The CLEI Center of Keratoconus was founded in 2002 by Dr. Peter Hersh. A graduate of Princeton University, Johns Hopkins Medical School, and Ophthalmology Residency and Fellowship in corneal surgery at Harvard Medical School, Dr. Hersh envisioned a subspecialty center devoted to all aspects of keratoconus care.

The Center provides keratoconus patients with state-of-the-art keratoconus diagnosis, therapeutic care, subspecialty contact lens care, and the complete range of surgical treatments. At CLEI, keratoconus patients candidates undergo a comprehensive and lengthy evaluation using all the newest state-of-the-art technologies.

Using this evaluation, your individual needs can be matched to the proper treatment – our goal to optimize results and achieve a good, long-term stable vision. In addition to clinical care, Dr. Hersh and the CLEI Center for Keratoconus are at the forefront of research and innovation in keratoconus treatment.

Keratoconus Background

Keratoconus is a non-inflammatory corneal dystrophy, found in approximately 1 in 500 people, in which the cornea (the clear lens that is the front of your eye, like the crystal on a watch) deforms due to thinning and protrusion.

The biomechanical strength of the cornea depends upon the lamellar (pancake-like) organization of the collagen fibers which comprise the corneal stroma, regulated by an interconnecting network of proteoglycans (biological sugars).

While the pathogenesis of keratoconus remains unclear, it appears that a primary event (which is likely biochemical and may be genetically linked) leads to the loss and/or slippage of collagen fibrils and changes to the extracellular matrix in the cornea.

The result of this is thinning and weakening of the cornea, causing it to become unstable. As a result, the cornea bulges out of its smooth, dome-like structure, and assumes a more conical and irregular configuration.  This distortion tends to worsen over time.

Keratoconus diagramIncoming Rays of Light are Scattered by the Distorted Cornea Causing “Visual Static”

Because of this distortion, the cornea loses its ability to form a clear image in the eye and the patient’s vision can decrease drastically. Why is this? In the keratoconus cornea, light is not completely focused because of the corneal distortion.

This causes scattering of light rays and the formation of “visual static”, much like the static that you may find on a TV. This distortion, and consequent visual static, can increase over time, with a progressive decrease in vision.

The presentation and impact of keratoconus can vary widely from person to person. In its earliest stages, keratoconus often masquerades as astigmatism or nearsightedness, two of the more common eye conditions.

The CLEI Center for Keratoconus has extensive experience in the complete range of the many available procedures and technologies to treat keratoconus. These include:

Corneal Collagen Crosslinking (CXL)

Corneal Collagen Cross Linking ExampleThe corneal collagen crosslinking procedure (CXL) is designed to decrease the progression of keratoconus.

Here at CLEI Center for Keratoconus, we have been performing crosslinking for over 10 years. Crosslinking is accomplished by instilling riboflavin drops onto the cornea and then exposing the cornea to ultraviolet A (UVA – 365nm) light.

In fact, Dr. Hersh served as a medical monitor and was the lead author of the two studies leading to the U.S. FDA approvals of corneal collagen crosslinking for keratoconus and corneal ectasia.

CXL aims to halt the keratoconus disease process by strengthening the cornea. The treatment results in mechanical stiffening of the cornea, with the clinical goal being a consequent decrease in the progression of the disease process.

Laboratory studies show that immediately after CXL, strength measurements increase in human corneas by over 300%. This occurs through a relatively complex photobiologic process. When activated with UVA light in the presence of oxygen, riboflavin is converted into excited singlet and triplet states, which then undergo a series of chemical reactions resulting in the formation of reactive species that interact with corneal proteins and lead to the formation of chemical bonds.

Several different pathways lead to the formation of crosslink bonds, driven by the relative availabilities of oxygen, riboflavin, and ultraviolet light. Under aerobic conditions, singlet oxygen and hydroxyl radicals are the reactive oxygen species (ROS) produced that react with the collagen to form these bonds.

Under anaerobic conditions, radical riboflavin may also lead to the production of crosslinking molecular bonds. Balancing the competing aspects of the reaction, by controlling the rate of oxygen consumption, allows for control of the distribution of crosslinking bonds formed in the cornea.

