Eye pathology case 16

I recently received a query as to whether I’ve come across corneal copper deposition, as we might see in the Kayser-Fleischer ring of Wilson disease. Not sure who Kayser, Fleischer or Wilson were? Here’s a little information.

There’s a nice picture of the clinical appearance and an overview of Wilson disease here.

On checking our archives, I found just one case of corneal copper deposition from several years ago. It was rare enough that I presented it at a meeting.

I suspect that the patients don’t often have corneal surgery. Presumably the hypercuprinaemia is is treated medically. There’s a fairly recent report on a resolving ring in this article by Khurana et al (2019).

Copper has an affinity for basement membrane. So in the cornea, we’d expect to see it mostly at the level of Descemet’s membrane. My specimen is a sheet of Descemet’s membrane.

Haematoxylin and eosin stain, x20 objective lens

You can see from the haematoxylin and eosin-stained section that the endothelium is quite well preserved. There’s a distinct coppery colour to Descemet’s membrane.

PAS stain

The PAS stain demonstrates Descemet’s to be of regular thickness. The copper tinge doesn’t show up here. I don’t know enough about histochemical stains to say why – if anyone can explain it, please let us know in the comments!

UNstained section

Out of curiosity, I asked for an unstained section. So this is a 4 μm section that has simply been coverslipped (with mountant). Again, we see the coppery colour, which appears rather granular, The copper seems more densely distributed towards the endothelium than towards the stroma.

Toluidine blue

Here’s a toluidine blue stain. Toluidine blue is often used when preparing material for electron microscopy. It’s typically cut at 1 μm thickness, a quarter of the thickness of our regular sections. Light microscopists will refer to these as “semi-thin” sections, while electron microscopists will call them “thick” sections. It’s all relative!

Electron microscopy

And here’s an electron microscope image. We have the endothelium on the top/left of the section, with the (absent) stroma on the bottom right. The electron-dense deposits are our copper particles. We can see they’re more heavily distributed in the posterior region of Descemet’s (closer to the endothelium).

I don’t think there are many references about the histological appearance of copper in Descemet’s membrane. Interestingly, I came across this article from 1970 by one of my predecessors at the UCL Institute of Ophthalmology, the late Dr John Harry. It’s funny that 50 years later, here I am, looking at the same entity!

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