Ocular Surface Pathology in Patients Suffering from Acute Intoxication with Occupational Mercury

Abstract

Purpose : To report ocular surface pathology in a cohort of patients accidentally exposed to inorganic mercury.

Methods : Workers suffering from acute intoxication with mercury vapor in 2012 were referred for evaluation 3 years later. Tests were performed in the following sequence: 1) dry eye (DE)-related symptoms (ocular surface disease index, OSDI questionnaire; 2) tear osmolarity (nanosmometer); 3) tear collection for analysis of 23 molecules (inmunobead-based assay); 4) tear break-up time (T-BUT); 5) corneal fluorescein and conjunctival lissamine green stainings; 6) tear production with Schirmer test and tear lysozyme levels; 7) corneal sensitivity (mechanical, hot/cold temperatures) (non-contact esthesiometer); and 8) corneal nerve analysis (density, length, tortuosity, reflectivity, and ramifications) by in vivo confocal microscopy (HRT-III). Mean±SD and median-interquartile range described quantitative and ordinal variables. Student’s t-test or non-parametric tests analyzed differences between means. Cytokine levels were analyzed as base-2 log-transformed variables. Values were compared with matched controls.

Results : Twenty two male patients, mean age 42.0±7.6 (range 28-56), were evaluated. OSDI increased (mean 44.5±22.0, range 12-84; abnormal>12) in 21 patients. Tear osmolarity increased (336.2±28.7 mOsm/L) (abnormal>308mOsm/L) in 82.5% of patients. Mean TBUT (9.5±4.4 seconds) decreased in 47.8% of cases. Corneal and conjunctival stainings were present in 26.1% and 21.7% of cases, respectively. Mean Schirmer values (10.8±7.1 mm) decreased (<5 mm) in 13.6% of patients and tear lysozyme level increased (≥1000 µg/ml) in 63.6% of cases. Mean mechanical and hot temperature corneal sensitivity thresholds were significantly higher (147.8±53.4 and 2.3±1.1, respectively). Some parameters evaluating sub-basal corneal nerve parameters were significantly lower: density (6.4±2.9 n/mm²), length (15.9±4.5mm/mm²) and ramifications (2±2.5 n/mm²). Tear levels of EGF, IL-12p70, IL1-RA, RANTES, and VEGF were increased whereas IL-6 and IP-10/CXCL10 were decreased.

Conclusions : Mercury poisoning produced ocular surface pathology, not described previously, by mainly targeting the V cranial trigeminal nerve, as shown by the alterations in corneal sensitivity and sub-basal nerve morphology. This damage would be responsible for the neurogenic DE-related changes observed.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.