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PRK or not to PRK

Q by Doctor P:

I have a 37 yo high myope (-9.00) with 500 u corneas.

She has a small area in the left nasal cornea of endothelial haze

No other signs/symptoms

No history of HSV etc.

specular right and left eyes

clearly abnormal OS>OD (increased coefficient of variation, lower cell count, weird dark centers OS>OD)Would you offer PRK?

Answer by Doctor Ronal from Brazil:

Me not PRK for this case , too much myopia

yes. Artisan

Answer by Doctor P:

I thought about ICL or Artisan but I would be more worrier about endothelial decompensation with an intraocular procedure rather than modern surface ablation…

Answer by Doctor Jim:

It’s natural to reflexively back away from this patient. But lets look at the case objectively.

On a Visx with a Blend / Large zone ablation this would be 129 u (less with a small zone and/or no blend). Assuming 50 u epithelium, this produces a RSB of 321 u and a PTA of 35.8%. Those numbers are acceptable to many of us, per a recent conversation. Also, with CCT of 500 u, it seems unlikely that there is currently any significant endothelial pump failure.

(1) Would the PRK negatively impact the clinical course of the endothelial abnormality? To my knowledge, ablations have not been shown to impact the endothelium, and endothelial transplantation should not be compromised by the ablation as long as there is no ectasia.

(2) Would the endothelial abnormality negatively impact the clinical course of PRK? Without any evidence of corneal edema currently, the epithelium should heal properly. It seems possible that, if the epithelial-stromal attachment is weaker than normal, as I noted in a previous thread, bullous keratopathy might be more likely after PRK, but this would be treated with endothelial transplantation anyway at that point even without the history of PRK.

It would be valuable to the patient to prognosticate on the future of the endothelial issue, if possible, but I would offer this patient PRK.

Answer by Emil Chynn:

It’s incorrect that “ablations are not known to affect the endothelium”

This was studied during FDA trails of the excimer laser I believe. The acoustic shockwave during ablation kills endothelial cells

I recall FDA trial data showed a small decrement in endothelial cell count densities, that then was flat, rather than progressive, indicating a one-time decrement, with no further accelerated induced loss

Because we’re normally born with excess endothelial cells, FDA extrapolated that this small one-time loss wouldn’t cause clinical edema later in life

At this is my 20-year old recollection as a PI for one of the excimer laser FDA trials.

Marc might have a more accurate recollection or maybe even some citations

Hope this helps

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