Inter-Eye Osmolarity Differences A Weak Proxy for Dry Eye Signs 

Inter-eye osmolarity differences of 8 mOsmol/L do not provide strong diagnostic value in signs or symptoms of dry eye disease , according to research published in Clinical Ophthalmology. The Inter-eye osmolarity differences did not correlate with symptoms, non-invasive tear film break up time (NIKBUT), or ocular surface staining (OSS), researchers report.

The researchers used data from an unpublished prospective interventional study of dry eye disease and cataract surgery to evaluate the diagnostic value of an inter-eye osmolarity difference of 8 mOsmol/L in relation to dry eye symptoms and other non-osmolar signs of dry eye disease. 

A total of 191 participants were included in the analysis. All participants underwent dry eye diagnostics according to the Tear Film and Ocular Surface Society’s International Dry Eye Workshop II (DEWS II) criteria. Tear osmolarity was assessed in both eyes. Non-invasive tear film break up time and ocular surface staining were assessed in the test eye. To assess symptoms, participants also completed the Ocular Surface Disease Index (OSDI) questionnaire. 

Because inter-eye osmolarity differences of 8 mOsmol/L or larger is considered a sign of dry eye disease according to the equipment’s user manual, the researchers evaluated participants’ eyes for osmolarity and compared the values with other non-osmolar signs of dry eye disease.

The participants were divided into 3 groups according to osmolarity measurements: those with normal osmolarity (below 308 mOsmol/L in both eyes and less than 9 mOsmol/L difference between the eyes), those with high osmolarity (308 mOsmol/L or higher in one of the eyes), and those with a high inter-eye osmolarity differences (>8 mOsmol/L or higher, with neither eye having osmolarity higher than 307 mOsmol/L).

Of the 191 participants, 65 had normal osmolarity (mean age, 74.6; 50.8% women); 107 had high osmolarity (mean age, 74.8 years; 59.8% women); and 19 had a high inter-eye osmolarity difference (mean age, 74.6 years; 57.9% women). 

The researchers found that 37% of the eyes with a high inter-eye osmolarity difference had a normal OSDI score and reported that all eyes with an inter-eye osmolarity difference of more than 15 mOsmol/L had an OSDI score indicative of dry eye.

When comparing signs and symptoms of the high inter-eye osmolarity difference group with those of the high osmolarity group and the normal group separately in a pairwise fashion, they found no significant correlations. They also reported that the signs and symptoms of the high inter-eye osmolarity difference group trended closer to those of the normal osmolarity group than those of the high osmolarity group. 

“Based on this, we believe the inter-eye difference cutoff that is diagnostic for dry eye (8 mOsmol/L) should be re-evaluated,” the researchers explain.

Limitations of the study included a small sample size in the inter-eye difference group, the subjective evaluation of some signs of dry eye, and data collection by 3 individuals. 

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.