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Femtosecond laser penetrating corneal relaxing incisions combined with cataract surgery

Wang, Li MD, PhD; Zhang, Suhua MD*; Zhang, Zhe MD; Koch, Douglas D. MD; Jia, Yading MD; Cao, Weifang MD; Li, Xiaoyan MD

Author Information
Journal of Cataract & Refractive Surgery: July 2016 - Volume 42 - Issue 7 - p 995-1002
doi: 10.1016/j.jcrs.2016.04.020
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Abstract

It is reported that 15% to 20% of cataract patients have more than 1.50 diopters (D) of keratometric astigmatism, refractive astigmatism, or both.1,2 Options in reducing preexisting astigmatism simultaneously during cataract surgery include toric intraocular lens (IOL) implantation,3–5 astigmatic keratotomy,6–9 limbal relaxing incisions (LRIs) or peripheral corneal relaxing incisions (CRIs),10–14 and a clear corneal cataract incision along a steep meridian.15–17

Traditionally, astigmatic keratotomy and peripheral CRIs have been performed using a diamond knife. Recently, femtosecond laser arcuate keratotomy has been used to treat corneal astigmatism in eyes with naturally occurring high astigmatism or in eyes with astigmatism after penetrating keratoplasty (PKP) or cataract surgery.18–24

Corneal relaxing incisions performed during femtosecond laser–assisted cataract surgery can be placed in the stroma without penetrating the anterior and posterior corneal surfaces (intrastromal incisions) or penetrating the anterior corneal surface (penetrating incisions). To our knowledge, there are no studies assessing the effectiveness of penetrating CRIs performed during femtosecond laser–assisted cataract surgery using other platforms, and there is no nomogram available in the literature to guide the determination of penetrating CRI length.

In this prospective study, the purpose was to evaluate the effectiveness of femtosecond laser penetrating CRIs in reducing corneal astigmatism during cataract surgery using a femtosecond laser and to develop a nomogram.

Patients and methods

Patients

Institutional review board approval was obtained for the project. This study followed the tenets of the Declaration of Helsinki. After a detailed explanation, informed consent was obtained from each patient prior to enrollment.

Prospectively, consecutive patients having femtosecond laser–assisted cataract surgery combined with penetrating CRIs using the Lensx laser (Alcon Laboratories, Inc.) were enrolled between March 2014 and February 2015. Inclusion criteria were a postoperative follow-up of 1 month or longer, corrected distance visual acuity of 20/32 or better, and no intraoperative or postoperative complications.

Corneal Astigmatism Measurements

Preoperatively, ocular biometry was performed using a devices based on partial coherence interferometer (PCI) (IOLMaster, Carl Zeiss Meditec AG). Scanning-slit corneal topography (Orbscan II, Bausch & Lomb Inc.) was also used to measure the corneal power and astigmatism. One month and 3 months postoperatively, corneal power and astigmatism were also measured using the scanning-slit corneal topographer.

Corneal Relaxing Incisions

The Donnenfeld nomogram that is part of the Abbott Medical Optics LRI calculatorA was used to calculate the length and number of CRIs. This calculator was intended to support the use of manual LRIs only. Because no calculator is available to determine the length and number of the CRIs with femtosecond laser–assisted cataract surgery, this calculator was used for initial cases with the hope of developing a nomogram for femtosecond laser–assisted CRIs based on primary results in this study.

The values for the steep keratometry (K), flat K, and steep meridian that were entered into the calculator were determined by the surgeon with consideration of data from the PCI device, scanning-slit corneal topographer simulated K and central 3.0 mm zone astigmatism, and preoperative manifest refractive astigmatism. For surgically induced astigmatism (SIA), 0.2 D was entered based on a previous analysis of SIA (data not published). The incision location was 120 degrees. If the CRI was close to the primary incision, the incision location was shifted to between 130 degrees and 140 degrees. The length and number of the CRIs displayed on the calculation sheet were used to program the femtosecond laser treatment.

