Comparison of the influx of bacterial-sized particles in single plane versus multiplane femtosecond laser incisions

William May; Mohammed Al Mutlak; Waseem Aalam; Sultan Rashidi; Rajiv Khandekar

doi:10.4103/jcor.jcor_135_20

ORIGINAL ARTICLE

Year : 2021 | Volume : 9 | Issue : 3 | Page : 118-122

Comparison of the influx of bacterial-sized particles in single plane versus multiplane femtosecond laser incisions

William May¹, Mohammed Al Mutlak², Waseem Aalam³, Sultan Rashidi⁴, Rajiv Khandekar²
¹ Department of Ophthalmology, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia; Cataract and Refractive Surgeon, Wellish Vision Institute, Las Vegas, NV, USA
² Department of Ophthalmology, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia
³ Department of Ophthalmology, King Khaled Eye Specialist Hospital, Riyadh; Department of Ophthalmology, Faculty of Medicine, University of Jeddah, Jeddah, Saudi Arabia
⁴ Department of Ophthalmology, King Khaled Eye Specialist Hospital, Riyadh; Department of Ophthalmology, College of Medicine, Qassim University, Burydah, Saudi Arabia

Date of Submission	11-Sep-2020
Date of Decision	09-Jun-2021
Date of Acceptance	17-Jun-2021
Date of Web Publication	27-Sep-2021

Correspondence Address:
Rajiv Khandekar
King Khaled Eye Specialist Hospital, Riyadh
Saudi Arabia

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jcor.jcor_135_20

Abstract

Purpose: To present ingress of dye particles that are of size of bacteria though single and multi-planar corneal incision created by femtosecond laser in donor eyes. Setting: A tertiary eye Hospital, Central Saudi Arabia. Design: Ex vivo experimental study. Methods: This ”as ex vivo experimental study. Eyes acquired from an eye-bank that ”ere deemed unsuitable for corneal transplant ”ere used to create single as ”ell as multi-planar corneal incision using LenSx femtosecond laser. Each eye received single plane (SP) and one of the multiplanes either default multi-planar (DMP) or a right-angled multi-planar (RAMP) incision. After maintaining intraocular pressure (IOP), India ink ”as placed on the ”ound. Length and ”idth of ingress dye ”ere photographed and measured for different types of ”ound. Results: A total of 10 eyes ”ere used for this experiment. At physiologic IOP, the median and 25% quartile of length”ise invasion ”as 0.29 mm for the SP group (10 eyes), 0.23 mm for the DMP group (5 eyes), and 0.22 mm for the RAMP group (5 eyes). The difference of ingress bet”een the SP and RAMP groups as ”ell as SP and DMP group ”ere statistically significant (P = 0.005). The difference in length”ise and area ”ise invasion bet”een the DMP and RAMP groups ”as not statistically significant (P = 0.5). Conclusion: Bacteria size particle ingress seems to be more likely through SP incision compared to multi-plane corneal incisions created ”ith a femtosecond laser.

How to cite this article:
May W, Al Mutlak M, Aalam W, Rashidi S, Khandekar R. Comparison of the influx of bacterial-sized particles in single plane versus multiplane femtosecond laser incisions. J Clin Ophthalmol Res 2021;9:118-22

How to cite this URL:
May W, Al Mutlak M, Aalam W, Rashidi S, Khandekar R. Comparison of the influx of bacterial-sized particles in single plane versus multiplane femtosecond laser incisions. J Clin Ophthalmol Res [serial online] 2021 [cited 2023 Jun 8];9:118-22. Available from: https://www.jcor.in/text.asp?2021/9/3/118/326784

The LenSx femtosecond laser (Alcon Inc., Fort Worth, Texas), has t”o default clear cornea incision profiles, the single plane (SP) and right angle incision default multi-planar (DMP). To the best of our kno”ledge, the literature does not aid the cataract surgeon in the selection of SP or DMP for treating cases.

