Nothing better than direct eye to lens contact!  When that happens, fire away!

Here I am on a tripod, and I will usually take multiple shots, manually tweaking the focus on the eyeball between bursts of the shutter.

In other words, I autofocus on the eye (click, click, click), then manually tweak the focus (click, click, click), and manually tweak again  (click, click, click).  Out of 9 (or more) shots, That usually assures that at least one will be tack sharp on the eyeball.

Great Horned Owl.  Block Creek Natural Area, Texas Hill Country.  I just set up a workshop at Block Creek for April 24-27.

Great Horned Owl

Canon 1d Mark IV.  500 mm lens + 2x teleconverter.  Aperture Priority.  f.22 @ 1/250 sec. +2/3 EV.