Impact of Small Incision Lenticule Extraction for High Myopia on Intraocular Pressure Measurements With Pneumotonometry.

PURPOSE: To evaluate the medium-term impact of small incision lenticule extraction (SMILE) on air-puff tonometry (APT) and how it may be corrected. METHODS: In this controlled prospective study, 69 eyes from 69 patients treated with SMILE for high myopia (mean: -7.22 diopters) were included. Central corneal thickness (CCT), spherical equivalent refraction (SEQ), corneal power, and intraocular pressure (IOP) (assessed by APT) were measured before and 3 months after surgery. RESULTS: The measured IOP decreased significantly after SMILE surgery (mean: -6.43 mm Hg), indicating a significant underestimation of the true IOP by APT. There was a significant correlation between change in SEQ, CCT, and apparent IOP. Correcting the apparent IOP measurement by applying a multiple regression correction did not provide significantly better estimates compared to adding 6.4 mm Hg to the measurement. CONCLUSIONS: This study showed that previous SMILE surgery should be considered when interpreting APT measurements, because the measurements underestimate the true IOP. Multiple regressions cannot estimate the true IOP with certainty. For screening purposes, adding 6.4 mm Hg to the apparent IOP of a patient treated for high myopia may be sufficient. [J Refract Surg. 2023;39(9):606-611.].

Impact on binocular visual function of small-incision lenticule extraction for high myopia.

PURPOSE: To assess whether small-incision lenticule extraction (SMILE) for high myopia reduces the binocular visual function assessed by stereoacuity, binocular visual acuity, binocular contrast sensitivity, and binocular summation. SETTING: University hospital. DESIGN: Prospective case series. METHODS: Patients with a myopic spherical equivalent of at least 6.00 diopters (D) scheduled for SMILE aimed at emmetropia were included. Psychophysical testing was performed with correction preoperatively but no correction postoperatively. Stereoacuity was assessed with the Randot Circles test and the near Frisby test, visual acuity (monocular and binocular) was assessed with high-contrast Early Treatment Diabetic Retinopathy Study charts, and contrast sensitivity (monocular and binocular) was assessed with the Pelli-Robson chart and the Freiburg Acuity and Contrast Test. Binocular summation was calculated by comparing the binocular score against the best monocular score. RESULTS: A total of 138 eyes of 69 patients were included. The mean spherical equivalent changed from -7.46 D ± 1.06 (SD) to -0.23 D ± 0.40 postoperatively. Stereoacuity did not change significantly postoperatively; median change (interquartile range) was -0.32 (-6.21 to 1.55) seconds of arc with the Frisby test and 0.00 (-7.5 to 5.0) seconds of arc with the Randot test (P ≥ .06). Binocular postoperative uncorrected distance visual acuity was not different from the preoperative corrected distance visual acuity (P = .40). Contrast sensitivity declined slightly monocularly with both tests of contrast sensitivity but was unaltered binocularly (P ≥ .08). Binocular summation for visual acuity and contrast sensitivity was unaltered following surgery (P ≥ .09). CONCLUSIONS: SMILE for high myopia did not reduce the binocular function assessed by stereoacuity, binocular visual acuity, binocular contrast sensitivity, and binocular summation.

Visual image quality after small-incision lenticule extraction compared with that of spectacles and contact lenses.

PURPOSE: To assess the influence of small-incision lenticule extraction (SMILE) for high myopia on the visual image quality assessed by the logarithm of the visual Strehl ratio (logVSX) and put this into a clinical context by pairwise comparing the logVSX of postoperative eyes with those of myopic controls wearing spectacles and/or contact lenses. SETTING: University hospital. DESIGN: Prospective and cross-sectional clinical study. METHODS: Patients with a myopic spherical equivalent of at least 6.00 diopters treated with SMILE aimed at emmetropia and correspondingly myopic controls corrected with spectacles and/or contact lenses were included. The logVSX calculation was divided into habitual logVSX based on the wavefront aberration measurement directly and optimal logVSX calculated in a theoretical through-focus experiment to obtain the best-achievable logVSX. RESULTS: A total of 117 eyes of 61 patients and 64 eyes of 34 myopic controls were included. SMILE did not affect the habitual logVSX but worsened the optimal logVSX (P < .001). The postoperative habitual logVSX was statistically significantly worse compared with contact lenses (P = .002). The postoperative optimal logVSX was significantly worse compared with both spectacles (P < .01) and contact lenses (P = .003). There was no statistically significant difference in habitual or optimal logVSX between spectacles and contact lenses. CONCLUSIONS: SMILE for high myopia does not affect the habitual logVSX but decreases the optimal logVSX slightly. The postoperative habitual logVSX is worse than for contact lenses but not spectacles, and the postoperative optimal logVSX is worse than for both contact lenses and spectacles. There is no statistically significant difference in either habitual or optimal logVSX between spectacles and contact lenses.

