Article Text

Modified big-bubble deep anterior lamellar keratoplasty using peripheral air injection
  1. Sepehr Feizi,
  2. Amir Faramarzi,
  3. Mohammad Ali Javadi,
  4. Mohammad Reza Jafarinasab
  1. Department of Ophthalmology, Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
  1. Correspondence to Dr Sepehr Feizi, Department of Ophthalmology, Ophthalmic Research Center, Labbafinejad Medical Center, Boostan 9 St., Pasdaran Ave., Tehran 16666, Iran; sepehrfeizi{at}yahoo.com

Abstract

Purpose To introduce a modification to big-bubble deep anterior lamellar keratoplasty (DALK) which can decrease the risk of Descemet membrane (DM) perforation during air injection.

Method In Anwar's big-bubble technique, a 27-guage needle is inserted from the trephination site and advanced into the corneal stroma up to the centre. The technique we introduce modifies the original technique in the following fashion. After trephination to approximately 80% of corneal thickness, a 27-guage needle is inserted into the stroma peripherally from the trephination site towards the limbus. Air is injected gently into the deep stroma until a big bubble is formed. This technique was performed in 16 consecutive keratoconic eyes undergoing DALK. Additionally, peripheral air injection was carried out in 27 eye-bank corneas using a peripheral approach.

Results In all (100%) eye-bank and 13 (81.3%) live corneas, a successful big bubble was easily achieved following peripheral air injection. In these 13 live corneas, all bubbles were formed at the central (n=10) or paracentral (n=3) cornea and extended centrifugally (type 1 bubble). In one of these corneas, an additional three bubbles were noted in the periphery between the DM and the pre-Descemet posterior stromal layer (Dua's layer, type 2) after a type 1 bubble was formed. In two live corneas in which peripheral air injection failed, a big bubble was successfully formed after air was injected inside the trephination site.

Conclusions Air injection peripheral to the trephination site is a reproducible modification to the standard technique which can decrease the risk of DM perforation during air injection.

  • Cornea
  • Experimental &#8211 laboratory
  • Treatment Surgery
  • Dystrophy

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Introduction

Different techniques of deep anterior lamellar keratoplasty (DALK) have been introduced to create a uniform recipient bed, thereby reducing complications, such as interface irregularity and opacification encountered with conventional lamellar keratoplasty.1–5 The big-bubble technique introduced by Anwar and Teichmann3 ,4 provides a planned, safe, quick and consistent baring of Descemet membrane (DM) by injection of air deep into the stroma. Nevertheless, this technique has a long learning curve with a low success rate of big-bubble formation and a high rate of DM perforation when performed by surgeons in training.6 ,7

Perforation of DM can occur during any step of surgery, including air injection into deep stroma. Herein, we describe a new location for air injection which in our experience has reduced the risk of DM perforation during injection and yielded more reproducible results compared with the original technique.

Patients and methods

The study was initially conducted on eye-bank corneas. After observing a favourable result in our laboratory experiment, we then proceeded to implementing the technique in human eyes scheduled for surgery. Both laboratory and clinical experiments were performed by an experienced anterior segment surgeon (SF). The Ethics Committee at the Ophthalmic Research Center approved the clinical part of the study and the participating subjects signed the consent form.

Laboratory experiment

Twenty-seven human corneoscleral buttons deemed unsuitable for transplantation were obtained from the Central Eye Bank of Iran in Optisol-GS (Chiron Vision, Irvine, California, USA). The procedure was performed in the following manner. The corneoscleral button was placed endothelial side up on a donor Barron punch (Katena, Denville, New Jersey, USA) and fixed by grasping the outer scleral edge. A 27-gauge bevel-up needle attached to a 2 mL syringe filled with air was inserted just outside Schwalbe's line and advanced to the peripheral cornea approximately 1.5 mm in front of the limbus in a tangential way immediately beneath the endothelium (figure 1). Air was injected to achieve DM detachment and the bubble was enlarged as far as possible into the corneal periphery (see online video, supplemental digital content 1, which demonstrates type 1 big-bubble formation after peripheral air injection in a corneoscleral button; a small type 2 bubble was formed afterwards in the far periphery. The mark indicates the central 9 mm zone).

