Toxic optic neuropathy from heavy metal exposure: A comprehensive review and case reports

Abstract

Purpose

This article explores heavy metal toxicity as a significant cause of optic neuropathy, and aims to raise awareness among ophthalmologists evaluating patients affected, to a cause that is often not on their radar. We conducted a comprehensive literature review to highlight the clinical presentations and diagnostic strategies.

Methods

We searched for cases of toxic optic neuropathy (TON) secondary to heavy metal exposure in patients seen at the Neuro-Ophthalmology Clinic at Cleveland Clinic Abu Dhabi and identified relevant cases for review. We conducted a literature review of the English-language literature using PubMed to identify published cases of heavy metal-induced optic neuropathy, focusing on keywords including toxic optic neuropathy, heavy metal poisoning, lead, arsenic, mercury, thallium, cadmium, and chromium. Articles were selected based on relevance to clinical presentations and diagnostic findings.

Results

We identified four cases of heavy metal-induced optic neuropathy in patients aged 34 to 76. All experienced gradual, painless vision loss over months to years, accompanied by impaired color vision and visual field defects such as cecocentral scotoma and peripheral constriction. Key findings included pale optic discs and thinning of the retinal nerve fiber layer and ganglion cell layer on optical coherence tomography. Despite normal brain imaging and extensive testing to rule out infectious, autoimmune, and nutritional causes, elevated heavy metal levels were identified in all cases. Arsenic toxicity from contaminated water was the cause in three cases, while mercury exposure from workplace inhalation accounted for the fourth. Similar findings have been reported in the literature, where cases ranged from 22 to 75 years of age, affected both sexes, and shared comparable presentations, including optic disc pallor, retinal thinning, and associated neurological symptoms like peripheral neuropathy.

Conclusions

Heavy metal toxicity as a cause of optic neuropathy is an uncommon yet critical condition that can often be overlooked in clinical practice. Differentiating optic neuropathy due to heavy metal toxicity from other similar conditions can be challenging, three of the four patients were initially diagnosed with glaucoma and were later referred due to a lack of evidence supporting this diagnosis. Clinical suspicion, thorough history taking, and comprehensive laboratory work-up are essential for accurate diagnosis.