148: Primary Open Angle Glaucoma

Key Points

• Disease summary:

  • Primary open angle glaucoma (POAG) is a genetically and clinically complex disease with multiple genetic risk factors and environmental exposure influencing disease susceptibility.

  • POAG is defined by progressive degeneration of the optic nerve. Elevation of intraocular pressure (IOP) is a risk factor for optic nerve degeneration, however, approximately 30% of POAG patients have optic nerve degeneration despite IOPs in the normal range (called normal-pressure glaucoma or NPG, also normal-tension glaucoma or NTG).

  • Ocular traits other than IOP also contribute to POAG risk including the thickness of the central cornea, the size of the optic nerve (optic nerve area), and the size of the optic nerve “cup” relative to the overall size of the nerve (optic nerve cup-to-disc-ratio, CDR).

• Differential diagnosis:

  • Exfoliation glaucoma, pigment dispersion glaucoma, developmental glaucoma, angle-closure glaucoma

• Monogenic forms:

  • Autosomal dominant juvenile-onset primary open-angle glaucoma caused by mutations in the MYOC gene.

• Family history:

  • Siblings and first-degree relatives have a 7 to 10 times increased risk of developing POAG overall.

• Twin studies:

  • Monozygotic twins have an increased risk of disease when compared to dizygotic twins.

• Environmental factors:

  • Postmenopausal hormone use and body mass index (BMI) have been suggested as environmental risk factors for POAG.

• Genome-wide associations:

  • Genome-wide association studies (GWAS) have identified five genes or loci for POAG: CDKN2BAS (POAG and NPG), CAV1/CAV2 (POAG), TMCO1 (POAG), SIX1/SIX6 (POAG), and 8q22 (NPG). GWAS for ocular quantitative traits relevant to POAG have also yielded results: CDKN2BAS (CDR), SIX1/SIX6 (CDR), ATOH7 (optic nerve area), and a number of genes or loci for central corneal thickness (CCT), a trait that is a risk factor for the disease. Disease-associated genetic variants (single-nucleotide polymorphisms [SNPs]) have provided insight into disease pathogenesis; testing for SNPs is not yet clinically validated to diagnose or guide management of POAG.

• Pharmacogenomics:

  • Testing for common variants has not yet been shown to influence management of POAG.

Diagnostic Criteria and Clinical Characteristics

Diagnostic Criteria for POAG

Diagnostic evaluation should include the following (Fig. 148-1 algorithm):

• Clinical examination of the ocular anterior segment (cornea, trabecular meshwork, iris, lens) using the slit lamp

• Evaluation of the optic nerve by fundoscopy and other imaging modalities (optic nerve photography, laser scanning imaging [HRT], ocular computed tomography [OCT])

• Visual field evaluation

• Measurement of IOP

• Measurement of CCT

And the absence of

• Narrow angles (angle-closure glaucoma)

• Exfoliation material (pseudoexfoliation syndrome)

• Increased pigment in the trabecular meshwork (pigment dispersion syndrome)

• Absence of transillumination defects in the iris (pigment dispersion syndrome)

• Developmental abnormalities of the anterior segment (developmental glaucoma)

A patient potentially at risk for glaucoma is identified through general eye care screening because of elevated IOP (>21 mm Hg), asymmetry of the optic nerve ...