Figure 1

Peripheral air injection in an experimental setting. (A) The needle is inserted just outside Schwalbe's line and advanced to the peripheral cornea beyond the 9 mm zone mark in a tangential way immediately beneath the endothelium. (B) After air injection, several small bubbles are formed on both sides of the needle coalescing in a circular fashion. (C) Then, a type 1 bubble is formed in the centre and enlarges circumferentially toward the periphery. (D) A small type 2 bubble is next formed at a limited sector of the button in the periphery (white arrow).

Clinical setting

Sixteen consecutive keratoconic eyes were enrolled in this part of the study. All eyes were operated on under general anaesthesia using Anwar’s big-bubble technique6 which was modified in the following fashion. After trephination to approximately 80% of corneal thickness using a Hessburg–Barron suction trephine (Katena, Denville, New Jersey, USA), a 27-guage needle bent 100° (bevel facing downward) and attached to a 5-mL syringe was inserted into the deep stroma from the trephination site and advanced into the peripheral cornea to approximately 1.5 mm anterior to the limbus (figure 2). Subsequently, air was injected gently into the deep stroma to achieve detachment of DM, and a big bubble was formed extending to the borders of the trephination site (see online video, supplemental digital content 2, which demonstrates type 1 big-bubble formation after peripheral air injection).

Figure 2

Modified big-bubble deep anterior lamellar keratoplasty using peripheral air injection. (A) A 27-guage needle is inserted into the deep stroma from the trephination site and advanced into the peripheral cornea to 1.5 mm anterior to the limbus. (B) After air injection, a classic white-margin big bubble is formed at paracentral cornea (white arrow) and extends centrifugally as an advancing white band (C) to reach the trephination site (D).

In the laboratory experiment and clinical setting, the type of bubbles formed was noted and classified according to Dua et al.8

Type 1: a white, semi-opaque disk with a circular outline starting in the centre of the cornea and enlarging circumferentially toward the periphery.

Type 2: one or multiple clear edge bubbles forming in the periphery and enlarging centrally to form a large bubble.

Type 3: the mixed type in which one type is initially formed followed by the formation of the other type.

Results

Laboratory experiment

A total of 27 human corneas from 27 cadavers including 21 male and 6 female donors with mean age of 31.2±15.5 (range 7–65) years were procured. A big bubble was obtained in all cases. Type 1 big bubbles were observed in 3 (11.1%) corneas, type 2 bubbles developed in 15 (55.6%) corneas, and type 3 bubbles were noted in 9 (33.3%) corneas (figure 1D).

Clinical experiment

A total of 16 subjects with keratoconus including 11 male and 5 female subjects with mean age of 24.9±4.1 (range 19–38) years were included for the purpose of the study. The mean keratometry reading was 49.2±6.3 (range 46.5–58.25) D and the mean central corneal thickness was 483.6±54.1 (range 395–522) μm. The recipient trephination size was 7.75 mm in four cases and 8.0 mm in 12 cases. Big-bubble formation was successful in 13 (81.3%) eyes after air was injected peripheral to the trephination site. In four eyes, the first peripheral injection failed and the big bubble was successfully achieved after the second peripheral injection in a different quadrant. Initially, there was focal stromal emphysema at the point of injection reflected by stromal opacification and haziness. A classic white-margin big bubble was then formed at the central (n=10) or paracentral (n=3) cornea (figure 2B); this extended centrifugally as an advancing white band (type 1 bubble) to reach the trephination site (figure 2C,D). In one cornea, three type 2 bubbles were noted in the periphery after a type 1 bubble was formed.

In two eyes in which several peripheral air injections in different quadrants failed, a big bubble was successfully formed after air was injected inside the trephination site (standard technique). In one remaining eye layer-by-layer stromal dissection was performed after both peripheral and central injections were unsuccessful. No case of DM perforation or disinsertion, or air penetration into the anterior chamber was encountered in the clinical setting.

Discussion

Anwar's big-bubble DALK is relatively quick to perform and has been shown to yield visual results comparable to penetrating keratoplasty.4 ,9 However, this technique is associated with a long surgical learning curve and difficulty in achieving dissection down to the level of bare DM, resulting in an initial success rate of approximately 50%.6 ,7

One of the obstacles facing the surgeon using the original technique is the risk of DM perforation when the deeply inserted needle is advanced centrally. This problem is due to the curvature of the central cornea causing less distance between the needle tip and DM as the needle is advanced centrally (figure 3, left). With our modified technique the opposite situation occurs; when the needle is deeply inserted outside the trephination site and advanced peripherally, its tip gets farther away from DM as the corneal periphery is flatter and thicker than the central cornea, thereby reducing the risk of DM perforation (figure 3, right).

