This is your problem. You aren't drawing an eye in the first place; you are drawing three concentric circles with relatively random shading and hoping it'll look like an eye.

A comic style is not about simplifying everything, it's about selective simplification. If a small part of a larger image, this eye would look fine. But since it is the sole focus of the picture, it needs more detail than it would otheerwise. Even if you're not drawing a photorealistic eye, you have to understand how an eye is built and what it looks like.

This picture shows a very extreme closeup quite well. The iris isn't just a circle with lines on it; it contains muscle tissue that dialiate the pupil, and is covered by a transparent, moist lense. The reflections in the lense tend to be VERY sharp, and not only reflect a specular highlight but fully mirror the lighting in their surroundings. With a closeup of an eye, you should at least have a vague idea of what the person is looking at.

And don't forget to shade the white part of the eye! Unless this eye is out on an inspection table and under a bright light, there is SOMETHING casting a shadow over it or tinting it. It could use some veins too.

This is another pretty good picture; this guy has prettier eyes than the last one. The photo was taken in a dark room with a desklamp as the only light source. Note how the pigment from his iris fades into the whites, and the sort of marble-like quality to the eye.

Now, I'm not saying you need to toss comicness and do something photorealistic, but you are simplifying all the wrong things. Tint everything, especially the eyewhites, based on the surroundings. Have the iris pigment bleed into its surroundings a bit. Sharpen the reflections and try to give the iris a more marble-y, fiber-y look.