<unk>  is a technique to obtain an objective measurement of the refractive condition of a patient's eyes. The examiner uses a<unk>  to shine light into the patient's eye and observes the reflection (reflex) off the patient's retina. While moving the streak or spot of light across the pupil the examiner observes the relative movement of the reflex then uses a phoropter or manually places lenses over the eye to "neutralize" the reflex.<unk>  is especially useful in prescribing corrective lenses for patients who are unable to undergo a subjective refraction that requires a judgement and response from the patient (such as mentally handicapped or non-verbal people). It is also used to evaluate accommodative ability of the eye and detect latent hyperopia.<unk>  works on a principle called Foucault's principle. Basically it indicates that the examiner should simulate the infinity to obtain the correct refractive power. Hence a power corresponding to the working distance is subtracted from the gross<unk>  value.
Static<unk>  is performed when the patient has relaxed accommodative status viewing a distance target; dynamic<unk>  is performed when the patient has active accommodation from viewing a near target.
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