Thyroid disorders linked to glaucoma

Research published ahead of print in the British Journal of Ophthalmology finds that people with thyroid disorders may have a higher likelihood of developing the eye disease glaucoma.

The thyroid is responsible for making hormones that are necessary for every cell in the body to function. The growth and rate of chemical reactions is also partly regulated by hormones that originate in the thyroid. Glaucoma is an eye disease that results from progressive damage to the optic nerve. Left untreated, glaucoma will hinder central (fine detailed) vision and eventually lead to blindness. In fact, the eye disease is leading cause of irreversible blindness in the world.

Researcher Jennifer Moren Cross (University of Alabama at Birmingham, United States) and colleagues studied the relationship between thyroid disorders and glaucoma using a nationally representative sample of 12,376 adults in the US who participated in the 2002 National Health Interview Survey. Participants responded to questions covering demographic information as well as items that probed their histories of thyroid gland disorders and glaucoma.

About 4.6% of respondents indicated that they had glaucoma and 11.9% indicated that they had had a thyroid disorder. The researchers found that 6.5% of participants had glaucoma and thyroid problems while 4.4% had glaucoma and had not been diagnosed with a thyroid disorder. Cross and colleagues statistically controlled for risk factors such as gender, race, and smoking habits, and the relationship between glaucoma and thyroid problems maintained its significance. Having a thyroid problem at some point in life was linked to a 38% increase in likelihood of developing glaucoma.

The researchers suggest that there is a biological link between the two conditions. For example, hypothyroidism (an underactive thyroid) can help to increase chemical deposits in the group of vessels that bring blood to and from the eye. This can lead to an increase in pressure within the eyeball, which is a main symptom of glaucoma.

"The association between thyroid disorders and the development of glaucoma is important to establish, given the high prevalence of both conditions in the general population. Thus, prospective research based on a large, clinical sample is warranted on the development of glaucoma and thyroid disorders to more definitively ascertain whether thyroid problems instigate and/or exacerbate glaucomatous damage," conclude the authors.

(Source: British Journal of Ophthalmology: The Association between Thyroid Problems and Glaucoma: October 2008)