Iris scans analyze the features that exist in the coloured tissue surrounding the pupil which has more than 200 points that can be used for comparison, including rings, furrows and freckles. The scans use a regular video camera style and can be performed from further away than a retinal scan.
The user may be able to do this from up to 2 feet away or may need to be as close as a couple of inches depending on the device. Verification time is generally less than 5 seconds, although the user will only need to look into the device for a couple moments. To prevent a fake eye from being used to fool the system, these devices may vary the light shone into the eye and watch for pupil dilation.
The uniqueness of eyes, even between the left and right eye of the same person, makes iris scanning very powerful for identification purposes. The likelihood of a false positive is extremely low and its relative speed and ease of use make it a great potential biometrics. The only drawbacks are the potential difficulty in getting someone to hold their head in the right spot for the scan if they are not doing the scan willingly. It also requires more memory for the data to be stored, but with the advances in technology, this is unlikely to cause any major difficulty.