KERATOCONUS - Cornea Transplant

During a cornea transplant, an eye surgeon removes a portion of your cornea and replaces it with a new section of cornea from a donor.

The procedure is also called a corneal transplant or a keratoplasty. About 40,000 cornea transplants are performed in the U.S. every year.

You may need a cornea transplant if your cornea no longer lets light enter your eye properly because of scarring or disease.

Role of a Healthy Cornea

Your cornea is a clear tissue that covers the front of each eye. Light entering your eye first passes through the cornea, then your pupil (the dark spot at the center of the colored iris), and then your lens.

The cornea must remain clear for you to see properly. However, a number of problems can damage the cornea, affecting your vision. These include:

• Corneal scarring from trauma and infection.
• Keratoconus. A degenerative condition in which the cornea becomes thin and misshapen.
• Inherited corneal conditions (dystrophies) like Fuchs' dystrophy, Lattice dystrophy, and others.
  

Types of Cornea Transplants

The cornea contains five layers. Cornea transplants don't always transfer all the layers.

Types of cornea transplants include:

Penetrating (full thickness) cornea transplant. This involves transplanting all the layers of the cornea from the donor.

Lamellar cornea transplant. During this procedure, the surgeon only replaces some of the layers of the cornea with the transplant.

In a lamellar cornea transplant, selected layers are transplanted, which can include the deepest layer, called the endothelium (posterior lamellar cornea transplant). A commonly performed version of this procedure is the Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK).

Or it can include layers closer to the surface (anterior lamellar cornea transplant).

Lamellar transplants may be more appropriate than full penetrating transplants when the disease process is limited to only a portion of the cornea.

How Full Thickness Cornea Transplants Are Performed

The surgery can be done using local anesthesia. This uses medication to numb the eye and stop it from moving. The patient stays awake although sedated during the surgery.

Another option is general anesthesia. In this case, the patient is put to sleep for the procedure.

The surgeon uses a special cutting instrument called a trephine, which works like a cookie cutter. It removes a round section of damaged cornea from the front of your eye.

The same process is used to remove a similar-sized circle of cornea from the donor's eye. The surgeon places the new section of cornea onto your eye. Then he or she sews it into place using ultra-thin stitches with the help of a microscope.

Success Rates of Cornea Transplants

Experts know more about the long-term success rates of penetrating cornea transplants, which use all the layers of the cornea.

Success rates are also affected by the problem that needed to be fixed with the transplant. For example, research has found that the new cornea lasts for at least 10 years in:

• 89% of people with keratoconus
• 73% of people with Fuchs' dystrophy
• 60% to 70% of people with corneal scarring
  

Recovery From a Cornea Transplant

The risks of complications vary depending on how many layers of the cornea are transplanted. Your body is less likely to reject the transplant if only the outer layers are used, compared to using all the layers or the deepest layer. Rejection happens in about 20% of cases overall.

Other problems can include:

• Bleeding (rare)
• Scarring
• Cataract formation, retinal detachment, and damage to other parts of the eye
• Leakage of fluid from the transplant incision
• Infection (rare)
• Vision problems. Full thickness transplants can heal with large amounts of astigmatism, nearsightedness and farsightedness, requiring thick lenses on eyeglasses or contact lenses.

In addition, some ailments that damage people's original cornea can also harm the new cornea. For example, there is the possibility of recurrence of herpes simplex infection in the transplant.

The cornea tends to heal slowly. To help protect your eye in the days after the surgery, your doctor may ask you to wear a protective shield over it.

You will need to use eyedrops for several months after the transplant. The stitches may remain in your eye for months or years. Your eye doctor can remove them in a simple procedure during an office visit.

Your vision may improve slowly after the surgery. It's important to avoid any possible trauma to your eye, such as from sports. This can damage your new cornea. You should report new irritation or any decrease in vision to your corneal surgeon. These may be signs that your body is rejecting the donor cornea.

Rejection may even occur years after the surgery. If you notice any of these signs that last for more than six hours, call your eye doctor promptly. The doctor can give you medicine that can help prevent as well as treat rejection.

Source: http://www.webmd.com/

EYE HEALTH - Keratoconus Symptoms and Diagnosis

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The earliest signs of keratoconus are usually blurred vision and  frequent changes in eye glass prescription, or  vision that cannot be corrected with glasses. Symptoms of keratoconus generally begin in late teenage years or early twenties, but can start at any time.

Other symptoms include:

See more images at KCvision.org

• Increased light sensitivity
• Difficultly driving at night
• Halo’s and ghosting especially at night
• Eye strain
• Headaches and general eye pain
• Eye irritation, excessive eye rubbing

Keratoconus, especially in the early stages can be difficult to diagnose and all of the above symptoms could be associated with other eye problems. Simply recognizing symptoms does not by itself diagnose keratoconus.

Keratoconus requires a diagnosis from a competent eye doctor trained not only in recognizing the symptoms but also observing signs of keratoconus through direct measurement as well as inspection of the cornea at a microscopic level using a slit lamp.

Always consult your doctor to confirm a diagnosis of Keratoconus.

Diagnosis

Keratoconus can usually be diagnosed with a slit-lamp examination.  The classic signs of keratoconus that the doctor will see when examining your eyes include:

• Corneal thinning
• Fleischer’s ring (an iron colored ring surrounding the cone)
• Vogt’s striae (stress lines caused by corneal thinning)
• Apical scarring (scarring at the apex of the cone)

The doctor will also measure the curvature of the cornea. This is done by:

• Keratometry:  an instrument that shines a pattern of light onto the cornea. The shape of the reflection of the pattern tells the doctor how the eye is curved.
• Corneal topography: a computerized instrument that make three-dimensional “maps” of the cornea

A typical corneal topography map looks like this:

Corneal topography has facilitated the diagnosis of keratoconus, helping establish the diagnosis earlier, follow progression more accurately and differentiate keratoconus from other conditions.

