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Editors Selection IGR 10-3

Clinical Forms of Glaucoma: Pseudoexfoliation and aqueous humor dynamics

Robert Ritch

Comment by Robert Ritch on:

21746 Aqueous humor dynamics in exfoliation syndrome, Johnson TV; Fan S; Camras CB et al., Archives of Ophthalmology, 2008; 126: 914-920


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Glaucoma associated with exfoliation syndrome (XFS) is typically a high-IOP disease characterized by increased resistance to aqueous outflow. Accumulation of exfoliation material (XFM) in the trabecular meshwork may derive from both passive deposition from the aqueous on the surface of the uveal meshwork and local production by trabecular cells and Schlemm's canal endothelial cells in the juxtacanalicular tissue and canal wall. The amount of XFM within the juxtacanalicular region correlates with the presence of glaucoma, the average thickness of the juxtacanalicular tissue and the mean cross-sectional area of Schlemm's canal, and also with the IOP level and the axon count in the optic nerve.1-3 Johnson et al. (946) examined the effect of XFS with or without elevated IOP on aqueous humor dynamics in patients with and without ocular hypertension (OHT) and with and without XFS. Uveoscleral outflow was significantly decreased in XFS patients compared with age-matched controls, independent of IOP.

Uveoscleral outflow was significantly decreased in patients with exfoliation syndrome compared with age-matched controls
Patients with OHT with or without XFS had decreased trabecular outflow facility compared with normotensive patients with or without XFS. The authors consider the possibility that dysregulation of various pathways (elevated homocysteine, upregulated TGF-β1, decreased matrix metalloproteinase activity) in XFS may impair the stability, organization, and integrity of the extracellular matrix, which, in the ciliary muscle, may be an important factor influencing the rate of uveoscleral outflow. Aging eyes are characterized by a decrease in uveoscleral outflow. Deposits of XFM are found throughout the anterior segment in patients with XFS. Thus, one would expect to find XFM in the uveoscleral pathway. However, this has been little studied. In the one publication devoted to this,4 XFM was present only in the innermost 20 microns of tissue bordering the iridocorneal angle, and none between the ciliary muscle cells, in the suprachoroidal space, or in the sclera. The authors concluded that XFM does not pass uveosclerally.

References

  1. Schlötzer-Schrehardt U, Naumann GOH. Trabecular meshwork in pseudoexfoliation syndrome with and without open-angle glaucoma. A morphometric, ultrastructural study. Invest Ophthalmol Vis Sci 1995;36:1750-1764.
  2. Gottanka J, Flügel-Koch C, Martus P, Johnson DH, Lütjen-Drecoll E. Correlation of pseudoexfoliation material and optic nerve damage in pseudoexfoliation syndrome. Invest Ophthalmol Vis Sci 1997;38:2435-2446.
  3. Gottanka J, Flügel-Koch C, Martus P, Johnson DH, Lütjen-Drecoll E. Correlation of severity of optic nerve damage with changes in the trabecular meshwork in different forms of glaucoma. Invest Ophthalmol Vis Sci 1997;38(Suppl):S160.
  4. Ringvold A, Davanger M. Notes on the distribution of pseudoexfoliation material with particular reference to the uveoscleral route of aqueous humor. Acta Ophthalmol 1977;55:807-813.

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