Keratoconus

Some conditions affect the shape and thickness of the cornea—the clear, dome-shaped front surface of the eye. These are called corneal ectatic disorders. Ectasia is a medical word for abnormal thinning and outward bulging of a structure. Conditions in this group include keratoconus, pellucid marginal degeneration, keratoglobus, and post-laser-assisted in situ keratomileusis (LASIK) ectasia. What they share is a gradual weakening of the corneal tissue that causes the eye’s front surface to lose its normal round shape. This distorts the way light enters the eye and makes clear vision increasingly difficult.

Keratoconus is the most common of these conditions. The word comes from the Greek words for cornea and cone. In keratoconus, the cornea gradually thins and begins to bulge outward into a cone-like shape instead of staying round and smooth. Because the cornea accounts for a large portion of the eye’s ability to focus light, even small changes in its shape cause significant blurring, distortion, and sensitivity to glare. Keratoconus typically affects both eyes, though one eye is usually more severely affected than the other. The condition generally begins in the teenage years and tends to progress through a person’s twenties and thirties before stabilizing.

Keratoconus was once classified as a rare disease, affecting roughly 1 in 2,000 people. More recent research suggests it is considerably more common than that, with global estimates ranging from 1 in 375 to 1 in 2,000, and a large study across 15 countries finding an average rate of about 1.4 per 1,000 people. It is a leading reason for corneal transplant surgery in many countries, though advances in a treatment called corneal cross-linking have significantly reduced how often transplants are needed. Keratoconus is progressive, but it is also very treatable—especially when caught early.

The exact cause of keratoconus is not fully understood. Researchers consider it a multifactorial disorder—meaning it develops from a combination of genetic vulnerability and environmental triggers rather than a single cause. One widely accepted explanation is sometimes called the two-hit hypothesis: a person inherits a genetic predisposition that weakens corneal collagen, and then an environmental factor—most often chronic eye rubbing—acts as the second trigger that sets the progression in motion.

At the tissue level, keratoconus develops because the collagen fibers that give the cornea its strength and shape gradually break down. An enzyme called lysyl oxidase (LOX) plays a critical role in keeping collagen fibers linked and strong. In keratoconic corneas, LOX activity is measurably lower than in healthy corneas, and this deficiency worsens as the disease progresses. Additional mechanisms include oxidative stress (damage from unstable molecules that overwhelm the cornea’s natural defenses), changes in proteins that regulate how corneal cells break down and rebuild tissue, and the death of specialized corneal cells called keratocytes in the central front layer of the cornea. Together, these changes cause the stroma—the thick middle layer of the cornea—to thin and lose its structural integrity.

Genetic mutations account for approximately 8% of cases, with the remaining 92% attributed to environmental and other nongenetic factors. Several genes have been implicated, including VSX1, TGFBI, LOX, and COL5A1, but no single causative gene has been identified. The condition likely involves multiple genes interacting in complex ways, which explains why its inheritance pattern varies considerably from family to family. Key contributing factors include:

• Chronic eye rubbing: the most important modifiable risk factor. Repeated mechanical pressure from rubbing is believed to damage corneal collagen directly and accelerate thinning.
• Genetic predisposition: A family history of keratoconus increases individual risk. Approximately 8% of patients have an identified genetic mutation, and around 13 to 14% report a positive family history.
• Atopy (allergic conditions): Allergies, eczema, and hay fever are strongly associated with keratoconus. The link is thought to be partly direct (inflammatory mediators) and partly behavioral (itchy eyes lead to rubbing).
• Down syndrome: Keratoconus is found at significantly higher rates in individuals with Down syndrome, with prevalence estimates varying widely across studies.
• Connective tissue disorders: Conditions that affect the body’s structural proteins, such as Ehlers-Danlos syndrome and Marfan syndrome, are associated with a higher rate of keratoconus.
• Oxidative stress: An imbalance between damaging free radicals and the cornea’s ability to neutralize them contributes to collagen breakdown in susceptible individuals.

