Forensic Clinical Evaluation of Visual Impairment after Methanol Poisoning:Two Cases Reports
Objective and accurate assessment of visual impairment has been one of the challenging tasks in forensic identification.In forensic practice,visual impairments are commonly seen as caused by physical factors,but rarely by chemical factors such as methanol poisoning.Methanol and its metabolites can directly damage eye tissues and cause vascular paralysis and dilatation,damaging the nervous system.Visual impairment can appear after a few hours to 2～3 days of poisoning,manifesting as diplopia,blurred vision,and eyeball swelling and pain,followed by rapid vision loss and even blindness.Ophthalmologic examination reveals dilated and fixed pupils and diminished or absent light reflexes.Funduscopic examination reveals dilated veins,optic nerve papilla congestion,and edema,followed by pallor or optic nerve atrophy.Optic nerve damage rarely returns to normal completely.The mechanism of visual function impairment in methanol poisoning is mainly its metabolite formic acid or format,which is excreted very slowly in vivo and has a selective affinity for the eye's neural tissues,inhibiting the oxidative phosphorylation process,affecting cellular respiration,and inhibiting ATP synthesis in mitochondria,leading to tissue toxicity and hypoxia and then degenerative changes of the cells,oligodendrocytes and astrocytes swelling myelin sheath loss,optic nerve edema and pressure on the optic nerve in the posterior sieve plate region,thus resulting in toxic optic neuropathy.Toxic optic neuropathy occurs when the optic nerve is compressed in the posterior region of the sieve plate,etc.Optic nerve atrophy often occurs after 1 to 2 months,and irreversible damage to the optic nerve and visual function can occur at a later stage.Two injury degree identification cases of visual impairment after methanol poisoning were reported.The methanol poisoning confirmation,the objective assessment of visual impairment,as well as the causal relationship between methanol poisoning and visual impairment,were discussed and comparatively analyzed,with a view to similar cases to provide a reference clue.
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