Converting text into shapes allows you to distort the text as you like while retaining straight, clean edges.

Use a clipping group to place an image inside of a background of text, with another layer of text placed in front to create depth.

This Photoshop CS3 video tutorial demonstrates a method to achieve a realistic change in eye color. The tutorial covers topics such as selection, feathering, selective color adjustment, brightness and contrast, and hue and saturation.