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CASE REPORT
Year : 2023 | Volume
: 13
| Issue : 1 | Page : 97-100
Corneal ectasia after an incomplete flap creation in an abandoned laser-assisted in situ keratomileusis
Hsiao-Fan Tung, Ho-Ling Chen, Yu-Ling Liu, Chang-Ping Lin
Department of Ophthalmology, Changhua Christian Hospital, Changhua City, Taiwan
Correspondence Address:
Prof. Chang-Ping Lin
Department of Ophthalmology, Changhua Christian Hospital, No. 135, Nanxiao St., Changhua City
Taiwan
Source of Support: None, Conflict of Interest: None
DOI: 10.4103/2211-5056.364565
To report a unique case of a 31-year-old woman developing corneal ectasia after an abandoned laser-assisted in situ keratomileusis (LASIK) procedure with incomplete flap creation without laser ablation. A 31-year-old Taiwanese woman presented with corneal ectasia after a failed LASIK with an incomplete flap creation without laser procedure in her right eye 4 years ago. A visible scar was observed in the flap margin from the 7 to 10 o'clock position. The auto refractometer revealed myopia with high astigmatism, −1.25/−7.25 × 30. Keratometry was 47.00/40.75 D. In contrast, no sign of keratoconus was found in the fellow eye, which did not experience any surgery. Corneal tomography indicated that the incomplete flap scar was compatible with the main area of corneal ectasia. Furthermore, anterior segment optical coherence tomography showed a deep cutting plane and a relatively thin corneal bed. Both findings explained the cause for corneal ectasia. Corneal ectasia can occur whenever corneal structure or integrity is compromised.
Keywords: Corneal ectasia, incomplete flap creation, laser-assisted in situ keratomileusis
Corneal ectasia is one of the most disastrous complications of laser-assisted in situ keratomileusis (LASIK). Many studies and guidelines have been reported to avoid it. Current consensus points out several risk factors such as low residual stromal bed thickness, high myopia, and forme fruste keratoconus.[1],[2] Although most post-LASIK corneal ectasia cases present with at least one of the risk factors, some showed no abnormalities during preoperative evaluation. We report a unique case of corneal ectasia after an abandoned LASIK procedure with incomplete flap creation without laser ablation.
Case ReportA 31-year-old Taiwanese woman consulted our ophthalmology clinic with the main complaint of progressive blurred vision in the right eye for 4 years. Five years ago, according to her statement, she experienced a failed LASIK with incomplete flap creation in her right eye, and the laser procedure was abandoned.
Ocular examinations of her right eye are as follows: uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) were 20/1000 and 20/50, respectively. Auto refractometer revealed myopia with high astigmatism, −1.25/−7.25 × 30. The keratometry result was 47.00/40.75 D. An incomplete flap with a visible scar at the flap margin was observed from 7 to 10 o'clock [Figure 1]. Corneal tomography disclosed ectasia with anterior and posterior corneal surface protrusion over the lower temporal side [Figure 2]. Anterior segment optical coherence tomography (OCT) showed an uneven plane of the corneal flap [Figure 3]. Corneal thickness was 559 μm over the center and 529 μm over the thinnest point. We measured the thickness of the corneal flap and residual stroma using anterior segment OCT. In the central 6-mm optical zone, the thinnest residual stroma was found at the 7 o'clock position (residual stroma: 133 μm and flap: 470 μm). Conversely, the thickest residual stroma was found at the 10 o'clock position (residual stroma: 211 μm and flap: 484 μm) [Figure 4]. From the above data, we could tell that the incision plane tilted toward the inferior side, which meant that the inferior side was deeper than the superior.
Figure 1: External photography showed a visible scar at the flap margin from 7 to 10 o'clock position (red arrow: the margin of the flap)
Figure 3: The anterior segment OCT showed that the incision depth was deeper in the inferior cornea than in the superior side. OCT: Optical coherence tomography. (green arrow: the position of the OCT scan; white arrow: the incisional plane)
Figure 4: Manifestations of the corneal flap and the residual stromal thicknessOn the other hand, the UCVA and BCVA were 20/400 and 20/20 in her left eye. Auto refractometer and keratometry were −3.00/−0.50 × 10 and 42.25/41.50 D, respectively. Corneal thickness was 565 μm over the center and 554 μm over the thinnest site, similar to the right eye. Corneal tomography results were normal [Figure 1]. A scleral lens was suggested under the impression of corneal ectasia, which achieved a BCVA of 20/32. However, the patient was hesitant and left her right eye uncorrected.
