ocular surface. It has been shown that tear cytokines are elevated in patients on topical medications and can cause complications post-trabeculectomy.5 Bleb dysesthesia can also disrupt normal tear surface properties exacerbating dry eye disease. A study of 124 glaucoma patients, 23 of which were control patients, examined dry eye disease using the high validity Ocular Surface Disease Index (OSDI) twelve item questionnaire. Those with an OSDI score greater than or equal to 12 were diagnosed as having dry eye disease. The study showed that the “OSDI score increased significantly with increasing glaucoma severity”.5 Using univariate analysis, albeit not as strong as a multivariate model, daily dose of BAK greater than four drops and more than two topical glaucoma medications were strong predictors of OSDI score. The opposite of that was true for those taking no glaucoma treatments where the OSDI score was low.Dry Eye Disease and Glaucoma
On multivariate analysis, a daily dose of BAK greater than four drops was an independent risk factor for higher OSDI scores.5 The duration of glaucoma diagnosis also affected the OSDI score in a significant and predictable way. Those with a glaucoma diagnosis of less than six years had a mean OSDI score of 18 indicating mild DED and those with a diagnosis of greater or equal to six years had a mean OSDI score of 23 indicating moderate DED. The scores were statistically significant between the two groups (p = 0.03).6 The difference between OSDI scores with each addition of a topical glaucoma medication was clinically relevant; however, not statistically significant.6
The same study evaluated the quality of life of the patients diagnosed with glaucoma using the glaucoma quality of life questionnaire (GQL-15). The GQL is a 15-item patient questionnaire aimed at evaluating subjective ability to perform visually demanding tasks in normal daily living.
There are four main categories assessed: reading and recognizing faces (central/near vision), peripheral vision, darkness/glare, and navigating outside and walking along side roads.
Patients are asked to rate their experience with each question on a scale from 0 to 5 (do not perform for non-visual reasons to severe). The higher the score, the worse the quality of life for the patient. The test has been validated and has shown high reproducibility and consistency.
It is well known that peripheral vision loss decreases quality of life (increasing the raw score of the GQL); however, Skalicky et. al. showed that patients with DED had higher GQL-15 raw scores than those without DED. 5. GQL-15 summary scores were found to be the strongest independent predictor of OSDI score. It must be noted however that a patient’s subjective response to a questionnaire may be influenced by psychosocial factors and that there may be overlap between conditions causing worsening of quality of life. However, Skalicky et. al. go on to say “the correlation between the 2 scores [GQL-15 and OSDI] indicates a significant additive impact of both factors with an increased burden from each condition [Glaucoma and DED].”5
Due to the effects of glaucoma on dry eye disease, I recommend having all glaucoma patients fill out a qualified DED questionnaire and have their tears tested with an osmolarmeter. This can identify patients at risk for a decreased quality of life and improve ocular health. It should also be noted that topical glaucoma medications are created and tested on eyes with a normal tear osmolarity and having a high tear osmolarity may have detrimental effects on the effectiveness of topical medications.
These known toxic effects have pushed pharmaceutical companies to produce preservative-free glaucoma medications as well as alternative preservatives.
Prostaglandins are considered a first-line therapy for glaucoma management in most patients. For those with BAK sensitivities or DED symptoms, Zioptan (tafluprost) is the only preservative-free option in the prostaglandin drug class. It should be noted that bottles of Zioptan not in current use should be stored in a refrigerator. The only other preservative free IOP lowering medications available for our patients are Timoptic (timolol maleate) in Ocudose™ and the combination drug Cosopt PF (dorzolamide/timolol).
There are a few other glaucoma medications that offer an alternative to BAK preservatives. The “P” in Allergan’s Alphagan-P alpha-agonist glaucoma medication stands for Purite®. Purite® is a preservative that breaks down when exposed to air. It works by oxidizing microbial cells, but has no significant effect on corneal epithelial cells. SofZia® is found in Travatan-Z and is effective at killing bacteria, which lack specific enzymes, by oxidative destruction. Human cells have the necessary enzymes to protect against the harmful actions of SofZia®.7
Glaucoma can easily be treated with non-preservative topical medications for patients with BAK sensitivities or concomitant DED. Prostaglandins and beta-blockers tend to be the most commonly prescribed initial medications for glaucoma, both of which have preservative-free treatment options. If the target IOP is not reached with a combination of these two drops, Timoptic can be replaced with Cosopt PF.
We must talk with each patient to understand their concerns and issues and consider their OSDI score, osmolarity score, and quality of life when prescribing topical glaucoma medications.
Sources:
- Glaucoma Facts and Stats. Glaucoma Research Foundation. http://www.glaucoma.org/glaucoma/glaucoma-facts-and-stats.php. Accessed November 1, 2016.
- Skalicky, Goldberg, & Mccluskey. (2011). Ocular Surface Disease and Quality of Life in Patients With Glaucoma. American Journal of Ophthalmology, American Journal of Ophthalmology.
- Garcia-Fejioo J, & Sampaolesi Jr. (2012). A multicenter evaluation of ocular surface disease prevalence in patients with glaucoma. Clinical Ophthalmology, 2012(Default), 441-446.
- Kahook MY. The Pros and Cons of Preservatives. Review of Ophthalmology. https://www.reviewofophthalmology.com/article/the-pros-and-cons-of-preservatives. Published April 15, 2015. Accessed November 22, 2016.
