Table 3.

Summary of devices to detect keratoconus.

Device	Indices used to diagnose keratoconus	Corneal anatomy
Keratometer	Qualitative visualization through mires [10]	Anterior
Placido disc-based Imaging	Refer to Table 1a, b for individual indices, Table 2 for multivariate keratoconus systems	Anterior
Dynamic skiascopy	Combines placido-disc-based corneal topography with a ray tracing aberrometer and provides information on refractive error, keratometry and patient’s quality of vision [23]	Anterior/posterior
Slit-scanning topography	Provides anterior corneal curvature indices, pachymetry, focal elevations, and depressions from a computer-generated best-fit sphere Indices to diagnose keratoconus include I–S value, central keratometry, posterior float, thinnest point pachymetry [29]	Anterior/stromal/posterior
Scheimpflug imaging	Provides data on anterior and posterior elevation of the corneal apex, keratometric values, pachymetric data based on comparing reconstruction of the anterior and posterior corneal surface to a best-fit sphere Belin ABCD keratoconus grading system assesses the anterior and posterior corneal surfaces to help diagnose keratoconus [35]	Anterior/stromal/posterior
Dual Scheimpflug imaging	Provides data on anterior and posterior elevation, keratometric values, and surface indices Indices to diagnose keratoconus include irregular astigmatism index, standard deviation of corneal power, and surface regularity index [48]	Anterior/stromal/posterior
Time-domain optical coherence tomography	Asymmetric thinning and focal central corneal thinning derived from pachymetric data [58]	Anterior/stromal/posterior
Spectral-domain optical coherence tomography	Corneal epithelial, stromal, and pachymetric pattern standard deviation scores [59]	Anterior/epithelial/stromal/posterior
Swept source-optical coherence tomography	Keratometric data, anterior corneal elevation, posterior corneal elevation, pachymetric, and Fourier indices [59]	Anterior/epithelial/stromal/posterior
Polarization-sensitive optical coherence tomography	Disruptions in fibril arrangement via birefringence data [70]	Stromal/posterior
Slit confocal microscopy	Anterior and posterior stromal keratocyte density, epithelial cell shape, pleomorphism and polymegathism of endothelial cells, mean subbasal nerve density, and stromal nerve diameter [78]	Epithelial/stromal/endothelial
Noncontact tonometry	Corneal hysteresis and corneal resistance factor with Ocular Response Analyzer (ORA, Reichert, Inc., Depew, NY) [82, 84] Radius value of central concave curvature at highest concavity, central corneal thickness, Corvis biomechanical index, tomographic and biomechanical index with CorVis ST (CST; Oculus, Wetzlar, Germany) [88]	Stromal
Brillouin light-scattering microscopy	Brillouin frequency shift [93]	Stromal
Atomic force microscopy	Stiffness of anterior corneal stroma [94]	Stromal
Optical coherence elastography	Localized mechanical stress via noncontact based or contact-based system [98]	Stromal