Correction of hyperopia by intrastromal cutting and liquid filler injection

Abstract

Correction of hyperopia requires an increase of the refractive power by steepening of the corneal surface. Present refractive surgical techniques based on corneal ablation (LASIK) or intrastromal lenticule extraction (SMILE) are problematic due to epithelial regrowth. Recently, it was shown that correction of low hyperopia can be achieved by implanting intracorneal inlays or allogeneic lenticules. We demonstrate a steepening of the anterior corneal surface after injection of a transparent, liquid filler material into a laser-dissected intrastromal pocket. We performed the study on ex-vivo porcine eyes. The increase of the refractive power was evaluated by optical coherence tomography (OCT). For a circular pocket, injection of 1 μl filler material increased the refractive power by +4.5 diopters. An astigmatism correction is possible when ellipsoidal intrastromal pockets are created. Injection of 2 μl filler material into an ellipsoidal pocket increased the refractive power by +10.9 dpt on the short and +5.1 dpt on the long axis. OCT will enable to monitor the refractive change during filler injection and is thus a promising technique for real-time dosimetry.

Keywords: astigmatism; hyperopia; laser dissection; optical coherence tomography; refractive surgery.

Fig. 1

(a) Experimental setup for the investigation of intrastromal cutting dynamics. UV laser pulses are focused through the microscope objective ($\mathrm{NA}=0.38$) into the cornea of the aplanated eye in the eye holder [photograph in (b)]. The cover glass for aplanation is marked by an arrow, the needle inside the bulbus for adjustment of the intraocular pressure is marked by a star. UV light of the laser for dissection becomes visible by fluorescence in the lens at longer wavelengths.

Fig. 2

(a) Photographs of the porcine eye in the eye holder immediately after laser-induced cutting of a circular intrastromal pocket with 6 mm diameter, and (b) after removing the aplanating cover glass. (c) An elliptic pocket with a short axis of 5 mm and a long axis of 7 mm. The residual bubble layer demarcates the cutting area, which is additionally marked by a white line. The small side cut for simplification of the injection process of the filler material is visible at the top of the areas (arrows).

Fig. 3

(a)–(c) Photographs of the porcine eye below the OCT system before injection, and after injection of $1.5\mu \mathrm{l}$ transparent filler material into the intrastromal pocket with 6 mm diameter in (b) lower and (c) higher magnification. Photographs were taken through a stereo operation microscope (Zeiss OpMi-1). The white ring in (a) is a reflection from the circular LED illumination of the OCT system. The filler material in the pocket is hardly visible and can be discerned only in the higher magnification image.

Fig. 4

OCT images of the porcine cornea (a) before cutting, (b) after cutting, and (c, d) after injection of the transparent filler material into the intrastromal pocket. The OCT scan of the back surface in (d) contains a part of the front surface as an inverted image, which is an OCT artifact. The circular pocket has a diameter of 6 mm and was located $90\mu \mathrm{m}$ deep within the corneal stroma. The side cut for filler injection is visible on the right-hand side (arrow) in (b) and (c). The red and blue lines are circular arcs fitted to the corneal (c) front surface and (d) back surface before and after filler injection. The reference bar of $100\mu \mathrm{m}$ is given for air; inside the corneal stroma the optical path length is increased by the factor $n_{\text{cornea}}=1.376$.

Fig. 5

OCT images of the porcine cornea (a, c) after cutting and (b, d) after injection of $2\mu \mathrm{l}$ transparent filler material into an elliptic intrastromal pocket. Changes in corneal curvature differ along the two axes. The red and blue lines are circular arcs fitted to the front surface before and after injection. The reference bar of $100\mu \mathrm{m}$ is given for air; inside the corneal stroma the optical path length is increased by the factor $n_{\text{cornea}}=1.376$.

Fig. 6

OCT images of the posterior surface of the porcine cornea (a) after cutting and after injection of (b) $2\mu \mathrm{l}$ and (c) $6\mu \mathrm{l}$ transparent filler material into an intrastromal pocket of 5.5 mm diameter located in $400\mu \mathrm{m}$ depth within the cornea. The OCT scan contains a part of the front surface as an inverted image, which is an OCT artifact. The flattening of the corneal back curvature increases with increasing filler volume from $\mathrm{\Delta }h=90$ to $287\mu \mathrm{m}$. The red and blue lines are circular arcs fitted to the back surface before and after injection. They are used to determine the central flattening $\mathrm{\Delta }h$. The reference bar of $100\mu \mathrm{m}$ is given for air; inside the corneal stroma the optical path length is increased by the factor $n_{\text{cornea}}=1.376$.