The following is a guest post by Rob Levin. Rob is a Senior UI/UX Developer at Mavenlink, and coauthor of the Unicorn UI CSS Button Library. Their 2.0 release is using an SVG icon system, and here he shares some issues he's ran into along the way, and how you can watch out for them and fix them.
Many causes of eye pain also cause the eye to look red (see Eye Redness). Other symptoms may be present depending on the cause of eye pain. For example, people may have blurred vision (see Vision, Blurred), a bulging eye (see Eyes, Bulging), or pain worsened by bright light. The cornea (the clear layer in front of the iris and pupil) is highly sensitive to pain.
To test visual sensitivity a more careful experiment must be performed. The retina at the back of the human eye has two types of receptors, known as cones and rods. The cones are responsible for colour vision, but are much less sensitive to low light than the rods. In bright light the cones are active and the iris is stopped down. This is called photopic vision. When we enter a dark room, the eyes first adapt by opening up the iris to allow more light in.