Speaking of astigmatism...

Something's been puzzling me lately involving astigmatism. As I understand it, astigmatism is the optical distortion that gets described as "seagulls" towards the periphery of the field and coma is radial smearing (like a certain "free" widefield ep )

I've been noticing the seagull effect more or less in all my scopes with all my ep's from f4.9 to f10. But more to the point - the distortion moves around the field with eye movement. Is this to be expected or is it possibly an artifact from a lens implant?
It's more noticeable at low powers/f-ratios. I never got to do much observing before cataracts made an appearance so I don't have any benchmark observations and don't really know how bad it is.
Thanks in advance for any thoughts.

Mark, As I understand it....

Astigmatism means star images are not perfectly
round, but have some linear elongation. This
will be especially noticable inside or outside
best focus. Also the direciton of the
elongation will change when going from
inside focus - best focus - outside focus.

Coma has literal derivation similar to "comet" and
means comet-shaped star images. Usually there is a
bright spot with rays or arcs on one side.
Eyepieces can show this at the field edges,
as can fast newtonians.

There is also lateral color, where stars are
spread into small little spectra -- red at one
side and blue on the other. This shows up
sometimes near the field edges of ultra-wide
eyepiece types.

But most eyepieces, especially cheaper wide
fields, will show some combination of all three.

One way to tell if the aberration is in your eye,
is to rotate your head relative to the eyepiece,
and see what happens. If its fixed relative
to your head, then its probably in the eye.

Most scopes and eyepieces have almost no
aberration at the field center, so if you see
something at the field center it might well
be some eye aberration.

Astigmatism is common from corneal defects with large exit pupils. The aberration is caused by a spoon-shaped lens surface rather than a spherical one, and it occurs at the edge of field of many eyepieces because this is the shape that the light cones encounter as they pass through the eyepiece at an angle. People don't expect this from everyday experience, but if you have your eyes dilated you can probably see, as I do, a substantial amount of aberration when a wide swath of the cornea plays a role in photopic image formation. It's possible that your implants are playing a role, but it could easily be just normal corneal imperfections. As you have observed, the smaller the exit pupil the better.
--
Mike