Posterior corneal elevation is “an essential indicator” of corneal stability after refractive surgery, according to a study published in the Journal of Cataract and Refractive Surgery. The study shows that patients who underwent small-incision lenticule extraction (SMILE) surgery to treat moderate or high myopia managed to maintain corneal stability at least 7 years following the procedure.

Researchers evaluated the patient records for increases in 3 posterior corneal elevation parameters that traditionally indicate early corneal ectasia: posterior central elevation (PCE), posterior elevation at the thinnest point (PTE), and posterior maximal elevation (PME). The research team reviewed 33 eyes of 20 patients (13 women, mean age 30.1±9.5 years) who underwent SMILE to treat moderate or high myopia by a single surgeon at Eye & ENT Hospital of Fudan University in Shanghai, China between September 2011 and December 2012. 

At baseline, the participants’ mean PCE was 1.94±2.94 µm. At the 1, 3, 5, and 7 year follow ups, the mean change in PCE was -1.42±0.95 µm, -2.67±0.98 µm, -2.44±1.06 µm, and -1.91±0.92 µm, respectively. At baseline the mean PTE was 3.82±3.53 µm, and the mean checkups at the examinations were -2.82±1.19 µm, -3.55±1.22 µm, -3.47±1.32 µm, and -2.39±1.15 µm, respectively. Finally, their PME started off with a mean baseline of 10.70±3.49 µm, which increased by 0.75±1.05 µm, 0.15±1.09 µm, 1.85±1.17 µm, and 2.45±1.02 µm, respectively. 


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The PCE, PTE, PME, and elevation across the 4 quadrants did not exhibit an increasing trend, the study explains. The participants’ PTE and PCE were, in fact, reduced at the 7 year examination by 2.39±1.15 µm and 1.91±0.92 µm, respectively. However, researchers say this change is “significant but clinically irrelevant.” Regarding the PME, the investigators did note an increase. “Although the PME remained stable for 7 years, time had no significant impact on it (P =.096), and it still showed an increase of 2.45±1.02 µm (P =.017) at the 7-year follow-up,” researchers explain.

The study shows that the refractive outcomes were strong with 29 eyes (87.9%) within ±0.50 D of target refraction, and all but 1 eye (96.99%) within ±1.00 D. The investigators examined the patients’ corneal parameters 1, 3, 5, and 7 years after the procedure. After 7 years, 94% of the eyes achieved 20/20 or better, according to investigators. And 39% of eyes in this study gained 1 or 2 lines of corrected distance visual acuity.

The study was limited in that the sample size was small and not all possible corneal biomechanical measurements were performed.

The SMILE procedure, which utilizes a 2 mm flap, was approved by The US Food and Drug Administration for the treatment of myopia in 2016. 

Reference

Chen Z, Zhao Y, Zhou X, Xia F, Zhao J, Zhou X. Seven-year observation of posterior corneal elevation after small-incision lenticule extraction in patients with moderate and high myopia. 2021;47(11):1398-1402. doi:10.1097/j.jcrs.0000000000000639