Clinical outcomes of wavefront-guided laser in situ keratomileusis to treat moderate-to-high astigmatism

Figures & data

Table 1 Definitions of vector parameters¹⁷

Vector parameter	Definition
IRC (D)	The vector difference between the preoperative astigmatic correction vector and the target postoperative cylinder vector.
	If the target refractive state is emmetropia, the IRC vector is equal to the preoperative astigmatic correction vector
SIRC (D)	The vector difference between the preoperative and postoperative astigmatic correction vectors. SIRC represents the achieved correction
EV (D)	The vector difference between the IRC and SIRC. When the refractive target is emmetropia, the EV is identical to the postoperative astigmatic correction vector
ER	The proportion of the intended correction that was not successfully treated (|EV|/|IRC|)
CR	The ratio of the achieved correction magnitude to the required correction (|SIRC|/|IRC|). A ratio of 1 is ideal, whereas <1 implies undercorrection and >1 implies excessive application of the treatment
EM (D)	The arithmetic difference of the magnitudes between SIRC and IRC (|IRC|–|SIRC|)
EA (°)	The angular difference between the achieved treatment and the intended treatment. The EA is negative if the SIRC is clockwise from the IRC and positive if the SIRC is counterclockwise from the IRC

Abbreviations: IRC, intended refractive correction; D, diopter; SIRC, surgically induced refractive correction; EV, error vector; ER, error ratio; CR, correction ratio; EM, error of magnitude; EA, error of angle.

Table 2 Refractive and visual outcomes (n=611 eyes)

	Preop	1 week	1 month	3 months	P-value* (preop to 3 months)
	Mean ± SD [median] (range)	Mean ± SD [median] (range)	Mean ± SD [median] (range)	Mean ± SD [median] (range)
Sphere (D)	−2.79±2.32 [−2.25] (−9.75 to 0.00)	+0.10±0.30 [0.00] (−1.00 to +1.50)	+0.14±0.35 [0.00] (−1.25 to +1.75)	+0.16±0.34 [0.00] (−1.25 to +1.50)	<0.01
Cylinder (D)	−2.76±0.81 [−2.50] (−6.00 to −2.00)	−0.26±0.33 [−0.25] (−2.75 to 0.00)	−0.33±0.38 [−0.25] (−2.75 to 0.00)	−0.37±0.38 [−0.25] (−2.00 to 0.00)	<0.01
MSE (D)	−4.17±2.31 [−3.63] (−11.38 to −1.00)	−0.03±0.29 [0.00] (−1.13 to +1.50)	−0.03±0.33 [0.00] (−1.88 to +1.00)	−0.03±0.33 [0.00] (−1.75 to +1.25)	<0.01
UDVA (logMAR)	0.95±0.36 [1.00] (0.30−1.60)	−0.02±0.10 [−0.08] (−0.20 to 0.60)	−0.03±0.10 [−0.08] (−0.18 to 0.70)	−0.04±0.09 [−0.08] (−0.20 to 0.52)	<0.01
CDVA (logMAR)	−0.04±0.07 [−0.08] (−0.18 to 0.22)	−0.05±0.07 [−0.08] (−0.20 to 0.22)	−0.08±0.07 [−0.08] (−0.20 to 0.22)	−0.07±0.06 [−0.08] (−0.20 to 0.22)	<0.01

Notes: Preop – preoperative visit; 1 week, 1 month, and 3 months – postoperative visits after laser in situ keratomileusis.

* P-value – paired t-test comparing preoperative data and 3-month postoperative data.

Abbreviations: SD, standard deviation; D, diopter; MSE, manifest spherical equivalent; UDVA, uncorrected distance visual acuity; CDVA, corrected distance visual acuity.

Figure 1 Comparison of postoperative cumulative monocular UDVA and preoperative CDVA.

Abbreviations: UDVA, uncorrected distance visual acuity; CDVA, corrected distance visual acuity.

Figure 2 Predictability of MSE at 3 months postoperatively.

Notes: The area between two dotted lines is the postoperative MSE within ±1.00 D. The solid red line represents linear regression.
Abbreviations: MSE, manifest spherical equivalent; D, diopter.

Table 3 Stability of refraction between 1 week, 1 month, and 3 months postoperative visits (n=611)

	1 week to 1 month	1–3 months
Change in sphere by ≤0.5 D	94.4% (577 eyes)	95.1% (581 eyes)
Change in sphere by ≤1.0 D	99.7% (609 eyes)	99.7% (609 eyes)
Mean change in sphere ± SD (P-value)	+0.04±0.32 (P<0.01)	+0.02±0.30 (P=0.10)
95% CI	+0.01 to +0.06	−0.00 to +0.04
Change in Cyl by ≤0.5 D	88.1% (538 eyes)	93.3% (570 eyes)
Change in Cyl by ≤1.0 D	99.2% (606 eyes)	99.7% (609 eyes)
Mean change in Cyl ± SD (P-value)	−0.08±0.39 (P<0.01)	−0.03±0.34 (P=0.01)
95% CI	−0.11 to −0.05	−0.06 to −0.01
Change in MSE by ≤0.5 D	93.1% (569 eyes)	92.1% (563 eyes)
Change in MSE by ≤1.0 D	99.2% (606 eyes)	98.9% (604 eyes)
Mean change in MSE ± SD (P-value)	0.00±0.32 (P=0.85)	0.00±0.31 (P<0.82)
95% CI	−0.03 to +0.02	−0.02 to +0.03

Abbreviations: D, diopter; SD, standard deviation; CI, confidence interval; Cyl, cylinder; MSE, manifest spherical equivalent.