Keratoconus can develop in any person, but the following factors are associated with a higher likelihood of developing the condition or experiencing faster progression. Identifying risk factors early allows for closer monitoring and, when needed, earlier treatment to protect vision.

• Age: The condition typically begins during puberty and progresses most rapidly through the twenties and thirties. It generally stabilizes by the third or fourth decade of life.
• Family history: Having a parent or sibling with keratoconus increases the likelihood of developing it. About one in seven patients reports a family member with the diagnosis.
• Ethnicity: Keratoconus is significantly more common in people of Asian and Middle Eastern heritage. Rates are much higher in South Asian and Middle Eastern populations than in white populations.
• Atopic conditions: Allergic eye disease, eczema, and asthma increase risk, both through direct inflammatory effects on the cornea and through associated eye rubbing.
• Chronic eye rubbing: Habitual eye rubbing—particularly hard, knuckle-based rubbing—is one of the strongest modifiable risk factors for both developing keratoconus and for progression in those already diagnosed.
• Down syndrome: People with Down syndrome have a substantially higher prevalence of keratoconus than the general population.
• Connective tissue disorders: Ehlers-Danlos syndrome, Marfan syndrome, and Leber congenital amaurosis are each associated with increased keratoconus risk.
• Prior refractive surgery: LASIK surgery performed on a cornea with undetected early keratoconus can accelerate ectasia. Thorough preoperative screening is essential to identify at-risk corneas before any refractive procedure.

Keratoconus caused by genetic susceptibility cannot be prevented. However, identifying the condition early—before significant corneal shape change has occurred—is critical because treatment options are most effective in the earlier stages. Anyone with a family history of keratoconus, chronic eye allergies, or a connective tissue disorder should discuss proactive screening with their eye doctor.

The most important screening tool is corneal topography—a computerized map of the front surface of the cornea that can detect abnormal patterns of curvature before the patient notices any change in vision. An advanced version called corneal tomography (using a device such as the OCULUS Pentacam®) also maps the back surface of the cornea and measures thickness at every point, making it possible to catch very early or subclinical cases that would be invisible on standard topography alone. These tests are noninvasive, painless, and take only a few minutes. They are strongly recommended before LASIK or any other refractive surgery, as undetected early keratoconus is a contraindication to these procedures. Slit-lamp examination—a microscope that allows the doctor to view the cornea in magnified detail—is used to identify physical signs of more advanced disease, such as Vogt striae (fine stress lines in the deep cornea), Kayser–Fleischer ring (an iron deposit ring at the base of the cone), and corneal scarring.

While keratoconus cannot be fully prevented, one highly effective step for at-risk individuals is to stop rubbing the eyes. Treating the underlying allergy that drives the urge to rub—with non-sedating antihistamine eye drops or other allergy management strategies—is a practical and important preventative measure. Genetic counseling is available for families with a known history of keratoconus and can help assess risk in other family members and guide decisions about when and how frequently to screen.

The hallmark of keratoconus is vision that becomes progressively more blurred and distorted in ways that are difficult or impossible to fully correct with standard eyeglasses. Early in the condition, a new prescription for glasses may seem to help, but the improvement is temporary—the prescription changes again within months as the cornea continues to change shape. Over time, the irregularity of the corneal surface increases, and vision becomes increasingly difficult to correct by any means other than specialized contact lenses or surgery.

Common signs and symptoms of keratoconus include:

• Blurred or distorted vision: Objects appear unclear or wavy. Straight lines may look bent or smeared.
• Frequent prescription changes: Eyeglass or contact lens prescriptions change more often than expected and still do not fully correct vision.
• Increased nearsightedness and astigmatism: Worsening myopia (difficulty seeing at a distance) and astigmatism (uneven focus caused by the irregular corneal shape) are characteristic early signs.
• Ghost images or double vision in one eye (monocular diplopia): Multiple overlapping images appear when looking with one eye at a time.
• Sensitivity to light and glare (photophobia): Bright lights, oncoming headlights, and sunlight cause significant discomfort.
• Halos and starbursts around lights: These are particularly noticeable at night, around streetlights and car headlights.
• Difficulty seeing at night: Low-contrast vision and glare make night driving increasingly difficult and, in advanced disease, unsafe.
• Eye strain and headaches: The effort of trying to focus through a distorted optical system causes fatigue and discomfort.
• Munson’s sign: In advanced disease, a V-shaped indentation appears in the lower eyelid when the patient looks downward. This is caused by the cone-shaped cornea pushing against the lid and is a visible sign of significant protrusion.
• Sudden worsening of vision with pain (acute hydrops): In some cases, a crack in the inner layer of the cornea causes fluid to suddenly flood the stroma, producing rapid swelling, clouding, and acute pain. This is called acute corneal hydrops. It is a medical urgency and should be evaluated by an eye doctor as soon as possible.

