Angle κ and its effect on the corneal elevation maps in refractive surgery candidates

Area of Science:

• Ophthalmology
• Corneal Surgery
• Ophthalmic Imaging

Background:

• Accurate corneal imaging is crucial for refractive surgery planning.
• Angle kappa and decentration indices are key parameters in corneal topography.
• Understanding their impact on elevation maps is essential for reliable preoperative assessment.

Purpose of the Study:

• To investigate the relationship between angle kappa, Pentacam decentration indices, and corneal elevation maps.
• To evaluate potential confounding factors in refractive surgery candidate assessments.
• To compare these parameters between normal eyes and keratoconus eyes.

Main Methods:

• Retrospective analysis of 173 normal refractive surgery candidates and 148 keratoconus patients.
• Corneal elevation maps, keratometry, decentration indices (Pentacam HR), and angle kappa (Orbscan IIz) were analyzed.
• Pearson correlation coefficients were used to assess associations, with comparisons made between best-fit sphere (BFS) and best-fit toric ellipse (BFTE) calculations.

Main Results:

• Angle kappa correlated positively with temporal elevations (BFS) and corneal astigmatism correlated with nasal/temporal elevations (BFS).
• These associations disappeared when using BFTE for elevation calculations.
• Thinnest point to vertex decentration was associated with back temporal elevation (BFTE) in both normal and keratoconus eyes.

Conclusions:

• Corneal elevation maps derived using BFS may be influenced by angle kappa and astigmatism, potentially affecting refractive surgery assessments.
• Employing BFTE as the reference for elevation data calculation is recommended to mitigate diagnostic issues.
• BFTE-based analysis offers a more reliable method for evaluating corneal topography in refractive surgery candidates.