Calculation of Nott dynamic retinoscopy

Abstract

The accommodation that the eye uses to focus at a certain distance does not correspond exactly with the value of the accommodative stimulus. Such accommodation matches the diopter value of what is called the accommodative response. The Nott method is used in the optometric examination to measure the accommodative response at 40 cm by dynamic retinoscopy. The test is performed with the eye compensated by its neutralizing lens (PNL), obtained from binocular subjective examination. In the literature one can find a measurement procedure in which an accommodative test is situated at a distance of 40 cm, starting from that distance, the optometrist without moving the test, shifts the retinoscope until he finds the point of neutralization. The value of the lead or lag of accommodation is usually obtained by subtracting at 2.50D the inverse of the distance to the point of neutralization (in meters). The value of 2.50D is considered accommodative stimulus at 40 cm. The normal value of the accommodative response, considered for the test at 40 cm, is +0'50 or +0.25 D with a standard deviation of ± 0'25D.