CASE REPORT

Customized miniflap for a nondissected flap island during femtosecond laser–assisted laser in situ keratomileusis

Hassouna, Abdallah K. MD, PhD; Wahba, Sherine S. MD, PhD; Hermina, Marian S. MD, MSc; Samy, Sameh N. BOptom

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Journal of Cataract and Refractive Surgery: April 2020 - Volume 8 - Issue 2 - p e00004
doi: 10.1097/j.jcro.0000000000000004
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Abstract

One of the latest innovations in refractive surgery is femtosecond laser–assisted laser in situ keratomileusis (FS-LASIK), which precisely creates variable thickness and diameter corneal flaps with improved predictability and safety compared with conventional procedures.1–3 Nevertheless, femtosecond flap creation has several unique known complications, such as opaque bubble layer, difficult flap lift, anterior chamber gas bubbles, and gas breakthrough.4–6

It is reported in the literature that the site of gas breakthrough bubbles greater than 1.0 mm is harder to break when lifting the flap. Therefore, it is recommended to wait for 1 to 2 weeks for the flap to heal and then attempt another flap 40 to 50 μm deeper, provided that there is sufficient stromal tissue. However, this could result in gas breakthrough again or intersecting flap interfaces. The other safer option is to perform photorefractive keratectomy with mitomycin C to decrease the risk of corneal haze.3,7

Here 3 case reports are presented about another complication, anterior chamber gas bubble escape between the cornea and the cone through the canal, which leads to a nondissected island. Moreover, we describe a new technique, customized miniflap (CMF), that can be applied in the same session to treat the nondissected island.

CASE REPORTS

Case 1

A 29-year-old woman had bilateral FS-LASIK. Her preoperative refraction was 0 −3.0 × 180 in the right eye and −0.5 −3.0 × 180 in the left eye, with a corrected distance visual acuity (CDVA) of 1.00 diopter (D) in each eye. Corneal tomography using Pentacam HR (Allegro Oculyzer II, WaveLight GmbH) was normal in both eyes, with a keratometry (K) reading of 41.4/46.0 D @ 5.6 in the right eye and 41.1/46.6 @ 6.6 in the left eye.

An FS-LASIK procedure was performed with a flap diameter of 8.9 mm and a target depth of 120 μm (FS 200, WaveLight GmbH, Alcon Laboratories, Inc.). After successful canal formation in the right eye and at the beginning of the flap bed cut, an anterior gas bubble escape, about 2.0 × 1.7 mm in diameter, appeared between the cornea and the cone near the hinge, so the surgeon did not complete the flap bed cut (Figure 1, A).

Figure 1.
Figure 1.:
Case 1. A: The aborted flap showing the anterior chamber gas bubble escape. B: The anterior chamber gas bubble escape after completing the flap. C: Completion of the customized miniflap. D: Anterior segment optical coherence tomography cut section and inset showing the flap depth.

A new procedure was started after changing the hinge position to be 115 degrees instead of 90 degrees. Unfortunately, after successful canal formation and at the beginning of the flap bed cut, the anterior gas bubble escape reappeared near the hinge (Video 1, available at, http://links.lww.com/JC9/A1). The surgeon completed the flap bed cut and the flap side cut successfully, but the anterior gas bubble escape resulted in a nondissected area of about 2.5 × 1.5 mm near the hinge (Figure 1, B).

The decision was made to start a CMF of 3.0 mm diameter to cover the nondissected area, of the same target depth of 120 μm, with adjusted side-cut and hinge position parameters, as there was no option in the FS 200 software to cancel these steps (the least energy with widest line separation and spot separation and the default hinge position were used) and canal formation (Table 1, Figure 1, C and Video 1, available at, http://links.lww.com/JC9/A1). The flap was lifted successfully without creating a button hole. The excimer ablation procedure was performed, and the flap was repositioned. The surgery in the left eye was uneventful.

Table 1.
Table 1.:
Parameters of the aborted flap, the completed flap, and the CMF of case 1.

On the first day postoperatively, the patient had an uncorrected distance visual acuity (UDVA) of 1.00 D in each eye with a clear and well-centered flap, centered postmyopic ablation, and within the normal regularity index and index of surface variance by Pentacam. The anterior segment optical coherence tomography (AS-OCT) revealed the depth of the original flap to be 125 μm and that of the CMF to be 127 μm (Figure 1, D).

Case 2

A 43-year-old woman had preoperative refraction of −2.0 −1.0 × 85 in the right eye and −1.25 −1.0 × 105 in the left eye, with a CDVA of 0.70 D in the right eye (amblyopic eye) and 1.00 D in the left eye. Corneal tomography was normal in both eyes with K reading of 43.1/43.7 @ 99.1 in the right eye and 42.5/43.5 @ 113 in the left eye.

A FS-LASIK procedure was planned with a flap diameter of 8.8 mm and a target depth of 110 μm. The surgery in the right eye was uneventful. After successful canal formation in the left eye and at the beginning of the flap bed cut, an anterior gas bubble escape appeared between the cornea and the cone. The surgeon decided to complete the procedure (Figure 2, A).

Figure 2.
Figure 2.:
A: Case 2. After completion of the flap showing the anterior chamber gas bubble escape. B: After completion of the customized miniflap. C: Anterior segment optical coherence tomography cut section and en-face picture showing the flap depth.

