Comparison of Corneal Power Difference Maps with Achieved Myopic Correction Using Scheimpflug Tomography After LASIK, PRK, and SMILE

Figures & data

Table 1 Patient Demographics

Variable	Mean ± SD (Range)
	LASIK	PRK	SMILE
	n=172 Eyes (95 pts)	n=187 Eyes (101 pts)	n=46 Eyes (25 pts)
Age	33.6 ± 7.04 (20 to 51)	33.25 ± 5.66 (20 to 45)	33.09 ± 5.98 (22 to 45)
Male / Female	108 / 64	92 / 95	19 / 27
Pre-op Sphere (D)	−3.03 ± 2.01 (−7.5 to 1.5)	−3.24 ± 1.72 (−7.75 to 1)	−5.17 ± 1.68 (−8.5 to −2.25)
Pre-op Cylinder (D)	−3.02 ± 0.91 (−5.75 to 0)	−0.97 ± 0.88 (−4.25 to 0)	−0.42 ± 0.39 (−1.25 to 0)
Pre-op MRSE (D)	−3.51 ± 1.98 (−8.38 to −0.25)	−3.73 ± 1.64 (−8 to −0.375)	−5.38 ± 1.67 (−8.5 to −2.75)
^†SIRC (D)	−3.27 ± 1.82 (−7.3 to 0)	−3.52 ± 1.54 (−7.05 to −0.12)	−4.98 ± 1.29 (−7.63 to −2.88)
Pre-op BCVA (LogMAR)	−0.01 ± 0.03 (−0.1 to 0.1)	−0.02 ± 0.04 (−0.1 to 0)	−0.02 ± 0.04 (−0.1 to 0)
Post-op BCVA (LogMAR)	−0.03 ± 0.05 (−0.1 to 0.2)	−0.02 ± 0.04 (−0.1 to 0)	−0.02 ± 0.04 (−0.1 to 0)

Note: Patient demographics for myopic refractive groups: LASIK, PRK, and SMILE.

Abbreviations: ^†SIRC, Surgically Induced Refractive Change (manifest refraction SE_before - manifest refraction SE_after) used for comparisons with TCRP, TNP and SagF in the LASIK and PRK groups AND for all comparisons in SMILE group; BCVA, Best corrected visual acuity.

Table 2 Mean Differences Between SIRC and Corneal Power Difference Maps

Best Mean Difference Between ^†SIRC and Each Corneal Power Difference Map (∆map) (D) ± SD
Patient Group	TCRP ∆map	TNP ∆map	RP ∆map	SagF ∆map
LASIK (= 172)	*0.190 ± 0.42	0.007 ± 0.42	*‒0.198 ± 0.47	*‒0.285 ± 0.48
	6mm Apex Zone	5mm Pupil Zone	5mm Apex Zone	4mm Pupil Zone
High Myopia (n = 29)	−0.004 ± 0.46	−0.168 ± 0.46	*‒0.576 ± 0.50	*‒0.744 ± 0.46
	6mm Apex Zone	5mm Apex Zone	4mm Apex Zone	4mm Apex Zone
Mod Myopia (n = 60)	*0.230 ± 0.43	0.002 ± 0.44	*‒0.256 ± 0.51	*‒0.390 ± 0.44
	6mm Apex Zone	4mm Apex Zone	4mm Apex Zone	4mm Pupil Zone
Low Myopia (n = 83)	*0.229 ± 0.38	0.031 ± 0.37	−0.008 ± 0.32	−0.039 ± 0.34
	6mm Apex Zone	6mm Apex Zone	5mm Pupil Zone	5mm Pupil Zone
PRK (n = 187)	*0.287 ± 0.54	*0.066 ± 0.45	*‒0.143 ± 0.51	*‒0.222 ± 0.51
	6mm Apex Zone	5mm Apex Zone	4mm Apex Zone	4mm Apex Zone
High Myopia (n = 21)	0.043 ± 0.43	*‒0.414 ± 0.35	*‒0.797 ± 0.32	*‒0.948 ± 0.32
	4mm Pupil Zone	4mm Apex and Pupil Zone	5mm Pupil Zone	4mm Apex Zone
Mod Myopia (n = 98)	*0.447 ± 0.53	−0.004 ± 0.42	*‒0.234 ± 0.42	*‒0.337 ± 0.42
	4mm Pupil Zone	5mm Apex Zone	4mm Apex Zone	4mm Apex Zone
Low Myopia (n = 68)	*0.519 ± 0.44	*0.191 ± 0.31	*‒0.094 ± 0.32	0.003 ± 0.32
	6mm Apex Zone	6mm Apex Zone	6mm Pupil Zone	6mm Pupil Zone
SMILE (n = 46)	0.011 ± 0.50	*‒0.399 ± 0.48	*‒0.723 ± 0.47	*‒0.857 ± 0.50
	4mm Apex Zone	4mm Apex Zone	4mm Pupil Zone	4mm Pupil Zone
High Myopia (n = 15)	−0.219 ± 0.46	*‒0.695 ± 0.46	*‒1.071 ± 0.46	*‒1.272 ± 0.45
	4mm Pupil Zone	4mm Pupil Zone	4mm Pupil Zone	4mm Pupil Zone
Mod Myopia (n = 29)	0.066 ± 0.46	*‒0.253 ± 0.39	*‒0.520 ± 0.36	*‒0.662 ± 0.37
	6mm Apex Zone	4mm Apex Zone	5mm Pupil Zone	4mm Apex Zone
Low Myopia (n = 2)	−0.140 ± 0.68	−0.133 ± 0.69	−0.340 ± 0.69	−0.323 ± 0.84
	5mm Apex Zone	5mm Pupil Zone	5mm Pupil Zone	5mm Pupil Zone

