Woman getting eye exam

CLEI Center For Keratoconus

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.

Now joined by Dr. Steven Greenstein and Dr. John Gelles, the Center provides keratoconus patients with state-of-the-art keratoconus diagnostic and analysis technique, therapeutic care, subspecialty contact lenses of numerous customized designs, and the complete range of surgical procedures. 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, the CLEI Center for Keratoconus at the forefront of research and innovation in keratoconus treatment.

What is Keratoconus?

Introduction to Keratoconus

Keratoconus occurs in about one out of every 1,000 individuals. In fact, as we develop better screening tools, it is likely that many more are affected.

Keratoconus is caused by the weakening of the cornea, the clear lens that is the front of your eye (like the crystal on a watch). As a result, the cornea bulges out of its smooth, dome-like structure, and assumes a more conical and irregular configuration.

Because of this change in shape, the cornea loses its ability to form a clear image in the eye.  Furthermore, this irregularity of the corneal optics and visual perturbations progress over time.

Why is this? Optically, in the keratoconic 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 decrease in vision and visual symptoms such as light glare and halo as well as double or triple vision.

static image on TV
kamra diagram
example of glare
example of double vision

Like static on a TV, non-focused light in keratoconus causes “visual static” which causes glare and multiple vision.

The presentation and impact of keratoconus can vary widely from person to person. Usually, it is first detected in a patient’s teens or twenties.  In its earliest stages, keratoconus often masquerades as astigmatism or nearsightedness, two of the more common eye conditions.

Often, it is only after numerous unsuccessful attempts at vision correction with glasses or soft contact lenses that your doctor may look elsewhere for a diagnosis.

What Causes Keratoconus?

The actual cause of keratoconus is unclear. It may have a genetic, inheritable component. However, in many patients, there are no family members with the disease.

Similarly, most children of keratoconus patients do not have keratoconus, but they should be checked in early adolescence for signs of keratoconus because early treatment can prevent the progression of the condition over time.

Keratoconus is typified by corneal thinning and biomechanical instability. This may be caused by abnormalities in the normal collagen structure of the cornea.

collage lamellae
Collagen lamellae (“pancakes”) create corneal superstructure

Collagen is the main structural component of the cornea. Collagen is a molecule that typically is very strong. For example, it makes up most of the structure of the tendons and ligaments of your muscles and bones. The weakness of the corneal structure causes keratoconus and its progression over time.

The normal cornea is made of pancakes (or lamellae) of collagen tissue in a complex array.  In keratoconus, the collagen lamellar architecture may be abnormal.

A complex arrangement of these pancakes and the extracellular matrix of biologic sugars maintains optical shape and structural integrity in the normal cornea.  The interweaving of the collagen lamellae and linkages between molecules gives the cornea its strength.  Around the edge of the cornea, the collagen bands change to a circular belt, providing additional support to the round corneal architecture.

Finally, transverse-oriented lamellae insert into the front layers of the cornea (Bowman’s layer), acting as roots to further support corneal structure.  This complex micro-organization is altered in keratoconic corneas.  In keratoconus, the collagen fibrils are unevenly distributed, with rearrangement of their normal conformation.

The keratoconic cone, itself, is most affected with loss and distortion of collagen fibers.  In addition, keratoconus corneas show less interweaving of the collagen pancakes and a decrease in the collagen anchors supporting the corneal structural shape.

These changes may allow the collagen pancakes to split and slide on one another and exacerbate keratoconus progression. Because of this, it is important that you do not rub your eyes in order to avoid the actual mechanical shearing of the collagen pancakes.

What causes the changes that we see in the corneal structure in keratoconus? There may be a primary biochemical event that triggers these changes, and, in some cases, these, in turn, may have a genetic predisposition.

There are enzymatic changes associated with keratoconus.  In particular, there may be an increase in collagen and extracellular matrix breakdown caused by enzymes such as matrix metalloproteinases (MMP) and others.

In addition, enzymes such as lysyl oxidate (LOX), which help the formation of mature collagen by creating natural crosslinks, may be low in keratoconus.

Assessing Your Keratoconus

In order to fully assess your keratoconus, understand the likely future course of the disease, and make appropriate treatment recommendations, an extensive eye examination is performed along with several specialized tests to fully analyze your problem. These tests also give you a complete baseline for your ongoing care in the future.

There are a number of goals of the comprehensive keratoconus evaluation at the CLEI Center for Keratoconus.

