Definition, Classification, and Pathophysiology of Canine Glaucoma

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Key points

  • Glaucoma is a group of diseases with optic nerve degeneration and blindness as a final outcome.

  • In primary glaucoma the main risk factors are age, breed, gender, and goniodysgenesis.

  • Classification is based on clinical evaluation and assessment of the iridocorneal angle and ciliary cleft with gonioscopy and ultrasound biomicroscopy.

  • Cellular and extracellular progressive changes occur at the level of the lamina cribrosa and in the trabecular meshwork and are responsible for retinal ganglion cell

Definition

Glaucoma is a heterogeneous group of progressive disorders characterized by retinal ganglion cell (RGC) apoptosis and a specific optic neuropathy (glaucomatous optic neuropathy [GON]) associated with cupping of the optic disc. In human patients, peripheral visual field loss and tunnel vision are common initial clinical signs, which may eventually progress to irreversible blindness.1, 2 Primary glaucoma is considered a bilateral disease, although both eyes may not be affected simultaneously.

This

Classification of glaucomas

A clear, comprehensive classification of the canine glaucomas is impossible. Glaucoma is considered a multifactorial disease in which numerous genes with varying numbers of alleles and related protein products are involved. Epigenetics may also cause the same genes and proteins to undergo differential regulation and expression. Just as an example, if 100 genes are estimated to be involved in a process and each of them have 5 alleles, then

Pathogenesis and pathophysiology of primary glaucoma

A current view of the pathogenesis of glaucoma must account for multiple factors (Fig. 6). Numerous genetic/epigenetic, age-related, immunologic, and vascular factors interact to activate a series of cascades with optic nerve degeneration as a common final outcome.

Ocular damage in the course of glaucoma, primarily GON, follows from mechanisms that lead to outflow obstruction (and subsequent increased IOP) and RGC apoptosis. Although not mutually exclusive, the two factors are not necessarily

Theories and mechanisms

The main end point in all forms of glaucoma is GON, the characteristic features of which are interlinked: RGC death, activation of glial cells, tissue remodeling, and changes in blood flow (Fig. 8).83

The cascades that cause RGC apoptosis are extremely complex. The RGCs are the innermost neurons of the retina and their axons form the optic nerve. All the photic information collected by photoreceptors is eventually carried to the brain by the RGC axons, which travel in the nerve fiber layer of

Summary

Comprehension of the mechanisms that may cause glaucoma is difficult and extremely complex (see Figs. 7 and 8). Structural changes in the anterior and posterior segments occur normally with age and the modulation of subsequent tissue remodeling can be an important event in the pathogenesis of glaucoma in predisposed individuals. The quality of tissue remodeling may be influenced by anatomic, immunologic, and genetic factors. Mechanical and vascular changes are primary triggers for cellular

Acknowledgments

The author would like to acknowledge the terrific help from Dr Stephanie Pumphrey for the editing of the article.

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