Cornea from a young adult with gradually worsening vision
This low power image shows a full thickness cornea with a little artefactual creasing. Remember, the 5 layers are: epithelium, Bowman’s layer, stroma, Descemet’s membrane and endothelium. The stroma is perhaps a little thinned towards the right of centre, and there is subtle scarring in the area. The most obvious abnormality is Descemet’s membrane (DM) being detached from the posterior surface with a large central defect. That is, the posterior corneal stroma is bare; pre-operatively, the stroma would have been in direct contact with aqueous fluid in the anterior chamber.
In the annotated image, I’ve roughly marked the stromal scarring with yellow hatches. The green line indicates where DM has come away from the stroma. Note how the broken ends have curled away from each other.
This is a PAS stain. If you’ve read previous posts from me, you’ll know that PAS is one of my favourite stains as it beautifully highlights basement membrane, of which DM is one. We can just about see a few cells at the point of detachment, supporting chronicity. Additionally, the free end of the broken DM has curled into a tight scroll.
In the annotated image, I’ve marked the point of detachment. I’ve outlined the DM scroll in green.
In this higher power view, we have a feature that’s said to be classic for this condition although I don’t see it all that often. There is an angulated break in Bowman’s layer.
In the annotated image, I’ve marked the angulated break with a blue asterisk, and an adjacent focal disruption with a green one.
This is a cornea with keratoconus, complicated by hydrops. Keratoconus is an “ectatic” disease of the cornea and a common diagnosis in our department (1-2 cases per week). Over time, the cornea gradually changes shape and distorts. There is worsening irregular astigmatism which can’t be corrected by glasses or contact lenses. In the acute complication known as hydrops, Descemet’s membrane ruptures. This allows aqueous into the corneal stroma, and it manifests as pain, reduced vision and a cloudy cornea (due to oedema). Although the oedema resolves over time, the stroma is left scarred. Additionally, the detached DM does not generally reattach, and so there is loss of endothelial cover over the posterior cornea.
The references below (all open access) provide more detailed information about keratoconus.
Selected references
Acute corneal hydrops in keratoconus by Maharana et al (2013). This is review article with striking clinical and OCT images of acute hydrops in keratoconus. The images don’t include a DM break, but you can get an idea of how it might look.
Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography by Martin (2018). This is a somewhat technical article about clinical assessment of corneal shape. It might help you appreciate the appearance of irregular astigmatism (remember, I’m a pathologist, not an optometrist!)
Molecular and Histopathological Changes Associated with Keratoconus by Khaled et al (2017). This is a comprehensive review of keratoconus, from clinical presentation and appearance through histology and then molecular mechanisms. If you’re not familiar with corneal histology (and/or you’re revising for exams!), Section 2 gives a nice summary.
The Genetic and Environmental Factors for Keratoconus by Gordon-Shaag et al (2015). This review article takes a population-based approach.
Now that our work is slowly heading back towards normal, I won’t be posting so frequently. If you’re looking for specific cases, you might want to look through the archives or word cloud here (under “Tags” at the bottom of this page). And if you’d like to peek at my speculative fiction writing, why not head over to my other website?
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