terminology and guidelines for glaucoma ii - Kwaliteitskoepel

) Plateau-iris mechanism
The isolated plateau iris mechanism causes angle-closure by direct obliteration of the chamber angle recess, crowded
by the iris base when the pupil is dilated. This can occur only with one or more of the following:
(1) the tissue of the peripheral iris is thick (iris rolls)
(2) the iris base inserts anteriorly, leaving only a very narrow ciliary band, or inserts at the scleral spur
(3) the ciliary processes are displaced anteriorly in the posterior chamber and push the iris base into the chamber
angle.
(4) the iris profile is almost flat from the perifery to the far periphery, where it becomes very steep, creating an extremely
narrow angle recess.
The iris root position and the posterior chamber anatomy can be confirmed by ultrasound biomicroscopy.
It is clear from these descriptions why the isolated plateau iris mechanism is not altered by iridectomy.
The pure plateau iris syndrome, causing angle-closure despite a patent iridotomy, is extremely rare compared with
pupillary block. Both mechanisms, however, may coincide when “plateau iris configuration” is present. This latter
condition is relatively common. The pure form of plateau iris syndrome can only be proven by the occurrence of
acute angle-closure triggered by mydriasis despite a patent iridectomy and a centrally deep anterior chamber.
Due to the above mechanisms, in all combined pupillary block/plateau iris cases iridotomy or iridectomy should be
performed first. Plateau iris can be treated by argon laser iridoplasty and/or miotic therapy, preferably with topical
sympatholytics like dapiprazole or thymoxamine. Strong miotics are to be avoided, because they cause anterior rotation
of the ciliary body. Ideally, treatment should be instituted before synechial closure of the angle occurs (see Ch.
4.4.1).
c) Lens mechanism
Large and/or anteriorly placed cristalline lens can predispose per se to angle-closure and be a factor in worsening
pupillary block. It can also cause secondary angle-closure glaucoma (see Ch. 2.5.1 and 2.5.3.).
d) Creeping angle-closure mechanism
Some cases of chronic angle-closure glaucoma result from synechial closure of the chamber angle, caused by a previous
acute angle-closure ‘attack’, while creeping angle-closure is probably a primary event. The iris base ‘creeps’ on
to the trabecular meshwork forming irreversible peripheral anterior synechiae (PAS). The IOP usually rises when
more than half of the angle is obstructed. It is not yet clear whether creeping angle-closure is the consequence of
undiagnosed intermittent angle-closure or a consequence of chronic miotic therapy causing worsening relative pupillary
block. This form seems to be more frequent in Asians.
e) Posterior aqueous misdirection mechanism
In rare cases posterior aqueous misdirection can be the cause of primary angle-closure, mostly resulting in chronic IOP
elevation. In these cases, usually younger or middle aged women, the ciliary processes come into contact with the lens
equator, and/or a firm zonule/posterior capsule diaphragm, causing misdirection of aqueous into the vitreous 8,9 . As a
consequence, the lens/iris diaphragm is pushed forward and occludes the chamber angle. Eyes predisposed to posterior
aqueous misdirection often have narrow anterior chambers (peripheral and axial) and hypermetropia. After iridotomy
or iridectomy, the use of miotics raises the IOP, whereas the use of cycloplegics reduces the IOP. This ‘inverse’ or ‘paradoxical’
reaction to parasympathomimetics should be tested only after iridotomy has been performed. Ultrasound biomicroscopy
can demonstrate abnormal posterior chamber anatomy in these rare cases (see Ch. 2.5.3).
Systemic drugs and angle-closure:
Systemic drugs which may induce angle-closure in pre-disposed individuals are phenothiazines and their derivatives,
tricyclic and non-tricyclic antidepressants, monoamine oxidase inhibitors, antihistamines, anti-Parkinson drugs, some
minor tranquilizers, parasympatholytic and sympathomimetic agent (see Ch. 1.4).
Ch. 2 - 14 EGS