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Y. Li, M. Tang, V. Thakrar, D. M. Meisler, D. Huang; Keratoconus Screening With High-Speed Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4019.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a keratoconus screening method using the corneal pachymetry map measured by a high-speed corneal and anterior segment optical coherence tomography (CAS-OCT) system.
The CAS-OCT prototype system used in this study was similar to the FDA-approved Visante OCT system. It worked at 1.3 µm wavelength and had a scan rate of 2000 axial-scan/second. A pachymetry scan pattern (8 radials, 128 axial scans each, 10mm diameter) centered at the corneal vertex was used to map the corneal thickness. The pachymetry map was divided into zones by octants (superior, superotemporal, temporal, inferotemporal, inferior, inferonasal, nasal, superonasal) and annular rings (2, 5, 7, and 10 mm diameters). The minimum, average, maximum thickness value from each zone was calculated. 37 keratoconic eyes of 21 subjects were scanned 3 times. 36 eyes of 18 normal subjects were also scanned to serve as a comparison.
The keratoconic cornea was significantly thinner (452.6±60.9 v. 546±23.7 µm at the thinnest) and the thinnest spot on the corneal map was inferiorly displaced (-0.81±0.48 v. -0.12±0.26 mm). The keratoconic cornea was significantly more asymmetric in terms of the thickness. The average difference between the pericentral inferior octant and the superior octant was -44.8±28.7 µm for the keratoconic corneas and -9.9±9.3 µm for the normal corneas. The average difference between the pericentral inferotemporal octant and the superonasal octant was -63±35.7 µm for the keratoconic corneas and -22±11.4 µm for the normal corneas. The keratoconic cornea also had larger minimum to median thickness difference inside the d<5mm zone (-95.2±41.1 v. -45±7.7 µm). All differences were statistically significant (t-test, P < 0.001).
OCT improves keratoconus screening by providing the corneal pachymetry map to detect abnormal corneal thinning. It can be used by its own or be complementary to the topography map for keratoconus or forme fruste keratoconus diagnosis and management.
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