Repeatability of Cornea and Sublayer Thickness Measurements Using Optical Coherence Tomography in Corneas of Anomalous Refractive Status.

PURPOSE: To assess the repeatability of epithelial, stromal, and total corneal thickness measurements with spectral-domain optical coherence tomography (SD-OCT; RTVue-XR; Optovue, Inc., Fremont, CA) in patients with myopia, keratoconus, and corneas after transepithelial photorefractive keratectomy (PRK), small incision lenticule extraction (SMILE), and femtosecond laser-assisted in situ keratomileusis (FS-LASIK).

METHODS

A total of 352 eyes of 352 patients (75 myopic, 68 post-transepithelial PRK, 61 post-SMILE, 75 post-FS-LASIK, 20 mild keratoconus, and 53 advanced keratoconus eyes) were included. The epithelial, stromal, and total corneal thickness were recorded from the pachymetric map in the following four zones: (1) central 2-mm region, (2) eight paracentral regions within 2- to 5-mm diameter, (3) eight midperipheral regions within 5- to 7-mm diameter, and (4) eight peripheral regions within 7- to 9-mm diameter. Three successive scans were performed to evaluate the repeatability.

RESULTS

For all zones up to 9-mm diameter, the coefficient of variation (CoV) for epithelial thickness measurements ranged from 1.7% to 3.5% for myopia, 2.6% to 6.2% for post-transepithelial PRK, 2.3% to 4.7% for post-SMILE, 4.0% to 6.3% for post-FS-LASIK, 2.5% to 6.2% for mild keratoconus, and 3.5% to 8.0% for advanced keratoconus. The CoV for stromal and total thickness measurements ranged from 0.2% to 2.0% for myopia, 0.7% to 4.2% for post-transepithelial PRK, 0.3% to 2.4% for post-SMILE, 0.3% to 1.9% for post-FS-LASIK, 0.6% to 3.0% for mild keratoconus, and 1.0% to 5.9% for advanced keratoconus.

CONCLUSIONS

RTVue-XR SD-OCT showed excellent repeatability when generating the pachymetric map in myopic eyes. Measurements, especially for epithelial thickness, were relatively more variable for corneas with keratoconus and those having undergone keratorefractive surgery. [J Refract Surg. 2019;35(9):600-605.].