Since the late 80s retinal scanning has been featured in a whole bevy of sci-fi and action films. It's been the security system of choice for some of the silver screen's top spies: James Bond used it in GoldenEye and Ethan Hunt in the Mission Impossible movies. As a result, whilst retinal scanning may not be the most versatile of the currently available biometric technologies it is definitely one of the coolest.
Retinal scanning has been in use since the 70s when NASA, the FBI and the CIA all began using it, although retinal scanning systems have only been commercially available for a few years. For big-budget military organizations retinal scanning is a solution that makes sense, being around 200,000 times more accurate than fingerprint identification.
For the rest of us, however, using retinal scanning systems would probably create more problems than it would solve. Currently, retinal scanners cost more than the vast majority of people or businesses can afford and are attended by similarly expensive subscription fees. This is without mentioning the less glamorous side of retinal scanning: unless the aperture is cleaned after each use, then eye infections would likely spread between users. In real life, if James Bond used a retinal scanner then he'd be increasing his risk of contracting pinkeye.
The technology itself is also notoriously finicky. Why do you think opticians usually work in a semi-lit environment? Retinal scanners are apt to malfunction in places with bright or inconsistent lighting, which could in turn lead to you forking over more money for new lighting arrangements.
Other pitfalls include the risk that with so much invested in the scanner technology, it may cease to work for any one of its users as a result of any number of eye conditions. If any user was to develop cataracts or astigmatism there would be know way of altering the scanner to accommodate them.
More importantly, there are some signs that the relative cool-ness of retinal scanners has peaked and is now going the way of the mullet. A brief glance at this list (http://pagesperso-orange.fr/fingerchip/biometrics/movies.htm) shows that retinal scanners have been used less and less in Holywood films over the past ten years. It seems that just as retinal scanners are becoming more commercially available, retinal scanners are beginning to be overtaken by a competitor, the iris scan.
Unlike retinal scans, iris recognition can be performed at a distance of around 10cms and carries less risk of damage from infra-red light. Providing a similar level of security with fewer risks and problems, iris scans are slowly becoming the more practical alternative to retinal scans. It is already being considered for future use in passports around the world, and has already been deployed in the Netherlands.
If you're looking to make a large investment in high-end security, iris scans are probably a smarter move than retinal scans. With world-governments now choosing iris recognition over retinal scans, it's easy to see where the smart money is in high-end biometrics.