Comparison of tear Matrix Metalloproteinase 9 (MMP-9) estimation with Schirmer's test in Ocular Surface Disorders

Background: Ocular surface disorder (OSD) is a vexed eye problem and a diagnostic conundrum. Diagnosis has traditionally depended upon symptoms and tests like Schirmer's, TBUT, staining with dyes, and tear meniscus height. Schirmer's test is the most popular. However, the test strips irritate with reflex tearing - producing false high results. Matrix Metalloproteinase 9 (MMP) in the tear is believed to be expressed by stressed epithelial cells of the corneal surface - a key pathology in dry eye disease. This study attempts to compare the results of Schirmer's test and MMP-9 so that the test can individually or severally add to a more definite diagnosis of dry eye disease.

Materials and methods: 100 eyes of 50 symptomatic patients underwent MMP-9 estimation and were divided into two groups (MMP-9+ve and MMP-9-ve). They were then sub-grouped as per DEWS-2007 based on Schirmer test levels and Ocular Symptomatology Score (OSS). The two groups were compared for severity of dry eye based on Schirmer's test and OSS.

Results: Mean Schirmer's value was 12.85 (SD 7.07) for MMP-9+ve and 19.18 (SD 8.94) for MMP-9-ve patients. 80% of patients with severe dry eye and 55.6% of moderate dry eye patients were positive for MMP-9. 85% of the MMP-9 patients had OSS values of 2 or 3.

Discussion: A higher OSDI and positive MMP-9 were shown to be correlated in a statistically remarkable way (p<0.001). The OSDI values of 0-12 for 3/44 (6.8%) positive results, 13-22 for 2/8 (25%) positive results, 23-32 for 4/14 (28.6%) positive results, and 33-100 for 13/35 (37.1%) positive results all showed an increase in MMP-9 positivity along with a rise in the subjective severity of the illness.

Conclusion: MMP-9 compares well with Schirmer's values and DED categories based on Schirmer's. The result pointed towards the usefulness of this test in diagnosing patients who may have not yet manifested symptoms.