Abstract
Purpose :
LIRIC is a non-invasive method for correcting aberrations in hydrogels, IOLs and the cornea. As such, the need exists for non-destructive metrology of LIRIC-induced optical phase change. Here we demonstrate the feasibility and validation of parallel phase resolved OCT for measurements of optical phase change induced by LIRIC in hydrogel.
Methods :
To produce the LIRIC sample, a femtosecond laser was focused inside a 0.5 mm thick hydrogel button (Contamac, Acofilcon A) and scanned throughout a single layer. Seven rectangular regions (0.1 x 0.4 mm each) of LIRIC piston wavefronts were induced. Each region was written at a distinct laser power (0.7 to 1.0 W, in 0.05 W steps). The LIRIC-induced phase shift was subsequently measured in two methods: (a) phase-resolved line-scan OCT and (b) phase-shifting interferometry (PSI). The line-scan, spectral domain OCT (λ=820 nm, Δλ=80 nm) was used to image a 3.5x2.5 mm field-of-view on the hydrogel. The 3D phase distribution was obtained in the reconstructed complex volume after segmenting the LIRIC layer in depth. The PSI consisted of a Mach-Zehnder interferometer (λ=632 nm) with a piezo-driven phase-shifting mirror in the reference arm. LIRIC was quantified from both OCT and PSI by computing the difference in optical phase between written and unwritten regions of the hydrogel.
Results :
The intended spatial profile of the LIRIC-induced wavefront was readily reproduced in both measurements. Both measurement techniques (OCT and PSI) showed a predictable increase in the magnitude of phase change with increasing laser power. With OCT, it ranged from 76±58 to 376±91 nm at 0.7 and 1.0 W, respectively. With PSI, it ranged from 61±29 to 334±40 nm. The OCT and PSI measurements were highly correlated (R-squared = 0.99).
Conclusions :
Phase resolved OCT was shown to accurately measure optical phase change in hydrogels induced via femtosecond laser processing (LIRIC).
This is a 2021 ARVO Annual Meeting abstract.