PRK and LASEK are "no Knife " operations.

The cornea has several layers and the top one, the "epithelium" has to be removed prior to firing the laser. This is because this tissue laser is very active and replaces itself every couple of days. It is 50 microns deep and if we just lasered this, then the tissue would remodel and reverse any effect. This has to be removed prior to surgery and can be done in several ways. These are scraping with a blunt blade, using an electric toothbrush- like instrument, using 17% alcohol (like Martini) or just lasering through the epithelium. I have tried all of these methods and prefer the alcohol one. This is because it reduces the risk of haze very markedly and also does not kill the epithelium, which can be replaced back onto the cornea, a bit like lasik. We originally called this "epiflap" and it is also known as LASEK (laser assisted epithelial keratomileusis) as it was independently thought up in Optimax  Manchester by Sunil Shah and in Italy by Massimo Camellin, who uses the latter term. It is also called EPI-LASEK. Using a machine similar to a microkeratome to remove the epithelium is called EPI-LASIK  Preliminary reports seem to indicate that whether the epithelium is removed by alcohol or by a machine gives very similar results.

18% alcohol is put onto the cornea for  35 seconds by dropping it into a sort of "well" placed on the anaesthetised eye   (click all pictures to enlarge).

The alcohol is soaked up with a sponge and the cornea washed thoroughly with balanced salt solution.

The epithelium is peeled back like a lasik flap and rolled up at the top out of the way of the laser beam.

The excimer laser is applied onto the cornea. This takes about 30 seconds for a 3 Dioptre correction.

The epithelium is peeled back onto the cornea and sticks on by osmotic pressure and suction from the endothelium like a lasik flap.    

A silicone contact lens is then placed on the eye and removed 4 days later. These new lenses have a very high oxygen permeability of about 4 times that of a normal soft lens. The lens holds the epithelial flap in place and also reduces post op pain dramatically. The main rationale behind LASEK is to keep the epithelium alive so as to prevent the biochemical changes in the cornea which can lead to haze formation.

A recent nice article on LASEK in the magazine "Optometrist" by my colleague Sunil Shah is here in PDF format

Scanning electron microscopy of epithelium folded back after alcohol debridement. The lower part of the picture is the epithelium folded over like a pancake and the upper part is the extremely smooth "Bowman's membrane", part of the cornea, ready for lasering. (Taken from an eye bank eye)

(Click pictures to enlarge)

Electron microscope view of a human epithelium after 30 seconds of 17% alcohol. All the intracellular structures are intact, indicating probable viability. Recent work in Italy has shown that if the alcohol is mixed with Balanced Salt Solution (BSS), then 70% of the epithelial cells remain viable rather than 45% with pure water and alcohol. We have now switched to this mixture.

Speed of recovery with LASEK

Unaided vision right after the operation (Our charts use the continental spacing of 1.2,  1.0,  0.8,  0.63,  0.5 which corresponds to the British 6/5,  6/6,  6/7.5,  6/10 and  6/12. ......6/10 is driving standard and 6/6 is "20/20" vision)

(click all pictures to enlarge)

Unaided vision at day 4 post-op

Unaided vision at day 7 post-op

How safe is PRK / LASEK for higher prescriptions?

  This is a small group of myopes of between -6 and -10 treated by LASEK (CVA = corrected visual acuity). This graph is of lines lost or gained on the Snellen chart. (See Lasik Audit for explanation). This shows that LASEK is comparable in safety to LASIK for these levels of myopia, although it takes longer to get there.

Results: with LASEK are the same as LASIK. (It is the same lasering in each but on a different part of the cornea so one would expect them to be the same). Look at the LASIK results charts to see more details of this.

Cooling: There are a number of reports now about doing PRK at a low temperature - similar to a fridge. This seems to reduce haze risks even further and one Japanese group claims to be doing PRK up to -20 Dioptres with no problem!  We now routinely cool the cornea before and after treatment with refrigerated drops. This also seems to lessen any post-op pain.

Mitamycin-C: This is a cytotoxic drug that has been used in drop form on the eye in children with glaucoma for some time. It has also been used over the last 4 years by some groups to get rid of persisting "haze". This is done by initially removing the haze with the laser or mechanically.  Then, using a sponge, a very diluted form of the drug is placed  onto the cornea  for a couple of minutes. This seems to work well, and there have been no reported long term problems after 4 years. I have used this drug for 2 years without any problems and it seems to work well. I also use it prophylactically in very high primary LASEK's over -8 . However, this use of mitamycin-C is totally "off label" and really done at the patient's risk.