Makindo Medical Notes

Keratoconus is a progressive eye disease that can lead to significant visual impairment if not diagnosed and managed early. Regular eye examinations are essential for individuals at risk.

About Keratoconus

Keratoconus is an acquired eye disorder characterized by an irregular, cone-shaped deformation of the cornea, leading to distorted vision. This condition typically affects both eyes but is often asymmetric. Keratoconus progresses over time, usually stabilizing in the third or fourth decade of life. Early detection and appropriate management are crucial to prevent severe visual impairment.

• Keratoconus is an acquired irregularity of corneal curvature, resulting in a cone-like shape.
• It has an incidence of approximately 50 cases per 100,000 individuals.

Aetiology

The exact cause of keratoconus is multifactorial, involving genetic, environmental, and biochemical factors. While the condition is primarily non-inflammatory, various factors contribute to its development and progression:

• Genetic Component: There is evidence of familial predisposition, suggesting a hereditary link.
• Onset: Generally begins during adolescence and progresses through the early twenties.
• Environmental Factors: Chronic eye rubbing and allergic eye conditions are associated with increased risk.
• Biochemical Factors: Imbalances in enzymes and collagen cross-linking contribute to corneal weakening.
• Associated Conditions: Conditions such as Down syndrome, connective tissue disorders, and ocular surface diseases can increase the risk of keratoconus.

Clinical Presentation

Patients with keratoconus present with a range of visual disturbances and may experience varying degrees of discomfort:

• Astigmatism: Often severe and irregular, leading to blurred and distorted vision.
• Visual Distortion: Objects may appear wavy or tilted, and straight lines may appear bent.
• Bilateral but Asymmetrical: Although both eyes are usually affected, one eye may progress more rapidly than the other.
• Increased Sensitivity to Light: Photophobia due to irregular corneal surface.
• Frequent Changes in Prescription: Rapid fluctuations in refractive error during the active phase of the disease.
• Glare and Halos: Difficulty seeing in low-light conditions and around lights.

Differential Diagnosis

Several ocular conditions can mimic the symptoms of keratoconus. Differential diagnoses include:

• Corneal Dystrophies: Such as Fuchs' endothelial dystrophy, which can cause corneal opacities and edema.
• Corneal Ectasia Post-Refractive Surgery: Development of corneal thinning after procedures like LASIK.
• Contact Lens-Induced Corneal Warpage: Irregular corneal shape due to prolonged contact lens wear.
• Infectious Keratitis: Severe corneal infections causing scarring and irregularity.
• Verner-Morrison Syndrome: Secondary to systemic diseases affecting the cornea.

Investigations

Accurate diagnosis of keratoconus relies on a combination of clinical evaluation and advanced imaging techniques:

• Optometry Review:
  • Comprehensive eye examination including visual acuity and refraction.
  • Slit-lamp examination to assess corneal integrity and detect signs of keratoconus.
• Computerized Video Keratography:
  • Detailed mapping of corneal curvature to identify irregularities characteristic of keratoconus.
  • Quantifies the degree of corneal thinning and protrusion.
• Pachymetry:
  • Measures corneal thickness, which is typically reduced in keratoconus.
• Topography and Tomography:
  • Provides three-dimensional imaging of the cornea to assess its shape and structure.
• Specular Microscopy:
  • Evaluates the endothelial cell layer for any abnormalities.

Management

The management of keratoconus depends on the severity of the condition and the degree of visual impairment. Early intervention can slow progression and improve visual outcomes:

• Mild Disease:
  • Corrective Eyeglasses: Suitable for managing mild myopia and astigmatism.
  • Soft Contact Lenses: Provide better vision correction compared to glasses.
• Moderate Disease:
  • Rigid Gas Permeable (RGP) Contact Lenses: Offer superior visual acuity by creating a smooth optical surface.
  • Hybrid Contact Lenses: Combine RGP centers with soft skirts for enhanced comfort.
• Advanced Disease:
  • Corneal Collagen Cross-Linking (CXL): A minimally invasive procedure that strengthens corneal collagen fibers to halt disease progression and provide sustained improvement in vision.
  • Intacs: Intrastromal corneal ring segments that reshape the cornea and reduce astigmatism.
  • Corneal Transplantation (Graft): Indicated in severe cases with significant corneal scarring or thinning where other treatments are ineffective.
• Additional Treatments:
  • Topography-Guided Photorefractive Keratectomy (PRK): Customized laser surgery to correct irregular corneal surfaces.
  • Customized Soft Contact Lenses: Designed to fit the irregular corneal shape for better comfort and vision.
• Supportive Care:
  • Regular Monitoring: Periodic eye examinations to track disease progression and adjust treatment as necessary.
  • Patient Education: Informing patients about the nature of the disease, treatment options, and the importance of adherence to prescribed therapies.

Prognosis

The prognosis for individuals with keratoconus varies based on the severity and timeliness of treatment. Early detection and intervention can significantly improve visual outcomes and quality of life:

• Early Stages: Patients typically maintain good visual acuity with corrective lenses and may experience stabilization or slight improvement with appropriate management.
• Progressive Stages: Without intervention, keratoconus can lead to severe visual impairment, requiring advanced treatments such as corneal cross-linking or transplantation.
• Long-Term Outlook: With modern treatments, most patients achieve satisfactory vision and prevent further corneal deterioration. However, ongoing monitoring is essential to manage any changes over time.

Conclusion

Keratoconus is a progressive corneal disorder that can significantly impact vision and quality of life. Early diagnosis through comprehensive eye examinations and advanced imaging techniques is crucial for effective management. Treatment options range from corrective lenses in mild cases to surgical interventions in advanced stages. With timely and appropriate care, most individuals with keratoconus can achieve optimal visual outcomes and maintain an active lifestyle.

References

• American Academy of Ophthalmology. Keratoconus. Available at: https://www.aao.org
• Mayo Clinic. Keratoconus. Available at: https://www.mayoclinic.org
• Rabena, R., & Kezirian, E. J. (2019). Advances in the Management of Keratoconus. Clinical Ophthalmology.
• Smolek, T., & Pavlin, E. (2018). Keratoconus: Pathophysiology and Current Treatment. Journal of Current Ophthalmology.
• Shetty, R., & Shetty, R. (2020). Corneal Collagen Cross-Linking in Keratoconus: A Review. Indian Journal of Ophthalmology.
• National Eye Institute (NEI). Keratoconus. Available at: https://www.nei.nih.gov