Sunday, December 23, 2007

7.2 Harder who?

Next time, when you visit your eye doctor, casually mention that you would like to have your Harderian gland checked. The doctor will look at you quizzically, "Harder who?"

With the long and rich history of human anatomy, you'd think that everything in the human body, big and small, young and old, have all been discovered and carefully documented. Not so. The Harderian gland has escaped attention, even though its existence in other mammals has long been known. In fact, it was first described in 1694 by an obstetrics professor in Basel, Johann Jacob Harder (1656-1711).

Indeed, one time, an excited nuclear medicine research group, who have just developed PET microscopy, informed us a large uptake of a certain compound (we are sworn to secrecy as to its identity) by the posterior portion of the eye, in a living rat. And they have traced it to the Gland of Harder. This uptake was later confirmed and quantified with another study. The excitement, however, was somewhat dampened when told that there was no such gland in the humans, at least not the ones we saw. In our collective knowledge, only one person recalled reading about this gland in non-primate mammals - in the comparative anatomy chapter of Wolfe's Anatomy of the Eye. This gland is hiding posterior to and underneath the eye ball, blended into the fatty tissues of the orbit. Easily missed if you are not looking for it intentionally.

What a shame - as PET (Positron Emission Tomography) microscopy is nothing to sneeze at. PET scans usually show low-resolution whole-body/brain images, to see images of a 3-mm rat eye is no small feat.

In 2006, two biologists in Pennsylvania finally published a paper: "Primate Harderian gland: Does it really exist?" in Annals of Anatomy - Anatomischer Anzeiger Volume 188, Issue 4, 3 July 2006, Pages 319-327. The finding? Indeed the Harderian gland is found in fetal and neonatal stages in humans but is largely absent from adults. And of course, its role is still unknown. (In contrast, numerous functions have been proposed for the Harderian gland in non-primates.)

Who knows why the humans do not have a functioning Gland of Harder, but then we don't have the nictating membrane, either.

Sometimes we run into an unknown. And to have found the answer is like discovering some new species in the deep jungles of Indonesia. Sometimes, however, the findings are to be filed away perhaps for another day. All part of the fun and game of research.

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