Abstract
PurposeTo evaluate the changes in posterior corneal elevation in thin corneas after small incision lenticule extraction (SMILE).MethodsIn this prospective study, 97 eyes of 97 patients undergoing SMILE were recruited. Eyes were categorized into the following groups based on the preoperative minimum central corneal thickness (CCT): group A (37 eyes, 480–499 μm), group B (30 eyes, 500–529 μm), and group C (30 eyes, 530–560 μm). The posterior corneal surface was measured with a Pentacam over a 3-year follow-up period. Changes in the posterior corneal elevation at the central point (PCE), thinnest point (PTE), and predetermined area were measured.ResultsNo iatrogenic keratectasia was observed during the follow-up period. The mean changes in PCE, PTE, and the inferior area in group A were 1.14 ± 3.40 μm, −0.11 ± 3.20 μm, and −0.26 ± 1.23 μm, respectively (P ≥ 0.125). Although statistically significant change in the central-4 mm area was noted, the value was quite small (0.98 ± 1.67 μm) and was not higher than that in the other two groups (P = 0.003). For all three groups, the elevation remained stable or showed a backward change in the central annulus, while there was a small forward displacement in the 6-mm optical zone. In group A, changes in elevation values yielded negative statistical correlations with residual bed thickness and CCT (P ≤ 0.006) (except for the inferior area, the 4-mm and 6-mm optical zone).ConclusionsWith a strict preoperative assessment, SMILE achieved good safety and efficacy in correcting myopia in thin corneas and enabled a stable posterior corneal surface over a 3-year follow-up period.SynopsisCareful preoperative assessment and suitable surgical design should be taken to ensure posterior corneal stability after SMILE in thin corneas.
Highlights
Since Professor Seiler first reported three cases of iatrogenic keratectasia after laser in situ keratomileusis (LASIK) in 1998, this severe postoperative complication has gained worldwide attention both from ophthalmologists and patients [1]
Eyes were categorized into the following groups based on the preoperative minimum central corneal thickness (CCT): group A (37 eyes, 480–499 μm), group B (30 eyes, 500–529 μm), and group C (30 eyes, 530–560 μm)
No iatrogenic keratectasia was observed during the follow-up period
Summary
Since Professor Seiler first reported three cases of iatrogenic keratectasia after laser in situ keratomileusis (LASIK) in 1998, this severe postoperative complication has gained worldwide attention both from ophthalmologists and patients [1]. Because the posterior corneal surface is not affected by the corneal refractive procedure, assessing its stability is of great importance in identifying iatrogenic keratectasia. Independent of orientation and axis, have been shown to be the most effective indicators for evaluating corneal stability, as well as for the diagnosis of iatrogenic keratectasia at an early stage [5,6,7]. Owing to the development of femtosecond laser technology, small incision lenticule extraction (SMILE), the flapless corneal refractive procedure using the femtosecond laser alone, leaves most of the anterior cornea tissue intact after surgery [8]. To the best of our knowledge, information regarding the long-term impact of SMILE on the posterior corneal surface of thin corneas is still lacking
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