Ultrahigh-resolution measurement by optical coherence tomography of dynamic tear film changes on contact lenses

Abstract

Purpose. To determine the dynamic pre- and postlens tear film (PLTF and PoLTF) thicknesses by using optical coherence tomography (OCT). Methods. Ultrahigh-resolution OCT was used to image the tear film of 22 subjects before and after contact lens wear. A soft lens with 1 drop of artificial tears on its concave surface was inserted onto one randomly selected eye. OCT images were taken before insertion, immediately afterward, and every 2 minutes for 10 minutes. For the contralateral eye, the lens inserted was not prewetted on the concave surface. OCT images were taken before insertion, immediately afterward, and at 3 minutes. Then another drop was instilled, and images were taken immediately afterward and every 2 minutes for 10 minutes. Images were processed by custom software to yield tear film thickness. Results. The thickness of precorneal tear film (PCTF) was 1.9 +/- 0.9 mum. The PoLTF was visualized clearly in all cases immediately after lens insertion, with 1 drop on the lens concave surface. Through the first 6 minutes after insertion, the PoLTF was greater than the PCTF. The PLTF (n = 12) and PoLTF (n = 9) were visualized immediately after lens insertion. After 3 minutes, the PLTF in most subjects and PoLTF in all subjects were invisible. The thickness of the PLTF increased after the instillation of artificial tears, whereas the PoLTF did not at any checkpoint for 10 minutes. Conclusions. Ultrahigh-resolution OCT is a promising tool for measuring the tear film. The PoLTF did not increase after instillation of artificial tears.

Figure 1.

Image processing of ultrahigh-resolution OCT images of PLTF and PoLTF over the central location. (A, B) Immediately after a lens was inserted with 35 μL artificial tears on the concave surface, the PLTF (green *) and PoLTF (red *), soft contact lens (CL), and the cornea (CO) were clearly imaged. The central 50 axial scans (0.30 mm width) of the central specular hyperreflective reflex were removed. Ten axial scans on each side of the specular reflex were then used to yield OCT longitudinal reflectivity profiles from the posterior surface of the cornea to the anterior surface of the PLTF. (C) Processing of the image produced peaks a, the posterior surface of the cornea; b, the anterior surface of cornea or posterior surface of PoLTF; c, the anterior surface of the PoLTF or the posterior surface of the contact lens; d, the anterior surface of the contact lens or the posterior surface of PLTF; and e, the anterior surface of the PLTF. The thickness of each layer was calculated by determining the number of pixels between each two peaks and then converting them to micrometers by the factor 1.13.

Figure 2.

Changes in PLTF and PoLTF after lens insertion with 1 drop of artificial tears on the concave side. (A) A soft contact lens (CL) was inserted onto the cornea (CO) with 1 drop (35 μL) of artificial tears on the concave surface of the lens. Both the PLTF (green *) and PoLTF (red *) were clearly visualized by SD-OCT immediately afterward. (B–F) After that, the PLTF and PoLTF gradually decreased. (F) At 10 minutes after lens wear, both the PLTF and PoLTF were still visible.

Figure 3.

Changes in PLTF and PoLTF after lens insertion. (A) 1 drop (35 μL) of artificial tears was placed on the concave surface of the lens before insertion. The PLTF and PoLTF were immediately increased compared with the precorneal tear film (PCTF, post hoc tests, P < 0.05). The PoLTF decreased continuously for the next 8 minutes (post hoc test, P < 0.05), and the PLTF decreased in a similar fashion (P < 0.05). (B) After lens insertion without prior application of a drop of artificial tears to the concave surface, the PLTF was immediately thicker than the PCTF at baseline (P < 0.05). However, the PoLTF was not different from the PCTF (P > 0.05). After 3 minutes of lens wear, both the PLTF and PoLTF decreased significantly compared with the moment of lens insertion (P < 0.05). When 35 μL artificial tears was instilled on the lens, the PLTF increased significantly and then decreased gradually in the following 8 minutes (P < 0.05). However, the PoLTF did not increase immediately after drop instillation and also did not change in the following 10 minutes (Re-ANOVA, P > 0.05).

Figure 4.

Changes in the PLTF and PoLTF after lens insertion followed by 1 drop of artificial tears on the convex surface of the lens. (A) A soft contact lens (CL) was inserted onto the cornea (CO) without the aid of the artificial tears. Immediately afterward, the PLTF (green *) and PoLTF (red *) were visualized by SD-OCT. (B) Three minutes later, the PLTF and PoLTF were no longer visible, as they became too thin. (C) One drop (35 μL) of artificial tears instilled onto the lens did not increase the PoLTF, whereas the PLTF was clearly increased immediately afterward. (D, E) In the following minutes, the PoLTF never increased sufficiently to become visible, and the PLTF decreased gradually with blinking.