Surgical Technique

Preoperatively, patients were prescribed pranoprofen 0.1% (Niflan 0.1%) and levofloxacin 0.5% eyedrops for use in the operative eye 4 times daily beginning 48 hours before surgery. The same experienced surgeon (S.Z.) performed all surgeries.

Using the femtosecond laser, a 5.2 mm capsulotomy was created. The lens was segmented into 4 quadrants (cataract grade II) or 6 quadrants (cataract grade III). Paired or single penetrating CRIs with a predetermined length were placed at a diameter of 8.0 mm with a depth of 90% of the corneal thickness, as recommended by the femtosecond laser manufacturer. A 2.2 mm primary 2-plane cataract incision and a 1.2 mm single-plane paracentesis were created using the femtosecond laser (6 μJ pulse energy). The incision was opened with blunt dissection. Phacoemulsification was performed using the Infiniti Vision System (Alcon Laboratories, Inc.), and an aspheric or multifocal IOL was implanted in the capsular bag. The CRIs were bluntly dissected open at the end of the surgery.

Data and Statistical Analysis

Data analyses were performed as follows:

  1. Changes in keratometric and refractive astigmatism. The mean arithmetic changes in keratometric astigmatism magnitude were calculated by subtracting the preoperative corneal astigmatism magnitude from the postoperative corneal astigmatism magnitude for simulated K and the central 3.0 mm and central 5.0 mm zone astigmatism obtained from the scanning-slit corneal topographer. In addition, the percentage of eyes within ±0.25 D, ±0.50 D, ±0.75 D, ±1.00 D, ±1.50 D, and ±2.00 D of the preoperative corneal astigmatism measured with the PCI device and the postoperative manifest refractive astigmatism were compared.
  2. Analysis of aggregate astigmatism. The vector analysis and double-angle plots were used to display the preoperative corneal astigmatism and postoperative manifest refractive astigmatism.25
  3. Determination of the with-the-wound (WTW) and against-the-wound (ATW) changes using the Holladay-Cravy-Koch formula.26 For these calculations, preoperative and postoperative K values of simulated K and the central 3.0 mm and central 5.0 mm zone obtained from the scanning-slit corneal topographer were used; the steep corneal meridian where the CRI was placed was used as the reference (ie, the wound). A WTW change indicates the astigmatic effect along the steep meridian. An ATW change shows the astigmatic effect at 90 degrees from the steep meridian. The WTW − ATW change demonstrates the total net effect or net corneal change induced by the incision along the meridian of the relaxing incision.
  4. Complications. Any complication related to the CRIs was noted, including overcorrection, which was defined as postoperative astigmatism of 0.50 D or more along a meridian 60 to 120 degrees from the original steep meridian.

For results presentation, data from eyes receiving paired CRIs and single CRIs were combined, except for the calculation of WTW and ATW changes. Analyses of eyes with single CRIs were not appropriate because of the small number of eyes in that subgroup. These eyes were not, however, removed from the study because they met the inclusion criteria and represent the reality of clinical practice. Although the effect of the single CRIs and paired CRIs was different, changes induced by paired CRIs also varied depending on the length of incisions. Therefore, data from eyes with paired CRIs and eyes with single CRIs were combined for aggregate analysis of keratometric and refractive astigmatism.

Data distribution for normality was checked. The paired Student t test for normally distributed data and Wilcoxon test for not normally distributed data were used to compare the differences before and after the surgery. The McNemar test was used to compare the differences in frequency in different groups. To account for the correlation between pairs of eyes of each individual, multiple regression analysis with generalized estimating equations was used to evaluate the following factors contributing to the effectiveness of CRIs represented by the net corneal changes calculated by subtracting the ATW changes from the WTW changes: age, eye (right or left), preoperative corneal astigmatism magnitude obtained with the PCI device, CRI length, and location of the CRI (vertical, 60 to 120 degrees; oblique, 30 to 60 degrees or 120 to 150 degrees; horizontal, 0 to 30 degrees or 150 to 180 degrees). The Bonferroni correction was applied for multiple tests. SPSS for Windows software (version 12.0, SPSS, Inc.) was used, and a probability of less than 5% (P < .05) was considered statistically significant.

