As bilirubin levels increase this can exhaust the ability of albumin to store it. Whether there is enough homogeny to explain the binding of bilirubin to both proteins with strong affinity is not clear.Īs to teleological benefit, one hypothesis is that the human body uses elastin as a place to “store” excess bilirubin that would otherwise have toxic effects. Structurally, elastin is considered an “albuminoid” protein, meaning it is albumin-like. The structural question asks, what is it about elastin that allows it to bind bilirubin? The teleological question asks, what purpose does this binding serve? Possible explanations could be approached from at least two perspectives: one structural and one teleological. The answer to this question has no clear answer. The area without chemosis lacked icterus. The area with chemosis showed “scleral icterus”. Instead, the authors show an image of a patient with chemosis (i.e., edema) of the conjunctiva. One more recent case report helps to demonstrate that it is conjunctival not scleral icterus – and it did not require removal and transection of the globe. The sclera, on the other hand, is relatively avascular. As the serum bilirubin increases, blood delivers more bilirubin to highly vascular structures such as the conjunctiva. The article is in German, though Google translate can help!Īnother part of the explanation is that the conjunctiva has a rich vasculature. Tissues with high concentrations of elastin are more apt to become jaundiced. One relates to a molecule to which bilirubin readily binds: elastin. It actually makes sense that we can identify jaundice by examination of the eye: as the overlying conjunctiva becomes jaundiced, the underling sclera appears yellow (but only appears so). More specifically, the bulbar conjunctiva that covers the sclera. The letter goes on to note that that bilirubin appears in the conjunctiva. They write, “We found that of all ocular tissues, the least amount of bilirubin staining is seen in the scleral stroma.” In one of their cases, the serum bilirubin reached 60 mg/dL and yet there was no bilirubin in the sclera. The two authors note that they had studied histological sections of globes from many patients with jaundice. It is titled “Conjunctival icterus, not scleral icterus.” The letter – written by two ophthalmologists – could not be any more to the point. One is a letter published in the Journal of the American Medical Association in December 1979. There are a few pieces of evidence in support of this. One of the most fascinating parts of the answer is worth noting early: the sclera do not become jaundiced instead it is the overlying conjunctiva. Unlike with Kayser-Fleischer rings – a difficult to see finding in a rare disease – icterus is absolutely something that most students who have been on a surgical or medical ward for even a few weeks have seen. For this episode, we discussed something else that deposits in or around the eye: bilirubin. In the first episode we talked about the connection between Wilson disease and copper deposition – the Kayser-Fleischer ring. This was the second episode in a two-part series called “The Eyes Have It”.
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