Many types of glaucoma exist. Some have stronger hereditary links than others, meaning blood relatives of glaucoma patients should pay special attention to their family history and their own eye health. The types of glaucoma include:

• Open-angle glaucoma. Damage to the optic nerve (which connects the retina to the brain) caused by increased eye pressure due to poor drainage of aqueous humor (fluid inside the eye). The process is gradual and painless. Vision loss may be significant and irreversible by the time a problem is detected. This is the most common form of glaucoma. The risk of open-angle glaucoma increases with age, and heredity may be a factor. Varieties of open-angle glaucoma include:
  
  
• Normal-tension glaucoma (also called low-tension glaucoma). Optic nerve damage accompanied by normal or low eye pressure and eventual loss of vision. Often seen in patients with thin corneas. This form of glaucoma accounts for one-third of glaucoma cases in the United States, according to the Glaucoma Research Foundation.

This condition is not fully understood.  Experts believe that hypersensitivity in the optic nerve fibers or reduced blood flow to the optic nerve due to a variety of diseases leads to death of optic nerve cells. Below-normal pressure is required in such cases to prevent further nerve damage and loss of vision.

• Pigmentary glaucoma. Shedding of pigment from the iris (colored part of the eye) clogs drainage of the aqueous humor. This hereditary condition is found more often in myopic (nearsighted) people and men, according to the Glaucoma Foundation. The condition begins in the 20s and 30s, threatening eyesight at an early age.
  
  
• Angle-closure glaucoma (also called closed-angle or narrow-angle glaucoma). The aqueous humor is partially or totally blocked from draining by the iris. This uncommon condition sometimes involves an acute, painful attack that is a medical emergency requiring immediate treatment. If untreated, blindness can result within a day or two. Whereas most cases of glaucoma are painless and gradual, acute angle closure is typically excruciating and sudden. Often inherited, it is found more often among Asians and farsighted people, according to the Glaucoma Foundation.
  
  More common than acute angle-closure glaucoma is the chronic variation, in which the iris intermittently blocks the drainage, with fewer apparent symptoms. Both forms are treated surgically with a peripheral iridotomy treatment using a laser in the ophthalmologist’s office, office or, if necessary, surgically in an operating room.
  
  
• Congenital glaucoma. An inherited birth defect where the drainage angle of the eye is blocked by a membrane and slows the normal fluid drainage and increases eye pressure. Children with this birth defect will have cloudy eyes, large eyes (buphthalmos) or one eye bigger than the other. They may also have a lot of tearing and turn away from bright lights. In children under age 3, the eye pressure increases the size of the eyes. Surgery (goniotomy) performed promptly can sometimes spare vision.
  
  
• Secondary glaucoma. Acute or chronic glaucoma caused by trauma or related to another condition, such as diabetes or cataracts. In one kind of secondary glaucoma, neovascular glaucoma, new blood vessels proliferate from the iris and block the flow of water from the eyes.

Neovascular glaucoma is often associated with a type of diabetic retinopathy known as proliferative retinopathy (involving new blood vessels growing in and scarring the retina) and is strongly linked to diabetes. Neovascular glaucoma is painful, progresses rapidly and damages vision.