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Custom PRK and Advanced Surface Ablation at the San Diego LASIK Institute


Advanced surface ablation (ASA) is a group of procedures that includes custom PRK with mitomycin C, LASEK, and Epi-LASIK. Patients who are candidates for this group of procedures at the San Diego LASIK Institute include patients that are not candidates for LASIK and patients who elect to have these procedures because they do not want to have a LASIK flap.

Corneal Anatomy

To understand the differences in these procedures it is important to review corneal anatomy. The cornea has five layers. The important layers for laser vision correction are the epithelial layer, Bowman's membrane, and the corneal stroma.

Layers of Cornea

  • Epithelium (Dynamic Layer)
  • Bowman's Membrane
  • Stroma (Layer changed by the laser)
  • Descemet's Membrane
  • Endothelium

The epithelium is the layer on top of the cornea. It is composed of cells that are always actively piding, growing, and changing. This is like the epithelial layer of our skin. It is a dynamic layer that always changes so if we lasered this layer only we will not make a permanent change.

The difference in LASIK, custom PRK, and other ASA procedures is how one gets to the deeper stroma layer. The stroma is a permanent layer.

Differences in Procedures


The LASIK surgeon creates a flap. Either a microkeratome (blade) or a laser makes the flap. the surgeon opens the flap, the stroma is lasered and the flap is placed back. 

Custom PRK:

In custom PRK, the San Diego LASIK Institute's surgeon uses a brush to remove the epithelial cells and let a new set grown in. The surgeon essentially make a scratch on the eye, lasers, and then a new epithelial layer grows in and closes the scratch.

PRK has gone through two major advances that have helped to reduce the incidence of corneal haze - lower spot sizes for the laser pulses and the use of Mitomycin-C.  


In Epi-LASIK or LASEK, a surgeon uses alcohol to loosen the epithelial layer. The surgeon then moves the epithelium to the side manually or with a mechanical device. After the laser, the surgeon puts these alcohol weakened cells back on the cornea. The idea with these two procedure is that there is less pain because the eye is covered up with cells as opposed to a true "scratch" with PRK.

Unfortunately there is a high failure rate in these alcohol weakened cells and they end up dying and then you would have a delayed PRK recovery. 

Why  the San Diego LASIK Institute Prefers Custom PRK with MMC:

  • We do not have to use alcohol on the eye.
  • Although the procedure is more painful, the healing is more predictable in our opinion.
  • There is no risk of nicking the eye with a mechanical device (epi-LASIK).
  • Our surgeon would rather a new layer of cells grow in than put alcohol weakened cells back on the cornea.

*There are pros and cons to all procedures that any website cannot completely cover. We would be happy to go in more detail with our patients at our consultation. All viewpoints in this website are meant to be used as an education aide and are the sole viewpoints of the doctors of the San Diego LASIK Institute.


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San Diego LASIK Institute

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2021 The San Diego LASIK Institute | Tony H. Pham, M.D.

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