Validation of the PowerRefractor for Measuring Human Infant Refraction

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Eccentric photorefraction provides an opportunity to gather rapid and remote estimates of refraction and gaze position from infants. The technique has the potential for extensive use in vision screenings and studies of visual development. The goal of this study was to assess the refraction calibration of the PowerRefractor (Multichannel Systems) for use with uncyclopleged infants.


The defocus measurements from the instrument were compared with the results of simultaneous retinoscopy in one analysis and with known amounts of defocus induced with trial lenses in another. Data were collected from infants 1 to 6 months of age and adults.


The PowerRefractor typically read <1 D of myopia when the retinoscopy reflex was judged to be neutral at the same working distance in both infants and adults. The slopes of both infant and adult validation functions (trial lens power vs. measurement of induced defocus) were close to 1 over a 4D range. The infant slopes were significantly greater than those of the adults, however.


The results suggest that the instrument is capable of detecting large amounts of defocus but needs individual calibration for detailed studies of accommodative accuracy and absolute levels of defocus, as has been recommended previously for adult subjects.

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