pinhole eye

A pinhole eye works on the same principle as a pinhole camera: a very small aperture allows only a narrow cone of light from each point in the environment to enter the deep pit and strike the photoreceptors. This geometry produces a focused image without any lens. The trade-off is that the small aperture admits very little light, limiting visual performance in dim conditions.

Pinhole eyes are found almost exclusively in nautiloids — the cephalopod molluscs (nautilus and its relatives). The nautilus eye has no lens and no cornea; the pupil is an adjustable aperture that opens in dim conditions. This remarkable eye is considered a living example of an intermediate evolutionary stage between simple pit eyes and lensed eyes.

Yes — the nautilus can regulate the size of its pinhole aperture, making it wider in darkness to admit more light (at the cost of image sharpness) and smaller in bright conditions to improve image resolution. This adjustable aperture is functionally analogous to the iris-controlled pupil of vertebrates, though achieved through a fundamentally different mechanism.