This is merely speculation on my part, but it’s also possible that the strength and integrity of the lens may be compromised after a certain time period has elapsed. All plastics have a time after which they become less stable. Infant carseats, for example, expire after five years or so because the plastic they’re made from gets brittle from exposure to the temperature extremes in a vehicle and from the aging process. After a certain amount of time, it cannot be guaranteed not to shatter under stress, like in an accident. It’s possible that contact lenses lose their flexibility and strength after expiration, and they might be more prone to tearing and ripping. Wearing a ripped lens or having one tear while it’s in can injure your eye, so that would be a good reason not to wear expired lenses if my theory is true.
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