Of the patients scheduled for cataract surgery, we enrolled 15 patients (15 eyes) who underwent cataract surgery in this prospective observational study from May 2018 to October 2018. Seven eyes on the right and eight eyes on the left were included from seven male and eight female patients. The research was performed at the department of ophthalmology, Dongsan Medical Center, affiliated with Keimyung University in Daegu, Korea. All clinical evaluations and measurements followed the tenets of the Declaration of Helsinki, and the research protocol was reviewed and approved by the Ethics Committee of Dongsan Medical Center (DSMC 2018-07-007). Informed consent was obtained from all patients after describing the details of the study. The inclusion criteria were age-related cataracts with favorable physical status and uneventful in-the-bag IOL implantations of one of both eyes. Those with a previous history of intraocular surgery, previous ocular trauma or uveitis, an axial length shorter than 22.0 mm or longer than 24.5 mm, pseudoexfoliation syndrome, poor pupil dilation, preoperative or perioperative zonular weakening were excluded.

Ophthalmologic examinations included several parameters. The preoperative values were axial length and anterior chamber depth acquired using optical low-coherence reflectometry (Lenstar LS900; Haag-Streit AG, Bern, Switzerland). Cataract nuclear opalescence was graded from 1 to 5 according to the Lens Opacity Classification System III criteria [20]. Preoperative and 1-day postoperative values included uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA) recorded in logarithm of the minimum angle of resolution units, spherical equivalent performed by autorefraction (RK-F2; Canon, Tokyo, Japan), and intraocular pressure (IOP) measured using a non-contact tonometer (NT-530P; Nidek, Tokyo, Japan).

Approximately 1 hour before surgery, each patient was twice-instilled with 0.5% tropicamide/0.5% phenylephrine fixed combination eye drops (Tropherine; Hanmi Pharm, Seoul, Korea) for 5 minutes in order to maximize pupil dilation. All surgeries were performed by the same surgeon (JHJ), who performed a 2.85 coaxial incision (Infiniti Vision System; Alcon, Fort Worth, TX, USA). After instillation of 0.5% proparacaine topical anesthetic eye drops (Paracaine, Hanmi Pharm), a clear corneal incision was made at the 9 o’clock (right eye) and 2 o’clock (left eye) positions. Before anterior capsulotomy, a viscoelastic device (DisCoVisc, Alcon) was placed in the anterior chamber through a sideport incision at the 12 o’ clock position (right eye) and 5 o’ clock position (left eye). During the capsulotomy procedure, we performed corneal marking using a 5.5-mm capsulotomy marker. The PPC device’s nitinol cutting element was inserted into the anterior chamber through the corneal incision and positioned centrally on the anterior capsule under the corneal marking. An assistant then applied suction to allow for the apposition of the nitinol ring with the capsule. After adequate suction was completed, the cutting procedure was performed, as indicated by the console, and the electrical energy was released. After the introduction of the Zepto PPC handpiece, the thermal profile of the corneal incision site adjacent to the Zepto PPC shaft was recorded using an infrared thermographer (T420bx; Flir Systems, Wilsonville, OR, USA) with a temperature range of −20°C to 350°C and thermal sensitivity of 0.04°C (Fig. 1A-1D). All thermographic profiles were recorded as sequence files on a connected laptop computer and analyzed using the Flir tool + (Flir Systems). To easily rotate the lens nucleus, hydrodissection was conducted, and phaco-chop was performed to emulsify and remove the nucleus. After removal of the remaining cortex material, insertion of the hydrophobic one-piece IOL (AcrySof IQ SN60WF, Alcon), and aspiration of the ophthalmic viscosurgical device (OVD), the corneal wound was hydrated. Patients were treated with 0.5% moxifloxacin eye drops (Vigamox, Alcon) and a 1% prednisolone acetate ophthalmic suspension (PredForte; Allergan, Irvine, CA, USA) four times a day after surgery for more than 3 weeks.

