A 1938 ARTICLE ON PATHOGENESIS OF GLAUCOMA

 

A wonderfully elaborate article was published in 1938 by Elwyn regarding the pathogenesis of chronic simple glaucoma (primary open-angle glaucoma).

According to him, intraocular pressure (IOP) depends on the tension exerted on the sclera by the intraocular structures. These structures include the sclera, the iridocorneal angle, the ciliary body, the vitreous, and the choroid.

The theories regarding the causation of glaucoma can be classified as follows:

1. Retention theories, based on a hindrance to the elimination of the aqueous
2. Theory based on an increase in the production of aqueous
3. Theory based on an increase in the volume of one or more of the intraocular structures

RETENTION THEORIES:

Retention due to a change in the sclera:

According to this theory, the sclera loses its elasticity and shrinks, and that affects the normal outflow of the aqueous out of the eye. The loss of elasticity is either due to a senile change or to the sequence of inflammatory changes.

Retention of aqueous in the eye due to block at the iridocorneal angle:

1. This can happen due to pressure of the iris against the angle. It can occur from inflammatory changes in the anterior segment of the eye followed by adhesions between the iris and the cornea;
2. It can also occur from deposits of pigment in the pectinate ligament
3. Or due to primary sclerosis of the pectinate ligament

Retention can also occur due to blocking of the aqueous outflow in the iris as a result of a deposit of pigment or from degenerative changes.

THEORY BASED ON AN INCREASE IN THE PRODUCTION OF AQUEOUS:

An increase in the production of aqueous has been assumed to be due to disturbances in innervation and to inflammatory and degenerative causes.

THEORY BASED ON AN INCREASE IN THE VOLUME OF THE INTRA-OCULAR STRUCTURES:

Vitreous:

The vitreous, behaves as a colloid, and swells when it is turned acidic. It is presumed in glaucoma the vitreous changes towards the acidic side. That causes it to swell and increases IOP.

Some investigations have shown that normally the pH of the vitreous is around 7.5 to 7.6. A change in the reaction toward the acidic side causes a diminution in the volume of the vitreous until the isoelectric point, which is 4.2, is reached. The contrary has been assumed by others, that is, that the vitreous becomes more alkaline and swells.

Under normal conditions the vitreous in the living eye is at its maximum turgescence.

Choroid:

The choroid is a highly vascular membrane that can easily change its thickness by varying its blood content. Obstruction of the vortex veins occurs owing to kinking of the veins at the sinus or due to endophlebitic or sclerotic processes in the veins. Relaxation of the vasomotor mechanism causes a relaxation of the uveal vessels and an increase in the blood content of the eye.

Several local and general factors play a role in the etiology of glaucoma, including disturbances in the regulation of the intraocular vascular apparatus which cause changes in the circulation and the exchange of fluid between blood and tissues.

A close study of these theories brings the conviction that they are insufficient to explain the pathogenesis of glaucoma.

Some authors, like Thiel, hint at a disturbance in regulation, at a multiplicity of factors, and at a relation to the endocrine and sympathetic nervous systems in a vague sort of way. However, no definite theory which is based on a disturbance in regulation has so far been advanced.