Juxtacanalicular tissue in pigmentary and primary open angle glaucoma. The hydrodynamic role of pigment and other constituents
C. G. Murphy, M. Johnson and J. A. Alvarado
Department of Ophthalmology, University of California School of Medicine, San Francisco 94143.
We tested the hypothesis that obstruction of the juxtacanalicular tissues,
by melanin granules in pigmentary glaucoma and by other impermeable
material in primary open angle glaucoma, leads to the development of a
chronic glaucomatous condition. The distribution and concentration of
melanin and other impermeable materials in the juxtacanalicular tissues and
elsewhere in the trabecular meshwork was determined in 13 specimens. Six
specimens were from patients with pigmentary glaucoma, two from patients
with pigment dispersion syndrome, and three from patients with primary open
angle glaucoma, as well as two from normal subjects. The effect of these
materials on flow resistance was estimated using two hydrodynamic models.
In model A, the electron-lucent spaces of the juxtacanalicular tissue were
assumed to be open spaces, while in model B, these spaces and spaces filled
with ground substance were assumed to be gel filled. In pigmentary
glaucoma, 3.5% of the pigment was found in the juxtacanalicular tissue,
while 96.5% was found in the corneoscleral and uveoscleral tissues.
Permeabilities calculated according to model A were much higher than those
expected from estimates of outflow facility in all groups, in agreement
with the previous report of Ethier et al. The gel-filled spaces available
for fluid flow, as determined by model B, showed no statistically
demonstrable differences (pigmentary glaucoma, 32.9%; primary open angle
glaucoma, 36.6%; pigment dispersion syndrome, 43.4%; normal, 44.1%).
Furthermore, the amount of pigment present in the juxtacanalicular tissue
was determined to have a negligible influence on permeability. Thus, the
development of the chronic glaucomatous condition cannot be directly
attributed to pigment accumulation in the juxtacanalicular tissue in
pigmentary glaucoma.
