Comparison of flange creation in three-piece intraocular lenses between high- and low-temperature cautery

Abstract

Background

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To compare flange creation using high- vs. low-temperature cautery for three piece intraocular lenses (IOLs) with PMMA and PVDF haptics.

Methods

The ends of the haptics from ten three-piece IOLs with PMMA haptics (AR40, Johnson & Johnson, USA) and ten three-piece IOLs with PVDF haptics (PU6AS, KOWA, Japan) were each heated for 1 mm to form a flange—using low-temperature cautery (593 °C) on the ipsilateral haptic and high-temperature cautery (1205 °C) on the contralateral haptic. Flange size, shape, and formation time were analysed.

Results

There were no differences in flange shape and flange size between high- and low-temperature cautery for each haptic type (p > 0.05). Average flange size of the AR40 IOL and the PU6AS IOL were 422 ± 22 μm and 363 ± 14 μm, respectively. Haptic diameter were 172 ± 5 μm and 126 ± 3 μm, respectively. The shape of the AR40 IOL flange was conic and the shape of the PU6AS IOL flange was mushroom-like, independent of cautery temperature. Flange formation time was 1.7 ± 0.6 s with the high-temperature cautery and 3.7 ± 0.6 s with the low-temperature cautery, regardless of the haptic material.

Conclusions

Flange size and shape in PMMA and PVDF haptics are independent of low- and high-temperature cautery. However, the extended flange formation time associated with low-temperature cautery may allow for greater control during flange creation.

Background

Scleral fixated intraocular lenses (IOLs) represent a critical advancement in the field of ocular surgery, particularly for patients who require lens implantation but have insufficient or damaged capsular support. The technique involves securing the IOL to the sclera using either sutures or more recently, sutureless approaches, through small incisions. Sutureless techniques for three-piece IOLs include transscleral tunnels (Scharioth’s technique) [1], glued haptics (Agarwal’s technique) [2] and recently flanged haptics (Yamane’s technique) [3]. Another sutureless method involves using a one-piece IOL [4] with a harpoon haptic for scleral fixation. However, our findings on scleral dislocation forces suggest that a flange (Yamane’s technique) provides a more secure fixation in the sclera compared to a harpoon haptic [5]. A recent study on real-life data indicates no difference between two different PMMA three piece IOL used in a modified Yamane’s technique [6]. Furthermore, Yamane’s technique provides better and more stable IOL centration compared to a modified double-flange technique [7].

The key elements of the Yamane technique include selecting the appropriate three-piece IOL, creating a long scleral tunnel, externalizing the haptic with a matching needle, and forming a proper flange. Three-piece IOLs with PVDF haptics offer superior loop memory and flexibility compared to those with PMMA haptics [8], which are prone to breaking and are more difficult to maneuver. The preferred needle for Yamane technique is the 30-gauge thin-walled needle [9, 10] and the proper flange for a 30-gauge needle tunnel is achieved when heating 0.5 to 1 mm of the haptic [11].

We have recently shown that Yamane’s technique compared to transcleral tunnels (Scharioth’s technique) and glued haptics (Argawal’s technique) gives the strongest support in sutureless scleral IOL fixation [12]. Moreover, we have shown that the shape and size of the flange play a crucial role for giving the most strongest hold in the scleral tunnel [10, 11]. The aim of this study is to compare flange creation in PMMA and PVDF three-piece IOLs using high- and low-temperature cautery.

Methods

Three piece IOLs

Ten three piece IOLs with PMMA haptics (AR40, Johnson & Johnson, USA) and ten three piece IOLs with PVDF haptics (PU6AS, KOWA, Japan) were used in this study. In detail, the AR40 IOL is a hydrophobic, acrylic, biconvex monofocal IOL with a 6 mm optic diameter, a total diameter of 13.0 mm and an angulation of 5 degrees. The three piece architecture of the AR40 IOL is characterized by extruded 60% blue core PMMA monofilament modified c-type haptics. The PU6AS IOL is a hydrophobic, acrylic, biconvex monofocal IOL with PVDF c-type haptics, with a total diameter of 13.0 mm, an angulation of 5 degrees, and an optic diameter of 6 mm.

Flange creation

Cautery of 1 mm of each haptic was performed either with low-temperature on one haptic or with high-temperature on the other haptic. For low-temperature cautery, we used the Bovic^® pen (Apyx Medical, USA), which provides a temperature of approximately 593 C° according to the manufacturer’s user guide. For high-temperature, cautery we used the BVI Accu-Temp^® pen (BVI Medical, USA), which provides a temperature of approximately 1205 C° according to the manufacturer’s user guide. During heating the haptics were kept in place by using a forceps just above 1 mm distance to the haptic end. Flange formation time using the heated cautery pen was measured through video analysis of three IOLs per type.

Flange analysis

For analysis of the flange shape and size, the IOL-samples were observed in reflection mode by circular differential interference contrast (C-DIC) using an optical upright microscope (Axio Scope.A1; Zeiss, Germany) equipped with a x 5 EC Epiplan Neofluar^® HD DIC lens. A compact CCD monochrome camera (Lumenera Corporation, Canada) recorded 1392 × 1040 pixels images with a resolution of 1.3 μm/pixel.

