What is a common concern regarding the use of retina scans for biometric authentication?

The concern regarding retina scans for biometric authentication centers on the fact that they can reveal information about medical conditions. The retina contains blood vessels and other structures that might display signs of various health issues, such as diabetes or hypertension. This means that when an individual's retina is scanned, it could potentially disclose sensitive health information that goes beyond just identifying a person. Thus, using retina scans can raise privacy and ethical concerns about how such health-related information is stored, used, and shared within biometric authentication systems.

On the other hand, while security is important in biometric systems, retina scans are generally considered secure because they are difficult to replicate or forge. The ability to identify different ethnicities is also not a primary concern regarding their use, as the technology is designed primarily for identification rather than social categorization. Lastly, while calibration is necessary for any biometric system, retina scans typically require only standard calibration processes that are manageable and do not present a significant barrier to their use in authentication. Hence, the focus on medical information makes the correct choice concerning the common concern with retina scans in biometric authentication.