Normalized corneal backscatter profiles of two baseline visits before lens wear showed good repeatability (standard deviation of the difference of the normalized backscatter between two visits: 0.07) as shown in
Figure 1 . The magnitudes of backscattered light were different among corneal sections (slices) from the epithelium to the posterior stroma (ANOVA: F
(10,190) = 30.24;
P = 0.000).
Immediately after contact lens removal, central corneal thickness increased significantly (13.8% ± 2.3%; mean ± SD) from baseline (
P = 0.0001, paired
t-test) then decreased during the deswelling course. The profile of corneal backscattered light changed significantly (Re-ANOVA: F
(50, 950) = 2.22,
P = 0.0001) after lens wear
(Fig. 2) and significant increases were found in the epithelium (EP: 36.4%), anterior (slice [S]1: 19.4%), and posterior stromal layers (S10: 35.6%) immediately after lens removal (post hoc test,
P = 0.005), compared with baseline, but returned to baseline by 100 minutes. The anterior (S1:
P = 0.005) and posterior (S10:
P = 0.003) stromal backscattered light increased significantly compared to the middle layers (S6).
Figure 3 shows examples of OCT images of central (1.13 mm) corneal scans before lens insertion and immediately after lens removal. The OCT image shows increased backscattered light depicted in the red and yellow. The quantitative measures of the backscattered light are represented by the reflectivity profiles. The “After” profile shows how the peaks have altered. The graphs of the slice profiles illustrate how the backscattered profile has become bowl shaped, reflecting an increase in light-backscattering in the epithelium, anterior, and posterior stromal layers (lower right graph). There was a strong correlation (
r = 0.937,
P < 0.05) between the changes in light-backscattering (the integrated area under each profile curve) and corneal swelling during the deswelling period, as indicated in
Figure 4 .
Figure 5 shows the light-backscattering recovery of the anterior and posterior stromal layers during the deswelling period. The Pearson correlation (
r) was 0.745 for the anterior layer (S1) and 0.934 for the posterior stromal layer (S10). According to exponential regression, the recovery rate (slope) was −1.08 for the anterior layers and −0.906 for the posterior layers (no significant difference between the two slopes,
P > 0.05). The recovery of backscattered light in the epithelium and posterior stromal layer correlated positively with corneal deswelling, as shown in
Figure 6 (Pearson correlation:
r = 0.938 for the epithelium and
r = 0.982 for the posterior stromal layer).
There was no significant change in light-backscatter in the control eyes (Re-ANOVA: F(20, 380) = 0.72, P >0.05) compared with baseline. However, total corneal thickness in the control eyes changed significantly during the post–lens-wear period (Re-ANOVA: F(4,76) = 5.57, P H-F = 0.003), due to thinning at 60 (−0.6%) and 100 (−0.5%) minutes compared with baseline (post hoc test: P = 0.004).