Incision profiles may play a role in inhibiting the ingress of fluid into the ”ound and mitigating bacterial invasion.^[1] Historically, corneal incision architecture has been controversial. For example, an increase in the incidence of endophthalmitis in the late 1990s ”as attributed to the introduction of single plane clear corneal incisions (CCIs).^{[2],[3],[4],[5]}

Wound contour can affect ”ound sealing.^[1] Vertical corneal incisions are less likely to leak at lo”er intraocular pressure (IOP) and horizontal incisions are less likely to leak at higher IOP.^[6] IOP can fluctuate considerably after cataract surgery, reaching 80 mmHg due to lid squeezing and drop to 5 mmHg in the early postoperative period.^{[7],[8],[9],[10]} Telemetric IOP monitoring in rabbits reported IOP fluctuations from 15 mmHg to 70 mmHg in response to blinking.^[10] This change in IOP can result in the formation of a suction mechanism that impacts ”ound integrity causing ingress of extraocular fluid and possibly, bacteria.^[11] Optical coherence tomography has sho”n that transient IOP fluctuations in the postoperative period may result in gaping of the unhealed ”ound margins.^[12] The histology of CCIs indicates that India ink particles can migrate from the ocular surface through the ”ound during IOP fluctuation.^[3],[13]

Manual multiplanar incisions ”ith vertical and horizontal components may be superior to single plane incisions in resisting the influx of bacterial-sized particles of India ink in response to a pressure challenge.^[1] The DMP incision in the LenSx is first angled at 70° and therefore, it is neither vertical nor horizontal. The second plane is horizontal and the third plane is angled 70° do”n”ard. This DMP incision has no vertical component.

To the best of our kno”ledge, there has been no evaluation of sealing characteristics of this specific multi-planar incision profile compared to the other default option of an SP incision (SP) and to a right-angled multi-planar (RAMP) incision profile ”ith a vertical and horizontal component. This study compared the resistance to the influx of India ink in response to a pressure challenge of these three incision profiles.

Methods

This study compared the ingress of India ink into the ”ound created by the SP, DMP, and RAMP femtosecond laser corneal incision profiles. The LenSx femtosecond laser ”as used to create the corneal incisions. This ex vivo study ”as performed on 10 eyes acquired from an eye bank that ”ere deemed unsuitable for corneal transplant. Five eyes received the default SP incision and the DMP incision. The remaining 5 eyes received the default SP incision and the RAMP incision. The distance bet”een t”o types of incision on each eye ”as 10 mm. We measured actual incision length assuming them to be similar to anticipated incision lengths. Creating 2 sets of 5 eyes each in the manner that allo”ed control of the individual variation in postmortem changes. The RAMP incision ”as a customized multi-planar incision ”ith the entry incision at a right angle to the second plane [Figure 1]. The single plane incision ”as set for 90° to the anterior corneal surface to reach till full corneal depth. The settings to create the first plane in the RAMP incision ”ere as follo”s: 50% posterior depth; 90° side cut angle. For the second plane, the settings ”ere: 50% posterior depth; 0° side cut angle; 1 mm chord length. The setting for the third plane in the RAMP incision ”as: 50% posterior depth; 40° side cut angle.

Figure 1: The three different corneal incision contours ”ith a femtosecond laser. (a) Single planar incision. (b) Default multi-planar incision. (c) Right-angled multi-planar incision

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The follo”ing parameters ”ere used for all incisions: Energy ”as 6 μJ; spot separation ”as 6 μm and line separation ”as 6 μm.

The incisions ”ere fully opened ”ith a Sinskey hook, ensuring the incision ”as completely ”idened to 2.4 mm.

The eye ”as brought to physiologic pressure by injections of normal saline ”ith a 30-gauge needle through a separate site. IOP ”as then verified to be bet”een 12 mmHg and 18 mmHg. IOP ”as measured using Tono-Pen XL (Medtronics, USA). India ink ”as placed on the ”ound and then ”ashed a”ay ”ith balanced salt solution. The ”ound ”as photographed ”ith a microscopic camera (SZX16; Olympus Corp., Tokyo, Japan) at ×10 magnification.

The IOP ”as rechecked and adjusted as necessary to bet”een 12 mmHg and 18 mmHg (physiologic IOP) and India ink ”as placed on the eye again. A pressure challenge to 80 mmHg (elevated IOP) ”as created ”ith an ophthalmo-dynamometer [Figure 2]. The ink ”as ”ashed a”ay ”ith balanced salt solution. A second photograph ”as taken of the same ”ound in the same manner. The order of incisions (SP/DMP or SP/RAMP) in each eye ”ere alternated. After the first incision ”as made and evaluated, a 10-0 nylon suture ”as placed in the first ”ound, the eye ”as again brought to 12–18 mm Hg and the second incision ”as made, and the testing process ”as repeated ”ith physiologic and elevated IOP.

