rize: The aqueous has direct access to the anterior uveal venous
system; the physiological thickening of the strands of the meshwork of
the iris angle supplies a mechanical obstruction between the anterior
chamber and the venous sinus of Schlemm; intra-ocular pressure stands at
the same level as the intra-venous, consequently, the hydrostatic
pressure is the same on both sides of the iris angle meshwork, because
the canal of Schlemm is a secondary venous system; lastly, the outflow
of aqueous into the venous sinus is by diffusion, not by filtration,
because the pressure is the same on both sides of the meshwork.

These facts and deductions have given rise to the present day
circulatory theory of intra-ocular pressure, so we now can approach the
predisposing and exciting factors which determine glaucoma.

The central fact to be borne in mind is, if the physiological pressure
is vascular in origin and nature, the pathological pressure must
likewise be derived from the same source.

Sclerosis of the meshwork of the iris angle is the predisposing factor
because it hinders free access of aqueous into the venous sinus of
Schlemm. Sclerosis alone, however, will not cause glaucoma so long as
access to the iris veins can keep the intra-ocular pressure at the
intra-venous level, and, too, as long as the exciting cause is absent.

The exciting cause is vascular, maintained and influenced by the general
circulatory pressure. A rise of the general vascular tension alone will
not cause glaucoma, because any alteration in intra-ocular pressure
resulting would be purely a temporary change, easily taken care of by
the extensive access of aqueous to the intra-ocular venous system. When
these two factors coexist in their varying combinations, pathological
increase of pressure results--in short, glaucoma.

Syphilis, rheumatism, gout, auto-intoxication and many other
constitutional disorders are well recognized agencies which induce
sclerosis in body tissues, so there can be little doubt that these
conditions produce pathological sclerosis of the meshwork of the iris
angle. Psychic disturbances, congested portal or renal system, hard
mental or muscular work, etc., etc., induce increased pressure of the
general circulation, and so simultaneously the intra-ocular pressure.

According to the edema theory advanced by Fischer, glaucoma is
"essentially an edema of the eyeball, and for its production we must
hold responsible the same circumst