What are the other Names for this Condition? (Also known as/Synonyms)

• Cone-Shaped Eye
• KCN (Keratoconus)

What is Keratoconus? (Definition/Background Information)

• Keratoconus (KCN) is a condition in which the cornea, the clear, front part of the eye, transforms into a cone-shaped dome
• Normally, the cornea is mostly round. In Keratoconus, the cornea becomes progressively thinner and steeper, causing the cornea to bulge outwards like a cone
• The cornea is the first structure of the eye to bend light rays towards the retina in back of the eye. When the cornea forms an irregular cone shape, light cannot get focused properly onto the retina, causing blurry and distorted vision
• The condition may be treated using glasses or contact lenses. In some cases, the cornea may be severely damaged that a corneal transplant surgery may be needed. The prognosis is generally good with adequate treatment, but it is generally dependent on the severity of Keratoconus

Who gets Keratoconus? (Age and Sex Distribution)

• Keratoconus is a fairly common condition that affects about 1 in 2,000 individuals
• It usually starts during one’s adolescent years and the third decade (ages 21-30), although it can affect individuals of any age group
• Males and females appear to be about equally affected by Keratoconus. However, women are more likely to experience dry eye from the condition
• No racial, ethnic group, or geographical predilection is noted

What are the Risk Factors for Keratoconus? (Predisposing Factors)

The risk factors for developing Keratoconus include:

• Although the exact genetic correlation is unknown, 14% of individuals with Keratoconus report a positive family history of the condition
• Chronic eye rubbing, as this may cause the cornea to stretch and change shape over time
• Eye allergies, as this increases the likelihood of chronic eye rubbing
• Preexisting corneal conditions, such as Fuchs’ dystrophy, posterior polymorphous dystrophy, granular dystrophy, and lattice dystrophy
• Obstructive sleep apnea, which has a strong association with floppy eyelid syndrome; individuals with floppy eyelid syndrome have an irregular eyelid-cornea interaction, which may change the shape of the cornea over time
• Obesity, as this increases the likelihood of obstructive sleep apnea
• Individuals with Down’s syndrome, Turner syndrome, Osteogenesis imperfecta, Marfan’s syndrome, and Ehlers-Danlos syndrome are more likely to develop Keratoconus

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Keratoconus? (Etiology)

Currently, the exact cause of Keratoconus is not well known. However, there are many factors that can contribute to the condition.

• Keratoconus results in the displacement of collagen, connective tissue proteins in the cornea, which causes the cornea to stretch and change into a cone shape
• Enzymes, called matrix metalloproteinases, seem to be elevated in the cornea during Keratoconus, which can lead to the degradation of the normal corneal structure and transformation into a cone shape

What are the Signs and Symptoms of Keratoconus?

The signs and symptoms of Keratoconus may include:

• Increased nearsightedness and/or astigmatism
• Progressively decreased vision
• Thinning and stretching of the cornea over time, with one eye more affected than the other
• Small stretch marks within the cornea (Vogt’s striae)
• Iron deposits towards the bottom of the coned-shaped cornea (Fleischer’s ring)
• Abnormal reflex of light noted in the back of the eye
• Abnormally high values obtained by a corneal topographer or keratometer, instruments that measure the steepness of the cornea
• Light sensitivity
• Glare
• Double vision
• Corneal swelling and corneal scarring

How is Keratoconus Diagnosed?

The diagnosis of Keratoconus may involve:

• Obtaining a thorough patient history, including history of allergies and eye rubbing, and family history of the condition
• History of sporadic, changing refractive error (nearsightedness and/or astigmatism)
• An eye examination may reveal:
  • Poor, decreased vision with glasses or contact lenses
  • Observation of a cone-shaped cornea overlapping the lower eyelid when the patient looks downward (Munson’s sign)
  • Observation of small, vertical stretch marks within the cornea (Vogt’s striae) during slit-lamp examination (instrument that gives a magnified view of the eye structures)
  • Observation of an iron deposit at the base of the cone (Fleischer’s ring)
  • Observation of a cone-like reflection on one side of the cornea when light is shined from the other side of the cornea (Rizzuti’s sign)
• Keratometer, an instrument that measures the steepness and curvature of the cornea, reads abnormally high values
• Corneal topographer, an instrument that maps the curvature of the entire cornea, shows abnormal steepness and thinning towards the center or bottom of the cornea
• Pachymeter is also an instrument that can be used to measure the thickness of the cornea, which would show a thinned cornea where the cone has developed

A differential diagnosis to exclude pellucid marginal degeneration (PMD) may be necessary, as PMD is similar in presentation to Keratoconus.

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Keratoconus?

The complications due to Keratoconus could include:

• Poor, decreased vision with glasses or soft contact lenses
• Distorted vision
• Sporadic, high amount of nearsightedness and/or astigmatism
• Pain due to swelling of the cornea during the late stages
• Vision loss due to corneal scarring after recurring episodes of swelling

How is Keratoconus Treated?

The treatment measures for Keratoconus may include:

• Discontinue (constant) eye rubbing
• Use of glasses and/or soft contact lenses for early and mild cases
• Use of hard or rigid gas permeable contact lenses for more moderate cases, when glasses and soft contact lenses no longer optimally improve vision; hard contact lenses create a pool of tears between the back of the contact lens and the irregular cornea, mimicking a more spherical refractive surface at the front of the eye
• Scleral lenses, for more advanced cases, similar to rigid gas permeable lenses, but are much larger and fit on the white part of the eye and vault the cone of the cornea, again mimicking a more spherical refractive surface at the front of the eye
• Corneal ring implants - small, ring-like devices that are inserted into the cornea to help flatten the irregular, cone-shaped cornea
• Collagen cross-linking - eye drops containing riboflavin (vitamin B2) are instilled in the eye and combined with special UV light, which flattens and strengthens the corneal tissue and prevents it from stretching or bulging further
• Corneal transplant (for most severe cases): Replacement of the irregular, cone-shaped cornea with healthy, donor corneal tissue may be necessary

How can Keratoconus be Prevented?

The preventive methods for Keratoconus could include:

• Avoidance of eye rubbing
• Allergy eye drops to treat itching, which may prevent eye rubbing
• Maintaining a healthy weight, which can prevent obstructive sleep apnea and floppy eyelid syndrome, which have associations to Keratoconus
• Collagen cross-linking can prevent progression of the condition if Keratoconus is already manifesting

What is the Prognosis of Keratoconus? (Outcomes/Resolutions)

The prognosis for Keratoconus is variable and depends upon its severity.

• It is usually better when collagen cross-linking is elected during earlier stages, as this can significantly prevent the condition from progressing
• Progression of Keratoconus usually decreases or ceases during the third, fourth, and fifth decades
• Prognosis is usually poorer for those diagnosed with Keratoconus during childhood or adolescence, as the condition has more time to progress to later stages
• If Keratoconus advances to later, more severe stages, the prognosis is usually worse, as it becomes very difficult to correct vision to a desirable outcome
• Even after corneal surgery, progression of the cornea back to a cone shape may occur

Additional and Relevant Useful Information for Keratoconus:

• Hybrid contact lenses, providing the benefit of soft contact lens comfort with rigid gas permeable contact lens vision quality, can also be an available lens option for individuals affected by Keratoconus
• Collagen cross-linking has gained popularity as the best treatment option to prevent Keratoconus progression