Notes: Best mean differences between ^†SIRC and corneal power difference maps (∆maps). All comparisons were performed as SIRC minus corneal power ∆map. If the difference was negative, the corneal power ∆map underestimated the SIRC. If the difference was positive, the corneal power ∆map overestimated the SIRC. Differences closest to zero are bolded in each group. Significant differences are marked with an asterisk [*]. Of note, the SMILE Low Myopia group only had 2 subjects and thus no meaningful conclusions can be drawn.

Abbreviation: ^†SIRC, Surgically Induced Refractive Change (manifest refraction SE_before - manifest refraction SE_after).

Table 3 Corneal Power Difference Map Comparisons by Study

Author	N (Eyes)	Follow Up (Months)	Surgery Type	Comparisons of ∆Maps	Most Accurate ∆Map
Lischke et al, 2021^Citation22	40	3	SMILE	TCRP and TK (IOL Master)	TK
Pan et al, 2019^Citation21	40	3	SMILE	SimK, EKR and TCRP	TCRP after correction
Ng et al, 2018^Citation23	71	1	LASIK	EKR, TNP and TCRP	EKR 4mm pupil zone
Whang et al, 2018^Citation19	18	12	Hyperopic LASIK	SimK, TNP and TCRP	TCRP 5mm apex zone
Qian et al, 2017^Citation8	144	6	SMILE	SimK, TNP and TCRP	TCRP 3mm pupil ring
Gyldenkerne et al, 2015^Citation20	410	3	SMILE	SagF, TNP and TCRP	TCRP 3mm apex ring
Gyldenkerne et al, 2015^Citation20	111	3	LASIK	SagF, TNP and TCRP	TCRP 4mm pupil zone
Gyldenkerne et al, 2015^Citation20	40	3	Hyperopic LASIK	SagF, TNP and TCRP	TCRP 2mm apex ring
Oh et al, 2014^Citation6	49	6	PRK	SimK, TNP and TCRP	TCRP 4mm pupil zone
Savini et al, 2014^Citation10	72	3	LASIK, PRK or LASEK	MPP and SimK	MPP 4.5 mm pupil zone
Savini et al, 2013^Citation18	36	6	LASIK	SimK, TNP and TCRP	TCRP 3mm apex zone
Mello et al, 2013^Citation24	58	3	LASIK	TCP and SimK	TCP 4mm apex zone
Savini et al, 2008^Citation25	16	1	LASIK, PRK or LASEK	SimK, TNP, BESSt Formula and EKR	EKR 2mm ring
Current Study	172	12	LASIK	SagF, RP, TNP and TCRP	TNP 5mm pupil zone
Current Study	187	12	PRK	SagF, RP, TNP and TCRP	TNP 5mm apex zone
Current Study	46	12	SMILE	SagF, RP, TNP and TCRP	TCRP 4mm apex zone

Note: Summary of studies comparing different corneal power difference maps (∆maps).