Results

The study included 51 eyes of 37 patients. Of the 51 eyes, 45 eyes received paired CRIs with lengths ranging from 20 to 58 degrees and 6 eyes had single CRIs with a length ranging from 35 to 65 degrees. Table 1 shows the patients’ demographic data.

Table 1
Table 1:
Patients’ demographics.

Changes in Keratometric and Refractive Astigmatism

One month postoperatively, the simulated K, central 3.0 mm zone, and central 5.0 mm zone astigmatism magnitude significantly decreased (all P < .05) (Table 2). Three months postoperatively, the simulated K astigmatism magnitude value significantly decreased (P < .05) and changes in the central 3.0 mm zone and central 5.0 mm zone were not statistically significant.

Table 2
Table 2:
Keratometric astigmatism changes (D) over time measured with the scanning-slit corneal topographer (postoperative − preoperative).

Compared with preoperative corneal astigmatism measured with the PCI device, the percentages of eyes within ±0.25 D, ±0.50 D, ±0.75 D, ±1.00 D, ±1.50 D, and ±2.00 D of the manifest refractive astigmatism significantly increased 1 month and 3 months postoperatively (all P < .05) (Table 3 and Figure 1).

Figure 1
Figure 1:
Percentage of eyes with a certain amount of preoperative corneal astigmatism and postoperative manifest refractive astigmatism at 1 month (47 eyes) (top) and 3 months (30 eyes) (bottom) (MR = manifest refraction).
Table 3
Table 3:
Percentage of eyes within certain levels of corneal astigmatism preoperatively and manifest refractive astigmatism postoperatively.

Aggregate Astigmatism

The preoperative corneal astigmatism points were scattered all over the double-angle plots (Figure 2). In contrast, the postoperative manifest refractive astigmatism dots moved closer to the origin, indicating reduced astigmatism values postoperatively. Compared with preoperative corneal astigmatism, the mean postoperative manifest refractive astigmatism decreased significantly 1 month postoperatively (P < .05) but not at 3 months (P > .05).

Figure 2
Figure 2:
Double-angle plot of aggregate vector analysis of preoperative corneal astigmatism and postoperative manifest refractive astigmatism at 1 month (47 eyes) (top) and 3 months (30 eyes) (bottom) (astig = astigmatism; ATR = against-the-rule; MR = manifest refraction; WTR = with-the-rule).

With-the-Wound and Against-the-Wound Changes

In the paired CRI group, there were significant WTW − ATW changes postoperatively at 1 month and 3 months based on simulated K, central 3.0 mm zone, and central 5.0 mm zone values (all P < .05) (Table 4). In the single CRI group, there were significant WTW − ATW changes postoperatively at 1 month based on simulated K and central 3.0 mm zone values (all P < .05); changes in WTW − ATW were not statistically significant in other subgroups.

Table 4
Table 4:
With-the-wound and ATW change and the corneal relaxing incision meridian at postoperative visits.

At 1 month in the paired CRI group, multiple regression analysis with generalized estimating equations showed that age, CRI length, and CRI location significantly contributed to the net corneal changes (WTW − ATW changes) based on simulated K and central 3.0 mm zone values, and the CRI length significantly contributed to the net corneal changes based on central 5.0 mm zone values (all P < .05). At 3 months, multiple regression analysis with generalized estimating equations showed that the CRI length significantly contributed to the net corneal changes based on simulated K, central 3.0 mm zone, and central 5.0 mm zone values (all P < .05). The regression equations were as follows:

For 1 month postoperatively:

For 3 months postoperatively:

Complications

No eyes had a complication related to the placement of the femtosecond laser–created CRIs. One month postoperatively, 7 (14.9%) of the 47 eyes were overcorrected; 5 of these eyes had with-the-rule (WTR) corneal astigmatism postoperatively. At 3 months, 2 (6.7%) of the 30 eyes were overcorrected; 1 of the 2 eyes had WTR corneal astigmatism preoperatively.

