Keratoconus; diagnosis and management:

Keratoconus (KC) is a progressive disorder of the cornea characterized by its thinning and conical protrusion, leading to irregular astigmatism and visual impairment. The global prevalence of KC ranges from 0.1 to 2%. For medical advice or diagnosis, consult a professional.

Diagnosis of Keratoconus:

• Clinical Examination: KC manifests clinically with changes in corneal curvature, irregular astigmatism, and symptoms such as visual impairment and increased sensitivity to light. The initial signs can mimic refractive errors like myopia and astigmatism, potentially delaying diagnosis.
• Corneal Topography and Tomography: Examination of corneal topography using devices like the Pentacam is crucial for diagnosis. These devices can measure anterior and posterior corneal surface curvature and corneal thickness with accuracy. Corneal tomography provides detailed maps of the cornea, aiding in the detection of the characteristic conical shape and thinning.
• Severity Classification: Keratoconus severity is primarily based on measurements of corneal curvature, specifically the K-values. Mild KC is indicated by a mean K-value of less than or equal to 48 diopters (D). Moderate KC has K-values ranging from 48 D to 53 D. Severe KC is marked by K-values exceeding 53 D.
• Corneal Densitometry: Corneal densitometry, measured using Scheimpflug tomography, provides an objective assessment of corneal clarity and is used to track the resolution of postoperative haze after corneal cross-linking (CXL).
• Wavefront Analysis: Topography-based wavefront analysis can be performed to calculate pupil size and angle kappa, and to measure high-order aberrations (HOAs) such as coma, which are typically increased in KC patients.
• Electromyography (EMG): A portable EMG system can be used for the objective evaluation of glare-induced discomfort in KC patients by recording the electrical activity of mimic muscles at different luminances. Patients with KC experience higher levels of discomfort when exposed to a glare source.
• Suspected and Subclinical KC: It is crucial to distinguish between suspected and subclinical KC, especially in candidates for refractive surgery. Multiparameter analysis using Pentacam and Corvis ST systems can aid in this differentiation. Corneal diameter has been found to be smaller in suspected KC compared to subclinical KC. Predictive models incorporating tomographic and biomechanical parameters are being developed to assess the risk of suspected KC progressing to subclinical KC or even manifest KC.

Management of Keratoconus:

• Corneal Cross-linking (CXL): CXL has become a well-established procedure for halting the progression of KC. It works by increasing the mechanical strength of the cornea. Different CXL protocols exist, including accelerated protocols and variations in riboflavin concentration. A novel Corneal Crosslinking Pen has shown promising initial results in terms of safety and effectiveness. Contact lens-assisted CXL (CACXL) is a technique for cross-linking thin corneas.
• Visual Correction:
  • Spectacles and Contact Lenses: In the early stages, vision can be corrected with glasses or soft contact lenses. As KC progresses and the cornea becomes more irregular, rigid gas permeable (RGP) lenses, scleral lenses, or customized soft lenses are often necessary to provide better visual acuity.
  • Orthokeratology: Orthokeratology involves wearing specially designed RGP contact lenses overnight to reshape the cornea and provide clear vision during the day.
• Surgical Interventions:
  • Corneal Transplantation: In advanced stages of KC with significant corneal scarring or when contact lens wear is no longer successful, corneal transplantation (penetrating keratoplasty or deep anterior lamellar keratoplasty) may be required.
  • Corneal Allogenic Intrastromal Ring Segments (CAIRS): CAIRS, sometimes combined with CXL, can be used to regularize the corneal shape and improve vision.
  • Cataract Surgery: Cataract surgery in patients with underlying KC requires careful consideration, particularly in intraocular lens (IOL) power calculation.
• Managing Associated Factors:
  • Inflammation and Oxidative Stress: Inflammation and oxidative stress play a role in KC pathogenesis. Management strategies may involve addressing these factors. For instance, topical cyclosporine A has shown to reduce the levels of inflammatory molecules.
  • Lifestyle and Environmental Factors: The role of lifestyle factors in ocular diseases, including KC, is being increasingly recognized, emphasizing the need for a holistic approach that considers dietary aspects. Environmental conditions can also impact the ocular surface.
  • Allergic Diseases: Associations between KC and allergic conditions like asthma, eczema, and allergic rhinitis have been observed, with eye rubbing being a potential link. Managing these allergies might be important in KC management.

In conclusion, the diagnosis of keratoconus involves a combination of clinical assessments, advanced imaging techniques, and increasingly, molecular analysis. Management focuses on halting disease progression with CXL and providing visual rehabilitation through various optical and surgical methods, while also considering associated inflammatory and environmental factors for a more comprehensive approach.

References:

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