Opera

Opera is a 1987 Dario Argento horror film. It's typical Argento. There has to be a better way to keep someone's eyes open.

plot teaser from Wikipedia:

The film centers around young, insecure opera singer Betty (Cristina Marsillach). After the lead in Verdi's Macbeth is injured in an car accident, Betty is reluctantly thrust into the role in the opera. During her first performance, a murder takes place in one of the opera boxes. Mysterious murders continue throughout the film...

You can watch it online at this link. Here's a trailer:

Moria says, "Opera astounds in its sheer ferocity and perversity." Slant Magazine gives it 4 stars and a positive review. Horror Review says, "Argento provides his audience with a barrage of engaging ideas which are brought to the screen with equally powerful visuals." Gore Girls Dungeon says, "Argento’s stylish and inventive visuals, great elaborate murder scenes and an absolutely amazing setting certainly make it an entertaining watch." DVD Talk says,

Opera contains some of the best thrill sequences in Argento's career. The camerawork is amazing, going from extreme close ups of crow eyes, knives, Betty's eyes, exacto blades, to the contrasting wide open spaces of the opera house, the fitting room, and Betty's apartment. The camera moves, across huge wonderfully designed sets, and in gliding point of views (from the killers, Betty's, to the flying crows over the opera audience)- just great cinematography and use of Dario's distinctive, wonderfully cruel, and beautifully brutal, imaginative eye.

Rotten Tomatoes has an 83% critics rating.