Explainig the gradual evolution of the eye is one of the biggest debacle experienced by most 'evolutionists' and hence they had to come up with the concept of spontaneous evolution.
In regards to the prior reference, you may have missed certain sections:
This point of view is supported by the evolution of eye organelles
in protists. Chlamydomonas, for example, has an eye organelle with
a rhodopsin-related photosensitive pigment and a shielding pigment
spot which allows it to determine the direction of the incoming light.
Analogous to jellyfish, the eye organelle is located directly at the base
of the effector organ, the flagellum, and the information is transmitted
directly from the eye organelle to the flagellum without an intervening
information processing organelle. It is worth pointing out that some
dinoflagellates like Erythropsis, have evolved the most elaborate eye
organelles consisting of a lens, shielding pigment and retina-like
structures with membrane stacks, closeling resembling the eyes of
multicellular organisms (Fig. 11). (Gehring 2002:72)
For further detailed research on this topic you may find that the paper by Glardon, et. al. (1998) addresses some of your questions. Note pp. 2708, 2709.