A patient from Camarillo in Ventura County recently asked me what "thin flap LASIK" was.

In PRK laser eye surgery, no flap is made.  In LASIK laser vision correction, the surface layer of the cornea is lifted as a "flap."  The excimer laser is then applied to the underlying cornea to deliver the new optical shape and then the flap is re-positioned.  

 It turns out that the thickness of the flap is a very important issue and one that a tremendous amount of technological attention has been paid to over the years.

The trend in modern LASIK eye surgery has been toward thinner and thinner flaps.  Ten or fifteen years ago, most flaps were approximately 160 - 180 microns thick (by comparison, a typical cornea is about 550 microns thick).  Flaps were thicker in that era partly because flap making technology was less advanced and was not sufficiently up to the task of reliably producing uniform, thin flaps.

Today, most researchers feel that flaps ideally should be 100 - 120 microns thick.   A thinner flap has several advantages.  First, it leaves more tissue under the flap (a greater "residual stromal bed" or RSB), meaning that the same excimer laser optical treatment will end up going less deep into the underlying tissue.  More tissue left undisturbed means a better safety maragin.  Also, recent studies have shown that thin flaps leave the cornea biomechanically less altered -- again because there is more cornea left to give structural support under the laser treatment.  Finally, in a wavefront era, thinner flaps can drape more perfectly over the highly intricate wavefront laser ablation and more perfectly maintain the optical shape the wavefront laser has sculpted into the cornea.  A thicker flap tends to "mute" some of the detail of the wavefront shape.

The only real downside to thinner flaps is that they can be technically a bit more challenging for the surgeon to handle.  However, with experience, this is a small issue and one that is significantly outweighed by the benefits of thin flap LASIK.

By the way, another name you'll hear for thin flap LASIK is "Sub-Bowman's Keratomileusis" or "SBK."  The outer layer of the cornea is Bowman's membrane, therefore the name SBK implies a flap just underneath Bowman's layer in the cornea.  The other characteristic of SBK flaps besides being thin is that SBK flaps are "planar," which means they are of uniform thickness throughout the flap.  Studies show that thin, planar SBK flaps can be equally accurately created with either the most modern mechanical microkeratomes or femtosecond laser flap making devices.  

In my opinion, SBK is the state of the art for LASIK flap architecture and one that I prefer for all my patients. 

"What happens if I move my eye during LASIK laser eye surgery?"

A patient from Santa Maria in Santa Barbara County asked me this question last week and I think it reflects a fear many patients have about undergoing LASIK -- a fear that they might somehow cause a problem if they don't hold perfectly still during surgery.

It turns out, reassuringly, the answer is that with today's technology, nothing will happen if you move your eye during LASIK!  The newest excimer laser systems have advanced eye tracking technology based on military missile tracking technology. With this eye tracking technology, the laser is able to keep up with the fastest and most minute movements your eye might make during surgery.   Because the laser is following the eye's movements, every laser pulse goes exactly where it is supposed to, even if you move your eye or have trouble looking straight ahead.  In fact, every patient moves their eye to some degree during laser eye surgery  -- either from involuntary eye movements or even from breathing and transmitted pulses of blood coursing throughout the body's circulatory system.  The latest tracking systems actually can track the fastest and most delicate eye movements in three dimensions!

Three dimensional eye tracking systems for LASIK are an important safety feature.  Before eye tracking systems were developed, it was possible to have the laser pattern applied incorrectly onto the eye based on involuntary eye movements. Now, patients can feel relaxed during LASIK laser vision correction knowing that the laser system easily can follow the eye through any movements the patient makes.