The anterior gas bubble escape resulted in a nondissected area about 2.00 × 1.50 mm near the hinge. A CMF of 4.3 mm diameter was started (Figure 2, B and Video 2, available at, http://links.lww.com/JC9/A2). Surgical parameters are reported in Table 2. The flap was completely lifted successfully without creating a button hole. The excimer ablation was performed, and the flap was repositioned.

Table 2.
Table 2.:
Parameters of the original flap and the CMF of case 2.

On the first day postoperatively, the patient had a UDVA of 0.7 in the right eye and 1.0 in the left eye with a clear and well-centered flap, centered postmyopic ablation, and within the normal index of surface variance. The AS-OCT revealed the depth of the original flap to be 117 μm and that of the CMF to be 121 μm (Figure 2, C).

Case 3

A 22-year-old woman with preoperative refraction of −5.50 −1.5 × 180 in the right eye and −5.25 −1.5 × 160 in the left eye, with a CDVA of 1.0 in each eye. Corneal tomography was normal in both eyes with a K reading of 43.5/45.4 @ 9.6 in the right eye and 43.6/54.5 @ 165.4 in the left eye. A FS-LASIK procedure was planned, with a flap diameter of 8.7 mm and a target depth of 120 μm.

The surgeon observed an opacity in the cone but decided to continue the procedure. The canal, bed cut, and side cut were done successfully in the right eye but with a nondissected area related to the site of the cone opacity at the lower temporal area, measuring about 1.5 × 1.5 mm (Figure 3, A). The cone was changed, and a CMF of 3.5 mm diameter was started (Figure 3, B and Video 3, available at http://links.lww.com/JC9/A3). Surgical parameters are listed in Table 3. The flap was successfully lifted without creating a button hole. The excimer ablation procedure was performed, and the flap was repositioned. The surgery in the left eye was uneventful.

Figure 3.
Figure 3.:
A: Case 3. Completion of the flap showing the anterior chamber gas bubble escape. B: A photograph after completing the customized miniflap in case 3. C: An anterior segment optical coherence tomography cut section and en-face picture of case 3 showing the flap depth.
Table 3.
Table 3.:
Parameters of the original flap and the CMF of case 3.

On the first day postoperatively, the patient had a UDVA of 1.0 in each eye with a clear and well-centered flap by slitlamp evaluation, centered postmyopic ablation, and within the normal index of surface variance by Pentacam (Table 4). The AS-OCT revealed the depth of the original flap to be 123 μm and that of the CMF to be 126 μm (Figure 3, C).

Table 4.
Table 4.:
Preoperative and postoperative ISV in the 3 cases.

DISCUSSION

The femtosecond laser achieves its surgical effect through photodisruption in which cavitation bubble of carbon dioxide gas and water is formed, creating a cleavage plane in the cornea and the side cut of the flap.7,8 It can achieve the specific flap depth and diameter with a standard deviation of about 5 μm.9 Although vertical gas breakthrough is already a well-known complication and its treatment is previously discussed, anterior gas bubble escape is a rarer and missed complication that is equally bothering and, therefore, deserves reporting and solution suggestion.10,11

In the first 2 case reports, we mentioned the occurrence of anterior gas bubble escape between the corneal surface and the cone after finishing the canal formation. Even when the surgeon changed the hinge position in case 1, the bubble reappeared near the new canal position and the surgeon decided to complete the flap bed cut. The anterior gas bubble escape resulted in a nondissected island.

We believe that anterior gas bubble escape appearance could be either due to short canal as in cases 1 and 2; since the opening of the canal should be outside the applanated area, or due to slight decentration of the flap as in case 3; since proper centration of the suction ring and suitable flap diameter are important factors.

Another complication could be the imperfect vacuum, which lead to a small potential space between the cone and the cornea. The factors causing such an imperfect vacuum could be similar to that of suction loss; significantly flat cornea, small palpebral apertures, or eyelid squeezing.12 In the first case, there was significant pannus with a relatively high index of surface variance, which could be the cause of imperfect vacuum. It could be also due to a problem in the vacuum tube connection with the suction ring or during the second automated suction, which secures the applanation cone within the suction ring during applanation.

The literature reported that forceful attempts to dissect this area can result in a tear through the surface.3,13 The current article described a new technique to treat the nondissected island occurred during FS-LASIK flap creation on the same session through the creation of the CMF, with a slightly larger diameter to the nondissected island.

The results were promising, as the surgeon was able to lift the flap very easily with no complications, and this was evidenced subjectively by the postoperative visual results and objectively through the postoperative index of surface variance of Pentacam.

Moreover, the AS-OCT revealed differences in the flap depth between the original flap and the CMF of few micrometers. The CMF was slightly deeper than the original one. This seems to be attributable either to the different cone calibration or to the effective vacuum in the beginning of the CMF. These few micron differences did not interfere with the dissection or cause any difficulty in lifting the flap.

The CMF is a promising new technique to solve the problem of the nondissected island in the same session, which could occur during FS-LASIK due to anterior gas bubble escape.

REFERENCES

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11. Farjo AA, Sugar A, Schallhorn SC, Majmudar PA, Tanzer DJ, Trattler WB, Cason JB, Donaldson KE, Kymionis GD. Femtosecond lasers for LASIK flap creation; a report by the American Academy of Ophthalmology. Ophthalmology 2013;120:e5–e20
12. Syed ZA, Melki SA. Successful femtosecond LASIK flap creation despite multiple suction losses. Digit J Ophthalmol 2014;20:7–9
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