Following this method, you'll get a pretty detailed and flexible file. So after you've put the work into your rendering, you'll be able to quickly fiddle around with color, size, light direction and shape. So go nuts adding eyeballs into all kinds of images and give all those trick-or-treaters the creeps. On the last step, I'm adding notes to the before and after images so that you'll know what I did to get the particular eyeball effects.
I know that not everyone has photoshop, so I'm attaching images of the rendered white of the eye and the iris. These elements take care of the fancier Photoshop filters, so if you use these images as elements, you should be able to make your own eyeball effects using any editing software that allows layers.
For rendering the veins I downloaded a set of brushes which are both free and awesome. You can get them here: http://www.adoberesource.com/veins-brushes-11-free-for-photoshop/.
Step 1: Set Up File
Create a new file, 600px by 600 px. Fill the background layer with black. Create a new layer and name it “white”. Use the elliptical marquee tool to select a circle that takes up most of the image. Use the paint bucket to fill that circle with white.
Step 2: Render Sphere
Select a very dark reddish gray color and a 200 px airbrush, and set the opacity to 30. Use the airbrush to sweep around the edge of the circle, rendering it. For this tutorial, I’m going to say that the light is coming from the upper left, but you can really make it coming from any direction you want, so long as you are consistent. Keep airbrushing (and erasing) until you are satisfied that your rendering is smooth and the edges are almost completely saturated, except for in the side where the light is coming from.
Go to the filter menu and select artistic, plastic wrap. Change the settings to highlight strength:11 , detail:5, smoothness:6. Go to image:adjustments:hue/saturation, and fiddle with the levels until you have a color that you are satisfied with for the white of your eye. (I desaturated and pushed toward yellow a little).
Step 3: Render Iris & Pupil
Select the 59 px. spatter brush and bump up the brush size to 300. Chose black for your brush color and set the opacity to around 30%. Click the brush over the surface of your cloud rendering until it is evenly speckled, and slightly darker at the edges. Select: filter:distort:pinch and set the strength to 100. Repeat the pinch filter once. Use the elliptical marquee tool to select a large circle for your iris. Invert your selection and delete the rest of the color outside of the circle.
Select the burn tool with a 200 px. radius, and the exposure set to 100%. Burn around the edges of the iris until they are very dark. Select edit:transform (or just press control+t) and scale down your iris until it is the size that you want for your eyeball.
Create a new layer and name it “pupil”. Select a small circle in the center of the iris and fill it with black. When you are happy with the spacing and proportion of the iris and the pupil, link the two layers together.
Step 4: Render Veins
Select filter: distort: shear, and adjust the distortion so that the shear bends to the left (see image). Now you have veins distorted for one half of the eye. Set your eraser to airbrush, 130 px, opacity 100% and erase all of the veins that fall outside the eyeball. It looks best if you erase the veins as they cross over into the darker rendered part of the white. Change the opacity of the eraser to 30% and carefully fade the veins until you are satisfied with their appearance. Select the entire layer, copy it and paste it. Rotate the pasted copy so that you have veins covering the rest of the eyeball. Use your eraser to touch up any areas of overlap and to fade the veins until you are satisfied with their appearance. Merge the new layer down to the “veins” layer.
Step 5: Render Lighting
On the “reflected light” layer select a large circle (larger than the whole eye is fine). Invert your selection (shift+command+I). Hold the shift key down and select another smaller circle, above and to the left of the larger circle. The two circles should overlap to give you a crescent shape. Now invert your selection again, and you should have only a crescent shape selected. Using your white airbrush, paint the outside edge of the crescent white. Copy the selection. Now transform the selection so that the crescent shaped reflection sits just inside the border of the iris. Rotate the crescent so that it is on the opposite side of the direct light.
Paste another copy of the crescent. Scale and rotate so that this reflection sits just inside the very outside of the eyeball, again on the side that is in the shadows. Rotate and size the reflection until you are satisfied with the appearance. Merge the layer down, so that both reflections are on the layer “ reflected light”. Set the layer opacity to around 70%.
Step 6: Finishing Touches
Now it’s time to go back and touch up the white of the eye. I burned around the edges and highlighted some of the middle. I also smudged a few little tweaks that were left over from the plastic wrap effect.
Since you’ve created everything on separate layers, you’re now free to play around with color, iris and pupil size and shape—just about anything.
Step 7: Editing Eyeballs Into to Other Pictures.
For inserting the eyeballs into other drawings, you can rotate and adjust the "white" layer and the "highlights" and "reflected light" layers so that they match the direction of light in the image you want to place them in. You can also distort the connected iris and pupil layers to make the eye look in another direction. Then you can experiment with inserting the eyeball as an overlay (that's what I did with the fried egg) or just as a separate layer with varying opacity. See the notes on the images for the specifics. Hope you have fun, and happy Halloween!