# Through the Eye: Retinal Changes of Prenatal Mercury Exposure in Grassy Narrows First Nation, Canada

## TL;DR

This study shows that prenatal mercury exposure in an Indigenous community is linked to long-term retinal thinning, detectable with OCT scans.

## Contribution

The study provides new evidence of enduring retinal effects from prenatal mercury exposure using OCT in an Indigenous population.

## Key findings

- Higher cord blood mercury levels were significantly associated with reduced thickness of GC-IPL retinal layers.
- Individuals with cord blood Hg ≥ 5.8 µg/L were more likely to have bilateral abnormal retinal thinning.
- OCT technology was shown to be effective in detecting mercury-related retinal changes.

## Abstract

Since the 1960s, Grassy Narrows First Nation, Canada, has been exposed to methylmercury (MeHg) from fish consumption following Hg discharge from a chloralkali plant. Prenatal exposure to MeHg is known to affect the neurodevelopment of fetuses and the retina is sensitive to neurodevelopmental damage. The multidisciplinary, cross-sectional Niibin study, developed with Grassy Narrows First Nations, included visual examinations with retinal evaluation using optical coherence tomography (OCT). The present analyses focused on the 59 participants (116 eyes) with umbilical cord Hg measurements, sampled between 1971 and 1992. Associations between cord blood Hg and retinal thickness layers surrounding the optic nerve head (RNFL) and inner macula (GC-IPL) were examined using mixed-effect models. Higher cord blood Hg was significantly associated with reduced thickness of GC-IPL layers across all macular sectors; less pronounced associations were observed for RNFL. A qualitative clinical assessment of the OCT results showed that persons with cord blood Hg concentrations ≥ 5.8 µg/L were more likely to present bilateral abnormal retinal thinning (OR = 3.51; [95% CI: 1.06–11.53]). These findings suggest that, in this Indigenous community, prenatal MeHg exposure may have enduring effects on retinal thickness and underline the importance of OCT technology in providing tailored eye care.