Chip I think you hit upon something. As you said tears may give you a refraction but is it the right one? Tears also may change a refraction if you don't believe me put a drop of tears plus or systane. ( I know systane is used primarily for dry eye's ). When you look up you will be completely blurred until a few blinks or I even have had patients take up to 2 minutes before they said their vision is clear. With artificial tears your adding another medium for light to pass through and doing so can effect the response of the patient if enough time has not been allowed for the tears to pass.
just my take
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