Retinoscopy is a technique to determine objectively the refractive error of the eye (farsighted, nearsighted, astigmatism) and the need for glasses. The test can be quick, easy, reliably accurate and requires minimal cooperation from the patient.
A hand held instrument called a retinoscope projects a beam of light into the eye [See figure 1]. When the light is moved vertically and horizontally across the eye, the examiner observes the movement of the red reflex from the retina. The examiner then introduces lenses in front of the eye until the movement is neutralized. The power of the lens required to neutralize the movement is the refractive error of the eye and indicates the lens strength needed to optimize vision with spectacles and/or contact lenses.
Retinoscopy is used to determine refractive error in children, developmentally delayed patients or in individuals whose behavior limits the ability to cooperate. It can even be used in very young infants.
Children's eyes are typically dilated for retinoscopy because the reflex is easier to see when the pupil is large and because the drops are needed to temporarily limit the eye's ability to accommodate or focus. This allows for a more accurate determination of the refractive error.
Autorefraction and subjective refraction are other techniques to determine refractive error. Autorefraction is a method of retinoscopy that is performed by a computer. This method can be precise, but requires the subject to be still and look at a target for several seconds to obtain an accurate measurement. Subjective refraction is a method that can be used to refine the results of retinoscopy or autorefraction. Subjective refraction requires participation in the process by telling the examiner which of a series of choices of lenses provides the clearest vision.
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