Keratoconus

Keratoconus

Introduction: Keratoconus is a progressive, non-inflammatory eye disorder in which the cornea thins and bulges into a cone-like shape. This alteration in corneal structure distorts light entering the eye, leading to significant visual impairment. The condition typically begins in adolescence or early adulthood and can progress over several years. Though the exact cause of keratoconus is still not entirely understood, genetic and environmental factors appear to play a role. One interesting risk factors associated with deterioration of keratoconus is eye rubbing especially in scenario of allergic eye disease. Timely diagnosis and intervention are crucial in managing the condition and preventing severe vision loss.

Symptoms:

1. Blurred or distorted vision: As the cornea becomes more conical, light entering the eye does not focus properly, leading to distorted or unclear vision.

2. Increased sensitivity to light (photophobia): The irregular corneal surface increases sensitivity to bright light.

3. Frequent prescription changes: People with keratoconus may experience frequent changes in their eyeglass prescription, as the cornea's shape changes over time. (Tip: this is one of the earliest presenting feature and sometimes a direct referral from optician cold be received regarding potential keratoconus).

4. Halos or glare: Distorted vision can result in halos or glare, especially in low-light or nighttime conditions.

5. Double vision: In some cases, individuals may experience double vision in one eye due to corneal irregularities.

Examination Findings:

1. Astigmatism: The corneal irregularity leads to significant astigmatism that cannot be corrected with standard glasses. (Tip: frequent or drastic prescription changes is a key part of history)

2. Corneal thinning: The central and paracentral cornea is typically thinned, particularly in the area corresponding to the bulging cone.

3. Munson's sign: A characteristic sign of keratoconus, Munson's sign refers to the downward bulging of the lower eyelid when the patient looks downward. It suggests advanced corneal protrusion.

4. Rizzuti's sign: This is a test where a light is shone at the side of the patient's eye, and the cone-shaped cornea reflects light at a different angle, causing a bright glow or reflection.

5. Scissoring of the red reflex: On ophthalmoscopic examination, the red reflex may be distorted, and there is often a "scissoring" appearance due to irregularities in the cornea.

Investigations:

1. Corneal topography: The gold standard for diagnosing keratoconus, this imaging technique provides a detailed map of the corneal surface, revealing irregularities and steepening typical of the condition.

2. Corneal pachymetry: This test measures the thickness of the cornea, which is usually thinned in keratoconus, particularly in the central area.

3. Scheimpflug imaging: This imaging technique provides detailed cross-sectional images of the cornea, aiding in the assessment of its shape and thickness.

4. Optical coherence tomography (OCT): OCT provides high-resolution, cross-sectional images of the cornea, allowing for a detailed assessment of its structure and thickness.

5. Keratometry: This technique measures the curvature of the cornea, helping to quantify the degree of astigmatism and corneal irregularity.

6. Wavefront aberrometry: This test helps identify higher-order aberrations caused by keratoconus, contributing to visual distortions and reduced visual quality.

Treatment: While there is no cure for keratoconus, a range of treatment options are available to slow progression and manage symptoms. The choice of treatment depends on the severity and stage of the disease.

1. Eyeglasses and soft contact lenses: In the early stages of keratoconus, patients may be able to correct their vision with eyeglasses or soft contact lenses. However, as the disease progresses and the cornea becomes more irregular, these options may become less effective.

2. Rigid gas permeable (RGP) contact lenses: These are commonly used in more advanced stages of keratoconus to improve vision by compensating for corneal irregularities. RGP lenses create a smooth refractive surface on the cornea, allowing for better light focus.

3. Corneal crosslinking (CXL): Corneal crosslinking is a minimally invasive procedure aimed at strengthening the corneal collagen fibers using ultraviolet (UV) light and riboflavin (vitamin B2) drops. This treatment is used to halt or slow the progression of keratoconus, especially in younger patients.

4. Intacs (intracorneal ring segments): These are small, crescent-shaped plastic rings implanted into the cornea to flatten and reshape it, improving vision and reducing astigmatism in mild to moderate keratoconus.

5. Topography-guided photorefractive keratectomy (PRK): This surgical option is sometimes used for patients with moderate keratoconus who do not respond to contact lenses or glasses. It uses a laser to reshape the cornea.

6. Corneal transplantation (keratoplasty): For advanced cases of keratoconus where other treatments fail, a corneal transplant may be necessary. This involves replacing the diseased cornea with a donor cornea. There are two main types of transplants: penetrating keratoplasty (full-thickness corneal transplant) and deep anterior lamellar keratoplasty (partial-thickness transplant).

Complications: Keratoconus, if left untreated or poorly managed, can lead to several complications:

1. Corneal scarring: Progressive thinning and irregularity of the cornea can lead to scarring, further worsening vision and making it difficult to fit contact lenses.

2. Hydrops: In advanced cases, a sudden rupture of Descemet's membrane in the cornea can lead to a condition called corneal hydrops, where fluid accumulates in the corneal stroma. This can cause severe pain and a sudden loss of vision, but with proper management, the cornea may recover over time.

3. Glaucoma: Elevated intraocular pressure can develop, especially after corneal transplantation.

4. Infection: Following corneal transplant surgery, there is a risk of infection, which can further compromise vision.

5. Persistent visual disturbances: Even with contact lenses or surgical interventions, some individuals may continue to experience visual distortions due to the nature of the corneal irregularity.

Conclusion: Keratoconus is a progressive eye condition that can significantly affect vision if not appropriately managed. Early detection through routine eye exams and the use of advanced imaging techniques like corneal topography can help in diagnosing the disease early and implementing the necessary treatment to slow progression. Although there is no cure, a variety of treatment options ranging from contact lenses to surgical interventions are available, depending on the severity of the condition. With proper management, most individuals with keratoconus can maintain good visual function throughout their lives.

References:

1. Kennedy, R. H., Bourne, W. M., & Dyer, J. A. (1986). Keratoconus and related noninflammatory corneal thinning disorders. Survey of Ophthalmology, 30(5), 255-268.

2. Gokhale, N. S., & Jhanji, V. (2019). Management of keratoconus: A review of current treatment options. Indian Journal of Ophthalmology, 67(11), 1670-1679.

3. Raiskup, F., & Hafezi, F. (2011). Corneal crosslinking in keratoconus: A systematic review of the literature. The British Journal of Ophthalmology, 95(7), 1040-1045.

4. Gatinel, D., & Abroug, N. (2018). Keratoconus: Diagnosis and Management. Springer.

5. Seitz, B., & Langenbucher, A. (2011). Intracorneal ring segments (Intacs) in keratoconus: Long-term results. Ophthalmology, 118(4), 722-728.

Author: Dr James Ng (5 mins read)