It's close, but theres much more to the eye than that if you want real accuracy. This, however, is a good basic start.
The cornea, yes, is convex. However, the Iris (the colored part of the eye) is not exactly concave. It's a sphincter muscle. It's purpose is to reduce the amount of light coming into the eye by 2 ways - absorbing it through the color, and opening and closing around the pupil.. It's more flat than anything, with some wrinkly tissue inside of it. This is a good macro photo of the iris: [link] The only part of it that is "concave" is immediately around the pupil, and even then, just micrometers. The lens inside the eye, however, is concave. But this really wouldn't affect drawing, as it isn't visible.
One thing far too many artists make a mistake of with the eyes is the pupil. People think because it takes in ALL light that there can be no reflection over it. That's very, very wrong. The cornea is a clear layer over the front of the eye, and the cornea can reflect light just like any other clear, sphereical object could. Perfect example: [link]
How do I know all of this? I'm an Optometric Technician I work for an Optometrist.
What is shown here is just a fragment of the whole tutorial. And of course I did not aim here to be super accurate, I believe all those details cloud the base image artist wants to get: that is concave, that is convex, this you shade that way, that you shade another, and so on. But whoa, thanks for the comment, I believe that it might be very helpful to those interested in extra details! So thank you very much! And second link is not working :c
i wish i could +1 or like this comment or something so i guess all i can do is thank you for your insight!! i guess the issue that we as (representational) artists have is that we're laymen when it comes to matters of biology, anatomy and even physics; we know the basics that allow us to observe but it's easy to mess up on more intricate or obscure details because of that lack of advanced knowledge so it's nice whenever people who can speak with a degree of authority can help clear things up!
Absolutely, I wish it happened more! And I'm not trying to say this tutorial isn't reliable, because it is for general shape and the way it sits with the eyelids, ect. Lots of people don't know the eye isn't a perfect sphere, so it's nice to see an artist explain that for others