A study of over five million American veterans found that those who used cocaine had a 45% increased risk for glaucoma, the second leading cause of blindness in the United States. Cocaine users in the study developed the disease about 20 years earlier on average than did non-drug users.

Dr. Dustin French and his colleagues at Indiana University School Of Medicine studied the medical records of 5.3 million veterans, of which 91% were males who had visited Veterans Administration medical clinics in 2009. Almost 83,000 or 1.5% had open-angle glaucoma, and nearly 178,000 or about 3.3% had been diagnosed with cocaine abuse or dependency.

Current and former cocaine users were at a much higher risk for glaucoma. Their average age when glaucoma was diagnosed was 54 years old, whereas non-cocaine users with glaucoma were not diagnosed on average until age 73. Those who had abused other amphetamines and marijuana were also at increased risk for the disease, but less so than those who had abused cocaine.

Glaucoma occurs when the drainage tubes within an eye become blocked. As fluids in the eye are unable to drain, pressure in the eye increases and damages the optic nerve. The person will lose peripheral vision, and eventually become blind without treatment. Eye medications and laser treatments can keep glaucoma from progressing, but cannot reverse its damage.

Cocaine is a very addictive and powerful stimulant of the central nervous system. It works by increasing the levels of brain chemicals associated with pleasure and movement, and can cause long-term damage to the brain's reward system as well as addiction. Cocaine use appears to be declining among young people; for example, the latest government statistics show that 6% of high school seniors tried it in 2008 compared to 2% in 2009. The decline may be related to the current economic recession in that cocaine is an expensive drug and people now substitute cheaper prescription drugs. However, cocaine remains the most commonly abused stimulant, and one of the most frequently cited drugs involved in emergency room visits. Cocaine is associated with heart disease, diseases of the lungs, infections, and pregnancy complications.

Dr. French emphasized that his study does not prove that cocaine causes glaucoma.

"The association of illegal drug use with open-angle glaucoma requires further study, but if the relationship is confirmed, this understanding could lead to new strategies to prevent vision loss," according to Dr. French, a research scientist with the Center of Excellence on Implementing Evidence-Based Practice at the Department of Veterans Affairs in Indianapolis.

Dr. French's study was published in the Journal of Glaucoma.