Click to learn more about Corneal Topography:

Video courtesy of Dr. Michael Hodkin

EYE HEALTH - What Causes Keratoconus?

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The exact cause of keratoconus is unknown. There are many theories based on research and its association with other conditions.However, no one theory explains it all and it may be caused by a combination of things.

It is believed that genetics, the environment and the endocrine system all play a role in keratoconus.

Genetic:

• One scientific view is that keratoconus is developmental (i.e., genetic) in origin because in some cases there does appear to be a familial association. From the presently available information there is less than a one in ten chance that a blood relative of a keratoconic patient will have keratoconus. The majority of patients with keratoconus do not have other family members with the disease. Some studies show that keratoconus corneas lack important anchoring fibrils that structurally stabilize the anterior cornea.  This increased flexibility allows that cornea to “bulge forward” into a cone-shaped appearance.

Environmental:

• Eye Rubbing: Keratoconus corneas are more easily damaged by minor trauma such as eye rubbing. Poorly fit contact lenses (that rub against the irregularity of the KC cornea) have been suggested as a possible cause of keratoconus; this has not been proven and remains questionable.

• Allergies: Many who have keratoconus report vigorous eye rubbing and also have allergies (which cause eye itching and irritation, leading to eye rubbing), however the link to allergic disease also remains unclear. A higher percent of keratoconic patients have atopic disease than the general population. Disorders such as hay fever, eczema, asthma, and food allergies are all considered atopic diseases. Those with KC are advised to avoid eye rubbing as much as possible.

• Oxidative Stress: Some studies indicate an abnormal processing of the superoxide radicals in the keratoconus cornea and an involvement of oxidative stress in the pathogenesis of this disease. Keratoconus corneas lack the ability to self-repair routine damage easily repaired by normal corneas. Like any tissues in the body, the cornea creates harmful byproducts of cell metabolism called free radicals. Normal corneas, like any other body tissue, have a defense system in place to neutralize these free radicals so they don’t damage the collagen, the structural part of the cornea, weakening it and causing the cornea to thin and bulge. The keratoconus corneas do not possess the ability to eliminate the free radicals so they stay in the tissue and can cause structural damage.

Hormonal:

• Another hypothesis is that the endocrine system may be involved because keratoconus is generally first detected at puberty and progresses during pregnancy.  This theory is still controversial and has not been proven.

EYE HEALTH - How the Eye Works

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To understand Keratoconus, we must first understand how the eye enables us to see, and what role the cornea plays in this process.

Light rays enter the eye through the cornea, the clear front “window” of the eye. The cornea’s refractive power bends the light rays in such a way that they pass freely through the pupil, black the size-changing hole in the iris, the colored part of the eye.

The iris works like a shutter in a camera. It has the ability to enlarge and shrink, depending on how much light is entering the eye.

After passing through the iris, the light rays pass thru the eye’s natural crystalline lens. This clear, flexible structure works like the lens in a camera, shortening and lengthening its width in order to focus light rays properly.

Light rays pass through a dense, transparent gel-like substance, called the vitreous that fills the globe of the eyeball and helps the eye hold its spherical shape.

In a normal eye, the light rays come to a sharp focusing point on the retina. The retina’s functions much like the film in a camera. It is responsible for capturing all of the light rays, processing them into light impulses through millions of tiny nerve endings, then sending these light impulses through over a million nerve fibers to the optic nerve.

Because the keratoconus cornea is irregular and cone shaped, light rays enter the eye at different angles, and do not focus on one point the retina, but on many different points causing a blurred, distorted image.

In summary, the cornea is the clear, transparent front covering which admits light and begins the refractive process. It also keeps foreign particles from entering the eye.

The pupil is an adjustable opening that controls the intensity of light permitted to strike the lens. The lens focuses light through the vitreous humor, a clear gel-like substance that fills the back of the eye and supports the retina.

The retina receives the image that the cornea focuses on the eye’s internal lens and transforms this image into electrical impulses that are carried by the optic nerve to the brain. We can tolerate very large scars on our bodies with no concern except for our vanity. This is not so in the cornea. Even a minor scar or irregularity in the shape can impair vision. No matter how well the rest of the eye is functioning, if the cornea is scarred, clouded or distorted, vision will be affected.

In keratoconus, the irregular shape of the cornea does not allow it to do its job correctly, leading to distortion of the image it passed to the retina and transmitted to the brain.

THE CORNEA

The eye is enclosed by a tough white sac, the sclera. The cornea is the transparent window in this white sac which allows the objects you are looking at to be carried in the form of light waves into the interior of the eye.

The surface of the cornea is where light begins its journey into the eye. The cornea’s mission is to gather and focus visual images. Because it is out front, like the windshield of an automobile, it is subject to considerable abuse from the outside world.

The cornea is masterfully engineered so that only the most expensive manmade lenses can match its precision. The smoothness and shape of the cornea, as well as its transparency, is vitally important to the proper functioning of the eye. If either the surface smoothness or the clarity of the cornea suffers, vision will be disrupted.

CORNEAL LAYERS

A cross-section of the Cornea showing distinct layers

Although appearing to be one clear membrane, the cornea is composed of five distinct layers of tissue, each with its own function.