An ophthalmologist (a medical doctor specializing in eye disease and surgery) or an optometrist (a licensed eye care provider) can diagnose keratoconus. Early cases are often detected incidentally during a routine eye exam or when a patient presents with vision that cannot be fully corrected with standard glasses. Because the changes in early keratoconus can be subtle, specialized imaging is essential to confirm the diagnosis, establish the severity, and monitor progression over time. The diagnosis can be challenging in very early or subclinical cases, which is why corneal imaging has become central to the diagnostic process.

• Visual acuity testing: an eye chart test that measures how sharp and clear vision is at a standard distance. Reduced best-corrected visual acuity (the sharpest vision achievable even with an optimal glasses prescription) is an important sign that the cornea’s shape is interfering with normal focusing.
• Slit-lamp biomicroscopy: a specialized microscope that illuminates and magnifies the cornea in cross-section. The doctor looks for characteristic physical signs, including Vogt striae (fine, stress-related lines deep in the cornea that disappear with gentle pressure), Kayser–Fleischer ring (a brownish-iron deposit ring at the base of the cone), and, in advanced cases, corneal scarring and visible protrusion.
• Corneal topography: a computerized map of the front surface of the cornea using reflected light patterns. It detects the characteristic pattern of inferior corneal steepening (increased curvature in the lower portion of the cornea) that is the hallmark of keratoconus. This test can identify changes before the patient is aware of any vision problem.
• Corneal tomography (Scheimpflug imaging): an advanced imaging system (such as the OCULUS Pentacam®) that maps both the front and back surfaces of the cornea, measures corneal thickness at every point (pachymetry map), and calculates total optical power. It is the gold standard for detecting early and subclinical keratoconus and for preoperative screening before refractive surgery.
• Corneal pachymetry: measurement of corneal thickness using ultrasound or optical technology. In keratoconus, the cornea thins progressively, particularly at the apex of the cone. Serial pachymetry measurements track how quickly thinning is progressing.
• Refraction assessment: a comprehensive measurement of the eye’s optical error, including the degree of myopia, astigmatism, and its axis. In keratoconus, the astigmatism is typically irregular—it cannot be fully corrected with standard cylindrical lenses—and the pattern shifts over time.

Keratoconus is not curable, but it is highly treatable—especially when identified early. Treatment follows a stepwise approach that matches the intervention to the stage of the disease. The two main goals of treatment are to improve vision to a functional level and to halt the progression of corneal thinning and shape change. Your treatment plan will depend on how far the condition has advanced, how quickly it is progressing, and the degree to which vision can be corrected with optical devices.

In the early stages, updated glasses or soft contact lenses may provide acceptable vision. As the corneal surface becomes more irregular, standard lenses lose effectiveness and rigid gas-permeable (RGP) contact lenses become necessary. RGP lenses work by creating a smooth, uniform optical surface over the irregular cornea, correcting distortion that glasses cannot. For more advanced irregularity, scleral contact lenses—large-diameter rigid lenses that vault completely over the cornea and rest on the white part of the eye—are often the preferred option. They provide a fluid reservoir between the lens and the corneal surface that keeps the eye comfortable and gives excellent optics even in significantly advanced keratoconus. Hybrid lenses, which combine a rigid center with a soft outer skirt, are another option for patients who cannot tolerate fully rigid lenses.

