Impact of the centre of rotation on the width of field

When wearers turn their eyes, they have an area of clear vision the width of which is defined by the progressive surface.

A long eye has a centre of rotation which is further from the lens than a short eye; therefore the optical axis sweeps a broader area for the same angle of rotation.

Impact of eye length on aberration density

When wearers move or turn their heads, so-called “swim-effects” can become apparent. These are directly linked to the density of aberrations in the peripheral zones of the lens.

The swim effects are stronger for an image projected onto a short eye (hyperope) and a flatter retina since the density of aberrations is more concentrated.

For an image projected onto a long eye ( myope ) and a curved retina the swim effects are less pronounced since the aberration density is less marked.