• Epithelium is the thin outermost layer of fast-growing and easily-regenerated cells.
• Bowman’s layer protects the corneal stroma, consisting of irregularly-arranged collagen fibers. It is 8 to 14 microns thick.
• Stroma, the transparent middle and thickest layer of the cornea, made up of regularly-arranged collagen fibers and keratocytes (specialized cells that secrete the collagen and proteoglycans needed to maintain the clarity and curvature of the cornea)
• Descemet’s membrane is a thin layer that serves as the modified basement membrane of the corneal endothelium.
• Endothelium is a single layer cells responsible for maintaining proper fluid balance between the aqueous and corneal stromal compartments keeping the cornea transparent.

EYE HEALTH - Corneal Transplants

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Corneal Transplants

Although only 15-20% of those with keratoconus ultimately require corneal transplant surgery, for those who do, it is a crucial and sometimes frightening decision. However, those who know what to expect before, during and after surgery are better prepared and feel more in control of their health care.In keratoconus, a corneal transplant is warranted when the cornea becomes dangerously thin or when sufficient visual acuity to meet the individual’s needs can no longer be achieved by contact lenses due to steepening of the cornea, scaring or lens intolerance. Lens intolerance occurs when the steepened, irregular cornea can no longer be fitted with a contact lens, or the patient cannot tolerate the lens.To receive our Corneal Transplant Booklet, please fill out our form here.

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About Corneal Transplant Surgery

Once the decision has been made, you will be less anxious and feel more in control if you know what to expect – what the “normal” routine is for this type of surgery. The more information you have, the more prepared you will be.

To request a copy of the NKCF booklet on corneal transplant surgery click here.

read more…

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Femtosecond Laser Improves Corneal Transplant Outcomes

The femtosecond laser is the most dramatic breakthrough seen in corneal transplant surgery in the past decade. The laser allows the surgeon to focus the laser energy at a particular depth and then rapidly cut the tissue at that depth without causing any additional injury to the surrounding tissue.

read more…

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Vision After A Corneal Transplant

Vision varies a great deal after a transplant and continues to change for many months. It may start out very poor and gradually improve or be very good immediately after surgery and then worsen. It could take up to a year to develop good, stable vision.

read more…

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Cataracts And KC

Have you noticed a slow decline in your vision? Do colors seem not as bright as they used to be? Has night driving, which was already difficult, become more difficult? Have changes in your contact lenses not helped? You could be developing a cataract. Cataract formation, which is ‘clouding’ of the lens, can cause declining vision and visual disturbances very similar to those from keratoconus.

read more…

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Transplant Glossary Of Terms

Medical terminology is a language of its own. It can be confusing and alarming if you don’t know what the words mean. This will help you sort out the language of transplant surgery.

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EYE HEALTH - Corneal Crosslinking

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Crosslinking

Corneal Collagen Crosslinking with Riboflavin (CXL) is a developing keratoconus treatment.  CXL works by increasing collagen crosslinks which are the natural “anchors” within the cornea. These anchors are responsible for preventing the cornea from bulging out and becoming steep and irregular.

Corneal Crosslinking System

During the corneal crosslinking treatment, custom-made riboflavin drops saturate the cornea, which is then activated by ultraviolet light. This process has been shown in laboratory and clinical studies to increase the amount of collagen cross-linking in the cornea and strengthen the cornea

Collagen crosslinking is not a cure for keratoconus. The aim of this treatment is to arrest progression of keratoconus, and thereby prevent further deterioration in vision and the need for corneal transplantation. Glasses or contact lenses will still be needed following the cross-linking treatment (although a change in the prescription may be required) but it is hoped that it could limit further deterioration of vision.

This procedure, developed at the Technische Universität Dresden, Germany has been shown to slow or arrest the progression of keratoconus in published European studies. CXL is currently in US Food and Drug Administration (FDA) clinical trials.

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Corneal Crosslinking Clinical Trial Sites in the US

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CXL Presentation

At the recent Vision Symposium sponsored by The Discovery Eye Foundation, Dr. Ronald N. Gaster presented this lecture on Corneal Crosslinking.

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First US Corneal Collagen Crosslinking Study

The U.S. Food and Drug Administration (FDA) recently permitted the start of three clinical trials in the United States to evaluate the safety and effectiveness of riboflavin/UVA light corneal collagen cross-linking (CXL) in patients with progressive keratoconus or corneal ectasia after previous refractive surgery.

Read more…

EYE HEALTH - Intacs for Keratoconus

Source : NKCF

Intacs For Keratoconus

Intacs is the trademark name for micro-thin prescription insertswhich were previously used as a form of refractive surgery in the treatment of low levels of myopia or nearsightedness, but has recently received FDA approval for keratoconus.

Intacs are thin plastic, semi-circular rings inserted into the mid layer of the cornea. When inserted in the keratoconus cornea they flatten the cornea, changing the shape and location of the cone. The placement of Intacs remodels and reinforces the cornea, eliminating some or all of the irregularities caused by keratoconus in order to provide improved vision. This can improve uncorrected vision, however, depending on the severity of the KC, glasses or contact lenses may still be needed for functional vision.

FDA Approval

Intacs were approved under a Humanitarian Device Exemption (HDE) by the FDA in July 2004, allowing Intacs to be used for treating keratoconus. As part of the HDE approval, Addition Technology, the manufacturer of Intacs, has implemented an extensive training program in which each surgeon will be required to participate.

What is a Humanitarian Device Exemption (HDE)?

The humanitarian device regulations were first established in October 1994. Humanitarian Use Devices (HUDs) are medical devices specially designated by the FDA for use in the treatment of fewer than 4000 patients per year with rare medical conditions. CPT Code is: Category III CPT code 0099T

Intacs received a Category III CPT code 0099T from the American Medical Association. Category III CPT codes are temporary codes to designate emerging technologies and are not assigned a value. It is up to the insurance company to determine the amount to be paid. A Category III code has 5 years to become mainstream, whereupon it may be promoted to a permanent Category I code.

