Understanding Keratoconus: When the Cornea Loses its Shape

The cornea, the eye’s clear front window, normally has a smooth, dome-like curvature that helps focus light accurately onto the retina for sharp vision. In Keratoconus, this normally round cornea progressively thins and begins to bulge outward into a cone-like shape. This irregular shape prevents light from focusing correctly, leading to distorted and blurred vision.

Keratoconus typically begins in puberty or the late teens and can progress into the 30s or 40s, although the rate and extent of progression vary widely among individuals. It usually affects both eyes, often one more severely than the other.

What Causes the Cornea to Change Shape?

The exact cause of Keratoconus is not fully understood, but it’s believed to be a combination of genetic and environmental factors.

• Weakened Corneal Tissue: The condition involves a weakening of the collagen fibers within the cornea. Collagen provides strength and structure; when these fibers weaken, the cornea loses its ability to maintain its normal shape under the eye’s internal pressure, leading to the characteristic bulging.

• Genetics: A family history of Keratoconus is present in a percentage of cases, suggesting a genetic predisposition.

• Eye Rubbing: Chronic and vigorous eye rubbing is strongly associated with the development and progression of Keratoconus. The mechanical stress can further weaken an already susceptible cornea.

• Allergies and Atopic Conditions: Individuals with conditions like asthma, eczema, and hay fever often experience itchy eyes, leading to more frequent eye rubbing, which can be a contributing factor.

• Oxidative Stress: An imbalance between free radicals and antioxidants in the cornea may also play a role in the weakening of corneal tissue.

Recognizing the Symptoms of Keratoconus:

Symptoms often start subtly and can include:

• Progressive blurring and distortion of vision.

• Increased sensitivity to light (photophobia) and glare.

• Frequent changes in eyeglass prescriptions, often with increasing astigmatism and nearsightedness that glasses can no longer fully correct.

• Seeing “ghost images” or multiple images.

• Difficulty with night vision.

• Eye strain or headaches.

• Sudden clouding of vision and pain if acute corneal hydrops occurs (a rare complication where fluid enters the cornea due to a break in Descemet’s membrane).

Diagnosis:

An ophthalmologist or optometrist can diagnose Keratoconus during a comprehensive eye exam. Key diagnostic tools include:

• Slit-Lamp Examination: Can reveal characteristic signs like corneal thinning, Vogt’s striae (fine stress lines in the cornea), or a Fleischer ring (an iron deposit around the base of the cone).

• Corneal Topography (Mapping): This is the most crucial diagnostic test. It creates a detailed, color-coded map of the cornea’s surface curvature, clearly showing the irregular steepening and cone-like shape characteristic of Keratoconus, even in very early stages.

• Pachymetry: Measures corneal thickness, which is typically reduced in areas of conical protrusion.

• Refraction: To determine the degree of nearsightedness and astigmatism.

Treatment Options: From Glasses to Grafts

Treatment for Keratoconus aims to provide clear vision and, importantly, to halt or slow the progression of the condition. The approach depends on the severity and rate of progression:

1. Early Stages:

   • Eyeglasses: Can correct mild nearsightedness and astigmatism.

   • Soft Contact Lenses: Custom soft lenses may work for some mild cases.

2. Moderate Stages:

   • Rigid Gas Permeable (RGP) Contact Lenses: These are often the mainstay of treatment. RGPs create a smooth refractive surface over the irregular cornea, providing much clearer vision than glasses.

   • Scleral Lenses: Larger diameter RGP lenses that vault over the entire cornea and rest on the white part of the eye (sclera). They can offer excellent comfort and vision for moderate to advanced Keratoconus.

   • Hybrid Contact Lenses: Combine a rigid center with a soft outer skirt for comfort and clarity.

3. Slowing or Halting Progression:

   • Corneal Cross-Linking (CXL): This is a revolutionary treatment designed to strengthen the corneal tissue and stop the progression of Keratoconus. It involves applying riboflavin (vitamin B2) eye drops to the cornea, which is then activated by ultraviolet (UV-A) light. This process creates new bonds between collagen fibers, making the cornea stiffer and more resistant to further bulging. CXL is most effective in earlier stages before significant vision loss or scarring occurs.

4. Advanced Stages:

   • ICRS (Intracorneal Ring Segments): Small, clear, arc-shaped plastic rings are surgically inserted into the periphery of the cornea to help flatten the cone and improve its shape. This can make it easier to wear contact lenses or sometimes improve uncorrected vision.

   • CAIRS (Corneal Allogenic Intrastromal Ring Segments): Small, clear, arc-shaped rings derived from allogenic donor stroma to act as a spacer agent in ectatic keratoconic corneas thus improving visual and topographic parameters while avoiding risks known to be associated with the implantation of synthetic intrastromal ring segments.

   • Corneal Transplantation: If Keratoconus becomes very advanced, with significant scarring, extreme thinning, or contact lens intolerance, a corneal transplant may be necessary.

     • Deep Anterior Lamellar Keratoplasty (DALK): This is often the preferred transplant technique for Keratoconus because it preserves the patient’s own healthy endothelium, reducing the risk of graft rejection. It involves replacing the diseased anterior and stromal layers of the cornea.

     • Penetrating Keratoplasty (PKP): A full-thickness transplant may be required if DALK is not feasible or if there’s significant scarring involving the deeper layers.

Living with Keratoconus requires ongoing management and regular eye exams. However, with the range of treatments now available, from specialized contact lenses and corneal cross-linking to advanced surgical techniques, most individuals can achieve good functional vision and maintain their quality of life. Early diagnosis and intervention, particularly with CXL, are key to preventing severe vision loss.