Porcine eyes were obtained from a slaughterhouse approximately 3 to 5 hours after death. An in vitro study was carried out to record temperature using three conditions: (1) with the Zepto PPC nitinol ring positioned naïvely in open air or on the porcine lens surface, (2) with, or (3) without an OVD. During the procedures, the thermal profile was recorded by directly targeting the ring using a compact infrared thermographer (Flir C2, Flir Systems) with a temperature range of −10°C to 150°C and a thermal sensitivity of 0.1°C. All thermographic profiles were recorded and analyzed using the Flir tool +. To check the naïve temperature, the Zepto PPC handle was fixed using silk tape on the floor with nothing around the Zepto PPC nitinol ring, and the thermal profile was acquired during the suction and cutting procedures in the top, lateral, and bottom views. To keep the measurement conditions similar to the in vivo experiment in which the OVD could be placed in the anterior chamber, the porcine cornea was resected above the limbus in a dome shape. The lenticular surface was coated with a DiscoVisc OVD. The Zepto PPC nitinol ring was positioned at the center of the porcine lens surface. Suction was applied, and the cutting procedure was performed in the same manner as for the human eye (Fig. 2A-2C). To identify the possible heat damage to intraocular tissues such as the iris, endothelium, and corneal incision according to the presence or absence of the OVD, thermal profiles were obtained in the top and lateral views. However, the thermal profile of the bottom side was excluded because the Zepto nitinol ring directly contacted the lens capsule and tissues. Each experiment was repeated at least three times.

All temperature values were summarized as the means and standard deviations. Temperature changes and preoperative and postoperative parameters were compared using paired t-tests. Data were analyzed using IBM SPSS Statistics ver. 25.0 (IBM Corp., Armonk, NY, USA).

The mean age of the patients was 67.9 ± 9.7 years; nine patients (60%) had hypertension and seven (47%) had diabetes. The mean nuclear opalescence grade was 3.40 ± 0.91, and the mean axial length and anterior chamber depths were 22.92 ± 0.77 and 3.18 ± 0.48 mm, respectively. The mean preoperative UCVA and BCVA were 0.49 ± 0.33 and 0.42 ± 0.34, respectively, and the mean postoperative UCVA and BCVA were 0.22 ± 0.17 and 0.12 ± 0.12, respectively. The mean preoperative IOP was 12.9 ± 1.8 mmHg and the mean postoperative IOP was 15.1 ± 3.9 mmHg. Both UCVA and BCVA improved significantly (difference: UCVA, 0.27; p = 0.009; BCVA, 0.30; p = 0.003).

During the cutting procedure, the mean time to peak temperature after the temperature rose around the corneal incision was identified to be 4.43 ± 1.26 seconds (range, 1.93-6.57 seconds). Baseline and peak temperature were 28.6°C ± 1.7°C and 32.6°C ± 2.0°C (range, 29.2°C-37.2°C), respectively, which was insignificant (difference, 4.0°C ± 1.9°C; p = 0.063) (Fig. 3). The mean temperature rise ranged from 0.9°C to 7.2°C. The peak temperature was >30°C in 14 of 15 cases. The in vivo thermal profiles are presented in Table 1.

The temperature elevation of the Zepto nitinol ring was highest on the bottom side (Fig. 4A) among the top (Fig. 4B), bottom, and lateral views in the naïve cutting procedures. The mean temperature rise time of the bottom view was identified as 43.40 ± 11.06 seconds, and the mean temperature rise was 79.9°C ± 22.5°C. The baseline and peak temperatures were 29.1°C ± 1.0°C and 109.0°C ± 22.9°C, respectively (Fig. 4A). In the top view, the baseline temperature was similar with the bottom view, but the peak temperature was measured only half from the bottom’s value (Fig. 4B). When viewed through a thermographer, the temperature change of the Zepto shaft was significantly different depending on the presence or absence of the OVD in the lateral view. Without the OVD, the shaft’s color change was easily detectable; however, with it, the shaft’s color change was minimal and difficult to recognize (Fig. 4C, 4D). In the top view, the mean temperature rise time was 14.00 ± 3.61 seconds, and the mean temperature rise was 10.5°C ± 3.3°C without the OVD. The baseline and peak temperatures were 18.2°C ± 0.1°C and 28.7°C ± 3.4°C, respectively (Fig. 5A). The mean temperature rise time of the Zepto nitinol ring with the OVD in the top view was 11.67 ± 2.08 seconds and the mean temperature rise was 6.2°C ± 1.6°C. The baseline and peak temperatures were 19.7°C ± 0.8°C and 25.9°C ± 2.3°C, respectively (Fig. 5B).