Those example images use much more magnification than a standard macro setup usually provides. In one case, the photographer used stacked macro lenses on a zoom lens, and the image also appears to rely on very careful focusing or focus stacking.

To get this kind of iris detail, you generally need:

• more magnification than a normal macro lens alone
• very strong, even light on the eye
• precise focus, because depth of field becomes extremely thin
• a patient subject, since tiny movements ruin focus

A 100/105mm macro lens can get close, and extension tubes can push magnification further. Without extra optics or tubes, you’ll likely get a good close-up eye shot, but not as extreme as your first example.

Lighting matters as much as ISO. Use lots of light so you can keep shutter speed high and preserve detail. Don’t be afraid to use ISO 400 or 800 if needed; a sharp, well-lit image at moderate ISO is better than a low-ISO image that lacks detail or suffers from blur.

In short: for that level of detail, you’ll likely need added magnification, lots of light, and possibly focus stacking.