Nomogram

For nomogram development, the net corneal changes (WTW − against-the-rule [ATR] changes) were calculated based on simulated K corneal astigmatism 1 month postoperatively. For eyes with WTR and ATR corneal astigmatism, based on age and the length of paired CRIs (Table 5), the regression formulas were as follows:

Table 5
Table 5:
Nomogram: total net corneal change (WTR − ATR change) based on age and length of CRI in eyes with WTR and ATR corneal astigmatism.

Discussion

To our knowledge, this is the first prospective study to evaluate the effectiveness of femtosecond laser–created CRIs during cataract surgery using the Lensx platform. We also propose a preliminary nomogram.

In our study, after femtosecond laser–created CRIs, the simulated K corneal astigmatism was significantly decreased compared with preoperative corneal astigmatism, by a mean of −0.67 D to −0.65 D. In addition, the percentages of eyes within ±0.25 D and ±0.50 D of astigmatism were significantly higher 1 month and 3 months postoperatively. Vector analysis showed that compared with preoperative corneal astigmatism, the mean postoperative manifest refractive astigmatism was significantly lower 1 month postoperatively. Using vector analysis, we calculated the WTW and ATW changes, which represent the total net effect induced by the incisions. Postoperatively in the paired CRI group, the mean WTW and ATW changes were −1.05 D and −1.0 D at 1 month and 3 months, respectively.

Multiple regression analysis with generalized estimating equations showed that age, CRI length, and CRI location significantly contributed to the total net corneal changes (WTW − ATW changes) based on simulated K 1 month postoperatively, with older age, longer incisions, and horizontal incisions in eyes with preoperative ATR corneal astigmatism producing a greater amount of net corneal changes. We used these results to develop a nomogram based on age and length of paired CRIs separately for eyes with WTR astigmatism and eyes with ATR astigmatism. The greater effectiveness of CRIs along the horizontal meridian could be attributable to the variability in the biomechanical response of the cornea to incisions along different meridians. We found a similar difference in our studies of manual diamond knife incisions in virgin eyes and eyes having cataract surgery.11,13 If we consider the effect of posterior corneal astigmatism,27 we would expect the opposite; that is, relative flattening of the posterior cornea along the horizontal meridian (if indeed this occurs) would lead to more ATR refractive power of the posterior cornea. Because of the small number of eyes with a single CRI, a nomogram for single CRIs was not developed. The nomogram was developed based on preliminary results from a small number of eyes and will be modified when more cases are enrolled.

There were significant mean net corneal changes (WTW − ATW) after penetrating paired CRIs, although the standard deviation was large relative to the mean values. A possible reason for this variable effectiveness of femtosecond laser–created incisions might be the different corneal wound-healing responses of patients. We are unaware of studies comparing the results of femtosecond laser–created penetrating CRIs with outcomes after toric IOL implantation or corneal refractive surgery. In a previous study, Poll et al.14 compared the efficacy of astigmatic correction achieved at the time of cataract surgery using toric IOL implantation versus manual peripheral CRIs; both treatment modalities achieved comparable results with mild to moderate astigmatism. Higher degrees of astigmatism favor use of a toric IOL. Kessel et al.28 performed a systematic review and metaanalysis to evaluate the benefit and harm associated with the implantation of toric IOLs and the implantation of nontoric IOLs combined with manual CRIs during cataract surgery. They found that toric IOLs provided better uncorrected distance visual acuity, greater spectacle independence, and lower amounts of residual astigmatism than nontoric IOLs combined with CRIs. In a randomized controlled trial, Nagpal et al.29 compared the outcomes of phacoemulsification with toric IOL implantation versus phacoemulsification with monofocal IOL implantation followed by photorefractive keratectomy (PRK) 3 months later for correction of preexisting astigmatism. They found that PRK yielded less residual cylinder than toric IOL implantation. However, PRK causes greater postoperative pain and corneal aberrations and poor glare acuity. Further studies comparing the outcomes of femtosecond laser CRIs, toric IOLs, and laser in situ keratomileusis and PRK for residual corneal astigmatism correction would be beneficial.

