Eyeball Tutorial for Photoshop

The iris

Create a new document 512 x 512 pixels.
Make a new layer and fill with white.

Make foreground ink black and background white.
Apply filter:
Filter>Render>Difference Clouds:
about 8 times.

Apply:
Image>Adjust>Brightness/Contrast:
Brightness: 60
Contrast: -15

Make a copy of this layer to work on.
Hide the first layer.

Apply filter:
Filter>Distort>Pinch:
100%
twice.

With the elliptical marquee tool make a circle selection 475 x 475 in the centre of the image (use shift when dragging selection to keep it circular).
Create a transparency mask so the centre of the iris pattern is showing.

Remember the other layer you hid?

Copy that into a new document.
Resize the document
Image>Image Size:
Width: 512
Height: 5120
Constrain Proportions: unchecked

You should now have a long stretched cloud.

With the Rectangular Marquee tool select an area 512 x 512.
Then:
Image>Crop

Copy back into original document. You no longer need the second document.

Apply the filter:
Filter>Distort>Polar Coordinates:
Rectangular to Polar.

Set layer adjustment to Overlay

Create a transparency mask as before.

Select>Reselect:
to get the circle selection back, make a new layer and fill the circle with black.
Contract the selection
Select>Modify>Contract:
Contact By: 20 pixels
Then
Select>Feather
Feather Radius: 15 pixels

Hit delete. A softened dark outer ring should remain.

Set layer adjustment to Multiply and Opacity to 75%

Select>Reselect:
to get the circle selection back, create new layer and fill with light blue:
R: 85
G: 173
B: 173

Set Layer Adjustment to Color.

Make a transparency mask As before.

The pupil

Now we have the basic structure for the iris.
Time to move on to the pupil.

Create a new layer.

Make a circle selection 185 x 185 centre screen, and fill with black.

Select>Deselect:

Filter>Blur>Gaussian Blur:
5 pixels

Set layer adjustment to Multiply.

Make a copy of this layer and
Edit>Transform>Scale:
and drag a corner out and resize to 150 %

Drag back to centre and
Image>Adjust>Hue>Saturation:
Colorize: Checked
Hue: 41
Saturation: 35
Lightness: 50

Set Layer Adjustment to Color.

Filter>Blur>Gaussian Blur:
40 pixels

Set layer Opacity to 75%.

To bring out some extra detail in the iris, select the entire canvas (Ctrl-A) and
Edit>Copy Merged:
Paste on top of all the other layers (Ctrl-V)

Set layer adjustment to Hard Light and
Filter>Other>High Pass:
2 pixels.

For a really detailed iris, start out with a much larger canvas and increase all measurements accordingly. This iris was produced on a canvas 2048x2048

The eyeball

You now have a blue iris and pupil.
All you need now is an eyeball to set it in.

Open a new document 1024 x 1024 pixels.

Create a new layer.Make a circle selection 950 x 950 centre screen, and fill with light grey:
R 239
G 235
B 239

Layer>Layer Style>Bevel and Emboss:
Style: Inner Bevel
Technique: Smooth
Depth: 100%
Direction: Up
Size: 250px
Soften: 16px
Angle: 135°
Altitude: 45°
Highlight:
Screen: #FFFFFF 100%
Shadow:
Multiply: #000000 35%

Create a new layer and fill with pink:
R 239
G 211
B 198

Make a circle selection 950 x 950 and move diagonally up and left until the top left curve is outside the canvas.

Delete the selection and
Filter>Blur>Gaussian Blur:
40 pixels

Make a circle selection 950 x 950 centre screen, and invert selection.

Delete the area outside the eyeball.

This should leave you with a soft pink crescent.

Set layer adjustment to Color.

Now all you have to do is combine the eyeball and the iris.

Group all the layers in the iris document and drag into the eyeball document.

Place in the middle and voilla!

If you start with a larger canvas and do some extra work you can achieve results like this:

Done!