Stopping down is the main practical fix. Cat’s-eye bokeh is most noticeable when a fast lens is used wide open, especially toward the edges of the frame where the entrance pupil is partially clipped by the lens design. Using a slower lens, or simply not shooting at the maximum aperture, usually makes the blur circles rounder.

Lens choice matters too: lenses with a narrower field of view and designs that keep the full entrance pupil visible across the image tend to show less cat’s-eye bokeh. Better correction of astigmatism and field curvature can also help produce more uniform blur circles.

A lens hood is not a reliable cure. In some situations it may block very oblique off-axis light and reduce the effect for certain highlights, but it won’t generally solve cat’s-eye bokeh caused by the optical design of the lens.

So in practice: stop down, avoid the fastest apertures if round highlights are important, and choose a lens whose optical design is less prone to this behavior.