Assessment of Incisional Wounds Before and After Intraocular Lens Insertion In Microincision Cataract Surgery

1. Assessment of Incisional Wounds Before and After Intraocular Lens Insertion In Microincision Cataract Surgery Akimi Kizawa1), Shuichiro Hayashi2), Daijiro Kurosaka1) 1) Department of Ophthalmology, Iwate Medical University School of Medicine 2) The Center for Electron Microscopy and Bio-Imaging Reserch, Iwate Medical University

2. Introduction Currently, cataract removal is performed through an incision about 1.2 mm in width for bimanual PEA and about 1.8 mm in width for coaxial PEA. Intraocular lens (IOL) can be inserted using various techniques through an ultra-small incision. However, it is unclear whether the insertion of IOL damages ocular tissue around the wound site. To examine tissue damage around the wound site after IOL insertion, we evaluated the difference between the wound width before and after IOL insertion and observed the wound site with scanning electron microscope (SEM).

3. ① Materials ① ② • Slit knives 1.9mm～3.0mm (Kai Industries co.) • Cartridges and IOLs ③ ④ ⑤ ①,②,③:HOYA (in Japan) ④,⑤:Alcon

4. Methods After the corneal incision was made with 1.9 to 3.0 mm keratome in five porcine eyes, varieties of IOLs were inserted. Incision widths before and after IOL insertion were measured using an inner gauge. The porcine tissue around the corneal incisions were observed by SEM after inserting IOLs (Y60H with various widths and SN60AT at a 2.0mm).

5. Results The incision sizes before IOL insertion were smaller than the sizes of the slit knives although the incision sizes were proportional to the size of the slit knives. (Fig.1). After each IOL insertion, most of the incisions were enlarged. Although, the resistance ability of the human corneal tissue is different from that of a porcine, this should not decrease the value of this data(Fig.2). In addition, the smaller the sizes of the slit knives used, the smaller the difference between the incision sizes before and after IOL insertion (Fig.3). In SEM, tissue damage was not observed at the wound made with slit knives more than 2.5 mm and before the Y60H insertion (Fig.4). However, tissue damage such as elongation and rupture of collagen fiber was observed at wound after the Y60H insertion through incisions made with 1.9 to 2.4mm slit knives (Fig.5).

6. 3.00 Y60H 2.50 YA60BBR 2.00 VA60BB Incision widths before IOL insertion（ｍｍ） SA60AT 1.50 SN60WF 1.00 1.9 2.0 2.2 2.3 2.4 2.5 2.65 2.75 2.85 3.0 Slit knife（ｍｍ） Figure 1.Slit knife and incision widths before IOL insertion Incision widths before IOL insertion were measured using an inner gauge, and resulted in a smaller incision than the actual slit knife widths.

7. 3.50 3.00 Y60H YA60BBR Incision widths after 2.50 IOL insertion（ｍｍ） VA60BB SA60AT 2.00 SN60WF 1.50 1.9 2.0 2.2 2.3 2.4 2.5 2.65 2.75 2.85 3.0 Slit knife（ｍｍ） Figure 2. Slit knife and incision widths after IOL insertion With each IOL, the smaller the slit knife width, the greater the incision width after IOL insertion.

8. 1.20 1.00 Y60H 0.80 YA60BBR before and after IOL insertion（ｍｍ） 0.60 VA60BB Differences in incision widths SA60AT 0.40 SN60WF 0.20 0.00 1.9 2.0 2.2 2.3 2.4 2.5 2.65 2.75 2.85 3.0 Slit knife（ｍｍ） Figure 3. Slit knife and differences in incision widths before and after IOL insertion The smaller the sizes of the slit knives used, the smaller the difference between the incision sizes before and after IOL insertion. There is no difference between the incision width before and after SA60AT, SN60WF, and Y60H insertion with an incision made with a 3.0 mm, a 2.75 mm, and a 2.75 mm slit knife, respectively.

9. Normal tissue A cross section made by a slit knife Figure 4. Scanning electron microscopic image of the corneal incision made with a 2.0 mm slit knife before IOL insertion The collagen fiber of the incision margin is the same as normal tissue.

10. Y60H SA60AT Figure 5. The collagen fiber of the corneal incision margin made with a 2.0 mm slit knife after IOLs (Y60H and SA60AT) insertion ×10,000 Collagen fiber around the incision after each IOL insertion were elongated (orange circle) and ruptured (green circle).

11. Discussion The present study shows that an incision, made with less than a 2.5 mm slit knife, enlarged and damaged the corneal tissue. Although, the resistance ability of the human corneal tissue is different from that of a porcine, this should not decrease the value of this data. The difference between the incision size of human eyes before and after IOL insertion might be smaller than that of porcine eyes. Further studies are required to determine the adequate incision size for human eyes. However, this study suggests that the forcible insertion of the IOLs may damage tissue, leading to the deterioration of self-sealing and increasing the risk of induced astigmatism.

12. Conclusions When IOL inserted through ultra-small incision, the tissue damage, such as an elongation of collagen fiber, may occur. So insertion of the IOL through too small incision should be avoided.