The History of Ophthalmology
Part 8: LASIK Into the Twenty-First Century
Every era considers itself to be up-to-date, and of course, every era is indeed up-to-date for its time. In our 21st century, we are up-to-date also, and consider our modern laser vision correction to be highly sophisticated. No doubt future eras will chuckle and admire themselves for being properly up-to-date, and that’s the way history marches on.
1990s Diagnosis Technology
For LASIK treatments as they were FDA-approved in the 1990s, diagnosis was done using a phoropter. The eyes were examined in the same way as an eye doctor does it for prescribing glasses. A phoropter is that piece of equipment where you sit and look through an eye piece with one eye at a time. You can see the standard vision chart with rows of letters getting smaller towards the bottom.
The eye doctor changes from one lens to another asking you to read the lowest row of letters you can see clearly. In this way, he or she zeroes in on the lens that’s giving you the best vision, and bases your glasses or contact lenses on that. This is still done for glasses and contact lens prescriptions.
Early LASIK treatments were also based on that. The treatment laser reshaped your cornea to achieve that level of clear vision, instead of you having lenses made to achieve it.
There are more aspects to a person’s vision than just whether it is myopic, hyperopic, or astigmatic. Besides these three lower order aberrations, there are many higher order aberrations, and these are detected by wavefront technology.
Instead of looking into a phoropter, you look into a Wavefront-guided LASIK system eyepiece. By shining a light into your eye briefly, and analyzing the way it reflects back to the system’s sensor, the eye doctor can refine your vision correction treatment beyond what a glasses prescription offers. He can account for the higher order aberrations, which are more subtle.
Examples are night vision anomalies like halos around lights and starbursts; and ghosting – faint duplicate images of each object you focus on. These vision features have sometimes been side effects of traditional LASIK, based as it was on the less subtle phoropter diagnosis of your visual acuity. But Custom LASIK treats them along with the lower order aberrations, to give you both more clear vision and higher-quality clear vision.
If you are being prepared for a Wavefront LASIK treatment, you are in a sitting position when your eyes are diagnosed. When they’re treated, you’re lying down on the patient bed. As you move from one position to the other, the eyes rotate slightly and change shape, although you would not be aware of it.
This slightly moves the treatment area the laser will target. Iris Registration is hardware added to the Wavefront system to correct for those changes. It was first developed by VISX, Inc. for their CustomVue LASIK system. Now all four Wavefront systems include it under various names.
The eyes can make other changes too, in between diagnosis and treatment. The pupil can change size if the lighting in the room changes. You might slightly turn your head to one side. Iris Registration targets the laser beam in the center of the pupil. As you’re being treated, the system deals with two images:
The 3-D map developed during diagnosis
- Your eyes as they are while being treated
The system continuously re-matches these two images to each other, keeping the laser focused on the treatment area.
The LASIK Flap
The first step in all LASIK procedures is to somehow expose the stroma, the layer beneath the cornea’s top surface. Work is done on the stroma to reshape the eye permanently. In all LASIK procedures except IntraLase (see below), the stroma is exposed by folding a thin flap of surface tissue out of the way. After treatment it is replaced and heals up by itself.
Most complications of LASIK occur because of that corneal flap. Perhaps it was created poorly for that person’s particular eyes. Perhaps it forms ripples as it heals and must be repositioned. Sometimes an infection develops beneath it. By choosing a highly-qualified and experienced eye surgeon, you can minimize your chances of having any such complications.
Photorefractive Keratectomy (PRK)
PRK is an alternative refractive surgery to LASIK, and is done without any flap. The reshaping is still done on the stroma, but instead of making a replaceable flap, the eye surgeon gently removes surface cells altogether. This exposes the stroma and after treatment is done, for lack of any flap to replace, a bandage contact lens is placed over the eye while it heals.
This makes for a longer recovery period while the corneal cells regrow. However, it gives the same excellent vision improvement, and avoids any of the potential flap complications.
Other Types of LASIK
Not everybody with good eye health qualifies for a LASIK treatment because of either (a) the thickness of their corneas or (b) the steepness of their corneal curvature.
- Corneal thickness – Our eyes are filled with fluid. The cornea needs to be thick enough to hold its shape against the pressure of that fluid. After a flap is created, and some corneal tissue removed during treatment, there still needs to be enough thickness left. If there isn’t, the cornea will bulge forward, a condition called keratoconus. A normal cornea is between 500 and 600 micrometers thick. A LASIK microkeratome creates a flap between 100 and 200 micrometers thick.
- Corneal steepness – If the cornea is too steep (too myopic), the microkeratome which creates the flap may not be able to do it safely, without cutting it too deeply.
IntraLase creates the flap using a second laser. This is a femtosecond (very fast-pulsed) laser and can be set to penetrate to a very shallow depth. Each pulse creates a tiny bubble where bonds are broken between surface molecules. It creates these bubbles throughout the treatment area so that your eye surgeon is able to gently lift a thin layer of tissue up and fold it back on a hinge. Treatment is then done as in other LASIK procedures, and the flap replaced.
For people with corneas that are either too thin or too flat for LASIK, LASEK is another viable choice. LASEK creates a free flap, not one with a hinge. Rather than cutting it through to the stroma, LASEK confines it to only the epithelial tissue on the surface. Instead of the microkeratome blade, it uses an implement called a trephine which works like a cookie cutter.
Before lifting the tissue, your eye surgeon will soak it in an alcohol solution for about 30 seconds to make it hold together more strongly. Then it is lifted off and set aside. After treatment the epithelial tissue is replaced and a bandage contact lens or eye shield used for protection during the next few days.
Again, the flap is cut extra thin, and this procedure uses different instruments: an oscillating blade and then a plastic blade called an epithelial separator to lift the flap. For a few days after Epi-LASIK you would wear bandage contact lenses to help the thin flap heal.
Conductive Keratoplasty (CK)
After Svyatoslav Fyodorov worked to treat hyperopia using his hot needle technique, lasers became available. Other ophthalmologists obtained improved results, both for hyperopia and presbyopia, using lasers. Even better results are now obtained using Conductive Keratoplasty, which uses radio waves instead of a laser.
CK uses the same principle as the hot needle and lasers – that is, using heat to shrink corneal tissue around the edges. It is less invasive, as no instrument is inserted in the eye and no tissue is cut or removed. CK received FDA approval in 2002 for mild hyperopia, and in 2004 for presbyopia.
To treat presbyopia, CK uses monovision. One eye is treated for near vision and the other eye is left untouched for far vision. The brain adapts to this change within a couple of weeks.
As more refractive surgery is done by more eye surgeons worldwide, more techniques will no doubt be devised. The candidate pool will keep expanding as there are more ways of doing vision correction safely for more people.
If you would like to find out if you’d be a good candidate for a vision correction surgery, please contact a qualified and experienced LASIK surgeon in your area. You can use the links at the bottom of this page. If you are in or near Dayton, Ohio, you could could get excellent and highly skilled service from Dr. Stahl and Dr. Knowles at Stahl Vision Laser Eye Surgery Center.
History of Ophthalmology Part 1: The Ancient World
History of Ophthalmology Part 2: The Middle Ages: Spectacles
History of Ophthalmology Part 3: Anesthesia and Infection
History of Ophthalmology Part 4: The Nineteenth Century: Seeing the Eye
History of Ophthalmology Part 5: The Twentieth Century: Swift Progress
History of Ophthalmology Part 6: What is a Laser?
History of Ophthalmology Part 7: Leading up to LASIK