For patients whose keratoconus is actively progressing—confirmed by documented changes in corneal curvature, thickness, or prescription over time—corneal collagen cross-linking (CXL) is currently the only proven treatment that can halt progression. Cross-linking does not reverse existing damage; it stops further change. The procedure is U.S. Food and Drug Administration (FDA)-approved under the brand names Photrexa® Viscous and Photrexa®, used with the KXL® ultraviolet A (UVA) system. In the standard protocol, the outermost corneal layer is removed, riboflavin (vitamin B2) drops are applied to the cornea for 30 minutes to saturate the tissue, and then the cornea is exposed to controlled UVA light for 30 minutes. The UVA light activates the riboflavin to create new bonds between collagen fibers in the stroma, stiffening and strengthening the cornea. The procedure is performed in one eye at a time under topical anesthesia and takes about an hour. Most patients experience some discomfort for a few days during healing of the corneal surface, and vision may fluctuate for several months before stabilizing. Cross-linking is typically recommended as soon as progression is documented—waiting increases the risk of corneal scarring and the eventual need for a transplant.

For patients who have intracorneal ring segments (ICRS, also called Intacs®) as a potential option, thin curved plastic arcs can be surgically implanted into the mid-layer of the cornea to flatten its central curvature and reduce the cone shape. This can improve vision and contact lens tolerance in some patients, though it does not stop progression and is typically combined with cross-linking. For patients with advanced keratoconus where the cornea has become too thin, too steep, or too scarred for contact lenses to work—or where the cornea does not respond to cross-linking—corneal transplant surgery (keratoplasty) may be needed. Deep anterior lamellar keratoplasty (DALK) is the preferred technique when the inner cell layer of the cornea is still healthy. It replaces only the stroma and front layers while preserving the patient’s own endothelium, lowering the risk of rejection compared to a full-thickness transplant. Most patients achieve significantly improved vision after keratoplasty, though contact lenses or glasses are still needed in most cases. The rate of transplants for keratoconus has declined meaningfully in recent years as cross-linking has become more widely available.

If you’ve been diagnosed with keratoconus, it’s natural to feel concerned about your vision and future. The good news is that with early detection, appropriate treatment, and regular monitoring, most people with keratoconus can maintain excellent functional vision and continue their normal activities. Keratoconus is a manageable condition, and advances in treatment mean that fewer people than ever before require corneal transplant surgery.

In the early stages of keratoconus, many people achieve clear, comfortable vision with glasses or soft contact lenses. As the condition progresses, specialized contact lenses—including rigid gas-permeable lenses, hybrid lenses, or large-diameter scleral lenses—often provide excellent vision correction by creating a smooth optical surface over the irregular cornea. At Montefiore Einstein, our contact lens specialists have extensive experience fitting complex cases and can help you find the lens type that gives you the clearest vision and best comfort. Regular monitoring with sophisticated digital imaging allows your ophthalmologist to track any changes in corneal shape and adjust your treatment plan accordingly.

For patients diagnosed in the early to moderate stages, corneal cross-linking has been a game-changer. This procedure strengthens the corneal tissue and can halt progression in the vast majority of cases, potentially preventing the need for more invasive treatments. When keratoconus advances despite other interventions, or when scarring affects vision quality, Montefiore Einstein offers the latest technological advances in corneal transplant surgery. Our experienced cornea surgeons perform both full-thickness and partial-thickness transplant procedures tailored to your specific condition, with nearly all surgeries performed on a convenient outpatient basis. Many patients experience significant vision improvement and can return to activities they thought they might have to give up.

Living with keratoconus means building a partnership with your eye care team to preserve your vision and quality of life. At Montefiore Einstein’s Department of Ophthalmology and Visual Sciences, our cornea specialists provide comprehensive care from diagnosis through long-term management. With state-of-the-art facilities, more than 100,000 patient visits conducted annually, and a “bench-to-bedside” approach that brings cutting-edge research directly to patient care. We offer the full spectrum of keratoconus treatment—from specialty contact lens fitting and corneal cross-linking to advanced surgical options. Our team is committed to helping you maintain clear vision, independence, and the ability to pursue your goals despite this progressive condition.