I've had a lot of requests for a tutorial/steps for how I paint. This picture wasn't done with a reference, so a referenced eye would be even more photorealistic. You may also look at other eyes on my portraits to see different color variations.For more WIPs and resources : art blog feavre.tumblr.com
Full paint tutorial: fav.me/d6bux63
I used photoshop CS5, and this tutorial is for digital artists, and assumes you have a basic knowledge of these programs.
Step 1: Sketch the eye. I've drawn enough eyes to be very familiar with the shape and proportions. If you aren't, find a reference and work with that.
Step 2: Color blocking, begin to define the brow bone. I'm doing a blue eye, and colors vary widely depending on what color iris--a green eye for example will also have brown and gold. Play around, generally you can use this tutorial for any color.
Step 3: Shading. The top of the iris will always be the darkest because of shadow from the eyelid. This is also applied to the whites of the eyes. Also color the tear duct.
Step 4: I keep darkening the iris and below the lash line. The limbal ring is usually a desaturated, dark color. Darkening it (that's the ring around the iris) makes the eyes more dramatic. And I also define the crease, the skin under the eye, and the waterline.
Step 5: For the most dramatic eyes, with lots of depth, make the pupil and area above it black, as well as the lash line. The whites of the eyes are also high in contrast from the shadow. This makes them look rounder and "glowy."
Step 6: I usually do entire portraits on one layer (best for blending) but I recommend putting the reflection on a new layer. For photorealism, more layers can help. Below I have another box with alternative reflection. They can be any shape, depending on light source. They are nearest to the light, and the lightest part of the iris is opposite that. See the light blue on the right with the reflection on the left.
Step 7: Adding some details in tear duct and waterline. White makes it look wet/shiny. Also use a natural brush to make the base for the eyebrows. Keep in mind that the edge of the iris should be blurry--it's not a hard line. This will contrast with the hard edged reflection. There is also some brown near the edges of the iris. No iris is completely one color. There will be flecks of color blended in. I also added individual hairs on the eyebrow. Using a speckled brush with spacing, dabble in some skin texture. I put this on another layer set to overlay.
Step 8: Put your pen pressure on opacity and size jitter. Then brush in some eyelashes. They will curve outward from the eye, and curve from under and out from the eyelid. I put this on a new layer, set to multiply. Do the same on the bottom, though these will be much smaller. Lashes can be brown or black, dramatic or short. You may stop at this step, but I chose to add makeup.
Step 9: You may make another layer if you wish. A speckled brush comes in handy for shimmer. The color depends on what "eyeshadow" you want, but it will usually be a soft shade that is darker near the crease and eyelid. The brow bone should be defined with a lighter color, and the hollow near the inside of the eye is also darker. I also add lines on the lash line and bottom shading for a more dramatic effect.
Step 10: Tiny details. If you zoom you can see the tiny lines under the eye and specks that make the skin's texture. I also darken the eyebrows to match makeup.
I hope this is helpful to you! If you use it, let me know or link to it in the description.