Changes in accommodative function following small-incision lenticule extraction for high myopia.

PURPOSE: To examine whether the amplitude of accommodation, the accommodative response, and the accommodative facility is affected and correlated with changes in higher-order aberrations for patients with high myopia surgically treated with small-incision lenticule extraction (SMILE). METHODS: 35 highly myopic eyes (myopic spherical equivalent of at least 6 diopters) of 35 patients treated with SMILE were included. Assessments were made before and 3 months after surgery. Donders push-up-method was used to measure the amplitude of accommodation. The accommodative response was assessed using an open-field autorefractor"Grand Seiko WAM-5500" (Grand Seiko Co. Ltd., Hiroshima, Japan) in combination with a Badal optometer and stimuli of accommodation at 0.0, 0.5, 1.25, 2.0, 3.0, and 4.0 D, respectively. Accommodative facility was measured at 40 cm with ±2,00D flipper lenses. All measurements of accommodation were performed monocularly with the refractive error corrected with soft contact lenses. RESULTS: The amplitude of accommodation did not change statistically significantly (mean difference -0.24 D (SD 0.98), 95% CI of mean difference -0.58 D to 0.11 D, paired-sample t(34) = -1.39; P = 0.17). The accommodative responses at 0.0, 0.5, 1.25, 2.0, 3.0, and 4.0 D did not statistically significantly change either (F(6,29) = 1.15; P = .36). Finally, the accommodative facility was also unchanged with a mean difference of 1.11 cycles per minute (SD 5.11, 95% CI of mean difference -0.64 to 2.87, paired-sample t(34) = 1.29; P = 0.21). No clinically significant associations between changes in accommodation and higher-order aberrations were found. CONCLUSIONS: SMILE does not alter the amplitude of accommodation, the accommodative response, nor the accommodative facility for highly myopic patients, and the surgically induced corneal higher-order aberrations do not affect the accommodative function.

Astigmatism prediction in small-incision lenticule extraction.

PURPOSE: To investigate whether postoperative-induced refractive astigmatism after small-incision lenticule extraction (SMILE) could be predicted by preoperative objective astigmatism measured with autorefraction, keratometry, and Scheimpflug tomography. SETTING: University eye clinic. DESIGN: Retrospective case series. METHODS: Only eyes without preoperative subjective astigmatism treated with SMILE for myopia were included. Postoperative subjective astigmatism was compared with preoperative objective astigmatism. Examinations were performed before SMILE and 3 months postoperatively and included subjective refraction, keratometry, autorefraction, and Scheimpflug tomographer measurements. Astigmatism was analyzed using double-angle plots and multivariate statistics. RESULTS: A total of 358 eyes of 358 patients were included. The mean preoperative sphere was -7.33 diopter (D) ± 1.46 (SD). The postoperative spherical equivalent was -0.30 ± 0.49 D. Postoperatively, 79.6% and 98.9% of patients had a subjective cylinder ≤0.50 D and ≤1.00 D, respectively. Preoperative objective astigmatism measured with keratometry, autorefraction, and Scheimpflug tomography was significantly different (P < .05) from postoperative subjective refraction when all patients were analyzed; for patients with postoperative refractive astigmatism ≥0.50 D, preoperative astigmatism with keratometry and Scheimpflug tomography was not significantly different from postoperative refractive astigmatism. Preoperative objective astigmatism ≥0.50 D increased the risk ratio of postoperative subjective astigmatism ≥0.50 D by 2.2 (P < .001). CONCLUSIONS: Preoperative objective astigmatism could not be directly interchanged with postoperative subjective astigmatism, but the presence of preoperative astigmatism ≥0.50 D doubled the risk of inducing a postoperative subjective astigmatism ≥0.50 D. Extra care when performing subjective refraction should be taken in the presence of high objective astigmatism.

