A new, pachymetry-based approach for diagnostic cutoffs for normal, suspect and keratoconic cornea

Abstract

Purpose To analyze whether an association exists between keratometric and pachymetric changes in the cornea, and whether it can be used to create pachymetric cutoff criteria secondary to keratometric criteria. Methods In this cross-sectional study, 1000 candidates presenting to the refractive surgery services of a tertiary care hospital underwent bilateral Orbscan IIz (Bausch and Lomb) assessment along with other ophthalmic evaluation.Results Stepwise regression analysis-based models showed that simulated keratometry (simK) astigmatism was significantly predicted by the minimum corneal thickness (MCT) and difference between central and MCT (dCT), mean SimK by the MCT and dCT, and maximum keratometry in the central 10-mm zone by the MCT and dCT (Po0.001). The mean MCT values were 542.5±39.6, 539.9±39.2, 524.2±49.5, and 449.3±73.7 lm for flatter normal (o44 D), steeper normal (Z44 D), keratoconus suspect and keratoconic eyes, respectively (Po0.001). The mean differences between central corneal thickness and MCT (dCT) were 12.2 ± 7.1 lm, 12.4 ± 7.4 lm, 14.4 ± 8.9 lm and 23.2 ± 10.1 lm for the flatter normal, steeper normal, keratoconus suspect, and keratoconic eyes, respectively (Po0.001). Mean and 2SD cutoff were used to suggest that a cornea having MCTo461 lm or dCT427 lm has only a 2.5% chance of being normal and not a keratoconus suspect or worse. Conclusion Pachymetric diagnostic cutoffs can be used as adjuncts to the existing topographic criteria to screen keratoconus suspect and keratoconic eyes.

A combination of topographic and pachymetric parameters in keratoconus diagnosis

“…Although pachymetry based diagnostic algorithms are still being investigated, corneal pachymetry was not included in the formula of indices introduced by Rabinowitz-McDonnell [5,6,8,[18][19][20]. In the present study, ROC analysis of each Scheimpflug parameter revealed that both Kmax and TP had high diagnostic ability in discriminating keratoconic eyes from normals (with sensitivity-specificity values of 92.9-92.4% and 89.6-93.3%, respectively).…”

“…Hence, many researchers developed valuable indices and maps [5][6][7][8][9][18][19][20][21][22]. Rabinowitz and McDonnell [5] introduced the central K and dioptric difference between inferior and superior area (I-S).…”

Predictive Analysis Between Topographic, Pachymetric and Wavefront Parameters in Keratoconus, Suspects and Normal Eyes: Creating Unified Equations to Evaluate Keratoconus

“…1 However, recent attempts have shown the possibility to grade the keratoconus also on the pachymetric and corneal wavefront changes. [2][3][4][5][6][7] Authors have included a combination of these factors such as topography & pachymetry, topography & corneal aberrations/biomechanics to create composite grading scales. 4,[6][7][8][9] However, the ideal result would be to create a combined, multifactorial grading scale.…”

“…[2][3][4][5][6][7] Authors have included a combination of these factors such as topography & pachymetry, topography & corneal aberrations/biomechanics to create composite grading scales. 4,[6][7][8][9] However, the ideal result would be to create a combined, multifactorial grading scale. This seems biologically plausible because the changes seen in progressive keratoconus, such as increase in the corneal steepness, worsening of the wavefront profile and decreased corneal thickness are the manifestations of a same disease process.…”

Distinction between Early Keratoconus with Normal Vision and Normal Cornea based on Pattern Recognition Analysis

“…They reached a sensitivity and specificity of 82.00 and 80.00% respectively. In addition, Prakash et al 18 have proposed cut-off values of pachymetry in keratoconic patients using Orbscan IIz system. Their results suggest that a cornea with minimal pachymetry <461 µm or a difference between the minimum pachymetry and corneal central thickness greater than 27 µm has 97.50% risk of being suspected keratoconus or clinical keratoconus, and therefore, only 2.50% are likely to be normal.…”