Purpose:
Anterior segment tomographic imaging offers the ability to optically characterize the cornea without the limitations inherent to topographic imaging. This is especially important in corneas that have been surgically altered by laser refractive surgery and which no longer maintain the topographic assumptions. Spectral domain optical coherence tomography (SDOCT) offers the highest axial resolution of the clinically available tomographic imaging systems. However, due to its sequential imaging nature, SDOCT volumes of the cornea can be affected by motion artifacts. To mitigate these motion artifacts, we previously developed Distributed Scan SDOCT (DSOCT). In DSOCT, patient motion is encoded into high spatial frequencies by high-speed distribution of individual A-scans across the cornea; the motion artifacts can then be filtered . In previous work, we found DSOCT to be comparable to existing clinical imaging in determining corneal power in normal corneas. In this study, we examined the ability of DSOCT to characterize the corneal power in eyes after laser refractive surgery.
Methods:
Under an IRB approved protocol, subjects undergoing myopic LASIK had corneal imaging prior to and 3 months after surgery. The corneal imaging consisted of DSOCT, topography, and Scheimpflug photography. DSOCT used a commercial SDOCT system with =840nm, Δ=50nm, 10 kHz A-scan rate and a telecentric scanner in the sample arm (Bioptigen; RTP, NC). The portable telecentric scanner was mounted on a modified slit-lamp base with a chin and forehead rest for subject stability. A custom waveform was applied to the galvanometer scanners for high-speed distribution of A-scans across the central 6mm of the subject’s cornea. The change in pre to post-operative corneal powers obtained from the three imaging modalities was then compared to the manifest refraction change.
Results:
6 eyes of 5 subjects were imaged. The mean spherical equivalent pre-operative refraction was -3.75 D ± 1.49 D; the mean spherical equivalent post-operative change in refraction was 3.14 D ± 1.60 D.The mean differences between the clinical refractive power change and that reported by the imaging modalities was 0.19 D ± 0.51 D (DSOCT), 0.55 D ± 0.61 D (topography), and 0.32 D ± 0.46 D (Scheimpflug photography).
Conclusions:
Compared with topography and Scheimpflug photography, distributed scan SDOCT potentially better reflects the change in corneal refractive power after LASIK. However, there is similar variability in the comparison of DSOCT measurements to refractive change with respect to the other imaging modalities.
Keywords: refractive surgery: corneal topography • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: clinical