[quitit]

With surgeries on the eye the patient selection criteria extends well beyond the measurable aspects of their vision.

Instead the criteria is highly dependent on the patient's expectations and second to that that their willingness to work with the vision they receive. Notwithstanding physical limitations it's this difference in attitude which results in real world, measurable, improvements in the patient's visual acuity.

Outside of the op space, a similar-ish issue exists with multifocal glasses (and contact lenses) - these technologies work, but how well they work is highly dependent on the patient's expectations.