Although these biomechanical pathways may be complicated, CXL works simply by increasing corneal strength, and in our clinical trials appears to be effective in most patients to decrease the progression of keratoconus. In addition to stabilizing the cornea, there is, on average, improvement in topographic and visual acuity outcomes.

For example, in our study of crosslinking outcomes, the topography-derived maximum keratometry (K) value flattened by 1.7 diopters (D) and patients had an improvement in corrected distance visual acuity (CDVA) from 20/45 to 20/34 and in uncorrected distanced visual acuity (UDVA) from 20/137 to 20/117.

Moreover, there was a general improvement in several corneal topography indices, corneal and total eye higher-order aberrations, and subjective patient visual symptoms. Thus, corneal collagen crosslinking offers great promise in the treatment of keratoconus of KC.

It is important to remember that crosslinking is designed to decrease disease progression, not to improve your vision. There are a number of options that can help the keratoconus patient achieve better vision.  You can read about them on our other website pages.

Intracorneal Rings (Intacs)

Intacs are implantable intracorneal ring segments (ICRS). Intacs are made of polymethylmethacrylate (PMMA), an inert polymer that has been used in eye surgery for many years. Picture a hard contact lens, punch a hole through it to make it a doughnut, and then cut it in half… that’s basically what an Intacs looks like.

They were originally FDA approved in 1998 for the treatment of nearsightedness and later received approval for the treatment of keratoconus. The goal of Intacs is to reshape the cornea in keratoconus. This has 2 benefits: (1) it makes the corneal distortion more regular and optically smoother and (2) it helps to flatten the keratoconic cone.

The clinical benefit varies with your problem. Intacs can help to make contact lens wear easier with better results, improve vision with glasses by decreasing the “visual static” caused by the irregular keratoconus cornea, and improve general vision in some patients.

The size and position of the Intacs segments are chosen based on your individual corneal shape. One or two segments are placed depending on the individual measurements. In our procedure room, the first numbing drops are used for comfort.

The first step uses a laser (femtosecond) to create a tract within the cornea in which to place the Intacs. Segments are then placed in the proper position within the tunnel. Usually, sutures are not necessary and you will use drops for 1-2 weeks. Typically, patients may return to work one day after the procedure.

Intacs ExampleAt the CLEI Center for Keratoconus, we frequently combine Intacs with corneal collagen crosslinking. Intacs and crosslinking treat different aspects of keratoconus.

Crosslinking is used to stabilize the progression of keratoconus, whereas intracorneal ring segments are used to reshape the cornea. Therefore, the two treatments may have a synergistic effect, flattening the cornea with the Intacs segment, and performing CXL to stabilize the natural disease progression.

We have been studying the results of Intacs and crosslinking for several years and have found encouraging results.  Click below to hear Dr. Hersh discuss the Intacs procedure.

Topography-Guided PRK

Topography-Guided PRK ExampleTopography-guided PRK (TG-PRK) is a laser procedure that may improve visual function in select KC patients. PRK (photorefractive keratectomy) is similar to LASIK, which is used to correct nearsightedness and astigmatism.

In TG-PRK, the surface of the cornea is reshaped after the surface epithelial cells are removed. This differs from LASIK, in which the laser is applied beneath a corneal “flap”. In keratoconus, the goal of TG-PRK is to reduce corneal optical irregularities, thus decreasing “visual static” with the hope of improving glasses and contact lens vision. Some patients may also note a general improvement in visual function.

TG-PRK achieves this by incorporating your individual corneal topography map into the laser treatment. By utilizing your custom corneal topography data, the laser reshapes your corneal surface to improve your corneal optical architecture and visual performance.

In TG-PRK, we use the Wavelight laser which is the latest state-of-the-art excimer laser system and has recently been FDA-approved for topography-guided LASIK. This beam is moved rapidly across the corneal surface in a computer-controlled pattern of tiny overlapping spots guided by the individual patient’s corneal topography maps.

Though not FDA approved in keratoconus, we can use this technique on an “off-label” basis if decided on by Dr. Hersh and our patient.

PTK (Phototherapeutic Keratectomy)

Phototherapeutic Keratectomy (PTK)Phototherapeutic keratectomy or PTK also uses the excimer laser for treatment.