Optical and visual quality after small-incision lenticule extraction.

PURPOSE: To examine the relationship between corneal higher-order aberrations (HOAs), scatter, and residual refraction with visual symptoms and visual acuity after small-incision lenticule extraction (SMILE) for myopia and astigmatism. SETTING: University Eye Clinic, Aarhus, Denmark. DESIGN: Prospective case series. METHODS: Eyes had small-incision lenticule extraction for myopia or myopic astigmatism. Examinations were performed preoperatively and 1 day, 7 days, 1 month, and 3 months postoperatively and included subjective refraction, Pentacam HR measurements, scatter measurements (objective scatter index [OSI]), and questionnaires on visual quality and symptoms. RESULTS: The mean preoperative spherical equivalent (SE) was -7.08 diopters (D) ± 1.17 (SD). At 3 months, the mean uncorrected distance visual acuity (UDVA) was -0.03 ± 0.11 logarithm of the minimum angle of resolution and the mean SE, -0.17 ± 0.33 D; the OSI increased by a mean of 0.22 ± 0.53 (P = .06) and coma by 0.1 ± 0.1 µm (P < .001); spherical aberration did not change significantly. The severity of self-reported visual symptoms decreased postoperatively. Scatter, corneal HOAs, and residual refraction were not correlated with the degree of visual symptoms. On linear regression analysis, residual refraction was a significant predictor of UDVA (1 day: adjusted R2 = 0.16, P = .02; 3 months: adjusted R2 = 0.55, P < .001). Scatter and corneal HOAs were not associated with postoperative UDVA. CONCLUSIONS: Despite statistically significant changes in scatter and corneal HOAs, the severity of self-reported visual symptoms decreased postoperatively. Residual refraction was a good predictor of postoperative UDVA. Scatter and corneal HOAs had no effect on the postoperative UDVA.

Correction of astigmatism with small-incision lenticule extraction: Impact of against-the-rule and with-the-rule astigmatism.

PURPOSE: To determine the influence of against-the-rule (ATR) and with-the-rule (WTR) astigmatism on the outcomes of small-incision lenticule extraction for myopic astigmatism. SETTING: University eye clinic, Aarhus, Denmark. DESIGN: Retrospective case series. METHODS: One eye of each patient had small-incision lenticule extraction for astigmatism of 1.00 diopter (D) or more. Surgery was performed with a Visumax femtosecond laser. Subjective refraction and Scheimpflug tomography (Pentacam HR) were performed preoperatively and 3 months postoperatively. Cylinder data were evaluated by vector analysis and correlation analyses. Multiple linear regression was used to predict magnitude of error from age, sex, left or right eye, target-induced astigmatism (TIA), subjective ATR/WTR astigmatism, cap diameter, cap thickness, incision width, and back-surface astigmatism. RESULTS: The study enrolled 829 patients (505 women; median age 37 years). The mean preoperative subjective cylinder was 1.76 D ± 0.86 (SD). Overall, 66% and 95% of patients achieved a refractive cylinder within ±0.50 D or ±1.00 D, respectively. Astigmatism was WTR in 73% of eyes and ATR astigmatism in 16% of eyes. The linear regression model significantly predicted the magnitude of error (R2 = 0.23, P < .001), with TIA contributing -0.15 D per attempted diopter and subjective ATR astigmatism contributing a constant 0.32 D (both P < .001). No other parameters had a significant impact on the outcome. CONCLUSIONS: Almost 25% of the variation after small-incision lenticule extraction for myopic astigmatism might be explained by the size of the attempted cylinder correction and ATR/WTR astigmatism. Incorporating these parameters in preoperative planning might produce more consistent results in high cylinder corrections.

Comparison of corneal shape changes and aberrations induced By FS-LASIK and SMILE for myopia.

