Cool studies there, keep at it! That environment study looks complex 😳
So, as for what I was saying on eyes, I tried drawing out an example (ofcourse, I am no expert, this is all based on what I am currently learning on term 2)
So, just to explain what is shown, I based on a reference you have on post 155 as an example
I first drew an exaggerated example of a symbolic eye (almond shape, drawn in black and white with strong lines along the entire shape), in this example if you only look at the eye you wouldn’t get much info on the 3D form or lighting
Next I drew eyes as I learned them so far, starting out with a sphere, I add a small dot cross or line to see where the pupil is oriented towards then drew two “equators” to denote the minor and major axes of the ellipse for the iris within the cornea (transparent portion of the globe) - that’s why it is slightly elongated vertically and not a oerfect circle, as it is tilted around this sphere to the side and we are seeing it from the side. Next I add the ellipse for the pupil which is deeply recessed so seems to be a little sunken into the right
I wrap the sphere with the lids, they tightly follow the sphere and are partially hidden on the side near the nose, they have a thickness that will be more visible as the lid moves higher above our view or below it hence you see more or less of the thickness to denote that. They meet differently medial at the caruncle from the lateral portion where you can almost always see overlap of the upper eyelid going over the lower lid and depending on the tilt of the head the medial palpebral commisure or canthus is higher than the lateral canthus. I then add lines to denote the folding of the skin of the eyelids above and below and how they relate to the brow
When shading I start with the darks first, adding the darkest pupil, surrounded by a not so dark iris, I add the shade of the upper lid thickness and add light on the lower lid as the thickness is being hit by light. The globe itself is shaded as a partially occluded sphere and shadows are added to denote the cast shadows of the lids on the globe. Soft shading and a couple of slightly hard edges show the rest of the contours
Granted this is going for a realistic style and any of these things can be changed simplified or avoided depending on what the artist may be looking to create
Hope this helps you in some way cheers!