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Laser in situ keratomileusis flap measurements: Comparison between observers and between spectral-domain and
Reece C Hall1, Farook K Mohamed, Hla M Htoon
1Singapore National Eye Centre, National University of Singapore, Singapore.
Purpose:
To evaluate the between-observer (interobserver) and between-instrument (intraobserver) variability in flap thickness measurements after laser in situ keratomileusis (LASIK) using spectral-domain and time-domain anterior segment optical coherence tomography (AS-OCT).
Setting:
Singapore National Eye Centre.
Design:
Evaluation of diagnostic test or technology.
Methods:
Two independent masked observers measured flap thickness 1 month after LASIK using spectral-domain (RTVue) or time-domain (Visante) AS-OCT. The measurements were taken at central (0.0 mm), -1.5 mm, and +1.5 mm locations. Measurements were repeated to assess between-instrument variability.
Results:
There was no statistically significant difference in mean flap thickness between the 2 observers at -1.5 mm, 0.0 mm, and +1.5 mm on spectral-domain AS-OCT and at -1.5 mm and +1.5 mm on time-domain AS-OCT (P < .01). There was a statistically significant difference between the 2 observers in the central (0.0 mm) values on time-domain AS-OCT (P=.0008). There was stronger interobserver correlation for spectral-domain AS-OCT at -1.5 mm (r = 0.82), 0.0 mm (r = 0.88), and +1.5 mm (r = 0.88) than for time-domain AS-OCT (r = 0.73, r = 0.62, and r = 0.79, respectively). There was no statistically significant difference in between-instrument measurements. There was stronger between-instrument correlation with spectral-domain AS-OCT than with time-domain AS-OCT at all locations. The mean standard deviation (measure of instrument repeatability) for spectral-domain AS-OCT was 4.19 μm.
Conclusion:
Spectral-domain AS-OCT had closer agreement in between-observer and between-instrument measurements than time-domain AS-OCT and provided more consistent measurements of post-LASIK flap thickness.
