Keratoconus

Definition

Keratoconus is a progressive eye disorder that affects the cornea, the clear, dome-shaped front layer of the eye. This condition causes the cornea to become thinner and bulge outward into a cone-like shape. This alteration leads to blurriness and increased nearsightedness. As the cornea changes, irregular astigmatism forms. Keratoconus often develops around puberty. Typically, it progresses until the third or fourth decade of life, though it can occur at any age. While it usually affects both eyes, one eye may be impacted more severely. Keratoconus falls under the category of corneal ectasias.

Alternative names

KC; Bulging Cornea

Causes

The definitive cause of keratoconus is unknown, but it’s likely a combination of genetic and environmental factors. Keratoconus is associated with changes in the corneal collagen layers.

Genetic causes

Certain genetic conditions, including:
- Down syndrome
- Ehlers-Danlos syndrome

Family history

Individuals with a family history of keratoconus are more likely to develop the condition. Studies suggest that around 10% of those diagnosed have an affected parent.

Environmental causes

Conditions such as:

- Atopic dermatitis
- Asthma
- Eczema
- Hay fever

Other factors

Persistent and forceful eye rubbing can affect corneal changes and increase the risk of developing keratoconus.

Symptoms

In the early stages, keratoconus often presents with mild blurriness that worsens over time. Many affected individuals have a history of nearsightedness.

Other symptoms that may develop over time include:

Double vision when looking with one eye
Eye irritation and discomfort
Frequent headaches due to eye strain
Increased sensitivity to light
Rapid changes in eyeglass prescription, particularly worsening nearsightedness and astigmatism

Exams and tests

A cornea specialist will review medical and family history. Based on their findings, a comprehensive eye exam is conducted. Additional tests include:

Computerized corneal mapping – Provides a detailed map of the cornea’s shape and thickness. Computerized corneal mapping often detects keratoconus in its earliest stages
Keratometry – Evaluates corneal curvature by analyzing how light reflects off its surface
Pachymetry – Measures corneal thickness
Refraction testing – Determines the degree of vision impairment. It also identifies the best corrective lens prescription
Slit lamp examination – Uses a specialized microscope to assess corneal shape. It also examines structural abnormalities, particularly in later disease

Treatment

Treatment of keratoconus depends on disease severity.

Contact lenses - For moderate to advanced cases, rigid gas-permeable or scleral contact lenses may help. These lenses compensate for the irregular shape of the cornea.
Eyeglasses - In mild cases, vision can improve with glasses.

In severe cases, your doctor may offer additional treatment. Treatment can include intrastromal corneal ring segments or corneal transplant surgery. These approaches can help reshape the cornea so a contact lens fits better.

Corneal tissue addition procedures (CAIRS and CTAK) - These newer surgical techniques implant allogenic or human donor, corneal tissue. Rather than synthetic material to reshape and reinforce the cornea. Similar to intrastromal corneal ring segments, this is considered a procedure.
Corneal transplant surgery (keratoplasty) - In severe cases where corneal distortion is extreme, an eye surgeon may offer a corneal transplant surgery. The damaged cornea is replaced by a donated human cornea. This procedure is performed in an operating room. Visual improvement can take up to a year, often requiring additional rigid contact lens correction to maximize vision.
Intrastromal corneal ring segments – Synthetic implants can be inserted into the cornea to flatten its shape. This procedure helps improve vision and/or the fit of a contact lens. One such implant is the INTACS. The eye is temporarily numbed before the implants are placed. Eye drops may be prescribed in the recovery period to prevent infection and ensure proper healing.

The above treatments help improve vision. Corneal collagen cross-linking is a treatment that can prevent keratoconus from progressing.

Corneal collagen cross-linking (CXL) – This is a treatment for keratoconus and other corneal ectasias. This procedure uses ultraviolet (UV) and riboflavin (vitamin B2) eye drops. The eye drops strengthen corneal tissue and slow further deformation. Afterward, treatment may include a bandage contact lens. Medicated eye drops may be used to aid healing.

To prevent the disease from worsening, patients are advised not to rub their eyes. Seek treatment for conditions that contribute to inflammation, such as allergies.

Outlook (prognosis)

With appropriate treatment, most individuals with keratoconus achieve stable vision. The disease often slows by mid-30s to early 40s.

Possible complications

Keratoconus has some potential complications, including:

Corneal hydrops, where a small break in the layers of the cornea can cause:

- Acute corneal swelling, resulting in eye pain
- Blurriness
- Light sensitivity

Corneal scarring, causing further visual impairment
Vision loss

Possible complications of contact lens use:

Infection

Possible complications of intrastromal corneal segments and corneal tissue addition procedures:

Cornea scarring
Cornea thinning
Glare or halos
Implant extrusion
Infection

Possible complications of corneal transplants:

Corneal graft failure
Corneal graft rejection – The risk is much lower than with other organ transplants
Infection
Postsurgical glaucoma

When to contact a medical professional

Young adults’ vision who cannot be corrected to 20/20 with glasses should be checked by an eye doctor familiar with keratoconus. Parents with keratoconus should consider having their children screened for the disease starting at age 10. If you do have keratoconus, it is best to have routine exams with an eye care provider. Those with the condition should seek their provider or go to the ER if they develop sudden pain, redness, light sensitivity or vision loss.

Prevention

There is no way to prevent this condition. Your provider may recommend taking steps to control allergies. Avoid rubbing your eyes to prevent the progression of the disease.

Gallery

Digital image illustrating the shape of a normal cornea in contrast to a cornea with keratoconus. Creator is Javier Mariscal.

References/citations

American Academy of Ophthalmology. What Is Keratoconus? American Academy of Ophthalmology. Updated October 2024. Accessed December 17, 2024. aao.org/eye-health/diseases/what-is-keratoconus.

Feder RS, Neems LC. Noninflammatory Ectatic Disorders. In: Krachmer JH, Mannis MJ, Holland EJ, eds. Cornea. 4th ed. Elsevier; 2017:820-843.

Authors/reviewers

Lauren Jeang, MD

Clinical Assistant Professor, Cornea and External Disease, Director of Medical Student Education, UF Department of Ophthalmology
ljeang@ufl.edu