Eye pathology case 11

Middle-aged patient with worsening vision many years after a previous procedure

Low power of cornea

This low power view shows a full thickness corneal button. We’ve sliced it in two and embedded both halves on our cut surface. It is not obviously inflamed or vascularised (something I specifically mention in my reports as a negative finding). However, there is a subtle irregularity of epithelial and stromal thickness which I don’t think is artefactual. Additionally, there is a linear lamellar scar in the superficial stroma in both halves.

In the annotated image, I’ve marked the lamellar scar with a green line. Wobbliness of my hand drawing aside, the scar is remarkably uniform in depth and profile.


Medium power

This medium power view allows you to better appreciate the scar and its uniformity.


High power view of scar

This is a high power view of the edge of the scar. Note how it interrupts Bowman’s layer, with a little compensatory epithelial thickening.

Annotated

In the annotated image, I’ve marked the scar with a green line and the defect in Bowman’s layer (which does not regenerate) with an asterisk.

A regular lamellar scar in the superficial corneal stroma is a strong hint that the patient has had LASIK (“flap and zap”) surgery. However, that’s not all that’s going on in this cornea!


PAS of cornea

This is a PAS-stained slide. We routinely do haematoxylin and eosin (H&E) and PAS on corneal specimens. The PAS highlights the scar slightly, but the major feature to note is the presence of guttae on the posterior surface of Descemet’s membrane.

In addition to previous surgery, this patient has Fuchs’ corneal dystrophy. I recently posted a good example of this diagnosis here.

What is LASIK? The term stands for laser-assisted in-situ keratomileusis. Speaking simplistically (remember, I’m an eye pathologist and not a corneal specialist!), it’s a procedure to correct refractive error. Generally, it’s used for myopia (short-sightedness) although I believe it can also be used to treat hyperopia (long-sightedness) and astigmatism (corneal irregularity). Experts, please comment if I’m getting this wrong!

During the procedure, a very thin superficial slice is made into the cornea and lifted (the “flap”). The underlying corneal stroma is reshaped to change its refractive power using an excimer laser (the “zap”). Then the flap is replaced. This method preserves Bowman’s layer, which does not regenerate. In this case, we see the healed scar where the flap has reattached.

Selected references

I’ve gathered some open access references about refractive surgery.

Main Complications of Photorefractive Keratectomy and their Management by Spaldea and Giovannetti (2019). This is quite a “technical” article, with plenty of keratography images showing the odd and undesirable shapes corneas can adopt, post-LASIK, and issues about retreatment.

Laser In Situ Keratomileusis (LASIK) by Moshirfar et al (2020). This is a nice overview of the history of LASIK plus clinical aspects.

Epithelial ingrowth following laser in situ keratomileusis (LASIK): prevalence, risk factors, management and visual outcomes by Ting et al (2018). This is a review of a specific (and fortunately uncommon) complication after LASIK. We occasionally get specimens that show this. I’ll try to find one to post.

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