An unforgettable Peter Ustinov in the part of Nero in the film “Quo vadis”? It seems that Nero was suffering from a strong myopia
The glasses, the most commonly used tool to correct vision defects, they are a medieval invention, therefore in Ancient Rome, who was affected by visual disturbances of any kind, in practice had to resign themselves to living with it (https://www.pilloledistoria.it/2048/storia-moderna/come-curavano-miopia-gli-antichi).
It seems that Nero, strongly myopic, but he had found a stratagem with which he could see better from afar:looking through an emerald.
The Emperor always carried the precious stone with him when he had to attend a fight between gladiators, his great and well-known passion.