Two years later, the patient presented to our ophthalmology clinic again with the complaint of progressively decreasing visual acuity in the right eye for months. This time, BCVA was 20/100 in the right eye with higher astigmatism. The refraction and keratometry were −3.00/−9.25 × 35 and 48.25/40.75 D, respectively, in the right eye and −3.25/0 × 0 and 41.75/41.00 D, respectively, in the left. The severity of right corneal protrusion worsened significantly can be seen by tomography [Figure 5]. Under the impression of progressive corneal ectasia, corneal crosslinking with sequential Topolink PTK in another country was suggested since corneal crosslinking was not available in Taiwan at that moment. Due to the COVID-19 pandemic, the patient decided to try a scleral lens, which she refused 2 years ago. We prescribed a corneoscleral contact lens (SoClear, Brighten Optix, Taiwan) for her, and visual acuity of 20/25 in her right eye was achieved.
Figure 5: Tomography in the right eye 2 years later revealed the progression of corneal ectasia Discussion To our understanding, this is the first reported case that presented as corneal ectasia after incomplete flap creation of a failed LASIK surgery. The right ectatic cornea underwent LASIK surgery first, making the left eye an excellent control. No sign of keratoconus was observed in the left eye, and the corneal thickness map was similar to the right. All evaluations met the safe criteria for the LASIK procedure.
In the right eye, the incomplete flap scar was visible from the 7 to 10 o'clock position, which was compatible with the main area of corneal ectasia seen in tomography. In addition, the lower temporal border of the ectatic area seen by tomography was parallel to the margin of flap cutting. The central border showed a relatively straight line across the optical center, presumably where the microkeratome blade stopped. This is a strong evidence that ectasia was the result of aberrant microkeratome cutting.
Several previous studies analyzed the characteristics of post-LASIK-related corneal ectasia. The most common location of the cone was directly inferior to the central cornea, and the cone was oval or round. In addition, the topographic curvature in eyes with post-LASIK corneal ectasia is usually presented as a “bow-tie” pattern. In other words, the inferior segment would be much deeper than the superior segment with a straight or skew central axis.[2],[3],[4],[5] However, the ectatic features in our patient were different from the above findings.
Aside from ectatic corneal morphology, structural weakening due to flap creation and stromal ablation is now thought to be the leading cause of corneal ectasia after keratorefractive surgery. In the current consensus, a minimum of 250 μm is suggested as a relatively safe thickness of the residual stromal bed.[1],[2],[6],[7],[8],[9],[10] Since the stromal bed would be the main barrier against mechanical stress after flap creation, the thinner the stromal bed, the weaker the corneal strength. Besides, avoiding a thick flap was emphasized due to higher cohesive tensile strength found in the anterior 40% of the cornea, and a greater density of keratocytes was noted in the anterior 10% of the stroma.[5] In our patient, the cutting plane was deep and resulted in a relatively thin stromal bed that led to weak corneal strength, which also increased the risk of corneal ectasia. We hypothesized that suction loss, incorrect setting, or tilting of the microkeratome occurred when the patient underwent surgery.
According to the above data, we can almost confirm that a thin residual stromal bed resulted in ectasia in this case. Nevertheless, corneal ectasia may happen whenever a corneal structure is disturbed and integrity is compromised. Such a phenomenon can be explained by the disparity of elastic modulus within the cornea.[11] A weak area within the cornea would lead to a change of stress distribution and a greater deformation. This causes further corneal thinning and protrusion, aggravating focal corneal weakness, and eventually entering a vicious cycle of disease progression.[11]
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for the images and other clinical information to be reported in the journal. The patient understands her name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
Dr. Chang-Ping Lin, an editorial board member at Taiwan Journal of Ophthalmology, had no role in the peer review process of or decision to publish this article. The other authors declared no conflicts of interest in writing this paper.
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