I’ve seen some pretty detailed tutorials on eyes, they’re stunning but most are very high detail close up. That’s great if your eye is going to be printed on A3. Just zoom in on any of your favourite photos in Photoshop and you will see it’s made up of pixels, but if you zoom out, you cant see the pixels ;)
Keep that in mind as you often don’t need to go too overboard on details that you won’t see. Your mind can 'fill in the blanks' as it were. It’s great you can zoom up in Photoshop, but you don’t need to be photo-realistic at 900% zoom :p Thses eyes look pretty average zoomed up, you can see rough edges, etc. But zoom out to 100% and it looks fine.