In the Tajimi Study (Japan), the prevalence of POAG among subjects ≥40 years was 3.9%. The IOP was ≤ 21 mm Hg in 92% of those with POAG. The mean IOP in the nonglaucomatous eyes was 14.5 ± 2.5 mm Hg, about 2 mm Hg lower than observed in European-derived populations.

A meta- analysis estimated the global prevalence of POAG in 2013 to be 3.0% among persons 40–80 years of age. In this age group, the highest prevalence of POAG, an estimated 4.2%, is found in Africa. The same study estimated the prevalence of POAG in North Amer ica to be approximately 3.3%.

Population- based studies and prospective glaucoma clinical trials have identified a number of risk factors that are associated with POAG diagnosis and progression. The most widely accepted risk factors include higher IOP; lower ocular perfusion pressure; older age; lower central corneal thickness (thinner cornea); high myopia; and racial, ethnic, and ge ne tic susceptibility. Other pos si ble risk factors are discussed in Chapter 7.

The prevalence of primary angle- closure glaucoma (PACG) varies among racial and ethnic groups. A meta- analysis estimated the prevalence in Asia to be 1.1% among individuals aged 40–80 years; however, it is even higher in east Asia. Among people of Eu ro pean ancestry >40 years, the prevalence is estimated to between 0.1% and 0.4%. The estimated prevalence in African populations ranges from 0.1% to 0.6%. The highest- known prevalence, estimated to be between 2.5% and 4.8%, is found in Inuit populations >40 years in Alaska and Greenland.

Estimates of the prevalence of PACG vary among dif fer ent Asian populations. Among those ≥50 years in Guangzhou, China, the prevalence of PACG was 1.5%; and the proportion of these subjects with unilateral blindness was 43% compared with 17% for those with POAG in the same population- based survey. In the Tajimi Study, the prevalence of PACG was 0.6%.

Age, race, and ethnicity are risk factors for PACG. The prevalence of PACG may vary by sex, with a significantly higher prevalence observed in women in most studies. Hyperopia and a family history of angle closure are also impor tant risk factors. Other anatomic risk factors are discussed in Chapter 9.

American Acad emy of Ophthalmology Glaucoma Panel. Preferred Practice Pattern® Guidelines. Primary Angle Closure. American Acad emy of Ophthalmology; 2015. www . aao . org / ppp Cho HK, Kee C. Population- based glaucoma prevalence studies in Asians. Surv Ophthalmol. 2014;59(4):434–447.

In general, the early- onset forms of glaucoma are rare and often follow patterns of simple Mendelian inheritance with mutations that are highly penetrant. Previously, genes with such disease- causing mutations were identified by linkage analy sis in large, multigenerational families that show either autosomal dominant or autosomal recessive patterns of inheritance. Current approaches using whole-exome sequencing can successfully identify disease genes using smaller families without evidence of linkage. Ge ne tic regions associated with glaucoma are named according to the type of glaucoma— GLC1 for open- angle glaucoma, GLC2 for angle- closure glaucoma, and GLC3 for congenital glaucoma— followed by a letter to indicate the sequence of discovery: GLC1A, GLC1B, GLC1C, and so on. Table 1-2 lists the impor tant genes associated with glaucoma, for which genetic testing may be of clinical utility.

Juvenile open- angle glaucoma (JOAG) is defined by having an onset before 40 years of age, an open anterior chamber angle, and an absence of secondary features. The myocilin gene (MYOC, formerly known as trabecular meshwork– inducible glucocorticoid response, or TIGR, within the initial larger chromosomal region of GLC1A) was the first glaucoma gene discovered. Autosomal dominant disease- causing mutations in MYOC account for up to 36% of cases of JOAG and 4% of POAG. There is evidence that mutant myocilin accumulates in cells rather than being secreted, possibly resulting in toxicity to the trabecular meshwork.