Figure 3 IRC versus SIRC at 3 months postoperatively.

Notes: Green solid line represents the EM within 1.0 D, and green dashed line represents EM within 0.50 D of emmetropia. Solid red line is the linear regression.
Abbreviations: IRC, intended refractive correction; SIRC, surgically induced refractive correction; EM, error of magnitude; D, diopter.

Table 4 Vector analysis of changes in refractive cylinder stratified by the magnitude of preoperative cylinder

Vector parameter	All eyes		Preoperative cylinder (D)
	n=611		Mean (SD)
	Mean (SD)	Range	2.00–2.99	3.00–3.99	4.00–4.99	5.00–6.00
			n=410	n=130	n=53	n=18
IRC (D)	2.76 (0.81)	2.00–6.00	2.29 (0.27)	3.24 (0.26)	4.27 (0.27)	5.31 (0.30)
SIRC (D)	2.53 (0.80)	0.85–5.50	2.12 (0.44)	2.99 (0.44)	3.85 (0.54)	4.69 (0.59)
EV (D)	0.37 (0.38)	0.00–2.00	0.31 (0.33)	0.40 (0.41)	0.61 (0.46)	0.74 (0.55)
ER	0.13 (0.14)	0.00–0.78	0.14 (0.14)	0.12 (0.13)	0.14 (0.11)	0.14 (0.10)
CR	0.92 (0.14)	0.38–1.48	0.92 (0.15)	0.92 (0.12)	0.90 (0.12)	0.88 (0.11)
EM (D)	0.22 (0.40)	−1.25 to 1.71	0.17 (0.35)	0.25 (0.39)	0.42 (0.53)	0.62 (0.57)
EA (°)	−0.45 (2.99)	−22.33 to 10.78	−0.40 (3.06)	−0.53 (3.08)	−0.71 (2.42)	−0.14 (2.23)
Absolute EA (°)	1.52 (2.62)	0.00–22.33	1.49 (2.71)	1.57 (2.70)	1.64 (1.91)	1.41 (1.70)

Abbreviations: D, diopter; SD, standard deviation; IRC, intended refractive correction; SIRC, surgically induced refractive correction; EV, error vector; ER, error ratio; CR, correction ratio; EM, error of magnitude; EA, error of angle.

Figure 4 Double-angle polar plot of preoperative and postoperative (3 months) refractive cylinder in plus cylinder form.

Note: The centroid is the mean of x and y data points, and the axes of each ellipse are twice the standard deviation of the x and y values.
Abbreviation: D, diopter.

Figure 5 Distribution of NEV.

Note: NEV is calculated by setting the preoperative axis of refractive cylinder to zero and modifying the postoperative axis in relation to the preoperative axis.
Abbreviation: NEV, normalized error vector.

Table 5 Literature review of studies presenting results of moderate-to-high myopic astigmatic correction

Author (year)	Number of eyes	Follow-up (months)	Laser	Preoperative refractive cylinder	Postoperative refractive cylinder	Refractive cylinder within 0.50 D of intended correction	UDVA 20/20 or better	Loss of two lines of CDVA
				Mean ± SD (range) (D)	Mean ± SD (range) (D)
Arbelaez et al^Citation4 (2009)	50	6	Amaris (Schwind)	−3.54±0.85 (−2.00 to −4.75)	−0.50±0.26 (0.00 to −1.25)	76%	84%	0%
Igarashi et al^Citation5 (2012)	48	12	Technolas 217z (Bausch and Lomb)	−2.74±0.99 (−2.00 to −6.00)	−0.63±0.63 (0.00 to −2.50)	–	–	–
Hasegawa et al^Citation6 (2012)	351	12	MEL 80 (Carl Zeiss)	−1.95±0.39 (−1.50 to −2.75) (moderate cylinder group)	−0.27±0.29 (–)	91.0%	–	–
				−3.66±0.44 (over –3.00 D) (high cylinder group)	−0.68±0.52 (−)	53.3%	–	–
Ivarsen et al^Citation7 (2013)	46	3	MEL 80 (Carl Zeiss)	−3.92±0.82 (−2.75 to −6.00)	−0.97±0.52 (−0.25 to −2.25)	–	–	0%
Alió et al^Citation8 (2013)	37	6	Amaris (Schwind)	−3.64±0.55 (−3.00 to −5.25)	−0.45±0.38 (0.00 to −1.25)	67%	61%	0%
Katz et al^Citation9 (2013)	57	6	Allegretto 200/400 Wave-Light	−3.86±0.57 (−3.25 to −5.75)	−1.23±0.51 (0 to −3.75)	–	74%	–
Current study	611	3	Visx S4 IR (AMO)	−2.76±0.81 (−2.00 to −6.00)	−0.37±0.38 (0.00 to −2.00)	79.1%	83.8%	0.8%

Abbreviations: D, diopter; SD, standard deviation; UDVA, uncorrected distance visual acuity; CDVA, corrected distance visual acuity.

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