The Procedure

This procedure involves placing the plastic inserts just beneath the surface of the eye in the periphery of the cornea. The procedure itself takes approximately 15 to 20 minutes usually in the doctor’s office. Topical anesthetic drops are used to numb the eye, and a clamp is used to hold the eye open throughout the procedure to prevent blinking. There are 3 basic steps to the procedure:

Step 1: A single, small incision is made in the surface of the cornea. Instead of using mechanical cutting, some surgeons may use a laser to make the incision.

Step 2: A centering guide is placed on the surface of the eye for several minutes to help stabilize the eye and ensure proper alignment of the Intacs insert. During this time, the corneal layers are gently separated in a narrow circular band on the outer edge where the Intacs will be placed.

Step 3: The Intacs inserts are placed. Once this insertion is completed, the small opening in the cornea is closed with a suture.

Follow-up visits will be required to monitor the healing process and to evaluate the visual benefits of the procedure. Even after a successful procedure, glasses or contacts may be required.

As with any surgical procedure, there are some risks, including infection. Some patients experience visual symptoms including difficulty with night vision, glare, halos, blurry and fluctuating vision.

For more information go to: www.intacsforkeratoconus.com

EYE HEALTH - Contact Lens for Keratoconus

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Contact Lenses for KC

There is no one design that is best for every type or stage of keratoconus. The “best lens” is the one that fits your eye, corrects your visionand is comfortable to wear.  Rely on an experienced KC lens fitter to select the best lens for your eye.The needs of each individual is carefully weighed to find the lens that offers the best combination of visual acuity, comfort and corneal health Contact lens fitting for keratoconus is part science and part art. A great deal of patience is required both on the part of the fitter and the patient.

Here is a brief outline of the types of lenses available for keratoconus:

Soft Lenses

The role of soft lenses for keratoconus vision correction has changed dramatically in the past year. The new soft lens designs combine the latest technologies in silicone hydrogel materials and complex mathematics to offer comfortable wear and excellent vision.

Older soft lenses draped over the irregular keratoconus cornea assuming the same irregular surface as the KC cornea without correcting the visual distortion caused by the irregularly shaped KC cornea.

RGP Contact Lenses

Rigid Gas Permeable (RGP or GP) contact lenses are primary option for correcting KC vision. The rigid lens masks the underlying irregular cornea and functions as the new refractive surface of the eye, with the tear film filling in the space between the back of the contact lens andthe front of the eye. “Rigid” defines the type of lens. “Gas Permeable” describes the lens material. There are many different RGP lens designs.

To see an instructional video about RGP lenses visit the GP Lens Institute website.

Piggy-backs

This is a two lens system; an RGP lens worn on top of a soft lens. The RGP lens provides crisp vision and the soft lens acts as a cushion providing comfort.

Hybrid lenses

This is a lens design combination that has an RGP center surrounded by a soft peripheral “skirt”. Hybrid contact can provide the crisp optics of a GP lens and wearing comfort of soft contact lenses. They are available in a wide variety of parameters to provide a fit that conforms well to the irregular shape of a keratoconic eye.

For more information about hybrid lenses

Scleral lenses

These are large diameter lenses that rest on the white part of the eye, called the sclera, and vaults over the cornea. The size can be an alarming prospect for some, but scleral lenses have many advantages. Because of their size, they do not fall out and dust or dirt particles cannot get under them during wear. They are surprisingly comfortable to wear because the edges of the lens rests above and below the eye lid margins so there is no lens awareness. The introduction of rigid gas permeable (RGP) materials has made this design more readily available.

For more information about scleral lenses visit the Scleral Lens Education Institute website

EYE HEALTH - Keratoconus

From Wikipedia, the free encyclopedia

Keratoconus (from Greek: kerato- horn, cornea; and konos cone) is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve.

Keratoconus can cause substantial distortion of vision, with multiple images, streaking andsensitivity to light all often reported by the patient. It is typically diagnosed in the patient'sadolescent years. If afflicting both eyes, the deterioration in vision can affect the patient's ability to drive a car or read normal print.

In most cases, corrective lenses fitted by a specialist are effective enough to allow the patient to continue to drive legally and likewise function normally. Further progression of the disease may require surgery, for which several options are available, including intrastromal corneal ring segments, cross-linking, mini asymmetric radial keratotomy and, in 25% of cases, corneal transplantation.

Estimates of the prevalence for keratoconus range from 1 in 500 to 1 in 2000 people, but difficulties with differential diagnosis cause uncertainty as to its prevalence. It seems to occur in populations throughout the world, although it is observed more frequently in certain ethnic groups, such as South Asians. Environmental and genetic factors are considered possible causes, but the exact cause is uncertain. It has been associated with detrimentalenzyme activity within the cornea, and is more common in patients with Down syndrome.

Signs and symptoms

People with early keratoconus typically notice a minor blurring of their vision and come to their clinician seeking corrective lenses for reading or driving. At early stages, the symptoms of keratoconus may be no different from those of any other refractive defect of the eye. As the disease progresses, vision deteriorates, sometimes rapidly. Visual acuity becomes impaired at all distances, and night vision is often poor.

  

Some individuals have vision in one eye that is markedly worse than that in the other. The disease is often bilateral, though asymmetrical. Some develop photophobia (sensitivity to bright light), eye strain from squinting in order to read, or itching in the eye, but there is normally little or no sensation of pain. It may, in certain cases cause luminous objects appear like cylindrical pipes with the same luminous intensity at all points.

