Before even looking at the actual laser, consider that we have laser application options onto the cornea. The type of procedure is dependent on whether the epithelium is included or not with laser ablation.

1. PTK - PhotoTherapeutic Keratectomy

The epithelium is manually removed, sometimes with the help of alcohol or a brush. The laser is then applied to the exposed stromal bed. The refractive equivalent of this procedure is a PRK, PhotoRefractive Keratectomy.

2. TransPTK - Transepithelial PhotoTherapeutic Keratectomy

With this procedure the laser is applied straight to the epithelium and then stroma without pause. The epithelium acts as a masking agent. The refractive equivalent of this procedure is a TransPRK (Transepithelial PhotoRefractive Keratectomy).

3. WetPTK

Fluid is used as masking agent to smooth the stromal bed. Usually done after one of the other therapeutic profiles, or after removal of the epithelium alone.

4. SCTK - Sequential Custom Thereapeutic Keratectomy

This is a combination of multiple Wavefront / Topography guided profiles. First, a TransPTK / PTK is done. Then a WetPTK to smooth the stromal bed. The eye is remeasured immediately. A new custom PTK profile is planned, and steps one and two are repeated. The process can be repeated a few times, usually 3 or 4 times, but even up to 5 times or more is possible, all in one setting.

We can either go through the epithelial (TransPTK or Transepithelial Phototherapeutic Keratectomy profiles), as well as directly onto the stroma (traditional PTK or Phototherapeutic Keratectomy) after epithelial removal. Both techniques have their merits and indications. Both techniques change shape on a “global” corneal scale. 

We can also laser onto a masking fluid, the so called WetPTK. With this technique, energy is applied to the masking fluid that has been added to the stromal bed, and the energy is dispersed laterally instead of straight down into the stroma. Small “localized” vertical ridges are smoothed with this technique.

I almost always perform the WetPTK after any therapeutic laser, to smooth the bed as much as possible. This has two functions: one, to improve the stromal irregularity as much as possible, but two, to give the epithelium a smooth pathway to close quicker. This means, I do two laser runs on the same eye at the same setting. The so called “Dry Run”, where I apply the calculated profile that will give me global reduction in stromal irregularity. And the “Wet Run” that will smooth the stromal bed of small and localized irregularities. I plan the Dry Run on the eye (within the planning file) that I am operating on, and the Wet Run on the contralateral eye (within the same planning file) so that I do not have to switch to a new planning file in between the two runs on the same eye.

Any depth can be planned, from 1µm upward. It is not only the depth that can be manipulated, but also the profile shape which we laser. Profiles include:

• Uniform. With this profile, a single depth is chosen across the entire profile, with a specific ablation zone size. Certain lasers can also position this specific profile where you would like onto the cornea. And again, certain lasers can change the shape to a circle, ring, or an oval shape of any orientation.

• Corneal Wavefront Optimized. This profile is based on the mathematical expression of the wavefront measurement of the cornea.

• Topoguided. This profile is based on the topographical expression of the front surface of the cornea.

• Ocular Wavefront Optimized. This profile is based on the wavefront measurement of the whole eye.

• Refractive. Traditional refractive profiles can also be used. Note that with therapeutics one can sometimes see very interesting refractive shifts that cannot be wholly calculated by the uninitiated prior to the laser.

Therapeutic laser techniques then combine the different profiles with the different corneal applications. The technique chosen is completely dependent on the pathology.

1. Irregularities

2. Opacities or Scars

3. Recurrent Corneal Erosions. 

4. Corneal Dystrophies

5. Corneal Degenerations

6. Apical Syndrome.

7. Keratoconus and Ectasias