Demographics and clinical characteristics of cases that underwent epikeratoplasty
Demographic and clinical features are shown in Table 1. A total of 10 cases were available. Four female (40%) and six male (60%) patients were analyzed. Mean age at EKP was 24.2 years ±10.6 years (range, 5 years – 48 years). Nine patients received EKP for correction of high myopia, and only one patient underwent EKP for correction of traumatic aphakia. The mean age was 42.9 ± 12.7 years (range, 18 ~ 66 years) when the cases underwent removal procedure. The average period after EKP was 18.7 years ±5.0 years (range, 12 years – 30 years).
We removed epikeratophakic lenticules (EKPL) due to lenticular opacity in five eyes (50%), intraocular lens (IOL) insertion (n = 4, 40%) after cataract surgery (n = 3), or in aphakic eyes (n = 1), and lenticule-induced irregular astigmatism in one eye (10%).
Long-term outcome of epikeratophakia and biometric parametric changes after removal of lenticule
Best corrected visual acuity (BCVA) and ocular biometric parameters obtained by an auto-kerato-refractometer (Atlas; Carl Zeiss Meditec, Dublin, CA) are revealed in Table 2.
The mean BCVA was 20/30 ± 20/57 (range, 20/400–20/20, n = 8) preoperatively. Six months after EKP, it was maintained at 20/33 ± 20/57 (range, 20/100–20/20, n = 7). However, it decreased to 20/80 ± 20/800 (range 20/100–20/40, n = 10) at pre-EKPL removal and did not improve after EKPL removal (20/100 ± 20/100, range 20/1000–20/28, n = 8).
The mean of spherical equivalent refraction (SE) of high myopia cases was − 21.4 D ± 7.0 (range, − 12.75 – -30.75 D, n = 7) preoperatively, and − 4.64 D ± 5.26 (range, − 15.0 – + 1.25 D, n = 6) postoperatively. The average corrected refractive error quantities were 16.3 D ± 8.3. In the aphakia case, the preoperative manifest refraction was + 10.0–1.00 × 90, and postoperative manifest refraction was + 7.0–1.5 × 180.
Compared with Post-EKP (mean SE, − 3.2 D – ± 2.4, n = 3), excessive myopic shift was observed at pre-EKPL removal (mean SE, − 20.4 D ± 6.4, n = 3). Even the mean SE of the pre-EKPL removal state was more myopic than the preoperative mean SE (− 16.8 D ± 2.3, n = 3).
After EKPL removal, mean refractive power of the cornea (Km) revealed a tendency to increase from 43.8 D ± 3.4 (range, 36.62–50.75, n = 9) at pre-removal to 46.6 D ± 6.1 (range, 33.15–57.5, n = 10) at 6 months post-removal. The average amount of change in Km before and after removal was − 5.82 D ± 3.72 (range, 0.43–12.8 D). Out of nine cases, six cases showed corneal steepening and three cases revealed corneal flattening.
Contrary to prediction, corneal flattening was observed in two cases (Cases 8 and 10) who underwent EKP for high myopia correction.
To analyze whether the curvature of the cornea could restore the initial curvature after EKP removal, keratometric readings of pre-epikeratoplasty and post-lenticular removal were compared. Km was 44.6 D ± 1.0 (n = 8) preoperatively, and 47.1 D ± 6.8 (n = 8) at 6 month after EKPL removal.
When the keratometric readings of pre-epikeratoplasty and post-lenticular removal were paired and compared within the same case, the average difference was 5.1 D ± 4.0 (n = 8).
All five patients who underwent lenticular removal due to graft opacity showed reduced corneal opacity (Fig. 1).
Topographic changes after removal of lenticule
Table 3 presents an analysis of the topographies of six cases’ taken at pre-removal, and at one, six and twelve months after removal.
Simulated keratometry astigmatism (Sim K astig) increased in three cases after EKPL removal and decreased in the other three cases. Km increased in four cases (Fig. 2A-C, Fig. 3A-C) and decreased in the other two cases (Fig. 2D, Fig. 3D-E).
Depending on the different types of refractive errors to be corrected, the lenticule is shaped as a plus lens for aphakic hyperopia or a minus lens for myopia. Thus, in aphakic patients, the central cornea steepened in curvature by a lenticule that is thickest in the centre, and the central cornea is flattened in high myopic patients.
Therefore, the central cornea is supposed to flatten in patients with aphakia (Fig. 3D-E) and steepen in high myopia (Fig. 2A, C, Fig. 3A-C) after lenticule removal. However, the central cornea steepened in the two high myopic cases (Fig. 2B, D). These ectatic changes may be caused by the abnormal tensile strength of the collagen fibrils in high myopia .
When the Km at 1 month postoperatively and the Km after 6 months or more postoperatively were compared, they showed a relatively similar values (1 month vs 6–12 months; 50.2 D ± 4.84 vs 49.8 D ± 4.92, n = 5). Center corneal irregular astigmatism (IRA) within 3 mm also showed little change over time after removal, except for case 7, who developed keratoectasia (1 month vs. 6–12 months; 4.25 D ± 1.4 vs. 4.45 D ± 1.31, n = 4).
Compared to pre-removal data, IRA within 3 mm increased in three cases (pre-removal vs. 6–12 months post-removal; 5.5 D ± 1.4 vs. 8.0 D ± 2.8, n = 3), and decreased in the other three cases (pre-removal vs. 6–12 months post-removal; 7.73 D ± 3.2 vs. 3.3 D ± 2.0, n = 3). The central corneal thickness decreased significantly from 707 μm ± 156.5 to 519 μm ± 93.3 after EKPL removal (n = 6).
Additional adverse event after removal of lenticule
Seven cases revealed a normal recovery process after removal without adverse effects (Fig. 4A-D), but complications were observed in 3 of 10 cases.
As post-lenticular removal complications, excessive corneal flatness was observed in case 4 (Fig. 3D, E), and corneal ectatic changes were observed in case 7 (Fig. 3A-C). Likely keratoconus, inferior corneal thinning, and protrusion were clearly visible on slit-lamp examination (Fig. 4E-H).
In case 10, the epithelial cells abnormally invaded the groove to the corneal surface and filled the gap with ingrowth of the epithelial cells at 2 months after the removal surgery (Fig. 4I-L). Abnormal epithelial ingrowth induced corneal deterioration, including opacity, irregular astigmatism, and abnormal photophobia symptoms (Fig. 4L). Therefore, the epithelial ingrowth was removed, and the corneal gap was sutured to prevent recurrence of epithelial ingrowth. The cornea remained stable without recurrence, and the photophobia disappeared (Fig. 4K).
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