Keratoconus: Symptoms, Types, Causes and Treatment

Keratoconus is a progressive condition that affects the cornea—the clear, dome-shaped front surface of the eye—causing it to thin and bulge into a cone-like shape. This distortion leads to significant visual impairment and can dramatically impact daily life. Understanding the symptoms, types, causes, and available treatments is crucial for patients, caregivers, and clinicians alike. In this comprehensive guide, we’ll explore everything you need to know about keratoconus, drawing on current research and clinical insights.

Symptoms of Keratoconus

Living with keratoconus can be challenging, especially as the symptoms often start subtly and worsen over time. Early detection is essential for effective management, but the signs can be easy to overlook. Let’s break down the most common symptoms and their progression.

Symptom	Description	Stage	Source(s)
Blurred Vision	Loss of visual clarity, not corrected by glasses	Early	1 5
Distorted Vision	Vision appears wavy or misshapen	Early	1 5
Increased Astigmatism	Irregular cornea causes astigmatism	Early/Mid	1 5
Light Sensitivity	Eyes become sensitive to bright lights	Early/Mid	1 3
Frequent Prescription Changes	Rapid shift in glasses/contact lens power	Early/Mid	1 5
Dry Eye Symptoms	Increased dryness, discomfort, irritation	All	2 3
Halos/Glare	Halos around lights, especially at night	Mid/Late	1 5
Corneal Scarring	Permanent opacities reduce vision	Late	1 4 5
Fleischer’s Ring	Iron-deposit arc at cone base	Mid/Late	1
Vogt’s Striae	Fine vertical lines in cornea	Mid/Late	1
Munson’s Sign	V-shaped lower lid on downward gaze	Late	1
Acute Hydrops	Sudden corneal swelling, pain, vision loss	Late	1

Table 1: Key Symptoms

Understanding the Symptoms

Early Symptoms: Subtle but Significant

In its initial stages, keratoconus often causes blurred or distorted vision that is not fully correctable with glasses. Patients may notice frequent changes in their eyeglass or contact lens prescriptions and increasing astigmatism—a refractive error resulting from the irregular shape of the cornea. These changes can happen rapidly compared to typical refractive shifts seen with age 1 5.

Light sensitivity and halos or glare around lights, especially at night, are also common and can interfere with driving or reading. Many patients report that their vision becomes particularly troublesome in low-light or high-glare environments 1.

Dry Eye and Ocular Discomfort

Emerging research highlights that dry eye symptoms are prominent in keratoconus patients, who experience more tear instability, irritation, and discomfort than individuals without the disease. This is largely due to decreased mucin production and goblet cell density in the conjunctiva, leading to less stable and lower-quality tears 2 3. These symptoms can be exacerbated by contact lens wear, which is often used to correct vision in keratoconus 3.

Mid-to-Late Stage Symptoms

As keratoconus progresses, more distinctive signs appear:

• Fleischer’s Ring: A brownish, iron-deposit ring often visible at the base of the cone-shaped cornea 1.
• Vogt’s Striae: Fine vertical lines in the deep cornea caused by stretching 1.
• Munson’s Sign: A V-shaped bulging of the lower eyelid when looking down, visible in advanced cases 1.

Corneal scarring can develop over time, further reducing vision quality and making treatment more complex 1 4 5.

Advanced Complications

In rare, severe cases, sudden breaks in the inner corneal membrane (Descemet's membrane) can trigger acute hydrops—a painful, dramatic swelling of the cornea that results in sudden vision loss 1.

Types of Keratoconus

Keratoconus is not a one-size-fits-all disease. Its presentation varies in terms of severity, progression, and corneal shape. Understanding the types helps tailor treatment and predict outcomes.

