Green’s Dictionary of Slang

1. (N.Z. prison) a 100mg morphine sulphate tablet; a Mogadon capsule.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 131/2: opal n. 1 a 100mg morphine sulphate tablet 2 a Mogadon capsule.

2. (Polari, also ocal) an eye.

2019		P. Baker Fabulosa 296/1: opals, ocals eyes.
2023		R. Milward Man-Eating Typewriter 17: ‘Lay down your claw-crackers and lift your opals from your Thermidorean lobsters’.