The classic symptom of keratoconus is the perception of multiple "ghost" images, known asmonocular polyopia. This effect is most clearly seen with a high contrast field, such as a point of light on a dark background. Instead of seeing just one point, a person with keratoconus sees many images of the point, spread out in a chaotic pattern. This pattern does not typically change from day to day, but over time, it often takes on new forms. Patients also commonly notice streaking and flaring distortion around light sources. Some even notice the images moving relative to one another in time with their heart beat. The predominant optical aberration of the eye in keratoconus is the so-calledcoma. The visual distortion experienced by the patient comes from two sources, one being the irregular deformation of the surface of the cornea, and the other being scarring that occurs on its exposed highpoints. These factors act to form regions on the cornea that map an image to different locations on the retina. The effect can worsen in low light conditions, as the dark-adapted pupil dilates to expose more of the irregular surface of the cornea.

Diagnosis

Prior to any physical examination, the diagnosis of keratoconus frequently begins with anophthalmologist's or optometrist's assessment of the patient's medical history, particularly thechief complaint and other visual symptoms, the presence of any history of ocular disease or injury which might affect vision, and the presence of any family history of ocular disease. Aneye chart, such as a standard Snellen chart of progressively smaller letters, is then used to determine the patient's visual acuity.  

  

The eye examination may proceed to measurement of the localized curvature of the cornea with a manual keratometer, with detection of irregularastigmatism suggesting a possibility of keratoconus. Severe cases can exceed the instrument's measuring ability. A further indication can be provided by retinoscopy, in which a light beam is focused on the patient's retina and the reflection, or reflex, observed as the examiner tilts the light source back and forth. Keratoconus is amongst the ophthalmic conditions that exhibit a scissor reflex action of two bands moving toward and away from each other like the blades of a pair of scissors.

If keratoconus is suspected, the ophthalmologist or optometrist will search for other characteristic findings of the disease by means of slit lamp examination of the cornea. An advanced case is usually readily apparent to the examiner, and can provide for an unambiguous diagnosis prior to more specialized testing. Under close examination, a ring of yellow-brown to olive-green pigmentation known as aFleischer ring can be observed in around half of keratoconic eyes. The Fleischer ring, caused by deposition of the iron oxidehemosiderin within the corneal epithelium, is subtle and may not be readily detectable in all cases, but becomes more evident when viewed under a cobalt blue filter. Similarly, around 50% of subjects exhibit Vogt's striae, fine stress lines within the cornea caused by stretching and thinning. The striae temporarily disappear while slight pressure is applied to the eyeball. A highly pronounced cone can create a V-shaped indentation in the lower eyelid when the patient's gaze is directed downwards, known as Munson's sign. Otherclinical signs of keratoconus will normally have presented themselves long before Munson's sign becomes apparent, and so this finding, though a classic sign of the disease, tends not to be of primary diagnostic importance.

A handheld keratoscope, sometimes known as "Placido's disk", can provide a simple noninvasivevisualization of the surface of the cornea by projecting a series of concentric rings of light onto the cornea. A more definitive diagnosis can be obtained using corneal topography, in which an automated instrument projects the illuminated pattern onto the cornea and determines its topology from analysis of the digital image. The topographical map indicates any distortions or scarring in the cornea, with keratoconus revealed by a characteristic steepening of curvature which is usually below the centreline of the eye. The technique can record a snapshot of the degree and extent of the deformation as a benchmark for assessing its rate of progression. It is of particular value in detecting the disorder in its early stages when other signs have not yet presented.

Once keratoconus has been diagnosed, its degree may be classified by several metrics:

• The steepness of greatest curvature from 'mild' (< 45 D), 'advanced' (up to 52 D) or 'severe' (> 52D);
• The morphology of the cone: 'nipple' (small: 5 mm and near-central), 'oval' (larger, below-center and often sagging), or 'globus' (more than 75% of cornea affected);
• The corneal thickness from mild (> 506 μm) to advanced (< 446 μm).

Increasing use of corneal topography has led to a decline in use of these terms.

Pathophysiology

Despite considerable research, the etiology of keratoconus remains unclear. Several sources suggest that keratoconus likely arises from a number of different factors: genetic, environmental or cellular, any of which may form the trigger for the onset of the disease.Once initiated, the disease normally develops by progressive dissolution of Bowman's layer,which lies between the corneal epithelium and stroma. As the two come into contact, cellular and structural changes in the cornea adversely affect its integrity and lead to the bulging and scarring characteristic of the disorder. Within any individual keratoconic cornea, regions of degenerative thinning coexisting with regions undergoing wound healing may be found. Scarring appears to be an aspect of the corneal degradation; however, a recent, large, multicenter study suggests abrasion by contact lenses may increase the likelihood of this finding by a factor over two.

A number of studies have indicated keratoconic corneas show signs of increased activity byproteases, a class of enzymes that break some of the collagen cross-linkages in the stroma, with a simultaneous reduced expression of protease inhibitors. Other studies have suggested that reduced activity by the enzyme aldehyde dehydrogenase may be responsible for a build-up of free radicals and oxidising species in the cornea. Whatever thepathogenetical process, the damage caused by activity within the cornea likely results in a reduction in its thickness and biomechanical strength. While keratoconus is considered a noninflammatory disorder, one study shows wearing rigid contact lenses by patients leads to overexpression of proinflammatory cytokines, such as IL-6, TNF-alpha, ICAM-1, and VCAM-1 in the tear fluid.

A genetic predisposition to keratoconus has been observed, with the disease running in certain families, and incidences reported ofconcordance in identical twins. The frequency of occurrence in close family members is not clearly defined, though it is known to be considerably higher than that in the general population, and studies have obtained estimates ranging between 6% and 19%. Two studies involving isolated, largely homogenetic communities have contrarily mapped putative gene locations to chromosomes 16q and 20q. Most genetic studies agree on an autosomal dominant model of inheritance. A rare, autosomal dominant form of severe keratoconus with anterior polar cataract is caused by a mutation in the seed region of mir-184, a microRNA that is highly expressed in the cornea and anterior lens. Keratoconus is diagnosed more often in people with Down's syndrome, though the reasons for this link have not yet been determined.

