FormalPara Key Summary Points

Why carry out this study

A corneal pre-cut during cataract surgery makes the wound safer owing to the self-sealing effect and, as a consequence, a reduced risk of leakage through the wound.

The aim of this study was to assess the effect of a 600-µm corneal pre-cut on wound architecture, biomechanical properties of the cornea and surgically induced astigmatism. The images were acquired intraoperatively and postoperatively with high-resolution spectral-domain optical coherence tomography (SD-OCT).

What was learned from this study

Intraoperative wound gaping occurred more often in the stab-incision group, but this effect was more pronounced intraoperatively and not visible postoperatively.

There was no relevant difference concerning surgically induced astigmatism between the groups.

Digital Features

This article is published with digital features, including a summary slide, to facilitate understanding of the article. To view digital features for this article, go to https://doi.org/10.6084/m9.figshare.14077385.

Introduction

The most popular and widely accepted incision method in cataract surgery is a clear corneal incision (CCI) [1, 2]. CCI was shown to have faster recovery times compared to other incision techniques [3]. However, this technique also has a few disadvantages, which include the possible occurrence of irregular astigmatism or rarely insufficient wound closure [4].

In 1994 Langerman described a hinged incision with a 0.75-mm-deep corneal pre-cut, followed by a corneal tunnel. This concept implies that a hinged CCI makes the wound safer owing to the self-sealing effect and, as a consequence, a reduced risk of leakage through the wound [3, 5].

Corneal wound architecture in cataract surgery has been assessed using optical coherence tomography (OCT) in the past but, to our knowledge, intraoperative assessment of the wound architecture has not been published. OCT scans allow a three-dimensional depiction of wound architecture and a better understanding for the dynamic changes in wound structure during surgery [6,7,8,9,10,11,12].

The aim of the current study was to assess the effect of a 600-µm corneal pre-cut on wound architecture and its impact on surgically induced astigmatism. The images were acquired intraoperatively and postoperatively with high-resolution SD-OCT.

Methods

This randomized, patient and observer blinded, study with bilateral comparison included patients scheduled for cataract surgery in both eyes. Exclusion criteria included pregnancy as well as any ophthalmic abnormalities that could compromise the measurements, such as corneal scars, corneal ectasia, previously performed ophthalmic surgery, as well as an age below 21 years.

All the research and measurements followed the tenets of declaration of Helsinki and local ethics committee (Ethics Commission of Vienna) approved the study. Informed consent to participate in the trial was obtained from all patients prior to enrolment (NCT02155270, www.clinicaltrials.gov).

Suitable patients were screened on the day of their medical examination 1 week prior to cataract surgery (ophthalmic examination including slit lamp biomicroscopy and retinal examination).

Both eyes of each patient were allocated in a 1:1 ratio to one of two groups using an online randomization tool (www.randomizer.org). The first eye to be operated on randomly received either a 600-µm corneal pre-cut or a single-plane stab-incision, and the second eye received the other incision technique.

Preoperatively, routine optical biometry (IOLMaster 500) and topography (Atlas 9000, both Carl Zeiss Meditec AG, Germany) measurements were performed. Additionally, preoperatively and at 1 week and 1 month postoperatively, autorefraction (Topcon, Japan) and subjective refraction (ETDRS charts, Precision vision, USA) were assessed and all patients underwent a slit lamp and funduscopy examination. SD-OCT (Spectralis, Heidelberg Engineering) scans of the cornea were performed 1 h, 1 week and 1 month postoperatively. The maximum wound thickness and wound score developed by Calladine and Packard were used for assessment [7]. Outcomes were complete wound gaping, local detachment of Descemet’s membrane, epithelial or endothelial wound gaping and endothelial misalignment. Figure 1 shows pictures of the wounds of our patients. One observer (B.D.) assessed the wound score and measured the maximum wound thickness. Therefore, the thickest part of the wound was measured within the OCT image. All measurements were manually measured. Figure 2 shows an example of the measurement of the maximum wound thickness.

Fig. 1
figure 1

OCT images of wound architecture

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Fig. 2
figure 2

Shows an example of the measurement of the maximum wound thickness

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All surgeries were performed by the same experienced surgeon (O.F.), who is familiar with both incision techniques. Surgery was performed under topical anaesthesia. In all cases incision location was temporal and size was 2.4 mm with or without a pre-cut using a 600-µm guarded blade (BVI, USA), named ‘pre-cut group’ or ‘stab-incision group’. For both incision types a single bevelled knife was utilized (Xstar® Safety Slit Knife, 2.4 mm Beaver, BVI, USA). Injection of viscoelastic substance (Healon, Johnson & Johnson, USA), capsulorhexis, phacoemulsification, and bimanual irrigation/aspiration (I/A) of cortical material were performed as standard procedure; hydration at the end of the surgery was not done either for the pre-cut or for the stab-incision groups. Incision architecture was assessed intraoperatively using a continuous intraoperative iOCT device (ReScan 700, Carl Zeiss Meditec AG, Germany) after the incision, after I/A and after intraocular lens (IOL) implantation. To guarantee a standardized intraocular pressure the bottle height of the infusion was 30 cm above the patient’s eye level and holding a bimanual irrigating handpiece through the left paracentesis, which represents approximately 20 mmHg. After phacoemulsification, corticosteroids (Monodex, Laboratoires Thea, France) as standard regimen were applied. The postoperative standard medication was bromfenac eyedrops (Yellox, Bausch & Lomb, USA) twice a day for 4 weeks.

For statistical analysis Microsoft Excel 14.0 (Microsoft, USA) with a Statplus: Mac Version 5.8.3.8 plug-in (AnalystSoft, USA), and Xlstat 2012 plug-in (Addinsoft, USA) and a Solver plug-in in Excel (Microsoft, USA) was used.