PURPOSE: To compare corneal curvatures, corneal power calculations, and higher-order aberrations (HOAs) of femtosecond laser-assisted LASIK (FS-LASIK) with small incision lenticule extraction (SMILE) following surgery for moderate to high myopia. METHODS: A retrospective study of 736 eyes of 368 patients treated with SMILE and 148 eyes of 74 patients treated with FS-LASIK. Preoperative mean spherical equivalent was -7.3 ± 1.5 diopters in the SMILE group and -7.6 ± 1.3 diopters in the FS-LASIK group. Corneal curvatures, corneal power calculations performed by ray tracing, and HOAs measured with Scheimpflug technology before and 3 months after surgery were analyzed. RESULTS: Corneal curvatures changed significantly in the anterior corneal surface, but not in the posterior corneal surface, in both groups; after SMILE, the sagittal curvature was constant for the central 4-mm diameter, in contrast to FS-LASIK where the curvature showed a gradual steepening with increasing diameter. Corneal power calculations were different across the cornea depending on the measurement diameter between the two groups postoperatively. Measured over a 5-mm zone on the total cornea, FS-LASIK induced 0.11 µm more coma (P < .001) and 0.13 µm higher spherical aberration (P < .001) as compared to SMILE; similar results in other HOAs were seen for the anterior corneal surface. Negligible differences in HOAs were induced on the posterior corneal surface. CONCLUSIONS: SMILE and FS-LASIK produced distinct changes in anterior corneal shape evident in different postoperative corneal curvatures and power measurements between the two groups. Postoperative HOAs were much lower after SMILE as compared to FS-LASIK.

Assessing the corneal power change after refractive surgery using Scheimpflug imaging.

PURPOSE: To investigate whether the Pentacam HR could accurately predict the surgically induced refractive change in patients operated with small-incision lenticule extraction (SMILE) for myopia or femto-second laser in situ keratomileusis (FS-LASIK) for myopia or hyperopic astigmatism. METHODS: Data from three groups consisting of (1) 410 myopic eyes of 410 patients operated with SMILE, (2) 111 myopic eyes of 111 patients operated with FS-LASIK, and (3) 40 eyes of 40 patients with hyperopic astigmatism operated with FS-LASIK were retrospectively analysed. The change in manifest refraction due to surgery was compared with the objectively measured change in corneal power by the Pentacam HR in three different ways: Sagittal Power (calculated as for placido topographers), True Net Power (calculated by a Gaussian optics formula), and Total Corneal Refractive Power (calculated by ray tracing). Multiple linear regression analysis was performed to investigate which parameters influenced the Pentacam HR's prediction of the change in subjective refraction due to surgery. RESULTS: The Total Corneal Refractive Power Apex, Zone calculation in a diameter of 4.0 mm effectively predicted the surgically induced refractive change for all three patient groups. The spherical equivalent was predicted with an error of 0.08 ± 0.41 D for the SMILE eyes, 0.05 ± 0.61 D for the myopic eyes operated with FS-LASIK, and -0.15 ± 0.49 D for the hyperopic astigmatic eyes treated with FS-LASIK. Regression showed that preoperative refractive error had a significant impact on the prediction error of the Pentacam HR. CONCLUSIONS: Ray tracing calculations based on Scheimpflug imaging accurately assessed the change in manifest refraction due to corneal laser surgery.

Factors affecting the decision for refractive surgery in patients with high degrees of ametropia.

PURPOSE: To evaluate reasons referred patients do not have refractive surgery. SETTING: University Eye Clinic, Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark. DESIGN: Cross-sectional study. METHODS: The case records of patients referred for refractive surgery from January 2011 to December 2012 were examined for explanatory reasons. Data measured at the clinical preexamination of those who did and those who did not have refractive surgery were compared. A logistic regression model was used to assess the measured data's influence on the decision to have or not have refractive surgery. RESULTS: Of the 2150 patients whose records were reviewed, 939 (43.7%) refrained from having refractive surgery. The most common reason was a change of mind (40.7%) followed by low central corneal thickness (CCT) (12.6%) and unstable refraction (10.8%). The 939 patients who refrained from surgery had significantly higher astigmatism and lower intraocular pressure, CCT, and corrected distance visual acuity than the patients who had surgery. The patients who changed their minds were not significantly different in any parameter from the patients who had refractive surgery. Using an outcome threshold of 0.5, the logistic regression model classified 63.04% of the patients correctly. CONCLUSIONS: Reasons for refraining from refractive surgery were numerous, with a change of mind after the preexamination being the most common. Patients who changed their minds were very similar to those who had surgery, indicating that personal factors were important determinants. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.