28
11625-101-Rev. L
Instructions for Use
(continued)
Jackson Cross Cylinder Tests
One of the unique features of the Phoroptor is that the Cross Cylinder Unit (loupe) lenses are geared to-
gether with the correcting cylinder test lenses so that when a change in axis is made in the latter, a cor-
responding change will automatically occur in the axis of the cross cylinder lenses. This feature relieves
the practitioner of the necessity of manually changing the cross cylinder axis each time the correcting
cylinder axis is changed.
Note:
Because most practitioners prefer to check cylinder axis before checking cylinder power, the pro-
cedure is written in this sequence. If you prefer to check power first, reverse the sequence and
perform a final power check after the axis check.
Procedure
1. With the tentative sphere and correcting cylinder (determined by retinoscopy and/or the astig-
matic chart) in place, the Cross Cylinder Unit is positioned before the aperture of the eye being
tested.
2. The patient fixates on the smallest line of legible letters.
Axis Check
1. The Cross Cylinder Unit is in the correct position for axis check when the axis of the Finger
Roll Knobs (handles) correspond to the axis of the correcting cylinder and the red and white
dots are 45° from the correcting cylinder axis. Refer to Figure JC-1.
2. Rotate the Turret Assembly to position the Cross Cylinder Unit in front of the main aperture
(Roll Knobs should correspond to the axis of the correcting cylinder).
3. If the cross cylinder is not in the correct position (i.e. axis 45° from the correcting cylinder
axis), the practitioner need only rotate the Cross Cylinder Unit 45° counterclockwise to de-
tent.
-continued-
Figure JC-1 Finger Roll Knob
Roll
Knobs
