OCT layered tomography of the cornea provides new insights on remodeling after photorefractive keratectomy

Abstract

OCT (optical coherence tomography) of corneal layers was generated to analyze the remodeling of the epithelium and stroma after photorefractive keratectomy (PRK). Myopic PRK was performed in 15 patients. One eye underwent manual scraping of epithelium while the other was treated with Epi clear. Epi clear allowed a gentler removal of the epithelium compared to manual scraping. Scheimpflug (Pentacam, OCULUS Optikgerate Gmbh, Wetzlar, Germany) and OCT (RTVue, Optovue Inc., Fremont, California, USA) scans of the cornea were performed before and after PRK (3 months). The OCT scanner and Pentacam acquired 8 and 25 radial 2-D scans of the cornea, respectively. The results showed similar topographic changes on the anterior corneal surface between Scheimpflug and OCT imaging. The curvature of the underlying anterior surface of the stroma after PRK was similar to the anterior corneal surface (air-epithelium interface), when measured with OCT. Aberrometric changes were mostly similar between Scheimpflug and OCT. However, Scheimpflug imaging reported greater changes in spherical aberration and corneal higher order aberrations than OCT after PRK. This is the first study to quantify the curvatures of the stromal layers with OCT after PRK. New insights were gained, which could be useful for refinement of surgical ablation algorithms, refractive procedures and detection of ectasia.

Fourier-Domain OCT Imaging of the Ocular Surface and Tear Film Dynamics: A Review of the State of the Art and an Integrative Model of the Tear Behavior during the Inter-Blink Period and Visual Fixation

“…Currently, OCT imaging is capable of identifying the anatomical structure and measuring the thickness of various corneal layers, and also of detecting some ultrastructural features (such as the stromal striae departing from the anterior stroma to the Descemet membrane) [7,63,64]. This approach can be useful in keratoconus eyes (where an increased epithelial thickness may be predictive of corneal hydrops) [65], in corneal dystrophies involving the epithelium and/or basal membrane [66], in differential diagnosis between pterygium and pseudo-pterygium [67], after photorefractive keratectomy [68] or cross-linking (during the remodeling of epithelium, and the detection of the demarcation line) [69], and in monitoring the epithelia changes following chemical burns [70].…”

Unique corneal tomography features of allergic eye disease identified by OCT imaging and artificial intelligence

“…Twelve radial scans (24 semimeridians) spaced over 360 were acquired for each eye. A summary of the methods to derive curvature and aberrations from the B-scans is presented below from our earlier publications [10][11][12][13][14]. The corneal edge along with the air-Epithelium interface (A-E) and epithelium-Bowman's layer interface (E-B) were detected in the distortion corrected images provided by Triton.…”

“…The E‐B curvature and aberrations significantly improved the detection of forme fruste keratoconus [11]. The methods also showed unique remodeling features at the stromal level after photorefractive keratectomy [12]. Recently, the agreement of A‐E and E‐B curvature and aberrations between OCT and Scheimpflug imaging were also assessed in healthy and keratoconus eyes intraoperatively.…”

“…Excellent repeatability of A‐E and E‐B curvature and aberrations were also established in a recent prospective study [14]. While computing the curvatures and aberrations, both A‐E and E‐B were assumed to be exposed to air (refractive index of 1) so that direct comparisons of the shape of the two interfaces could be performed [10–14]. The tomographic parameters of the AED eyes were compared with A‐E and E‐B parameters of healthy, forme fruste keratoconus (FFKC) and keratoconus (KC) eyes.…”

Optical models for intraocular lens planning in keratoconus: A step in the right direction and more to do

“…[ 4 ] OCT tomography has also shed new information on postrefractive surgery eyes, which Scheimpflug imaging currently underestimates, for example, change in spherical aberration of the cornea after low-myopia photorefractive keratectomy was lower when measured with OCT than with Pentacam ® (Oculus Optikegrate Gmbh, Germany). [ 5 ] Eventually, every model will have to be tested on patients. Currently, there is very limited data available.…”