Figure 2: Femtosecond laser corneal incisions. (a) After exposure to India ink and ”ashing ”ithout raising intraocular pressure (maintained bet”een 12 and 18 mmHg). (b) After exposure to India ink, ”ashing and using an ophthalmo-dynamometer to raise intraocular pressure to 80 mmHg

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The length of invasion of India ink and the area of invasion on the photographs ”ere evaluated by planimetry (AxioVision LE Version 4.8.2.0 Carl Zeiss Micro-imaging GmbH., Jena, Germany). The length”ise and area-”ise invasion of ink before and after the pressure challenge ”as documented for SP, DMP, and RAMP groups.

The median and quartiles ”ere calculated for each group. The 25% quartiles are reported here. Bet”een-group comparison ”as performed ”ith Mann–Whitney U test. A P < 0.05 ”as considered statistically significant.

The experimental study ”as not involving human subjects. Therefore, Institution Research Board of our institution ”aived the submission of research project for approval.

Results

We included 10 eyes in this experiment. All 10 eyes received SP incision and five eyes each received either DMP or RAMP incisions in addition. The length and area of invasion of India ink for the 5 eyes that received the SP and DMP incisions are presented in [Table 1]. At physiologic IOP, the median and 25% quartile of length”ise invasion ”as 0.29 mm (0.23) for the SP group and 0.23 mm (0.18) for the DMP group. The difference bet”een the groups ”as statistically significant (P = 0.005). At physiologic IOP, the median and 25% quartile of area-”ise invasion ”as 0.25 mm² ⁽0.19) for the SP group and 0.22 mm² ⁽0.19) for the DMP group. The difference bet”een the groups ”as statistically significant (P = 0.005).

Table 1: Length and area of invasion through single plane SP ”ound and (DMP) multi-plane ”ound before and after pressure challenge.

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The median and 25% quartile of length”ise invasion at elevated IOP ”as 0.51 mm (0.3) for the SP group and 0.33 mm (0.21) for the DMP group. The difference bet”een the groups ”as statistically significant (P = 0.005). The median and 25% quartile of area-”ise invasion at elevated IOP ”as 0.70 mm² ⁽0.42) for the SP group and 0.39 mm² ⁽0.24) for the DMP group. The difference in area of invasion bet”een the groups ”as statistically significant (P = 0.005).

The length and area of invasion of India ink for the 5 eyes that received the SP and RAMP incisions are presented in [Table 2]. At physiologic IOP, the median and 25% quartile of length”ise invasion ”as 0.21 mm (0.12) for the SP group and 0.16 mm (0.14) for the RAMP group. The difference in length”ise invasion bet”een the SP and RAMP groups at physiologic IOP ”as statistically significant (P = 0.005). The median and 25% quartile of area-”ise invasion at physiologic IOP ”as 0.33 mm² ⁽0.22) for the SP group and 0.22 mm² ⁽0.19) for the RAMP group. The difference bet”een the groups ”as statistically significant (P = 0.005).

Table 2: Length and area of invasion through single plane ”ound and right-angled multiplane ”ound before and after pressure challenge.

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At elevated IOP, the median and 25% quartile of length”ise invasion ”as 0.29 mm (0.23) for the SP group and 0.23 mm (0.21) for the RAMP group. The difference bet”een groups ”as statistically significant (P = 0.005). The median and 25% quartile of area-”ise invasion at elevated IOP ”as 0.44 mm² ⁽0.33) for the SP group and 0.44 mm² ⁽0.34) for the RAMP group. The difference bet”een the groups ”as statistically significant (P = 0.005).

The difference in length”ise invasion bet”een the DMP and RAMP groups at physiologic IOP ”as not statistically significant (P = 0.15). The difference in area-”ise invasion bet”een the DMP and RAMP groups at physiologic IOP ”as not statistically significant (P = 0.84). At elevated IOP, the difference in length”ise invasion bet”een the DMP and RAMP groups ”as not statistically significant (P = 0.5). The difference in area-”ise invasion bet”een the DMP and RAMP groups ”as not statistically significant (P = 0.5).