Statistical analysis

Data were analyzed with Microsoft Excel 2021, R 4.3.2. and SPSS Statistics 29. All presented means are accompanied by their respective standard deviations. The significance limit was set to 0.05 and 0.95, respectively. The Shapiro-Wilk test was employed to assess data normality. If the data were normally distributed, paired t-tests were used to compare haptic differences within the same IOL type, and independent t-tests were applied to compare haptics between different IOL types. For non-normally distributed data, the Wilcoxon signed-rank test and the Mann-Whitney U test were used accordingly.

Results

The PMMA haptic diameter of the AR40 IOL was 172 ± 5 μm. Heating 1 mm of AR40 IOL’s haptic resulted in an average overall flange size of 422 ± 22 μm. Shape of the resulting flange was conic (Fig. 1). Flange size of the high-temperature group was 424 ± 20 μm and of the low-temperature group was 420 ± 23 μm (p = 0.54, paired t-test) (Fig. 2).

Fig. 1

PMMA and PVDF flange shape in high- and low-temperature cautery

Fig. 2

PMMA and PVDF flange size in high- and low-temperature cautery

The PDVF haptic diameter of the PU6AS IOL was 126 ± 3 μm. Heating 1 mm of the PU6AS IOL’s haptic resulted in an average overall flange size of 363 ± 14 μm. Shape of the resulting flange was mushroom-like (Fig. 1). Flange size of the high-temperature group was 360 ± 15 μm and of the low-temperature group was 365 ± 14 μm (p = 0.42, paried t-test) (Fig. 2).

The haptic diameter and the flange diameter of the AR40 IOL were significantly larger than those of the PU6AS IOL (p < 0.01, t-test) (Fig. 2).

With the low-temperature cautery pen (Bovie^®; Apyx Medical, USA), it took 3 to 5 s after activation to reach flange formation-ready heat. In contrast, the high-temperature cautery pen (BVI Accu-Temp^®; BVI Medical, USA) reached the required heat immediately upon activation. The time needed to form a flange by melting 1 mm of each type of haptic using the heated cautery tip was 1.7 ± 0.6 s with the high-temperature cautery (Video 1) and 3.7 ± 0.6 s with the low-temperature cautery (Video 2) (Table 1). The optimal distance between the haptic end and the heated cautery tip for successful flange formation was up to 1 mm with the high-temperature cautery and up to 0.5 mm with the low-temperature cautery. Longer distances between cautery tip and end of haptic stopped the flange formation process. (Video 1, Video 2)

Table 1 Time to create a flange by melting 1 mm of the haptic in high- and low-temperature cautery in AR40 and PU6AS IOLs

Discussion

In this dry lab experimental study, we tested high-temperature vs. low-temperature cautery for PDVF and PMMA haptics to create a flange suitable for scleral fixation. We found that flange formation was independent of the cautery temperature for both haptic materials.

In Yamane’s technique the haptic is usually held with a forceps during heating. To simulate this, we performed our flange creation with forceps grip at 1 mm distance to the haptic end. This is of importance since we observed a forceps distance dependence for PMMA haptics, i.e. longer distances between forceps grip of the haptic and end of the haptic during cauterization resulted in smaller prominences of the flange [11]. To achieve the perfect flange it is important to heat only 1 mm of the haptic [11]. In our dry lab set up, we used an operation microscope and a ruler to heat 1 mm, however, that can be challenging in clinical routine. Recently, Amado introduced the perfect flanger which is a forceps with a reference cylinder of 1 mm attached [13]. That allows the surgeon to stay within the range of perfect heating length.

The haptic diameter of the PMMA haptics was significantly larger than the haptic diameter of the PDVF haptics. This might lead to problems of feeding a 30-gauge thin-walled needle [9], especially for PMMA haptics. Consequently, melting of the PDVF haptics produced a significantly smaller flange than melting of PMMA haptics. However, the conic flange of PMMA haptics proved to be inferior to the mushroom-like flange of the PVDF haptics in terms of dislocation force between haptic and sclera [10, 14]

The longer flange formation time, observed in low-temperature cautery, may provide improved control during the creation of the flange. However, with low-temperature cautery, it took 3–5 s for the cauter to reach sufficient heat for flange formation, while high-temperature cautery allowed flange formation to begin immediately upon activation. That time lag in low-temperature cautery could negatively influence the procedure when forceps grip of the haptic is suboptimal during the heating procedure, i.e. the haptic slips through the forceps and without flange internalizes through the scleral tunnel. Typically, in low-temperature cautery the tip of the cautery pen does not glow red when activated even after 5 s (Video 3) as opposed to high-temperature cautery. (Video 4) Therefore, a visible feedback for the user when the tip is ready for action is missing with the low-temperature cautery. On the other hand, high-temperature cautery may lead to uncontrollable flange formation resulting in a flange that is too big to bury in the scleral tunnel. Too large flanges remain outside of the scleral tunnel and may further erode through the conjunctiva presenting an entry port for the surrounding flora pathogens [15].

There may be some possible limitations in this study. The experimental setup was restricted to dry lab conditions, which may not accurately replicate real surgical environments. Flange formation could vary on moist surfaces or when influenced by factors such as erythrocytes or ophthalmic viscosurgical devices (OVDs). Additionally, additives present in PMMA or PVDF materials may alter flange characteristics, potentially leading to differences across various intraocular lens (IOL) types.

In conclusion, we demonstrated for the first time that high-temperature or low-temperature flange creation in Yamane’s technique does not influence size and shape of the flange. Both high-temperature and low-temperature cautery can be used interchangeably, depending on the surgeon’s preference. However, the extended flange formation time in low-temperature cautery may allow for more controllable flange formation favouring low-temperature cautery in sutureless IOL fixation.