Whether PTK eye surgery is used alone or as an adjunctive strategy in traditional corneal surgical techniques, a number of disorders affecting the corneal surface may be successfully treated by taking advantage of the excimer laser’s ability to meticulously remove superficial corneal tissue.

These include a variety of corneal degenerations and dystrophies, corneal irregularities, and superficial scars. While some of these conditions, heretofore, could be treated by mechanical superficial keratectomy techniques, PTK may minimize tissue removal and surgical trauma.

The smoother stromal surface achieved by the excimer laser procedure may improve surface smoothness of the cornea, improve postoperative corneal clarity and decrease postoperative scarring, and facilitate subsequent epithelial adhesion.

Moreover, superficial corneal disorders which, in some cases, would otherwise require corneal transplant may be amenable to treatment with the PTK procedure.

Conductive Keratoplasty (CK)

Conductive Keratoplasty ExampleConductive Keratoplasty, better known as CK uses radiofrequency (RF) energy, instead of a laser, to reshape the cornea. Although not specifically FDA-approved for treatments of keratoconus, it too can be selected by the patient and surgeon as an “off-label” procedure if appropriate.

The CK procedure is performed using a small probe that releases radiofrequency (RF) energy. After the application of a topical anesthetic, CK applications are placed as guided by your corneal topography may help reduce astigmatism and center the keratoconic cone.

CK is frequently used after the Intacs procedure to further enhance results and allow for a better reshaping of the keratoconic cornea. In fact, we were the first to perform this combined procedure in the U.S.

The CK procedure itself is comfortable. There may be a dry eye or foreign body sensation for a day or two afterward. Once finished, you don’t have to wear a patch and can usually return to work the next day.

We will discuss this with you if we think you are a good candidate for Intacs/CK combined surgery.

Intraocular Lens (ICL)

The Visian ICL is an artificial lens that is implanted into your eye to correct high degrees of nearsightedness. It is a type of implant known as a phakic intraocular lens (IOL). Often, phakic intraocular lenses are suggested when LASIK or PRK are not appropriate options in the case of keratoconus.

Unlike LASIK or PRK in which the cornea is reshaped by a laser to improve vision, the ICL procedure does not involve the cornea; rather, it involves the placement of a permanent lens within the eye. In some cases, we will suggest either Intacs of TG-PRK before or after the ICL procedure.

Before the Visian ICL procedure, the proper power and size of your implant are selected based on your examination measurements.

ICL Example

About one to two weeks before ICL placement, a YAG laser iridotomy is performed in our laser suite. During this procedure, a YAG laser is used to make one or two small openings near the edge of your iris, which is the colored part of the eye.

These openings serve as outlets that will allow the fluid in your eye to circulate around the lens. The actual ICL procedure will take about 30-60 minutes. ICL implantations are done under topical anesthesia with eye drops to minimize discomfort. Often, a mild sedative is given to make you more relaxed.

Once you are comfortable, the procedure is started by creating two small openings at the edge of your cornea that will be used to position the lens. Next, a gel-like substance is placed inside your eye to protect the natural lens during ICL placement. After placement of the gel, a small opening will be made, through which the lens will be inserted.

The ICL is then inserted into your eye using a small cartridge that is placed through the incision. As the lens is inserted, it will gently unfold in your eye. Once it has fully unfolded, the four corners of the lens will be placed behind your iris.

This makes the lens invisible to both you and others. Because the incision made during surgery is so small, sutures are typically not needed following ICL surgery, but one or two small sutures may be placed.

Click on the video below to hear Dr. Hersh discuss phakic lens implants for keratoconus.

Corneal Inlays

Smaller and thinner than a contact lens, the KAMRA inlay is a mini-ring with an opening – or pinhole – in the center. The KAMRA inlay has been FDA-approved for the correction of reading vision, but may be helpful in some keratoconus patients.

This is because pinhole allows only focused light to enter your eye, decreasing “visual static” and, potentially reducing night vision glare and halos.

Corneal Inlay Example

Corneal Transplant Techniques

At the CLEI Center for Keratoconus, we offer all modalities of a cornea transplant, including full-thickness transplants, partial-thickness transplants (DALK), and laser-assisted modalities. Generally, for our KC patients, we prefer the newer femtosecond laser-assisted procedures (IEK, LACT) for many of our patients.

