Glaucoma is a collection of eye conditions that cause progressive damage to the optic nerve, which transmits visual information from the retina to the brain. This damage often correlates with elevated pressure inside the eye, known as intraocular pressure (IOP), although not all cases involve high pressure. Glaucoma is one of the leading causes of irreversible vision loss globally. It is frequently referred to as the “silent thief of sight” because the vision loss typically occurs slowly over time without immediate pain or noticeable symptoms.
Understanding the Genetic Risk
A family history of glaucoma is a major risk factor, meaning the condition definitively runs in families. Individuals with a first-degree relative—a parent, sibling, or child—who has glaucoma face a significantly heightened risk of developing the condition themselves. Studies indicate this risk is approximately two to nine times higher than for the general population.
This increased susceptibility stems from a familial tendency, including inherited genetic factors and potentially shared environmental or lifestyle influences. The risk increases further with the number of affected relatives within the family. For example, the lifetime risk for first-degree relatives of a glaucoma patient can be around 22%.
While a family history significantly elevates the likelihood, it does not guarantee that an individual will develop glaucoma. The disease is complex; most adult-onset cases involve a combination of multiple genetic variants working alongside other risk factors like age, ethnicity, and pre-existing medical conditions. Genetic predisposition is a powerful indicator, but environmental factors and age still contribute to the overall risk profile.
Glaucoma Types and Inheritance Patterns
Glaucoma is a group of disorders, and the strength of the genetic link varies among its different forms. Primary Open-Angle Glaucoma (POAG) is the most common type and carries the strongest familial inheritance pattern. POAG involves a gradual failure of the eye’s drainage system, located in the angle between the iris and the cornea.
The inheritance of POAG is often complex, meaning it is polygenic—influenced by multiple genes, each contributing a small amount to the overall risk. Rarer, early-onset forms, such as Juvenile Open-Angle Glaucoma (JOAG), follow a simpler, monogenic inheritance pattern. These forms are often passed down through an autosomal dominant pattern, where inheriting one copy of the mutated gene is sufficient to confer high risk.
Other types, such as Secondary Glaucoma, which develops as a complication of injury, inflammation, or medication use, are generally not inherited. Primary Angle-Closure Glaucoma (PACG) also has a hereditary component, often involving genetic variants related to the eye’s physical structure. For most adult-onset cases, the genetic risk is a cumulative effect of numerous common genetic variations.
The Role of Specific Genes
Specific genes have been identified that directly cause or significantly increase the risk for certain types of inherited glaucoma. The MYOC (Myocilin) gene was the first associated with the disease and is the most common known genetic cause of POAG. Mutations in MYOC are responsible for a small percentage of adult-onset POAG cases and a larger percentage of JOAG cases.
The MYOC protein is normally secreted by cells in the trabecular meshwork, a sponge-like tissue that drains fluid from the eye. When a mutation occurs, the abnormal Myocilin protein fails to secrete properly and accumulates within the meshwork cells. This accumulation causes cell dysfunction, clogging the drainage system and leading to a build-up of fluid and pressure.
Two other genes, OPTN (Optineurin) and TBK1 (TANK-binding kinase 1), are strongly linked to Normal-Tension Glaucoma (NTG). NTG is a form where optic nerve damage occurs despite normal eye pressure. The proteins produced by OPTN and TBK1 are involved in the health and survival of retinal ganglion cells, which form the optic nerve. Mutations in these genes compromise the optic nerve cells directly, making them vulnerable to damage.
Screening Recommendations for High-Risk Individuals
A family history of glaucoma places a person in a high-risk category, making proactive and regular eye examinations the most effective way to prevent vision loss. Screening should generally begin earlier and occur more frequently than for the general population. While general guidelines recommend initial screening around age 40, high-risk individuals often benefit from starting comprehensive eye exams sooner, sometimes in their 20s or 30s.
The recommended frequency for high-risk groups is typically an annual or biennial comprehensive eye exam, based on the eye doctor’s assessment of individual risk factors. A comprehensive glaucoma screening involves several specific tests. While tonometry measures intraocular pressure, other tests are necessary since glaucoma can occur with normal pressure.
The examination includes:
- A dilated fundus exam, where the eye care professional inspects the optic nerve for signs of damage.
- Visual field testing to check for peripheral vision loss, which is often the first sign of damage.
- Advanced imaging techniques like Optical Coherence Tomography (OCT) to measure tissue thickness and detect early thinning of the optic nerve.