Page 28 - Practical-Refraction-English

Subjective Refraction 4 2) Determining the cylinder power: 25a Proceed as detailed above, considering the starting point as the best vision sphere (in place) and the -0.50D corrective cylinder (in place) used to refine the cylinder axis. Have the patient continue to fixate on the cluster of dots Practical Refraction or a round optotype on the distance chart. The power © Essilor International of the corrective cylinder will be adjusted progressively in steps of -0.25 D as the patient is presented the diffe- rent views using the cross cylinder. 25b a. Position the cross cylinder such that its minus axis is along the axis of the (minus) corrective cylin- der. b. Twist the cross cylinder to present the two views and ask the patient which position they prefer. c. If the patient prefers the position with the © Essilor International minus axis of the cross cylinder in line with the minus axis of the corrective cylinder, add more minus (-0.25) D to the corrective cylinder; otherwise remove -0.25 D. Remember also to maintain the spherical equivalent - adjust 25c the sphere power by +0.25DS for every extra -0.50DC cylinder added, and by -0.25DS for every extra -0.50DC removed. d. Repeat steps a to c until the patient has no preference between the two views of the cross cylinder, almost no preference or their preference is reversed. © Essilor International e. Select the value of the weakest minus correc- tive cylinder giving maximum vision. 25d © Essilor International Figure 25 a, b, c, d: Determining the Cylinder Power 28 Copyright © 2008 ESSILOR ACADEMY EUROPE, 13 rue Moreau, 75012 Paris, France - All rights reserved – Do not copy or distribute.