Study method
Preop. Sph.eq. refraction (D)
N (eyes)
Follow-up (months)
Refractive outcome
Regression
Visual outcome
2-line loss in CDVA
Hjortdal et al. [6]
Prospective
−7.19 ± 1.30
670
3
80 % within ±0.5 D
Not reported
84 % UDVA ≥20/25
2.4 %
Vestergaard et al. [24]
Prospective
−7.18 ± 1.57
279
3
77 % within ±0.5 D
0.15 D
73 % UDVA ≥20/25
0.4 %
Ivarsen et al. [7]
Prospective
−7.25 ± 1.84
1,574
3
77 % within ±0.5 D
Not reported
Not reported
1.5 %
Zhao et al. [27]
Prospective
−6.67 ± 1.43
54
6
93 % within ±0.5 D
None
98 % UDVA ≥20/20
None
Vestergaard et al. [22]
Prospective
−7.56 ± 1.11
34
6
88 % within ±0.5 D
None
83 % UDVA ≥20/25
None
Kim et al. [10]
Prospective
−6.18 ± 1.67
293
6
86 % within ±0.5 D
None
98 % UDVA ≥20/25
0.3 %
Ang et al. [2]
Prospective
−5.84 ± 2.12a
35
12
88 % within ±0.5 D
None
77 % UDVA ≥20/20
None
Fig. 9.1
Error in spherical equivalent refraction given as the percentage of eyes obtaining the specified refraction 3 years after SMILE for high myopia (n = 174)
The long-term refractive stability after SMILE for correction of high myopia has not been extensively investigated. However, in one study on 279 eyes, refraction was found to be stable from 1 to 3 months after surgery, although a minor regression of −0.15 D was observed during the first month [24]. Another study on 54 eyes found no regression during the first 6 months after surgery [27], and similarly the study on SMILE for an average of −5.84 D found no significant changes in refraction from 1 to 12 months after surgery [2]. In our recent evaluation 3 years after SMILE for high myopia, we also found no significant refractive regression in 84 eyes from 1 month to 3 years after surgery (Fig. 9.2).
Fig. 9.2
Mean error in spherical equivalent refraction of 84 eyes from 1 month to 3 years after SMILE for high myopia
The refractive predictability in combined high myopia and astigmatism represents a particular challenge, but overall 77 % of 775 eyes have been reported to be within ±0.50 D of the attempted spherical equivalent refraction after 3 months, irrespective of the attempted astigmatic correction [8]. Nevertheless, increasing undercorrection of the astigmatic component was observed with higher attempted corrections at an average of 16 % per diopter.
Interestingly, the predictability after SMILE has been found to be unrelated to the degree of the attempted myopic correction [6]. This stands in contrast to excimer-based treatments where corneal hydration, room humidity, patient age, parallax error, and laser fluency affect the ablative procedure [1, 25], giving rise to decreasing precision with increasing myopic correction. Furthermore, preoperative corneal power, patient age, and gender have been found to have very limited impact on the refractive outcome after SMILE [6, 10].
9.2 Visual Outcome
In the few studies reporting visual outcome after SMILE for high myopia, 73–100 % of patients had an uncorrected distance visual acuity (UDVA) of 20/25 or better 3–6 months after surgery (Table 9.1). Ang et al. similarly reported 77 % of patients to have an UDVA of 20/20 or better 12 months after correction for an average of −5.84 D [2]. In our recent 3-year evaluation of SMILE for an average of −7.30 ± 1.35 D, we found an UDVA of 20/25 or better in 82 % of 174 eyes (Fig. 9.3).