Type	Defining Feature	Example/Notes	Source(s)
Forme Fruste	Subclinical, minimal changes	Often undetected	1 5
Mild	Early thinning, mild steepening	Correctable with glasses	1 5
Moderate	More pronounced bulging/irregular astigmatism	Needs contact lenses	1 5
Severe	Cone-shaped protrusion, scarring	May need surgery	1 5
By Morphology	Based on cone location and size	Nipple, oval, globus	1 5
By Progression	Stable vs. progressive	Progressive needs intervention	1 10
Associated Ectasias	Related disorders (e.g., pellucid marginal degeneration)	Overlapping features	5

Table 2: Types of Keratoconus

Breaking Down the Types

By Stage: From Mild to Severe

• Forme Fruste Keratoconus: The "hidden" or subclinical form, showing minimal or undetectable corneal changes. Often only found on corneal topography, it may not cause symptoms but can be relevant for refractive surgery screening 1 5.
• Mild: Noticeable only with special testing or mild symptoms, usually correctable with glasses.
• Moderate: More obvious changes—patients need rigid contact lenses to achieve good vision.
• Severe: Advanced thinning, extreme cone shape, corneal scarring, and vision loss. Surgical interventions are often needed 1 5.

By Morphology: Shape Matters

Keratoconus can be further classified based on cone shape and location:

• Nipple cones: Small, centrally located cones.
• Oval cones: Larger, often displaced towards the lower cornea.
• Globus cones: Affecting a wider area, up to 75% of the cornea 1 5.

By Progression

• Stable Keratoconus: Remains unchanged for years.
• Progressive Keratoconus: Worsens over time, particularly in younger individuals, and may require early intervention like crosslinking to halt progression 10.

Related Disorders

Other corneal thinning disorders such as pellucid marginal degeneration, keratoglobus, and posterior keratoconus can mimic or overlap with keratoconus, but they have distinct patterns of thinning and protrusion 5.

Causes of Keratoconus

Why does keratoconus develop? The answer is complex and involves a mix of genetic, environmental, and possibly inflammatory factors. Here’s an overview of the latest knowledge.

Factor	Role in Disease	Evidence/Notes	Source(s)
Genetics	Inherited predisposition	Family history, gene studies	7 9
Eye Rubbing	Strong risk factor	Major “second hit” trigger	6 7 9
Atopy	Allergy-related risk	Linked to eye rubbing	6 7 9
Environmental	UV exposure, geography, trauma	May contribute	7 9
Biomechanical	Weakening of corneal structure	Collagen/lamina alterations	4 7 8
Biochemical	Enzyme imbalance, oxidative stress	Under investigation	7 8
Inflammation	Possible role	Elevated cytokines, debated	8
Contact Lens Wear	Possible association	Not a primary cause	5 6 7
Systemic Diseases	Down’s, Marfan’s, connective tissue	Increased risk	5 6 9

Table 3: Causes and Risk Factors

Exploring the Causes

Genetic Factors

Research shows a clear genetic predisposition to keratoconus. Family-based studies and genome-wide association analyses have identified several genes associated with higher risk. However, having a genetic risk alone is not enough—most researchers believe a “second hit” is required for the disease to manifest 7 9.

Eye Rubbing and Atopy

Chronic eye rubbing emerges as the most significant non-genetic risk factor for keratoconus. Studies reveal that individuals who rub their eyes frequently—often due to allergies (atopy)—are much more likely to develop the condition. In fact, when controlling for other variables, eye rubbing remains the only consistently significant predictor 6 7 9.

Atopy (asthma, eczema, hay fever) is linked to increased risk, but primarily because it leads to itching and rubbing rather than directly causing corneal changes 6.

Environmental and Biomechanical Factors

Sun (UV) exposure, trauma, and certain geographic factors may play a role in disease onset, possibly by stressing or weakening the corneal tissue 7 9. Biomechanically, the cornea in keratoconus loses its normal structure, particularly in the basement membrane and collagen lamellae, resulting in progressive thinning and protrusion 4 7 8.

Biochemical and Inflammatory Aspects

Oxidative stress and imbalances in corneal enzymes are under investigation as potential contributors 7 8. Traditionally viewed as a "noninflammatory" disease, recent studies have found elevated levels of inflammatory cytokines in the tears and corneas of keratoconus patients, suggesting that inflammation may play a larger role than previously thought 8.

Other Associations

While contact lens wear and systemic diseases such as Down’s syndrome and Marfan’s syndrome are associated with higher risk, they are not direct causes. Rather, they may increase susceptibility or exacerbate underlying risk factors 5 6 9.