Furthermore, SPSS 21.0 for Mac (IBM, USA) was used for box plots. Missing data observations were excluded from analysis. Descriptive data is always shown as mean, standard deviation (SD) and range. P < 0.05 was considered statistically significant.

Results

In total, 90 eyes of 45 patients were included. In 21 patients data were missing (9 patients were lost to follow-up as a result of non-compliance, 8 patients had poor image quality intraoperatively on at least one eye, and in 4 cases the intraoperative measurement was not recorded in one eye because of technical issues). The remaining 48 eyes of 24 patients were analysed. Mean age of the remaining patients was 72.4 years (SD 8.9 years) with a range from 43 to 84 years. Of these, 12 were female and 12 male. As a result of randomization, 15 right eyes and nine left eyes received a pre-cut incision. No postoperative complications such as wound leaking or endophthalmitis were observed.

Wound thickness was significantly different between both groups within the first week, but no significant difference was found after 1 month (Table 1).

Table 1 Difference of wound thickness in millimetres between both groups within 1 h postoperative, the first week and after 1 month
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The wound score including epithelial and endothelial wound gaping, local detachment of Descemet’s membrane and endothelial misalignment is shown in Tables 2 and 3. Complete wound gaping after phaco was observed in the stab-incision and pre-cut group in 26% and 9%, respectively (p = 0.06). After lens implantation this was the case in 26% versus 13%, respectively (p = 0.15). Postoperatively no wound gaping was observed.

Table 2 Wound score including epithelial and endothelial wound gaping
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Table 3 Wound score including local detachment of Descemet’s membrane and endothelial misalignment
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Surgically induced astigmatism was low in both groups. The corneal astigmatism difference vector from preoperative to 1 week postoperatively in both groups is shown in Fig. 3. None of these was statistically significant (Table 4). For the IOL-Master 500 measurements there was a mean absolute difference vector of 0.65 D (SD, ± 0.43) in the stab-incision group from preoperative to the 1-week follow-up and 0.83 D (SD, ± 0.56) from the 1-week to the 1-month examination. In the pre-cut group the mean absolute change was 0.51 D (SD, ± 0.34) from the preoperative to the 1-week measurement and 0.65 D (SD, ± 0.37) for the 1-week to the 1-month follow-up.

Fig. 3
figure 3

Corneal astigmatism difference vector from preoperative to 1 week postoperatively in the pre-cut and the stab-incision groups

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Table 4 Surgically induced astigmatism in both groups using difference vector analysis (preoperative compared to 1 week and 1 week compared to 1 months)
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The results of the topography measurements showed in the stab-incision group a difference vector of 0.48 D (SD, ± 0.27) from the preoperative to the 1-week examination and 0.53 D (SD, ± 0.25) in the 1-week to the 1-month follow-up. In the pre-cut group there was a mean induced astigmatism of 0.49 D (SD, ± 0.24) in the preoperative to the 1-week examination and 0.43 D (SD, ± 0.43) in the 1-week to the 1-month follow-up.

Discussion

In this study the influence of a 600-µm corneal pre-cut on incision architecture and astigmatism was evaluated. Concerning wound thickness, the pre-cut group showed a significantly lower wound thickness from the 1-h to the 1-week measurement.

In our study the maximum wound thickness and wound score were analysed with a classification system developed by Calladine and Packard [7], including epithelial and endothelial wound gaping, endothelial misalignment, local detachment of Descemet’s membrane and complete wound gaping. Our findings showed that complete wound gaping during surgery occurred more often in the stab-incision group. To our knowledge, this is the first time that intraoperative wound gaping was measured. However, no difference was found at the postoperative follow-ups. We observed that epithelial and endothelial wound gaping, local detachment of Descemet’s membrane and endothelial misalignment were more common in the pre-cut group during surgery (after incision, after phaco and after lens implantation). One hour postoperatively epithelial wound gaping was found in all cases of the pre-cut group. This was expected since the outside part of the incision was incised with the 600-micron knife. However, 1 week and 1 month postoperatively, no epithelial wound gaping or local detachment of Descemet’s membrane was found in either group. So obviously, the epithelial closure happens in all cases within the first week after surgery. Endothelial wound gaping was more common in the pre-cut group 1 h, 1 week and 1 month postoperatively. This may be due to more distortion of the wound when passing the phaco and I/A tips as well as the injector through the incision. Endothelial misalignment was significantly higher 1 month postoperatively in the stab-incision group. This may be due to slight central “slippage” of the anterior part of the wound in stab incisions, which would be less pronounced with a pre-cut. Calladine and Tanner stated that endothelial misalignment is more common with stromal hydration, which is important for healing and decreasing the risk of endophthalmitis [13].

Surgically induced corneal astigmatism was similar in the stab-incision and the pre-cut groups. Several studies have assessed surgically induced astigmatism after different types of small incisions and incision locations [2, 11, 14,15,16]. Surgically induced astigmatism in our study was low in both groups, which is comparable to recent findings by Aykut et al. [14]. It is also stated that proper wound site plays an important role on low surgically induced astigmatism [11].

In our study the patient population was very small. A larger sample size needs to be considered for further investigations. Another limitation of the study is that some of the parameters assessed are subjective. Like we did, one observer should take all measurements, but it could be worth considering that two observers take the same measurement and compare their results.

Conclusions

Wound gaping occurred more often in the stab-incision group, but this effect was more pronounced intraoperatively and not visible postoperatively. There was no relevant difference concerning surgically induced astigmatism between the groups.