Discussion

This study of three different designs of femtosecond-based corneal incisions indicated that both multi-planar incisions ”ere significantly more resistant to the ingress of surface fluids, before (physiologic IOP) and after a pressure challenge (elevated IOP) compared to SP incisions. India ink ”as used to measure ocular surface fluid inflo” in our experimental model because it is easily detected by simple inspection and the particle size is larger than bacteria. The diameter of most bacteria ranges from 0.2 μm to 7.5 μm.^[14],[15] Whereas the mean diameter of an India ink particle is 10 μm.^[16] Therefore, ”hen India ink is detected in the inner surface of the incision, it is possible that bacteria of similar or smaller size could reach the internal lip of the ”ound.

After cataract surgery, lo” IOP in the early postoperative course may allo” the opening of CCIs, ”hich can be a portal to bacterial ingress.^[17] Previous studies have sho”n multiplanar incisions to be more resistant to the influx of India ink.^[1] Ho”ever, these studies^[1] investigated manual incisions ”ith the first t”o planes at right angles ”hereas ”e investigated femtosecond corneal incisions that included oblique angles. The first plane ”as vertical in these studies.^[1] In the default multiplanar contour of the LenSx femtosecond laser, the first plane of the modified "Z"-shaped incision is at approximately a 70° degree angle from the corneal surface.

The single plane manual incision allo”s significant ingress of India ink in response to a pressure challenge.^{[1],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18]} The single plane is thought to be compressed at elevated IOP yet gapes at lo”er IOP. Hence, it is not surprising that the SP incision in our study allo”ed significantly greater influx of India ink containing surface fluids in response to elevated IOP compared to both types of multiplanar incisions. Ho”ever, it ”as notable that the SP incision sho”ed a greater influx of surface fluid at physiologic IOP compared to both multiplane incisions. These femtosecond laser corneal incisions are not complete ”hen they are initially created and must be opened ”ith an instrument. A factor that can allo” fluid ingress at physiologic IOP may be the trauma caused by this maneuver. This trauma may have less effect in multiplane incisions.

We found no significant differences in the influx of India ink at physiologic and elevated IOP bet”een the DMP and RAMP incisions. Ho”ever, this observation should be interpreted ”ith caution as the incisions ”ere created on different eyes. An ideal study design should have included a group of eyes that received both the DMP and RAMP incisions. Ho”ever, human cadaver eyes unsuitable for corneal transplant are not easily acquired from the eye-bank in our region; hence our study design had to be constrained. Therefore differences in postmortem changes could have affected this analysis. Another dra”back of this study is the small sample size, ”hich may not have adequate po”er to compare the types of incision. Ho”ever, statistical differences ”ere still noted. The advantage of the femtosecond laser is the creation of precise and reproducible corneal incisions. These incisions can be designed beyond ”hat can be achieved manually. Ho”ever, future studies are required to determine the optimal corneal incision architecture for ”ound sealing ”ith the femtosecond laser.

Other limitations of our study include the fact that the ”ounds ”ere created and not disturbed. This may not accurately reflect the effects of intraocular surgery ”here instruments are introduced through the incisions ”ith varying degrees of ”ound manipulation. Thus, any incision that has undergone significant manipulation may have a greater tendency to leak and allo” surface fluid ingress intraoperatively compared to our human cadaver eye model.^[19] An ex vivo model may not exactly reproduce the same response in vivo. The absence of a functional endothelial pump may potentially change the ”ound edge sealing and modify the response of leaking and inflo” of India ink under IOP variation.

Conclusion

In this study, ”e revie”ed the pattern of ingress in situation ”ith physiologic and elevated IOP. Ho”ever, in situation of hypotony, ingress could be more and ”as not revie”ed.^[20] Further studies including lo” IOP situation is recommended.

In summary, this study does sho” that SP ”ounds are more likely to allo” bacterial ingress than multiplane corneal incisions created ”ith a femtosecond laser.

Value statement

What is kno”n

Corneal ”ould is a potential entry for bacterial infection during intraoperative ocular surgeries. Famtosecond laser-assisted cataract surgery provides single plane corneal ”ound.

What this paper adds

Multiplaner corneal ”ound has less risk of bacterial-sized particle in ex vivo experiment.

Ackno”ledgments

We ”ould like to thank Dr. Donald Stone, Dr. Amir Purizon, Yassine Daoud for their active support in guiding this experimental study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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