Abstract
Purpose :
To investigate the feasibility of corneal filler injection into intracorneal pockets of different ovalities for combined spherical and astigmatic correction.
Methods :
Femtosecond laser-assisted intracorneal oval pockets were cut in ex-vivo rabbit eyes, orthogonal to the steep axis of respective astigmatism at a 120µm depth (distance to the anterior corneal surface). Two different pocket ovalities were used: 4.5m x 6mm and 5.5mm x 6mm. Filler material (Hyaluronic acid 1%) was injected via a laser-cut tunnel connecting the pocket with a 300µm wide incision in the corneal periphery. Corneal refractive power was measured pre- and postoperatively using three-dimensional optical coherence tomography (OCT). A custom fit algorithm, including the correction of OCT immanent fan distortion and intraocular ray tracing, was implemented to quantify the images. The surgically induced astigmatism (SIA) was calculated according to Alpin’s method. To compare the SIA axis, the steep axis of the cornea’s astigmatism was normalized to 0°.
Results :
A linear correlation between the injected filler volume and the SIA was observed. The more oval the pocket, the greater the slope m of the filler volume-dependent change in SIA tended to be (4.5mm x 6mm: m = 0.65 dpt/mm3; 5.5mm x 6mm: m = 0.07 dpt/mm3, p = 0.25 (testing the null hypothesis that the slopes are all identical)). The change in spherical power remained constant using different pocket ovals (4.5mm x 6mm: m = 1.05 dpt/mm3; 5.5mm x 6mm: m = 1.29 dpt/mm3, p = 0.76). A mean SIA axis of 93.5 ± 50 degrees to the steep axis of the eye’s astigmatism was observed.
Conclusions :
We demonstrate the technical applicability of corneal filler injection for combined spherical and astigmatic refraction correction ex-vivo. Moreover, we describe the relationship between spherical power and SIA change and respective pocket ovality, which is the key to predicting refractive outcomes in the future. A major obstacle of this study is the increased variation in our data, presumably resulting from surgical manipulation and lack of recovery time after surgery and OCT imaging (unlike in clinical practice). Thus, further in-vivo studies will be necessary to overcome this inherent methodological problem and establish a meaningful metric for combined spherical and astigmatic correction using corneal filler injection.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.