Cornea from an elderly female with gradually deteriorating vision
Corneas make up a significant proportion of our workload. Most of our corneal specimens fall into four categories: endothelial failure, dystrophies, infections or interference with vision (eg scarring or ectasia).
This specimen is full thickness cornea, with the epithelium on the right and endothelium on the left. The epithelium shows bullae, suggesting oedema. The stromal lamella have lost their usual basketweave pattern and have a greyish appearance, again suggesting oedema. Finally, Descemet’s membrane appears thickened, and there are very few endothelial cells.
In the annotated image, I’ve marked the bullae (b). The endothelial cells are marked with asterisks. The yellow lines outline Descemet’s membrane.
This is a PAS-stained slide. PAS is particularly useful for demonstrating basement membrane. In this case, it highlights Descemet’s membrane and the epithelial basement membrane. Descemet’s membrane is usually of uniform thickness with a regular texture, but in this case both the thickness and texture are irregular. Epithelial basement membrane is typically a very thin (often barely visible) line. Here, it is thicker than usual. Additionally, it shows areas of reduplication and extension into the overlying epithelium.
In the annotated image, I’ve marked Descemet’s membrane (dm) and the foci of epithelial basement membrane protrusions (asterisks). I’ve marked the epithelial basement membrane with a yellow line.
Here’s a higher power image of Descemet’s membrane, again stained with PAS (which, remember, is particularly helpful for basement membrane). Its texture is laminated, and there are irregular lumps protruding from its posterior surface. These are exophytic guttae, which are classically seen in Fuchs endothelial dystrophy.
In another field, we have similar lumps, but they are buried in layers of basement membrane. These are buried guttae.
In the annotated images, I’ve outlined the posterior profile of the buried guttae in yellow. The layer posterior to that (outlined in blue) is an abnormal deposit.
Fuchs endothelial dystrophy is a common cause of endothelial failure. We now know it has a strong genetic component. With the reduction in endothelial cells, the relative dehydration of the stroma can no longer be maintained (with oedema developing), and vision becomes hazy. In later disease, fluid accumulates beneath and within the epithelium, leading to the bullae in the first image. Ruptured bullae can be painful as well as interfering with vision.
The articles below are freely accessible.
Fuchs Endothelial Corneal Dystrophy by Elhalis et al. This article from 2011 provides a comprehensive review of Fuchs dystrophy, including pathogenesis and genetics.
Genetics of the Corneal Endothelial Dystrophies: An Evidence-Based Review by Aldave et al. This review sets Fuchs dystrophy in the context of other posterior dystrophies. It provides nice clinical photographs.
Epithelial abnormalities in chronic corneal edema: a histopathological study by Eagle et al. This article from 1989 examines the mechanism of epithelial changes in Fuchs dystrophy and pseudophakic/aphakic bullous keratopathy (both of which can cause chronic oedema). The authors compare the appearance to that in map-dot-fingerprint dystrophy (an epithelial basement membrane abnormality which is not typically associated with chronic corneal oedema).