Keratoconus has been associated with atopic diseases, which include asthma, allergies, and eczema, and it is not uncommon for several or all of these diseases to affect one person. Keratoconus is also associated with Down syndrome and Marfan syndrome. A number of studies suggest vigorous eye rubbing contributes to the progression of keratoconus, and patients should be discouraged from the practice. Iatrogenic keratoconus has also been observed following LASIK surgery, caused by removal of excessivestromal bed tissue.

Treatment

Contact lenses

Main article: Contact lens

Rigid, gas-permeable lens for keratoconus

In early stages of keratoconus, spectacles or soft contact lenses can suffice to correct for the mild astigmatism. As the condition progresses, these may no longer provide the patient with a satisfactory degree of visual acuity, and most clinical practitioners will move to manage the condition with rigid contact lenses, known as rigid, gas-permeable, (RGP) lenses. RGP lenses provide a good level of visual correction, but do not arrest progression of the condition.

In keratoconic patients, rigid contact lenses improve vision by means of tear fluid filling the gap between the irregular corneal surface and the smooth regular inner surface of the lens, thereby creating the effect of a smoother cornea. Many specialized types of contact lenses have been developed for keratoconus, and affected people may seek out both doctors specialized in conditions of the cornea, and contact lens fitters who have experience managing patients with keratoconus. The irregular cone presents a challenge and the fitter will endeavor to produce a lens with the optimal contact, stability and steepness. Some trial-and-error fitting may prove necessary.

Traditionally, contact lenses for keratoconus have been the 'hard' or RGP variety, although manufacturers have also produced specialized 'soft' or hydrophilic lenses and, most recently, silicone hydrogel lenses. A soft lens has a tendency to conform to the conical shape of the cornea, thus diminishing its effect. To counter this, hybrid lenses have been developed which are hard in the centre and encompassed by a soft skirt. However, soft or earlier generation hybrid lenses did not prove effective for every patient. Early generation lenses like SoftPerm have been discontinued. The fourth generation of hybrid lens technology has improved significantly, giving more patients an option that combines the comfort of a soft lens with the visual acuity of an RGP lens.The new generation of technology fixes the issues prevalent in earlier generations and allows contact lenses to be fitted for the majority of patients.

Some patients also find good vision correction and comfort with a "piggyback" lens combination, in which RGP lenses are worn over soft lenses, both providing a degree of vision correction. One form of piggyback lens makes use of a soft lens with a countersunk central area to accept the rigid lens. Fitting a piggyback lens combination requires experience on the part of the lens fitter, and tolerance on the part of the keratoconic patient.

Scleral lenses are sometimes prescribed for cases of advanced or very irregular keratoconus; these lenses cover a greater proportion of the surface of the eye and hence can offer improved stability. The larger size of the lenses may make them unappealing or uncomfortable to some; however, their easier handling can find favor with patients with reduced dexterity, such as the elderly.

Mini sclerals have been available for a few years are a hybrid between a conventional RGP lens and a full scleral and just vault over the cornea into the limbus region. Light in weight, high in oxygen permeability and easy maintenance makes this an option for cases where a patients condition has advanced beyond specialized soft lens. An example is SoClear.

Surgical options

Corneal transplant

Main article: Cornea transplant

Corneal transplant for keratoconus, approximately one week after surgery - multiple light reflections indicate folds in the cornea which later resolved.

Between 11% and 27% of cases of keratoconus will progress to a point where vision correction is no longer possible, thinning of the cornea becomes excessive, or scarring as a result of contact lens wear causes problems of its own, and a corneal transplantation or penetrating keratoplasty becomes required. Keratoconus is the most common grounds for conducting a penetrating keratoplasty, generally accounting for around a quarter of such procedures. The corneal transplant surgeon trephines a lenticule of corneal tissue and thengrafts the donor cornea to the existing eye tissue, usually using a combination of running and individual sutures. The cornea does not have a direct blood supply, so the donor tissue is not required to be blood type matched. Eye banks check the donor corneas for any disease or cellular irregularities.

Spanish-born eye surgeonRamon Castroviejo successfully performed keratoplasty as early as 1936.

The acute recovery period can take four to six weeks, and full postoperative vision stabilization often takes a year or more, but most transplants are very stable in the long term. The National Keratoconus Foundation reports that penetrating keratoplasty has the most successful outcome of all transplant procedures, and when performed for keratoconus in an otherwise healthy eye, its success rate can be 95% or greater. The sutures used usually dissolve over a period of three to five years, but individual sutures can be removed during the healing process if they are causing irritation to the patient.

In the USA, corneal transplants (also known as corneal grafts) for keratoconus are usually performed under sedation as outpatient surgery. In other countries, such as Australia and the UK, the operation is commonly performed with the patient undergoing a general anaesthetic. All cases require a careful follow-up with an eye doctor (ophthalmologist or optometrist) for a number of years. Frequently, vision is greatly improved after the surgery, but even if the actual visual acuity does not improve, because the cornea is a more normal shape after the healing is completed, patients can more easily be fitted with corrective lenses. Complications of corneal transplants are mostly related to vascularization of the corneal tissue and rejection of the donor cornea. Vision loss is very rare, though difficult-to-correct vision is possible. When rejection is severe, repeat transplants are often attempted, and are frequently successful. Keratoconus will not normally reoccur in the transplanted cornea; incidences of this have been observed, but are usually attributed to incomplete excision of the original cornea or inadequate screening of the donor tissue. The long-term outlook for corneal transplants performed for keratoconus is usually favorable once the initial healing period is completed and a few years have elapsed without problems.

