There's no point wearing the mask without eye protection because the easiest route to the respiratory system is via the eyes. Tear ducts drain directly into the sinuses.
If someone in the same carriage who is infected sneezes the droplets containing the corona virus will be sprayed far and wide and enter the eye. The eye's natural response is to produce tears which will then drain into the nasal cavity via the Nasolacrimal duct thereby transporting the virus to the respiratory system where it can start to do its damage.
Nasolacrimal duct
The nasolacrimal duct carries tears from the lacrimal sac of the eye into the nasal cavity. The duct begins in the eye socket between the maxillary and lacrimal bones, from where it passes downwards and backwards. The opening of the nasolacrimal duct into the inferior nasal meatus of the nasal cavity is partially covered by a mucosal fold. Excess tears flow through nasolacrimal duct which drains into the inferior nasal meatus.
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Proper protection requires a fitted N95 mask plus air tight goggles. Otherwise you might as well not bother. Wearing a surgical mask without eye protection isn't just an inconvenience it's pretty much useless.
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