Abbreviations: TCRP, Total corneal refractive power; TK, Total keratometry; SimK, Simulated keratometry; EKR, Equivalent K-readings; TNP, True net power; SagF, Front Sagittal Curvature; MPP, Mean pupil Power; TCP, Total corneal power; RP, Refractive power.

Figure 1 Box plot representations of the difference between ^†SIRC and corneal power difference maps (∆maps) obtained by the Pentacam for LASIK, PRK, and SMILE (A) overall surgical groups (B) high myopia (C) moderate myopia (D) low myopia. Corneal power ∆maps that were significantly different from SIRC are marked with an*. There were only 2 low myopia patients in the SMILE group, thus no meaningful conclusions can be drawn regarding low myopia and SMILE.

Abbreviations: ^†SIRC, Surgically Induced Refractive Change (manifest refraction SE_before - manifest refraction SE_after); TNP, true net power; TCRP, total corneal refractive power; SagF, sagittal front curvature power; RP, refractive power.

Figure 2 Linear regression analysis between SIRC and corneal power difference maps (∆maps) of overall groups for (A) LASIK TNP ∆map 5mm pupil, (B) PRK TNP ∆map 5mm apex, and (C) SMILE TCRP ∆map 4mm apex vs ^†SIRC.

Abbreviations: ^†SIRC, Surgically Induced Refractive Change (manifest refraction SE_before - manifest refraction SE_after); TNP, True net power; TCRP, total corneal refractive power.

Figure 3 Bland-Altman Agreement plots of most accurate corneal power difference maps (∆maps) for (A) LASIK overall, (B) PRK overall and (C) SMILE overall compared with ^†SIRC. The solid line represents the mean difference between the corneal power ∆maps and the ^†SIRC. The dotted lines represent the 95% LoA = mean ± 1.96*SD.

Abbreviations: ^†SIRC, Surgically Induced Refractive Change (manifest refraction SE_before - manifest refraction SE_after); TNP, true net power; TCRP, total corneal refractive power; SagF, sagittal front curvature power; RP, refractive power; LoA, limits of agreement.

Figure 4 Bland-Altman Agreement plots of most accurate corneal power difference maps (∆maps) for (A) LASIK high myopia, (B) PRK high myopia and (C) SMILE high myopia compared with ^†SIRC. The solid line represents the mean difference between the corneal power ∆maps and the ^†SIRC. The dotted lines represent the 95% LoA = mean ± 1.96*SD.

Abbreviations: ^†SIRC, Surgically Induced Refractive Change (manifest refraction SE_before - manifest refraction SE_after); TNP, true net power; TCRP, total corneal refractive power; SagF, sagittal front curvature power; RP, refractive power; LoA, limits of agreement.

Figure 5 Bland-Altman Agreement plots of most accurate corneal power difference maps (∆maps) for (A) LASIK moderate myopia, (B) PRK moderate myopia and (C) SMILE moderate myopia compared with ^†SIRC. The solid line represents the mean difference between the corneal power ∆maps and the ^†SIRC. The dotted lines represent the 95% LoA = mean ± 1.96*SD.

Abbreviations: ^†SIRC, Surgically Induced Refractive Change (manifest refraction SE_before - manifest refraction SE_after); TNP, true net power; TCRP, total corneal refractive power; SagF, sagittal front curvature power; RP, refractive power; LoA, limits of agreement.

Figure 6 Bland-Altman Agreement plots of most accurate corneal power difference maps (∆maps) for (A) LASIK low myopia, and (B) PRK low myopia compared with ^†SIRC. No plot for SMILE low myopia group is shown given the small sample size of 2. The solid line represents the mean difference between the corneal power ∆maps and the ^†SIRC. The dotted lines represent the 95% LoA = mean ± 1.96*SD.

Abbreviations: ^†SIRC, Surgically Induced Refractive Change (manifest refraction SE_before - manifest refraction SE_after); TNP, true net power; TCRP, total corneal refractive power; SagF, sagittal front curvature power; RP, refractive power; LoA, limits of agreement.

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