Because no calculator is available to determine the length and number of penetrating CRIs during femtosecond laser–assisted cataract surgery, we used the Abbott Medical Optics LRI calculator for these initial cases. One month postoperatively, 14.9% of eyes were overcorrected and two thirds of the overcorrected eyes had WTR corneal astigmatism preoperatively. Presumably, these overcorrections were caused by ignoring the effect of posterior corneal astigmatism. Based on these preliminary results, we developed a nomogram that will be used in future cases. For corneal astigmatism measurements, we used the Orbscan II scanning-slit corneal topographer before and after surgery. In addition to the simulated K astigmatism, we also studied the corneal astigmatism within the central 3.0 mm and 5.0 mm zones. Further studies using corneal topography or tomography that measures posterior corneal astigmatism are desirable.

In a retrospective study, Chan et al.30 evaluated the outcomes of femtosecond laser arcuate keratotomy combined with cataract surgery in eyes with low to moderate corneal astigmatism using the Victus platform (Bausch & Lomb). A single arcuate keratotomy with a depth of 450 μm was performed at the 8.0 mm optical zone 180 degrees from the main corneal incision for phacoemulsification placed on the corneal steep meridian. The current study was a prospective study to evaluate the effectiveness of penetrating CRIs performed using the Lensx femtosecond laser. In the current study, the surgeon used a primary cataract incision around 120 degrees and created paired or single CRIs. Chan et al.30 reported that the mean preoperative astigmatism was reduced significantly, from 1.33 D ± 0.57 (SD) to 0.87 ± 0.56 D postoperatively. In our study, the mean total corneal change with single CRIs was −0.70 D. The difference in the amount of corneal changes induced by the CRIs made with different laser platforms might be attributed to the possible differences in the centration capability of these platforms, which might affect the outcomes, and differences in incision depth.

This study has limitations. First, the sample is small and longer patient follow-ups are needed. This study aimed to report the preliminary results and to propose a preliminary nomogram. Study is ongoing to enroll more patients with longer follow-ups, and the performance of the monogram will be evaluated. Second, a small number of eyes received single CRIs, and their keratometric and refractive outcomes were combined with those of eyes that received paired CRIs. These results represent the aggregate outcomes of these consecutive cases. For calculation and presentation of the WTW and WTW changes induced by CRIs, eyes were divided into paired CRI and single CRI groups. Third, a more advanced corneal topographer or tomographer for posterior corneal astigmatism measurements was not used. Studies using devices that measure posterior corneal astigmatism are desirable.

In conclusion, our study found that femtosecond laser CRIs made during cataract surgery were effective in reducing preexisting corneal astigmatism. A nomogram based on patient age and the length of CRIs was developed. The nomogram will be improved when more cases are enrolled. However, further study is needed to validate and refine the nomogram, to evaluate factors such as achieved incision depth and length and the role of corneal biomechanics, and to determine the long-term benefits of these incisions.

What Was Known

  • Femtosecond laser arcuate keratotomy has been used to treat corneal astigmatism in eyes with naturally occurring high astigmatism or in eyes with astigmatism after cataract surgery or PKP.

What This Paper Adds

  • Femtosecond laser–created penetrating CRIs significantly reduced corneal astigmatism.
  • A preliminary nomogram is proposed.

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Other Cited Material

A. Abbott Laboratories, Inc. Welcome to the AMO LRI calculator software. Available at: http://www.lricalculator.com. Accessed May 3, 2016
© 2016 by Lippincott Williams & Wilkins, Inc.