November 30, 2013

Glaucoma: Another Possible Risk of Testosterone Use?

August over at Hidden In Your Soul caught this one and sent it my way. It’s a study that is not directly related to transgender HRT, but that may have some implications for transfolk. 

The study, Female reproductive factors and primary open-angle glaucoma in the Nurses’ Health Study, assembled long-term data on genetic female’s chances of developing glaucoma later in life and what risk factors may add to chances of developing the eye condition. What it found was a small but statistically significant increase in glaucoma risk among females who spent five or more years on oral contraceptive. Why would this be? NPR has a clear explanation:

There could be a relationship between eyesight and estrogen, though. Scientists have long thought that the hormone could have a protective effect on the eye’s retina. So it makes sense that the pill, which lowers a woman’s total exposure to estrogen over a month, could affect her eyes, says Dr. Shan Lin, a professor of clinical ophthalmology at the University of California, San Francisco, and senior author of the study.

Birth control pills suppress cyclical spikes in women’s estrogen levels […] and over time that dampening may contribute to retinal damage.

This is far from the first study to suggest that estrogen levels can effect eyesight. In fact, last year Vajaranant & Pasquale performed a comprehensive literature review of the estrogen-eyesight link and found that “Strong epidemiological, clinical, and experimental evidence supports the proposed hypothesis that the early loss of estrogen leads to premature aging and increased susceptibility of the optic nerve to glaucomatous damage.”

Oddly, the estrogen connection to glaucoma appears to impact females but not males. Even though estrogen levels in genetic males is naturally lower, glaucoma impacts females more often than it does males. The reasons behind this aren’t entirely known, which is why researchers have been looking into the estrogen link recently.

The trans connection here is evident: transman are genetic females who artificially reduce their estrogen levels to a high degree. Does that put transman in a high risk category for glaucoma?

The honest answer is that we simply don’t know yet. Studies have drawn a preliminary link, but there are so many unknown variables here. For one, does age play a part in this? These studies all involve women who are losing estrogen as a natural part of aging; estrogen loss may be interacting with other changes in the body in old age. For another, what is the role of testosterone? Genetic males aren’t at as high a risk for glaucoma; maybe that’s because T has some sort of benefit against glaucoma. And neither genetic females not genetic males are exactly like transman, who artificially throw their endocrine systems into reverse and initiate changes akin to a second puberty. Even if we were more certain about the estrogen-glaucoma connection under normal circumstances, there’s no telling how transition might impact the situation.

it is worth noting that relative risk and absolute risk are not the same thing. As NPR notes, “the absolute risk of getting glaucoma after age 40 is small, about 1.86 percent […] So doubling that risk would bring it up to a bit under 4 percent.” In other words, even if transmen are increasing their risk of glaucoma it’s still a small risk, and it’s not a risk that will likely make one think twice when weighted against all the benefits of becoming one’s self.

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