MY DEAR DR. DEADY: Dr. Hubbell limits the discussion “to the
comparative value of the diplopia test, by Stevens’ phorometer” and
the Maddox rod test.
It would be interesting to follow out the idea with other
phorometers,—and with the Wilson phorometer my records do not show
quite such a marked difference in results,—but I have not taken
pains to get comparative results in any considerable number of
cases.
Dr. Hubbell says: “In the diplopia test, the dissociation is
effected by changing the visual axis of one eye by means of a prism.
The displacement of one image cannot be done without associating
with it, more or less, an impulse to some form of ocular effort....
In the obscuration test (Maddox rod) no such effort is invited, no
change of innervation takes place.” But in the rod test the light
seems nearer to the patient than in the prism test. This may account
for much of the difference in results and amount to “an extraneous
impulse to muscular contraction.”
Dr. Hubbell is entirely justified in his conclusion as made upon
experiments with the Maddox rod and the Stevens phorometer. I shall
watch cases along similar lines with the Wilson phorometer and
report later.
In the mean time the rod and the prism tests may well be taken in
each case and let judgment decide as to treatment.