Corneal ring segment inserts

Main article: Intrastromal corneal ring segments

A recent surgical alternative to corneal transplant is the insertion of intrastromal corneal ring segments. A small incision is made in the periphery of the cornea and two thin arcs of polymethyl methacrylate are slid between the layers of the stroma on either side of the pupilbefore the incision is closed. The segments push out against the curvature of the cornea, flattening the peak of the cone and returning it to a more natural shape. The procedure, carried out on an outpatient basis under local anaesthesia, offers the benefit of being reversible and even potentially exchangeable as it involves no removal of eye tissue.

The principal intrastromal ring available is known by the trade name Intacs. Internationally, Ferrara rings are also available. Intacs are a patented technology and are placed outside the optical zone, whereas the smaller prismatic Ferrara rings are placed just inside the 5 mm optical zone. Intacs are the only corneal implants to have gone through the FDA Phase I, II and III clinical trials and were first approved by the Food and Drug Administration (FDA) in the United States in 1999 for myopia; this was extended to the treatment of keratoconus in July 2004.

A pair of Intacs after insertion into the cornea

Clinical studies on the effectiveness of intrastromal rings on keratoconus are in their early stages, and results have so far been generally encouraging, though they have yet to enter into wide acceptance with the refractive surgery community. In common with penetrating keratoplasty, the requirement for some vision correction in the form of spectacles or hydrophilic contact lenses may remain subsequent to the operation. Potential complications of intrastromal rings include accidental penetration through to the anterior chamber when forming the channel, postoperative infection of the cornea, and migration or extrusion of the segments. The rings offer a good chance of vision improvement even in otherwise hard-to-manage eyes, but results are not guaranteed and in a few cases may worsen.

Early studies on intrastromal corneal rings involved use of two segments to cause global flattening of the cornea. A later study reported better results could be obtained for those cones located more to the periphery of the cornea by using a single Intacs segment. This leads to preferential flattening of the cone below, but also to steepening the over-flat upper part of the cornea.

Cross-linking

Removed corneal epithelium during CCR operation on an eye with post-LASIKcomplication, from Kymionis et al., 2009^[52]

Corneal collagen crosslinking with riboflavin, also known as CXL, CCR, CCL and KXL, involves a one-time application of riboflavin solution to the eye that is activated by illumination with UV-A light for approximately 30 minutes. The riboflavin causes new bonds to form across adjacent collagen strands in the stromal layer of the cornea, which recovers and preserves some of the cornea's mechanical strength. The corneal epithelial layer is generally removed to increase penetration of the riboflavin into the stroma.

Clinical trials began in Germany and Italy in 2002, and cross-linking has shown success in retarding or stopping progression of the disease. Results from an Australian study published in 2008 showed stabilization in all treated eyes, and a slight correction in visual acuity in most patients. The procedure, with epithelium removed, is approved for use throughout Europe, and commenced clinical trials in the USA in 2008. By 2010, over 300 patients were treated in the United States in those trials, which are composed of two randomized, controlled, multisite clinical trials for the treatment of progressive keratoconus and post LASIK ectasia.

In some cases, collagen cross-linking may also be combined with other treatments to improve corneal asymmetry or optical refraction. Successful treatment methods include corneal ring segment inserts (Intacs or Ferrara rings), Topography Guided Laser, or Keraflex. Corrective lenses are normally required after these treatments, but with smaller, more normalized prescriptions. Increased corneal symmetry allows for more comfortable contact lens wear, often of daily disposable lenses. These newer methods may have an important role in limiting deterioration of vision, increasing unaided and uncorrected vision, and reducing the case for corneal transplantation.

Radial keratotomy

Main article: Radial keratotomy

Radial keratotomy is a refractive surgery procedure developed by Russian ophtalmologist Svyatoslav Fyodorov in 1974, where the surgeon makes a spoke-like pattern of incisions into the cornea to modify its shape. This early surgical option for myopia has been largely superseded by LASIK and other similar procedures. LASIK is absolutely contraindicated in keratoconus and other corneal thinning conditions as removal of corneal stromal tissue will further damage an already thin and weak cornea.

For similar reasons, radial keratotomy has also generally not been used for keratoconic patients.

Mini asymmetric radial keratotomy

The mini asymmetric radial keratotomy is a surgical technique developed by Italian ophthalmologist Marco Abbondanza in 1994 and improved in 2005. It consists of a series of micro-incisions, always made with a diamond knife, designed to cause a controlled scarring of the cornea, which changes its thickness and shape. This procedure, if done properly, is able to cure astigmatism and the first and second stage of keratoconus, avoiding the need for a cornea transplant.

DALK transplants

One way of reducing the risk of rejection is to use a technique called deep anterior lamellar keratoplasty (DALK). In a DALK graft, only the outermost epithelium and the main bulk of the cornea, the stroma, are replaced; the patient's rearmost endothelium layer and theDescemet's membrane are left, giving some additional structural integrity to the postgraft cornea.^[70] Furthermore, it is possible to transplant freeze-dried donor tissue. The freeze-drying process ensures this tissue is dead, so there is no chance of rejection.

Some surgeons prefer to remove the donor epithelium; others leave it in place. Removing it can cause a slight improvement in overall vision, but a corresponding increase in visual recovery time.

Epikeratophakia

Rarely, a nonpenetrating keratoplasty known as an epikeratophakia (or epikeratoplasty) may be performed in cases of keratoconus. The corneal epithelium is removed and a lenticule of donor cornea is grafted on top of it. The procedure requires a greater level of skill on the part of the surgeon, and is less frequently performed than a penetrating keratoplasty, as the outcome is generally less favorable. However, it may be seen as an option in a number of cases, particularly for young patients.

