Acommuter loses his eyesight without warning in the first scene of the apocalyptic allegory Blindness. The puzzled eye doctor (Mark Ruffalo) determines that there’s nothing physically wrong with him: “Someone just turned out the lights.” “No, someone turned all the lights on,” declares his patient (Yusuke Iseya), who describes his vision as more of a whiteout than a pervasive blackness.

The commuter turns out to be Patient Zero in an epidemic of “white sickness” that spreads throughout an urban population despite brutal official intervention. Blindness never identifies the city or its characters by name, and Fernando Meirelles, the Brazilian director of City of God and The Constant Gardener, filmed his international cast in Ontario, Brazil and Uruguay. Anyone can see Meirelles’ goal to place Blindness in a kind of universal city, and though the film offers a powerful portrayal of societal collapse, it also suffers from a plague of metaphorical implications.

At first Blindness plays up the vulnerability of sudden sightlessness and the terrors of being caught in the middle of a busy street, or forced to rely on untrustworthy strangers. Meirelles creates tension that suggests both an Alfred Hitchcock thriller and one of those recent Japanese horror films in which the trappings of modern life turn against ordinary citizens without warning.

When the blindness spreads, guys in scary hazmat suits round up the infected and quarantine them in what looks like an abandoned asylum. The initial inmates include a car thief (Don McKellar, who wrote the film), a call girl (Alice Braga), the eye doctor and his wife (Julianne Moore). The twist is that the doctor’s wife accompanied him into quarantine even though she can see, and may be immune to the disease.

The patients discover that the government doesn’t intend to examine or even care for them, but simply use the wards as an isolated dumping ground for more and more of the infected. Armed guards will use deadly force to keep them in. Things turn worse when a hospital ward controlled by Gael García Bernal’s bullying criminal stages a Lord of the Flies-style coup.

Blindness offers a devastating portrait of institutional failure and governmental betrayal. Audiences can read multiple interpretations into the situation, from the opportunism of corrupt governments to the neglect of the health-care system to the rape rooms of totalitarian regimes.

Meirelles overplays his hand when pushing the film’s symbolic themes. Characters speak explicitly about the morality of their actions, while a clichéd wise old black man (Danny Glover) delivers storybook-style nostrums about right and wrong. When the “civilized” characters ignore their tactical advantages and tolerate Bernal’s tyranny, the script contorts itself into a stinging critique of pacifist inaction.

But Moore’s superb central performance finds the humanity in the film’s angry, abstract themes. The actress’s usual emotional transparency can make her characters seem fragile, but here she shows a woman discovering reservoirs of strength and empathy. When we first see her, she seems like a frivolous housewife, but her increasing decisiveness, indignation and maternal tenderness redeem the pessimism that nearly overwhelms Blindness. You can’t take your eyes off her.

BLINDNESS (2½) Directed by Fernando Meirelles • Starring Julianne Moore and Mark Ruffalo. • R, 120 min. • At Century Cinemas Del Monte Center, Maya Cinemas.