With subspecialty fellowship training in corneal surgery and years of transplantation experience, the CLEI team works to give you the best possible option for your surgery and visual outcome. The overall success rate of a corneal transplant is very high using modern eye banking and surgical techniques.

However, there are many factors that influence the outcome. For instance, keratoconus has one of the best prognoses for good vision with a greater than 90% chance of a clear graft. After surgery, the transplant must be monitored over time for signs of graft rejection. In most cases, vision returns gradually after surgery.

Patients must remember that the healing process may vary greatly from one individual to the next. Some patients may enjoy improved vision within a few weeks after surgery; for others, it may take up to a year. Glasses or contact lenses are still necessary after most corneal transplants. A variety of vision correction procedures after corneal transplantation may be useful.

Cornea Transplant Example

The procedure usually takes approximately one hour and is performed with either general or local anesthesia on an outpatient basis at a local ambulatory surgical center. If you are having a laser-assisted procedure, the laser portion of your surgery will take place at CLEI and then you will be transported to our outpatient surgery center.

After the surgery, you will go home with your eye covered by a patch and plastic shield to protect the eye. When you see us the day after surgery, we will start your medicated eyedrops. You may use drops for a year after surgery to prevent rejection of the transplant. Stitches may remain in the cornea for several years in some cases.

Research Studies

At the CLEI Center for Keratoconus, we have an active clinical research program. Dr. Hersh and the CLEI team have participated in numerous clinical studies over the years. Notably, Dr. Hersh was the lead author of the clinical study that led to the first FDA approval of laser vision correction in the United States in 1995.

He was also one of two investigators to present the conductive keratoplasty procedure to the FDA device panel, resulting in its 2002 approval. More recently, Dr. Hersh served as a medical monitor and was the lead author of the two studies leading to U.S. FDA approvals of corneal collagen crosslinking for keratoconus and corneal ectasia.

Currently, we are investigating a new surgical method to treat keratoconus called CTAK (Corneal Tissue Addition for Keratoconus). This a procedure in which a small disc of preserved corneal tissue obtained from the eye bank is placed within your own cornea. The goal is to increase the thickness of the cornea (which thins in keratoconus) and to decrease the irregularity of the keratoconic cornea.

By doing this, we hope to improve your glasses corrected vision and/or fit of a contact lens. It may also allow other procedures to treat keratoconus in the future. This study is open to patients who have keratoconus and are at least 18 years of age. Please contact for a full list of qualifications. An evaluation would be needed to see if this clinical trial may benefit you.

Specialty Keratoconus Contact Lenses

Lead by the director of our Contact Lens Division, Dr. John Gelles, the CLEI Center for Keratoconus offers the widest range of contact lens solutions for the keratoconus patient. The normal cornea supplies about 75% of the eye’s focusing power. In keratoconus, the cornea becomes thinner and loses its structural integrity.

As a result, it loses its uniform, domelike configuration and develops irregular astigmatism and other optical irregularities. Therefore, it is unable to produce a clear image inside the eye. Because the optical surface of the cornea is irregular in keratoconus, glasses cannot give crisp focused vision.

Contact lenses, in particular specially fit rigid gas permeable contacts (RGP) and a variety of specialty KC and therapeutic contact lenses, can cover these irregularities and better focus incoming light. Applying a rigid lens allows tears to fill the space between the contact lens and the cornea.

This layer of fluid optically neutralizes the irregularities of the cornea such that, for all practical purposes, the cornea itself ceases to have any optical effect. The front surface of the contact lens now effectively becomes a new corneal surface… but a surface that we can control, being perfectly smooth, clear, and regular, and also containing the patient’s prescription.

The contact lens produces a clear image in the eye, often with a dramatic visual improvement for the keratoconus patient. Adapting lenses of this type is challenging and rewarding for both doctor and patient.

These highly specialized lenses feature a complex series of curves to enable us to fit the lens such that patients may enjoy vast improvements in vision and be able to utilize the lenses throughout their active day.


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Thank you so much Doc! When I first came to you I was 20/50 now I'm 20/10. I'm ready to have a great year!

Randy Foye
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My experience at The Cornea and Laser Eye Institute has been amazing. All of the staff have been helpful and courteous...

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Dr. Hersh and his staff were excellent. I was comfortable from the time I walked in until the time I left after the procedure.

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