Popular in the 1970s to 1990s radial keratotomy, or RK for short, was the most popular refractive surgery technique. Today it has been replaced with techniques such as LASIK, PRK, and SMILE as they offer more predictable results with fewer complications and adverse effects over time.
While rarely performed today, radial keratotomy is still relevant as many individuals who have previously undergone this surgery are now symptomatic of adverse effects.
Anatomy of Refractive Surgery
Refractive surgery treatment zones are applied to the front most structure of the eye called the cornea.
The cornea is the first structure of the eye used to refract light on to the retina and create an image.
If light is refracted too much, it creates a focal point in front of the retina, creating near-sightedness (myopia). Corneas that are too steep can cause this.
If light is refracted too little, it creates a focal point behind the retina, creating far-sightedness (hyperopia). Corneas that are too flat can cause this.
Therefore, refractive surgeries such as RK, LASIK, PRK, and SMILE focus on surgically reshaping the cornea to create an optimally shaped cornea that refracts light directly onto the retina, thus eliminating refractive error and the need for prescription glasses.
The cornea has 5 layers. The front most surface is called the epithelium, then Bowman’s layer, stroma, Descemet’s membrane, and most posteriorly, the endothelium.
The stroma is the thickest layer. It is where treatment is applied in LASIK, PRK, and SMILE techniques.
Radial Keratotomy Surgery
While many refractive surgeries today are performed using lasers, in RK deep incisions are made using a diamond-bladed surgical knife.
Most commonly, 8 incisions were made 360 degrees around the cornea, however in some cases the numbers of incisions ranged from 4 to 32, depending on the patient’s prescription.
RK surgeries required deep penetrating treatment zones to be effective. Therefore, while recent techniques only affect the anterior layers of the cornea (epithelium, Bowman’s and some stroma) RK surgeries typically involved every layer besides the endothelium.
RK was usually used to treat nearsightedness and some astigmatism as the incisions were made to relax the cornea and flatten steep meridians.
The healing time, and thus prescription stabilization, following RK typically lasted anywhere from a few months to several years.
Complications of RK
There are many complications associated with RK, hence why it is no longer used today.
Immediate complications were not common. Most individuals had visual improvement following the surgery and were quite happy after the eye had healed completely.
Then, after many years, more and more patients began to have visual complaints.
Many individuals have complained of vision changing throughout the day—a process called diurnal fluctuation.
This occurs because the cornea’s integrity was altered during surgery, making it less rigid and more prone to fluctuate in shape throughout the day. As stated above, the shape of the cornea is one of the major parts of refractive error, thus when the cornea changes shape it can change prescription.
Fluctuations in corneal shape, and therefore refractive error, can occur as frequently as every few hours in post-RK patients.
This complication cannot be fixed easily. Since the amount of refractive error varies, the prescription changes as well. This results in the need for multiple pairs of glasses or contact lenses throughout the day with varying prescriptions.
In addition to diurnal fluctuations, many individuals also experienced high amounts of irregular astigmatism.
Astigmatism is a refractive condition that occurs when the cornea is not perfectly spherical but is instead oblongly shaped. When this occurs, multiple focal points are created within the retina creating complaints of increased glare, “ghost” or “shadowy” images, monocular double vision, and starbursts or halos around lights.
Both diurnal fluctuations and irregular astigmatic shifts have created further problems down the road when it comes time for cataract surgery.
In cataract surgery the natural lens of the eye is removed and replaced with an artificial one called an intraocular lens (IOL).
Doctors take an individual’s prescription into account when choosing an IOL to best correct their vision and potentially eliminate the need for distance glasses post-cataract surgery.
When the prescription of an individual is constantly changing, it makes it difficult to determine the true power needed in an IOL. Therefore, RK has been shown to alter the results of cataract surgery.
Unfortunately, at least for the time being, no treatments have been proven effective in treating these post-RK complications.
It is currently hypothesized that a treatment called corneal crosslinking (currently used to treat individuals with Keratoconus) could potentially strengthen the corneal integrity and therefore reduce at least diurnal fluctuations, however this treatment is still in the experimental phase.
Fortunately, refractive surgery methods have greatly improved over the years with the utilization of lasers. If you, or someone you know, is interested in refractive surgery, one of the other types (LASIK, SMILE, PRK, etc.) will be recommended.
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