Prognosis

A small rupture of Descemet's membrane(magnified view) ...

Patients with keratoconus typically present initially with mild astigmatism and myopia, commonly at the onset of puberty, and are diagnosed by the late teenage years or early 20s. The disease can, however, present or progress at any age; in rare cases, keratoconus can present in children or not until later adulthood. A diagnosis of the disease at an early age may indicate a greater risk of severity in later life. Patients' vision will seem to fluctuate over a period of months, driving them to change lens prescriptions frequently, but as the condition worsens, contact lenses are required in the majority of cases. The course of the disorder can be quite variable, with some patients remaining stable for years or indefinitely, while others progress rapidly or experience occasional exacerbations over a long and otherwise steady course. Most commonly, keratoconus progresses for a period of 10 to 20 years before the course of the disease generally ceases in the third and fourth decades of life.

... leads to corneal hydrops.

In advanced cases, bulging of the cornea can result in a localized rupture of Descemet's membrane, an inner layer of the cornea. Aqueous humor from the eye's anterior chamberseeps into the cornea before Descemet's membrane reseals. The patient experiences pain and a sudden severe clouding of vision, with the cornea taking on a translucent milky-white appearance known as a corneal hydrops. Although disconcerting to the patient, the effect is normally temporary and after a period of six to eight weeks, the cornea usually returns to its former transparency. The recovery can be aided nonsurgically by bandaging with an osmoticsaline solution. Although a hydrops usually causes increased scarring of the cornea, occasionally it will benefit a patient by creating a flatter cone, aiding the fitting of contact lenses. Occasionally, the cornea thins to the point where a partial rupture occurs at the level of Descemet's membrane, resulting in a small, bead-like swelling on the cornea that may become filled with fluid (cornea hydropsy). When this occurs, severe vision decrease may occur until the edema slowly resolves. Corneal transplantation is not usually indicated while the hydropsy persists.

Epidemiology

The National Eye Institute reports keratoconus is the most common corneal dystrophy in the United States, affecting about one in 2,000 Americans, but some reports place the figure as high as one in 500. The inconsistency may be due to variations in diagnostic criteria, with some cases of severe astigmatism interpreted as those of keratoconus, and vice versa. A long-term study found a mean incidence rate of 2.0 new cases per 100,000 population per year. Some studies have suggested a higher prevalence amongst females, or that people of South Asian ethnicity are 4.4 times as likely to suffer from keratoconus as Caucasians, and are also more likely to be affected with the condition earlier.

Keratoconus is normally bilateral (affecting both eyes) although the distortion is usually asymmetric and is rarely completely identical in both corneas. Unilateral cases tend to be uncommon, and may in fact be very rare if a very mild condition in the better eye is simply below the limit of clinical detection. It is common for keratoconus to be diagnosed first in one eye and not until later in the other. As the condition then progresses in both eyes, the vision in the earlier-diagnosed eye will often remain poorer than that in its fellow.

History

Practical observations on conical cornea, Nottingham's ground-breaking text on keratoconus, 1854

The German oculist Burchard Mauchart provided an early description in a 1748 doctoral dissertation of a case of keratoconus, which he called staphyloma diaphanum. However, it was not until 1854 that British physician John Nottingham clearly described keratoconus and distinguished it from other ectasias of the cornea. Nottingham reported the cases of "conical cornea" that had come to his attention, and described several classic features of the disease, including polyopia, weakness of the cornea, and difficulty matching corrective lenses to the patient's vision. In 1859, British surgeon William Bowman used an ophthalmoscope(recently invented by Hermann von Helmholtz) to diagnose keratoconus, and described how to angle the instrument's mirror so as to best see the conical shape of the cornea. Bowman also attempted to restore vision by pulling on the iris with a fine hook inserted through the cornea and stretching the pupil into a vertical slit, like that of a cat. He reported that he had had a measure of success with the technique, restoring vision to an 18-year old woman who had previously been unable to count fingers at a distance of 8 inches (20 cm). By 1869, when the pioneering Swiss ophthalmologist Johann Horner wrote a thesis entitled On the treatment of keratoconus, the disorder had acquired its current name. The treatment at that time, endorsed by the leading German ophthalmologist Albrecht von Graefe, was an attempt to physically reshape the cornea by chemical cauterization with a silver nitrate solution and application of a miosis-causing agent with a pressure dressing. In 1888, the treatment of keratoconus became one of the first practical applications of the then newly invented contact lens, when the French physician Eugène Kalt manufactured a glass scleral shell that improved vision by compressing the cornea into a more regular shape. Since the start of the 20th century, research on keratoconus has both improved understanding of the disease and greatly expanded the range of treatment options. The first successful corneal transplantation to treat keratoconus was done in 1936 by Ramon Castroviejo.

Related disorders

Several other noninflammatory eye disorders, generally rarer than keratoconus, also cause thinning of the cornea:

• Keratoglobus is a very rare condition that causes corneal thinning primarily at the margins, resulting in a spherical, slightly enlarged eye. It may be genetically related to keratoconus.
• Pellucid marginal degeneration causes thinning of a narrow (1–2 mm) band of the cornea, usually along the inferior corneal margin. It causes irregular astigmatism that, in the early stages of the disease can be corrected by spectacles. Differential diagnosis may be made by slit-lamp examination.
• Posterior keratoconus, a distinct disorder despite its similar name, is a rare abnormality, usually congenital, which causes a nonprogressive thinning of the inner surface of the cornea, while the curvature of the anterior surface remains normal. Usually only a single eye is affected.