(1) That the frequency of the association was the essence of the diagnosis,
(2) That there was absence of any other recognised cause, and
(3) In the former disease the effect of anti-syphilitic therapy?
Applying these rules to gout, we find—
(1) No marked frequency of association of ocular disease and gout,
(2) That when iritis does occur there is often some other possible source of origin, and
(3) That anti-gout treatment has only a doubtfully beneficial effect.
“Gouty” Iritis is not a Clinical Entity.—Before a symptom or affection can be classed as secondary to a primary disease there must be evidence of a connection stronger than post hoc, ergo propter hoc. For instance, in syphilis an iritis frequently follows which may be of the specific condylomatous type, and a laboratory examination of the inflamed iris may demonstrate the presence of the spirochæte. On the other hand, an iritis occurring in a gouty patient is indistinguishable from that form which results from infections of undifferentiated type. Moreover, iritis so seldom occurs associated with gout, and when it does there are so often present other well-recognised possible causes, such as pyorrhœa or gonorrhœa, that the doubt about the paternal relationship of gout to the iritis is overwhelmingly strong.
In the following table a comparison is made between types of iritis:—