Low Visual Pathway Alterations and Neurological Toxic Effects after Acute Mercury Poisoning in Zinc Manufacturer Workers

Abstract

Purpose : To describe the alterations in both the morphology and the function of the low visual pathway of a series of patients with acute intoxication due to inorganic mercury.

Methods : Observational case series consisting of 29 out of 50 patients who had been exposed to acute mercury poisoning at a multinational zinc manufacturing company located in Spain. Fifteen of them underwent late chelation for heavy metal intoxication. Complete ophthalmic examination including optical coherence tomography (OCT), visual field testing and functional tests such as ERG, pERG, mERG and VEP (Metrovision, following ISCEV standard) were used to confirm the retinal and visual pathway alterations. In addition, systemic symptoms and neurological examination including electromyography (EMG) and audiometry tests were recorded. Blood and urine samples were collected to assess initial mercury levels. Values were compared among different groups: non-chelated, late chelated, and healthy groups.

Results : There were significant high blood and urine levels of mercury in the chelated group (503.13 ± 291.92 ng Hg/ml and 492.93 ± 489.56μg Hg /L, respectively). 89.6% of patients exhibited erethism mercurialis symptoms insomnia and anxiety disorders. The chelated group exhibited more psychiatric involvement (p=0.025). EMG and audiometry tests showed similar decreased nerve conduction velocity and hearing loss of 25 to 40 dB in the intoxicated groups. Loss of contrast sensitivity in all frequencies, color vision alterations, a significant increase of latency and decrease of the extent of the b wave in ERG, and p50 of PERG were seen in all intoxicated groups. VEP latency was found over 100 m/s, and visual field alterations were registered in 62.1%in both eyes such as concentric constriction or widespread reduction of sensitivity in all intoxicated cases. No differences were seen among all groups in OCT tests. mERG test showed a significant decrease of N1-P1 wave at rings 10°-15° and >15°in all intoxicated cases. The most common patterns were peripheral loss and generalized loss (Figure 1 and 2).

Conclusions : Late chelation for mercury intoxication may not result in satisfactory relief of the symptoms. Although neurological and visual pathway involvement is clearly demonstrated, the electrophysiology tests (ERG, pERG, mERG and VEP) additionally established a clear retinal involvement.

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