This month’s microscopy session was a little different…
Simon from the Royal Veterinary College brought eyes from an elephant and a rhinoceros for comparison with our usual human eyes. He’s kindly provided some images which are at the end of this post. I guess it’s no surprise that rhinoceros sclera is substantially thick (after all, rhinoceroses are known for being thick-skinned). We were (maybe!) able to identify the elephant tapetum, a structure which always makes me smile since humans don’t have one. If you’re curious about the tapetum, my author website has an interview about it with Charlotte, a veterinary ophthalmologist who was also at yesterday’s session.
One further treat for the discussion this month was having slides from the recent European Ophthalmic Pathology Society meeting to review. At the annual EOPS meeting, society members present the pick of their rare and challenging diagnostic cases. Since the range of nationalities presenting is so large, it’s fascinating to learn how diagnosis and management is handled in different places, and how disease profiles vary.
Here are a few of the cases we discussed that have recently come through the department. As usual, I’ll only document the “more common” entities on this blog, for reasons of patient confidentiality. I hope you find them interesting.
Case 1 – Subconjunctival mass ?lymphoma
The haematoxylin & eosin-stained slide shows fibroconnective tissue with a dense lymphoid infiltrate. Germinal centres aren’t visible. The specimen is quite small but the appearance highly suspicious for a lymphoma.
Just based on the morphology, I thought this most likely to be an extranodal marginal zone lymphoma (MZL), which is the commonest “low-grade” lymphoma found at this site. However, I wouldn’t make a diagnosis on an haematoxylin & eosin-stained slide alone: diagnosis needs immunohistochemistry and maybe other investigations such as FISH, cytogenetics or PCR.
This is immunohistochemistry for CD3 (in these slides, brown is positive with blue being the counterstain to delineate the non-positive tissue). CD3 is a T-cell marker. In this case, a relatively small proportion of the cells are positive compared to a reactive process.
This is immunohistochemistry for CD5. CD5 is also a T-cell marker, and I would normally expect the expression of CD3 and CD5 to be similar. However, it is positive in nearly all of the cells, which suggests it’s positive in B-cells as well as T-cells. This finding (along with the rest of the immunoprofile – we use a default panel of 15 antibodies in our department) suggests a diagnosis of chronic lymphocytic leukaemia/small lymphocytic lymphoma.
Case 2 Blind painful eye
This is a low power view of the front part of the globe, which I’ve annotated. For orientation, the cornea extends to the top right of the image. Following the cornea and sclera clockwise, we pass the iris and ciliary body, and end up with the anterior retina at the bottom left of the image. a is an empty profile within the sclera where there was a silicone band, maybe as a result of a previous scleral buckle for retinal detachment surgery. b is a gap within the iris, which I interpreted as a peripheral iridectomy. c is cornea, but with iris adherent to the posterior surface – extensive peripheral anterior synechiae.
This higher power image shows the cornea (on the right) and a discontinuous portion of the iris. a identifies the iris sphincter muscle. b indicates a layer of epithelium on the anterior iris surface. The epithelium is nonkeratinising and stratified squamous (like corneal or conjunctival epithelium) and it’s most likely to reflect epithelial downgrowth.
Bonus case
We didn’t actually look at this case, but it’s a nice example of a normal temporal artery.
The low power shows the full artery in cross-section. a indicates the lumen, which contains fresh blood and appears of normal calibre. b is the wall, which appears “clean” in that there is no inflammation, fibrosis, necrosis or thickening. c indicates an adventitial blood vessel (vasa vasorum). In some cases of temporal arteritis, inflammation of the vasa vasorum is a clue if the arterial wall itself doesn’t appear inflamed.
This higher power view indicates the elastic lamina (a), the wiggly basophilic line. In temporal arteritis, it is typically fragmented.
Thanks again to Simon for the elephant and rhinoceros photomicrographs here. We think these eyes are probably fairly normal, but if any readers have experience to share, please feel free to add comments below.
Rhinoceros
This is the anterior part of a rhinoceros globe. For orientation, a marks the lens. b is the iris, which has a smoother anterior contour than I’d expect in a human. Additionally, it appears more richly vascular. Note that the iris pigment epithelium is clearly delineated on the posterior surface. The ciliary processes (c) are perhaps more delicate and complex than in a human although it’s difficult to be sure with just one section – some of the appearance may be due to oblique orientation.
Elephant
In contrast, this is the anterior part of an elephant globe. a marks the cornea. The iris (b) has a more undulating contour than the rhinoceros iris although still not to the extent I see in humans. The iris pigment epithelium seems less prominent than in the rhinoceros (and human). Again, the ciliary processes (c) seem quite delicate.
This image of the posterior part of the elephant eye includes the retina (a). The retinal pigment epithelium (b) is quite modest. The tapetum (we think – we’re not sure!) is marked by * and seems rather fibrous. The choroidal vasculature can be seen (c)
My next teaching session will run on 11 July. No guarantees about exotic animals, but hope to see you there anyway!
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