First, we want to fully assess and define your keratoconus in order to monitor progression over time. Second, this testing will allow us to best recommend a course of treatment to optimize your visual function.

The CLEI Center for Keratoconus incorporates all of the latest diagnostic technologies to assess your keratoconus and determine the proper course of treatment. Some of these diagnostic tools include:

Computerized Corneal Topography Analysis:

Corneal topography instruments assess your cornea’s optical surface. These are corneal maps that can assess many indices of your individual corneal shape and structure. We use a number of instruments, each of which may give different clues to the corneal shape, including the Pentacam, Topolyzer, and EyeSys units.

Keratoconic cone
Keratoconic “cone” is seen as the red elevation on the topography map

Corneal topography is analogous to looking at a mountain range from a satellite.  A normal cornea is green (like a gentle slope).  Red is a higher point (like a mountain) and can indicate keratoconus.

Blue is a lower point (like a lake).  In some cases of keratoconus, your corneal topography map can be used to help program a laser for topography-guided PRK treatments.

Corneal Ocular Coherence Tomography (OCT):


Ocular Coherence Tomography is analogous to an MRI of your cornea.  It gives cross-sectional, magnified pictures of your cornea from which we can study all of the corneal layers. OCT allows us to map your corneal thickness in detail.

Wavefront Analysis:

Wavefront analysis assesses the eye’s optical system and aberration profile. Because of the optical irregularities of the keratoconic cornea, light is not completely focused.


This causes scattering of light rays and the formation of “visual static”, much like the static that you may find on a TV. Wavefront analysis defines the particular types of static that are present in the keratoconic cornea. It is analogous to using a computer to check for any static on your TV.

Corneal Biomechanics Measurements:

The Optical Response Analyser (ORA): is a new instrument that measures the elasticity and flexibility of the cornea and is the first true clinical measurement of corneal biomechanics in keratoconus.

This may allow for better diagnosis of early keratoconus, help to predict its possible progression, and allow for monitoring of changes in the keratoconic cornea.

Corneal Thickness:

Corneal thickness (ultrasonic and optical pachymetry) measurements detect the degree to which a keratoconus cornea is thinned. In keratoconus, the cornea is thinner and weaker than normal.

Changes over time can be monitored by periodic assessment of the corneal thickness measure both by ultrasound and by optical imaging on the Pentacam unit.

Living with Keratoconus

There are some general precautions that a patient who has keratoconus can take to help decrease the chance of disease progression.

Young woman rubbing eyes under glasses.

1) Don’t rub your eyes.

This is probably the most important suggestion.  Remember that keratoconus is a problem of corneal mechanics and strength. The cornea gets its strength from the linkages of the collagen pancakes to one another.

Eye rubbing may exacerbate the slipping of the collagen pancakes of the cornea and possibly cause further destabilization of the corneal structure. It can also irritate the eyes, causing inflammation that is not good for the keratoconic cornea.

man rubbing eyes due to allergies

2) Control eye allergies.

Ocular allergy can cause inflammation, and also encourage eye rubbing. Therefore, use medications and drops as prescribed by your doctor to minimize symptoms of eye allergy.

3) Optimize your contact lens fit.

The impact of contact lens wear on the progression of keratoconus is unclear. Contact lenses are the mainstay of keratoconus treatment in many cases. Making sure that the contact lens fit is the best possible, will avoid problems secondary to irritation, inflammation, or mechanical trauma to the cornea.

young woman wearing sunglasses

4) Wear sunglasses in bright sun.

Ultraviolet light may increase the formation of inflammatory molecules which can further damage the corneal structure So, wear UV protecting sunglasses when you are going to get a lot of sun exposure.

5) Eat a good diet

Diets high in antioxidants (found in green, leafy vegetables, and colored vegetables such as tomato and pepper)) may combat some of the inflammatory mediators that can exacerbate keratoconus progression. Antioxidant vitamin and omega 3 supplements may also be helpful.

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.

Cornea diagram
Incoming 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:

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 diagram

At 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 image

Topography-guided PRK (TG-PRK) is a laser procedure that may improve visual function in select keratoconus 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 our doctors and our patient.

PTK (Phototherapeutic Keratectomy)

laser diagram

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 (CK)

Conductive 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 diagram

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 Transplant Techniques

Eye closeup

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 keratoconus 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 image

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. The CLEI team has 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 keratoconus 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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