At the London Science Museum some years back, I saw a device which projected a laser speckle pattern and had a sign explaining that it would appear stationary for people whose eyes were correctly focused, move in one direction for people who were near-sighted, and move in the opposite direction for people who were far-sighted. Looking at it with my glasses on and off suggested that the sign was accurate.
Merely saying that someone is nearsighted or farsighted doesn't seem like a very useful diagnostic tool in and of itself (since most near-sighted or far-sighted people could pretty easily tell whether near or distant objects appear clearer without need for any apparatus). On the other hand, it would seem like a device which could project a speckle pattern whose motion would depend upon how it was focused could provide more detailed visual diagnosis than conventional optometrist tools. Normal eye exams involve having the optometrist change lenses between the eye and what it's observing, and ask which changes make things better or worse. Since what's better or worse may depend upon how the eye refocuses, such questions can be hard to answer. If instead the patient stared at a test pattern through a consistent set of optics, and a speckle pattern was superimposed after going through adjustable optics, I would think the patient could judge the motion of the speckle pattern without having to focus on it, thus avoiding subjective issues caused by refocusing.
I don't know how old the concepts employed by that apparatus were when I saw it in the 1990s, but I've not seen anything similar since. Could the concept be used in diagnosing either human vision or artificial lens systems?