Figure 3

The needle tip gets closer to Descemet membrane (DM) when a deeply inserted needle is advanced centrally, increasing the risk of DM perforation (left). When the needle is advanced peripherally (right), its tip gets farther away from DM as the corneal periphery is flatter and thicker than the central cornea, thereby reducing the risk of DM perforation.

We believe that air injection outside the trephination has a shorter learning curve. Both laboratory and clinical results revealed that separation of DM from the corneal stroma by peripheral air injection is reproducible and allows wide and complete exposure of DM. Another advantage is that in the event of unsuccessful air injection or DM perforation, it is possible to change the site of air injection to the opposite limbus or even inside the trephination as employed in the original technique. In this situation, the perforated area will not interfere with successful big-bubble formation. In order to examine this speculation, we deliberately perforated DM peripherally in a corneoscleral button and then injected air at the opposite limbus. A type 1 big bubble was successfully achieved despite the peripheral perforation (figure 4).

Figure 4

The peripheral corneoscleral button is deliberately perforated (white arrow) followed by air injection at the opposite site of the button (black arrow); a type 1 big bubble is successfully achieved despite the peripheral perforation.

There are three concerns with peripheral air injection. First, since the injection is performed at one site, it is possible that air does not reach the borders of trephination at the opposite site. Clinical and laboratory experiments demonstrated type 1 bubbles started from the central or paracentral cornea in spite of the peripheral site of injection and enlarged centrifugally to thoroughly detach DM at the trephination site. This observation is in agreement with the findings of Dua et al8 who observed a type 1 bubble always starts in the centre of the cornea and enlarges circumferentially toward the periphery. This interesting observation can be a subject for future investigations to determine how peripheral air injection leads to DM separation starting from the centre. The second concern is that air injected close to the limbus can gain access to Schlemm's canal and find an alternative pathway into the anterior chamber. However, our observations speak against this possibility by the lack of a single case of such a complication. This means that peripherally injected air still finds its way into the cleavage plane within the deep stroma or between the DM and deep stroma rather than escaping into the anterior chamber. The third concern is that peripheral air injection would be more difficult to perform when recipient trephination size is larger than that selected in the present study. The recipient trephination size used in the clinical part of this study was 7.75 and 8.0 mm to prevent sutures from being placed very close to the limbus, hence reducing suture-related complications. The lamellar nature of DALK, however, allows the use of larger grafts (up to 9.0 mm) without increasing the risk of endothelial rejection. The results of our laboratory experiment suggest that a big bubble could be achieved even if the needle is inserted outside the central 9 mm zone (please see figure 1 and online supplemental digital content 1).

Air injection inside the trephination site quite often creates a type 1 big bubble and type 2 bubbles are rarely seen.10 In the current study, type 2 bubbles were observed in one cornea in the clinical setting and in 24 corneas in the laboratory experiment (figure 1D). Dua et al8 revealed that the pre-Descemet posterior stromal layer is a distinct well defined layer (Dua's layer) which ends before the termination of DM. Therefore, air is more likely to gain access to the plane between posterior stroma and DM when injection is carried out at the periphery of the cornea, leaving a truly bare DM in place. It is possible that this type of big bubble provides faster visual recovery and better visual acuity because no stroma remains. However, a true bare DM is very thin and could be more vulnerable to perforation with later manipulation. Further studies on big-bubble DALK using peripheral air injection will need to document the type of formed bubbles (type 1 vs type 2), and compare the rate of intraoperative DM perforation and visual outcomes between the two groups.

In summary the technique described herein appears to be a reasonable modification to the original big bubble technique. Potential benefits include a lower risk of DM perforation during air injection, relative ease of successful big-bubble formation, and a higher likelihood of true baring of DM. It is worth mentioning that this modification does not reduce the likelihood of DM perforation during other steps, including trephination and posterior stromal excision.

References

Supplementary materials

  • Supplementary Data

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Footnotes

  • Contributors SF designs and performs the study. SF and AF write the manuscript. MAJ and MRJ critically revise and approve the manuscript.

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval The Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.

  • Provenance and peer review Not commissioned; externally peer reviewed.