The History of Ophthalmology
Part 7: Leading up to LASIK
LASIK corrects vision by correcting an eye’s refractive error. First the refractive error must be diagnosed and quantified. Then a treatment is based on that information.
What Are Refractive Errors?
A refractive error in the eye is an incorrect way of bending (refracting) light. In a 20/20 eye, light that enters the eye through the outside clear part (the cornea) passes then through the lens and focuses clearly on the retina, the inside back surface.
Both the cornea and lens are clear, transparent structures and therefore they both refract light as it passes through them. The cornea refracts the incoming light about 60% and the lens refracts it about 40%. More on How the Eye Works.
When light is traveling from a distant object, it needs less refraction than light traveling from a nearby object.
- In a myopic eye, the light coming from distant objects is refracted too much, so that it focuses before it arrives at the retina, and then continues to the retina, resulting in blurry distance vision. Light from nearby objects is able to focus on the retina.
- In a hyperopic eye, the reverse happens. Light from distant objects is refracted about the right amount, giving clear distance vision. But light from close objects is not refracted enough, and cannot focus on the retina. If it could travel through the retina, it would focus behind it.
- In an astigmatic eye, the cornea refracts all light in two ways. If you think of the back of a spoon, and compare it to a ping pong ball, you will see that the spoon has two curvatures – the lengthwise curve is flatter than the sideways curve. An astigmatic eye has this shape and therefore focuses light in more than one place.
Refractive surgery corrects these errors by reshaping the cornea. The lens continues to refract light as it always has, but the corneal curvature is changed so that it will refract light differently according to what the person’s refractive error is.
- In a myopic eye, the cornea is made flatter, so it will refract light less
- In a hyperopic eye, the cornea is made steeper, to refract light more
- In an astigmatic eye, the cornea is made more round, to refract light in only one way
Photorefractive Keratectomy (PRK)
PRK was the first refractive surgery to use a laser and the first PRK patient was treated in Germany in 1988. Instead of creating a replaceable flap to temporarily expose the stroma for treatment, as LASIK does, PRK removes a thin layer of surface tissue completely. After treatment, those cells grow back in a couple of weeks. During that recovery time a bandage contact lens is worn for protection.
Although older than the earliest LASIK surgeries, PRK is still offered by most LASIK surgeons as an excellent alternative for people with corneas too thin for LASIK. It avoids the possibility of any flap-related complications. For that reason, the U.S. Federal Aviation Administration, the National Aeronautic and Space Administration (NASA), and the U.S. Army, Navy, Air Force, and Marines have all approved it for pilots. The FDA approved it in 1995.
Beginnings of Traditional LASIK
- The strands woven into the first LASIK surgeries come from:
Jose Barraquer’s microkeratome and his Keratomileusis procedure (see Part 5: The Twentieth Century
- Srinivasan’s APD procedure (see Part 5 also)
- The Excimer laser developed in 1968 at the University of California (see Part 6: What is a Laser?)
- PRK - In 1990, the first LASIK surgeries were performed by Lucio Buratto in Italy and Ioannis Pallikaris in Greece. They combined Keratomileusis and PRK techniques but with greater precision and fewer complications afterwards.
Using a modernized microkeratome, the eye surgeon cuts a thin flap over the targeted treatment area and folds it back. Using the excimer laser, he or she removes (ablates) tiny pieces of tissue from the corneal layer now exposed – the stroma.
- For a myopic eye, the cornea is flattened a little by removing tissue towards the center of the treatment area.
- For a hyperopic eye, the cornea is steepened a little by removing tissue from the periphery.
- For an astigmatic eye, the cornea is made more round instead of oval, so pieces are removed in a way appropriate for each individual’s astigmatism.
The FDA does not approve procedures. It approves devices and drugs for certain specified treatments; and in the case of vision correction, it has approved the excimer laser for refractive surgery within certain limits.
1.The 1995 FDA approval of Standard LASIK was a big breakthrough in U.S. vision correction. That first approval was for the excimer laser to treat mild to moderate myopia (nearsightedness) up to -6.00 diopters.
2. In 1997 the FDA approved it to treat astigmatism.
3. In 1998, VISX (now American Medical Optics [AMO]) obtained FDA approval for its excimer laser system to treat hyperopia (farsightedness).
Now all three of the lower order aberrations were being treated with lasers and giving increasing numbers of people freedom from glasses and contact lenses.
History of Ophthalmology Part 1: The Ancient World
History of Ophthalmology Part 2: The Middle Ages: Spectacles
History of Ophthalmology Part 3: The Nineteenth Century: Seeing the Eye
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 8:LASIK Into the Twenty-First Century