Biomedical Engineering Health & Medicine Issue I Volume II

Corneal Rings: A Revolutionary Invention in the Field of Corrective Eye Surgery

About the Author: Corey Crosser

In Fall 2001, Corey was a junior majoring in Biomedical Engineering at USC and is a huge fan of snowboarding, sailing, and Pearl Jam. Corey also has corneal inserts.

Corneal rings are micro-thin inserts that were recently approved by the Food and Drug Administration (FDA), in April 1999, for use in the correction of myopia and small degrees of astigmatism. This product of biomedical engineering offers patients another choice when searching for an alternative to glasses or contact lenses. The major advantage of corneal rings is the reversibility of the procedure as compared with other forms of corrective surgery.

An Alternative to Laser Eye Surgery

Blasting something with a laser in order to fix it may sound like a haphazard way to go about solving a problem, yet millions of Americans have paid good money to have just that done to their eyes in order to correct their vision. While many of these patients will swear by the results, the recent engineering of a new form of corneal implants may replace laser eye surgery in the years to come. These implants are called corneal rings and easily rank among the top medical innovations of the past century. Corneal rings are the newest viable option for people suffering from myopia (nearsightedness) and astigmatism (oblong shape of the cornea which can cause skewed vision).

What are Corneal Rings?

In medical terms, corneal rings are two micro-thin inserts made of polymethylmethacryla​te, the same biocompatible material that has been used for contact lenses for over 50 years [1]. In simpler words, corneal rings are two crescent shaped pieces of plastic that are inserted into the outermost layer of the eye, called the cornea (see Fig. 1). The first viable corneal rings were Intacs, developed by the company Keravision, and approved by the FDA in April of 1999 [1]. This recent approval makes Intacs the newest approved surgery available for patients seeking better vision, and according to Keravision’s estimates, approximately 20 million Americans have vision that falls within the correctable range and are eligible for Intacs.

Edouard Spooner/Wikimedia Commons
Figure 1: Intacs after insertion.

How do Corneal Rings Work?

In a relatively simple surgical procedure, a cut is made at the top of the cornea, the outermost layer of the eye, and the two crescent shaped corneal rings are slid gently into place within the layers of the cornea, on either side of the pupil. The cut made above the eye is then sealed with a single stitch. The corneal rings reshape the cornea’s curve to allow light rays (images) to focus properly in the eye. Myopia, or nearsightedness, is caused when the cornea is too curved, and rings act by flattening the cornea from within. This surgery takes an average of only 15 minutes per eye, a very short time considering it is a permanent procedure.
In this case, permanent means that the corneal rings are expected to remain in place for the patient’s entire life. It does not mean that the surgery is irreversible.
In fact, one of the biggest advantages of corneal rings over other forms of corrective eye surgery, such as laser assisted in situ keratomileusis (LASIK), photorefractive keratotomy (PRK), or radial keratotomy, is that corneal rings can be removed or replaced if necessary. If the patient’s vision changes, he can have the rings removed and either have new ones inserted or let his or her vision return to how it was before the surgery. Although the actual surgical procedure, including preparation, takes less than one hour, the healing period afterwards is somewhat lengthy. The patient cannot drive an automobile or see at their full potential until a few weeks after the surgery. Even then, optimal vision is not attained until 2 or 3 months afterwards. The time required for a patient’s eyes to heal is a large factor in opting not to undergo the procedure, as many patients are unable to allot 2-3 weeks of their time in which they cannot work and need assistance in traveling.

Corneal Rings Results

Keravision, Inc. is the major manufacturer of corneal rings, which they call Intacs. After the procedure was successfully performed on 449 out of 454 patients that fell within the range on Intacs, 97% of the patients were able to see 20/40 or better, 74% at 20/20, and an impressive 54% could see at 20/16 or better. Twenty-twenty is considered normal or perfect vision, and 20/16 means that what someone with perfect vision can read at 16 feet, the patient can read at 20! No doubt since these clinical studies were recorded, the doctors trained to perform the corneal ring surgery have gotten more adept at the procedure. As an added note: corneal rings do not interfere with the part of the cornea directly in front of the pupil, therefore the field of vision is not in any way degraded by the procedure by the inserted ring.

Cost of Surgery

Surgeries in general are not cheap, and eye surgeries are no exception. Glasses are by far the cheapest means of vision correction, with contacts a close second. The jump from these traditional forms of eyewear to the new surgeries is a big one. LASIK and similar procedures can cost as much as $2500 and as low as $500 per eye (the cost is constantly dropping due to more facilities competing for customers). Corneal ring insertion, on the other hand, can cost as mush as $5000 per eye, about twice that of LASIK surgery (and that does not include all of the other costs associated with a surgery: medication, tax, etc.) Unfortunately these surgical procedures are not often covered by health insurance companies because of their high cost and because they are elective surgeries (not necessary for the patient’s health). As a result of the high costs, these surgeries are generally unavailable to low-income patients. Hopefully, as the volume of corneal ring patients grows and the surgery becomes more common, its price will drop within a more affordable range [2, 3].

Future of Corneal Rings

America can expect to see an exponential growth of eye care facilities becoming equipped to perform this cutting-edge procedure. The number of corneal ring patients will grow rapidly as information of this option for vision correction spreads. Currently Keravision, Inc. only offers their corneal implant Intacs in 3 available thicknesses: 0.25mm, 0.30mm, and 0.35mm. While these are very small and precise pieces of medical grade plastic, future improvements in corneal ring technology might allow for even more accurate inserts to be produced. This means that current Intacs wearers could replace their Intacs with new ones, gaining better vision along with the technology. Advancements in the future of corneal rings could possibly lead to a much shorter recovery time. The field of optometry is ever growing, especially in the area of corrective eye surgery. Corneal rings are a revolutionary step towards the implementation of non-invasive and reversible surgeries. We are born with only two eyes, and they must last us a lifetime. Let’s take good care of them.


    • [1] “Intacs Corneal Implants.” Addition Technology Inc. Internet:, vol. 1, November 2001.
    • [2] Lasik Internet: http://www.lasik-new​​i? Detail=19&Field=key_​field&Key=fda&Scroll​=1 &All=yes&Sort=order&​Sort_num=on, Nov. 1, 2001.
    • [3] “The Excimer Laser – Its History”. Grendahl Eye Associates. Internet: http://www.grendahl.​com/excimerlaser/its​history.html, Feb. 2, 2001.

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