Tear osmolarity measures the relative saltiness of tears. I place importance on osmolarity testing because it has the highest predictive value of any diagnostic technique for dry eye at 87 perdent.2
Our osmolarity device is the TearLab Osmolarity System (TearLab). A recent randomized, masked, in vitro study showed that the TearLab system has the highest level of accuracy available in a device for individualized use, with a correlation with known solutions of r2=0.96 (coefficients of variation were 1.2 percent , 2.3 percent, and 1.4 percent, respectively, for solutions simulating normal eyes, moderately dry eyes, and severe dry eyes).3
In comparison, the Wescor 55110 Vapro Pressure Osmometer, the FDA gold standard for laboratory osmometers, demonstrated a correlation of r2=0.98, while the i-Med Pharma i-Pen (not available in the U.S.) had a correlation of r2=0.03.3
Strength of correlation with anticipated results is an important indicator of a device’s ability to measure accurately and precisely (see Table 1).
If my patient’s result is ≥308 mOsm/L or there is an intereye difference ≥8 mOsm/L, then I know aqueous tears are deficient, indicating dry eye disease. Even mild cases are accurate with osmolarity testing.
Because dry eye is an inflammatory disease, direct chemical analysis for the inflammatory marker enzyme matrix metallopeptidase 9 (MMP-9) is informative. In my practice, we use InflammaDry (Quidel), its positive results (MMP-9 levels ≥ 40ng/ml) have statistically significant correlation to dry eye disease,4 even in asymptomatic patients.5
When MMP-9 is elevated, indicating an active inflammatory process, I know that ocular surface disease is the likely cause, particularly when this result occurs alongside abnormal osmolarity testing. I can also discern that the inflammation is having a daily effect on the patient’s compliance with glaucoma therapy.
In addition to tear osmolarity and MMP-9 testing, I perform supervital dye assessment with lissamine green to visualize damage to the ocular surface and test tear break-up time (TBUT).
Examining the posterior meibomian glands is initially accomplished at the microscope with direct pressure and grading of the oils status. Once MGD is established, I use LipiView meibography (TearScience) to see the extent of the blocked or atrophied glands.
It is important for clinicians to remember to avoid manipulation of the lids, instillation of topical agents, or the use of increased illumination before point-of-care testing to avoid adulterating the outcomes.
Pre-existing dry eye
If a patient has dry eye disease before glaucoma treatment, I know that noncompliance with glaucoma medication is a distinct possibility unless I begin dry eye treatment concurrently. If the patient has severe dry eye, I may consider surgical options earlier, but generally I begin with a non-preserved prostaglandin (frequently tafluprost 0.0015% [Zioptan, Akorn]) and dry eye treatment.
Related: Managing glaucoma in women
Prescription medications are limited in part by glaucoma. Because steroids such as loteprednol (Lotemax, Alrex, Bausch + Lomb) and standard ketone steroids like difluprednate (Durezol, Novartis) are capable of raising IOP or blocking IOP reduction, they are generally avoided or used in limited duration for patients with glaucoma.
Cyclosporine (Restasis, Allergan) produces gratifying results over time. Because this medication is not inexpensive, affordability is a factor for patients, but those who are comfortable with the cost typically comply very readily. In my experience, it takes about eight to 12 weeks to see results.