The pointer of the phorometer should likewise be set on the neutral line of the red scale, causing the handle to point upward ([Fig. 16]). A distance point of light and a red streak laying in a horizontal position should now be seen by the patient.
Fig. 16—The phorometer handle placed vertically, denotes vertical muscles are undergoing test for right or left hyperphoria—as indicated by “R. H.” or “L. H.”
Instead of memorizing a vast number of rules essential where trial case prisms are employed for testing ocular muscles, the pointer of the phorometer indicates not only the degree on the red scale, but the presence of right hyperphoria (R. H.) or left hyperphoria (L. H.).
Fig. 17—The horizontal streak caused by Maddox rod bisecting muscle testing spot-light for vertical imbalance, as patient should see it.
Assuming that the patient finds that the streak cuts through the point of light, the refractionist instantly notes the absence of hyperphoria. Should the point of light and the red streak not bisect, prism power must be added by rotating the phorometer’s handle to a position that will cause the streak to cut through the light ([Fig. 17]). While testing for hyperphoria, the red scale should alone be employed, the white scale being totally ignored.
Fig. 18—The Maddox rods placed horizontally test esophoria or exophoria, causing a vertical streak to be seen by the patient.