Treatment of Keratoconus

The good news: advances in diagnosis and management mean that keratoconus is increasingly treatable at all stages. The choice of treatment depends on the severity and progression, as well as individual patient needs.

Treatment	Purpose/Stage Addressed	Benefits/Notes	Source(s)
Eyeglasses	Early/mild cases	Corrects mild refractive errors	1 5 11
Contact Lenses	Mild-moderate, irregular cornea	Improves vision, rigid/scleral best	1 3 5 11
Collagen Crosslinking	Stops progression	Strengthens cornea, standard for progressive KC	10 11 12
Intrastromal Ring Segments (ICRS)	Reduces irregularity, improves fit	May delay/avoid surgery	11 13 14
Bowman Layer Transplantation	Advanced, delays graft	New, promising, for severe cases	11 13
Corneal Transplantation (PK/DALK)	Severe/end-stage	Restores vision, last resort	1 5 11 12 13
Dry Eye Management	Symptom relief	Lubricants, treat underlying cause	2 3 11

Table 4: Treatment Options

Treatment Approaches Explained

Early to Moderate Disease

• Eyeglasses: For mild cases, glasses can correct vision when the cornea remains relatively regular 1 5 11.
• Contact Lenses: As the cornea becomes more irregular, rigid gas-permeable (RGP) or scleral lenses are preferred. Scleral lenses often provide greater comfort and better vision by vaulting over the cone 1 3 5 11. However, dry eye symptoms may be exacerbated by lens wear, so careful fitting and management are essential 3.

Collagen Crosslinking (CXL)

A major breakthrough, corneal crosslinking uses riboflavin (vitamin B2) drops and ultraviolet (UVA) light to strengthen corneal collagen fibers, halting disease progression and, in some cases, slightly reversing thinning. This is now the standard of care for progressive keratoconus, especially in younger patients 10 11 12. Crosslinking is safe and effective when performed on corneas of adequate thickness (>400 μm) 10.

Intrastromal Ring Segments (ICRS)

ICRS (e.g., Intacs, CAIRS) are small, semi-circular inserts placed in the cornea to flatten its shape and reduce irregularity. They can improve vision and make contact lens fitting easier, often postponing the need for a corneal transplant. Some newer techniques use donor tissue for the ring segments (CAIRS), sometimes combined with crosslinking for added benefit 11 13 14.

Advanced Interventions

• Bowman Layer Transplantation: An emerging option for advanced cases, this technique involves transplanting the Bowman’s layer (a tough layer in the cornea) to stabilize the cornea and delay the need for a full corneal transplant 11 13.
• Corneal Transplantation (PK/DALK): When scarring or thinning is too severe for other treatments, penetrating keratoplasty (PK) or deep anterior lamellar keratoplasty (DALK) may be necessary. These procedures replace part or all of the cornea. While often effective, they carry risks like rejection, irregular astigmatism, and suture complications 1 5 11 12 13.

Symptom Management

As dry eye is common in keratoconus, ocular lubricants, anti-inflammatory drops, and careful lens hygiene are crucial for comfort and ocular surface health 2 3 11.

Conclusion

Keratoconus is a complex, multifaceted eye disease with a profound impact on vision and quality of life. Early recognition and intervention have transformed patient outcomes in recent years. Here’s a quick summary of what we’ve covered:

• Symptoms include blurred and distorted vision, increased astigmatism, dry eye, and, in advanced cases, corneal scarring and acute hydrops.
• Types of keratoconus vary by severity, morphology, and progression, with related disorders sometimes mimicking its features.
• Causes are multifactorial, involving genetic predisposition, eye rubbing (especially in allergic individuals), environmental, biomechanical, and possibly inflammatory factors.
• Treatment options range from glasses and contact lenses to collagen crosslinking, ring segments, and corneal transplantation, with newer therapies offering hope for even advanced cases.

Key Takeaways:

• Early diagnosis and management are vital to preserving vision.
• Avoiding eye rubbing and managing allergies can help reduce risk.
• Collagen crosslinking has revolutionized disease stabilization.
• A personalized approach is essential—no single treatment fits all.
• Research into genetics and inflammation may unlock future therapies.

Living well with keratoconus is possible, especially with timely, tailored care and the support of knowledgeable eye care professionals.