The process that we know as “vision” involves multiple, complex functions and numerous anatomical structures along the visual pathway. A disruption to any of these functions – from the movement of the eye muscles to the focusing of light into the eyeball to the transmission of the visual signal through the brain to interpretation of this signal – can result in various problems, including headaches, double vision, failure to process the visual signals meaningfully, loss of areas of the visual field, and of course, blurry vision.

For the majority of humans, blurry vision arises from problems at a specific step in the visual pathway – the refraction and focusing of light through the eyeball. This leads to what we call “refractive error.”

 
Refractive Error: A Quick Recap
Refractive error encompasses myopia (short-sightedness), hyperopia (long-sightedness), presbyopia (the progressive age-related decline of near vision) and astigmatism (uneven curvature of either the cornea or the lens of the eye). The result of this is that light entering the eye is not focused to a clear point on the retina at the back, causing a distorted or blurry image in your vision. Most cases of refractive error are easily corrected using glasses or contact lenses, which bend the light to focus properly – but wouldn’t it be great to achieve clear vision without worrying about breaking your glasses or getting an eye infection from your contact lenses or spending tens of thousands of dollars over your lifetime on updating your script and ensuring that you don’t look like Harry Potter as spectacle frame fashion evolves?

 
Enter Early Refractive Surgery
Fortunately, many intelligent people have walked this earth before us and developed precise surgical techniques to correct refractive error, providing clear vision without the need for optical aids. Also fortunately, we have come a long way from the mid-1800s where the use of a special invention was claimed to “restore eyesight and render spectacles useless” by flattening the cornea with a spring-mounted mallet.

From as early as the 19th century we can see the basic principles of most refractive surgery procedures are based on reshaping the cornea, the transparent dome at the front of the eye, to change the angle at which light rays pass through the eye (crossing your fingers that your mallet-flattened cornea now somehow directs light perfectly onto your retina).

The second half of the 1800s saw more sensible physicians attempting surgical correction of refractive error. Norwegian doctor Hjalmar Schiotz was the first to use surgical incisions in a patient’s cornea to change its curvature, successfully reducing 19.50 dioptres of astigmatism to 7.

In the 1940s, a Japanese ophthalmologist by the name of Tsutomu Sato introduced an early technique now known as radial keratotomy, based on the work of Schiotz. In the following three to four decades, this technique was further refined with improved understanding of how the cornea reacts to incisions of varying number, depth, and location, as well as advances to surgical instruments. A significant contributor to the development of radial keratotomy was Svyatoslov Fyodorov of the former Soviet Union though he found little support from his colleagues at the time.  In 1978, Leo Bores introduced radial keratotomy to the USA.

 
Keratoplasty, Keratomileusis, and Keratophakia
Before we get carried away with talking about lasers, the contribution of Spanish ophthalmologist Jose Ignacio Barraquer is worth a mention, as his research with corneal reshaping lay the groundwork for modern day procedures such as LASIK.

In the mid-1900s, Barraquer developed a technique to reshape the cornea by sculpting it with a blade. Though it may sound a bit like butchery, advances from the use of a freehand surgical blade to the invention of a more precise bladed tool called a microkeratome found that reshaping of the cornea by removing select sections could correct significant degrees of myopia and hyperopia. Keratomileusis required removal of a disc of corneal tissue, which was then frozen solid and sculpted before being reinserted. Keratophakia involved a donor cornea inserted into the recipient’s cornea to adjust its shape; this was the precursor to another branch of refractive surgery with the use of corneal implants made from inert materials to either steepen or flatten the central cornea and correct refractive error.

 
Enter the Laser
The excimer laser, using a combination of inert and reactive gases, was first described by Nikolai Basov in Moscow in 1970 though three IBM researchers from the USA, Samuel Blum, Rangaswamy Srinivasan, and James Wynne, are often credited with its invention. Regardless of this discrepancy, engineer and ophthalmologist, Stephen Trokel, is known as the first to develop the use of the excimer laser for vision correction once it was determined that the argon-fluoride laser was capable of precise tissue removal without collateral damage of surrounding structures.

The rest is history. We first saw the introduction of PRK (photorefractive keratectomy) by Trokel in 1987, using the excimer laser to ablate and remove specific areas of the inner corneal layers (the stroma) after removing the superficial epithelial layer. PRK is still a valuable technique used today, particularly for patients wishing to avoid the potential complications of the corneal flap required in the LASIK procedure.

LASIK was first performed in the USA in 1991 and is now considered the most commonly performed laser refractive procedure around the world due to its reliability, short recovery time, and wide range of treatable prescriptions. A flap of corneal tissue is created either using the good ol’ microkeratome or a specialized femtosecond laser, uncovering the corneal stroma for the excimer laser to do its work and reshape the tissue.

LASEK, laser epithelial keratomileusis, a variation of PRK, involves loosening the corneal epithelium from the underlying layers to allow it to be pushed aside for the excimer laser to gain access to the stroma. Unlike traditional PRK, this epithelial layer can then be repositioned, aiding the healing process.

The application of the femtosecond laser for vision correction in the early 21st century not only gave a more precise alternative to the corneal flap creation in LASIK surgery but also paved the way for a technique known as SMILE (small incision lenticule extraction). A sculpted disc of corneal stromal tissue is formed using the femtosecond laser and then removed through a keyhole incision, leaving the epithelium and outer corneal structures more or less intact. This eliminates the need for the excimer laser as well as improves recovery time and reduces risk of complications. SMILE is gaining popularity though LASIK and PRK still remain common and well-accepted procedures.

From a spring-loaded mallet to keyhole surgery, refractive eye surgery has come a long way. Luckily for those of suboptimal vision, intelligent people continue to walk our earth, meaning we can look forward to new and improved techniques of surgical vision correction in the years to come.

References
The history of refractive surgery. https://www.healio.com/optometry/refractive-surgery/news/print/primary-care-optometry-news/%7B4d4562f8-d10f-4100-b594-36db7ac9a5c7%7D/the-history-of-refractive-surgery
Corneal refractive surgery: past to present. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1444-0938.2012.00761.x
History of refractive surgery. http://www.eyedoctornetwork.org/history-of-refractive-surgery.htm
Small incision lenticule extraction (SMILE) history, fundamentals of a new refractive surgery technique and clinical outcomes. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4604118/