Comparison of surgically induced astigmatism following different glaucoma operations

Figures & data

Table 1 Subject characteristics

Parameters	LEC	EXP	exLOT	µLOT	P-value
Eyes/subjects, n/n	20/20	20/20	20/20	20/20
Age (years)					0.9345^#
Mean ± SD	65.1±12.3	66.8±10.7	65.6±19.9	68.0±16.1
95% CI	59.3–70.9	61.8–71.8	56.3–74.9	60.4–75.5
Sex, n (%)					0.5682^§
Male	11 (55)	10 (50)	7 (35)	8 (40)
Female	9 (45)	10 (50)	13 (65)	12 (60)
Glaucoma type, n (%)
POAG	14 (70)	16 (80)	10 (50)	12 (60)
SOAG	3 (15)	3 (15)	7 (35)	3 (15)
PACG	1 (5)	1 (5)	2 (15)	4 (20)
SACG	2 (10)	0 (0)	0 (0)	1 (5)
Preoperative BCVA (logMAR)					0.0054^#
Mean ± SD	0.33±0.58	0.02±0.17	0.00±0.10	0.08±0.24
95% CI	0.07–0.60	−0.06 to 0.1	−0.05 to 0.04	−0.03 to 0.19
P-values^‡
Against EXP	0.0028^*	–	–	–
Against exLOT	0.0016^**	0.8551	–	–
Against μLOT	0.0157	0.5398	0.4267	–
Postoperative 3 months BCVA (logMAR)					0.0003^#
Mean ± SD	0.43±0.50	0.09±0.27	0.03±0.14	0.06±0.21
95% CI	0.20–0.66	−0.04 to 0.21	−0.04 to 0.10	−0.03 to 0.16
P-values^‡
Against EXP	0.0008^**	–	–	–
Against exLOT	0.0001^**	0.5644	–	–
Against μLOT	0.0004^**	0.8337	0.7137	–
Preoperative IOP (mmHg)					0.1463^#
Mean ± SD	24.8±10.1	19.4±7.1	22.5±11.4	19.2±5.8
95% CI	20.1–29.5	16.1–22.7	17.2–27.8	16.4–21.9
Postoperative 3 months IOP (mmHg)					0.0016^#
Mean ± SD	10.6±5.5	9.4±3.7	12.9±3.4	14.3±3.8
95% CI	8.0–13.1	7.7–11.1	11.3–14.4	12.5–16.1
P-values^‡
Against EXP	0.3871	–	–	–
Against exLOT	0.0860	0.0109	–	–
Against μLOT	0.0058^*	0.0004^**	0.2762	–

Notes: P-values are calculated among four glaucoma surgeries by one-way analysis of variance (^#) followed by comparison between each pair of groups using the post hoc Student t-test (^‡) for the continuous variables, and by the chi-square test (^§) for the categorical variables. In the post hoc test, based on Bonferroni’s method to correct multiple comparisons, P<0.0083 and P<0.0017 are considered significant at the probability levels of 5% (^*) and 1% (^**), respectively.

Abbreviations: LEC, trabeculectomy; EXP, EX-PRESS^® shunt; exLOT, ab externo trabeculotomy; μLOT, microhook ab interno trabeculotomy; SD, standard deviation; CI, confidence interval; POAG, primary open-angle glaucoma; SOAG, secondary open-angle glaucoma; PACG, primary angle-closure glaucoma; SACG, secondary angle-closure glaucoma; BCVA, best-corrected visual acuity; logMAR, logarithm of the minimum angle of resolution; IOP, intraocular pressure.

Figure 1 A scatter plot of SIA in each surgical group. The red and blue dots in each chart indicate the mean SIA vectors of the group and the SIA of each eye, respectively. The red circles indicate 95% confidence interval. All the astigmatic values are expressed in a plus-cylinder format. The astigmatism in the direction of 0° indicates against-the-rule astigmatism, and that in the direction of 90° indicates with-the-rule astigmatism. Each ring indicates 1.5 D.

Abbreviations: SIA, surgically induced astigmatism; LEC, trabeculectomy; EXP, EX-PRESS^® shunt; exLOT, ab externo trabeculotomy; μLOT, microhook ab interno trabeculotomy.

Table 2 Comparison of astigmatism parameters among the surgical groups

Parameters	LEC	EXP	exLOT	µLOT	P-value^#
Preoperative astigmatism					0.0732
Vector magnitude (D)	0.22±1.30	0.18±1.05	0.37±0.87	0.42±1.69
Vector meridian (degrees)	38±10	44±11	21±17	17±7
Arithmetic magnitude (D)	1.18±0.52	0.95±0.44	0.79±0.50	1.33±1.09
95% CI	0.94–1.43	0.74–1.16	0.56–1.02	0.82–1.83
Postoperative 3 months astigmatism					0.0002
Vector magnitude (D)	1.20±2.32	0.72±1.40	0.14±1.15	0.31±1.40
Vector meridian (degrees)	53±26	68±23	20±18	21±10
Arithmetic magnitude (D)	2.21±1.32	1.41±0.63	0.94±0.64	1.11±0.88
95% CI	1.60–2.83	1.12–1.71	0.64–1.24	0.70–1.52
P-values^‡
Against EXP	0.0068^*	–	–	–
Against exLOT	<0.0001^**	0.1052	–	–
Against μLOT	0.0003^*	0.3001	0.5526	–
Surgically induced astigmatism					<0.0001
Vector magnitude (D)	1.01±2.27	0.62±1.20	0.23±1.04	0.12±0.75
Vector meridian (degrees)	56±26	74±24	112±17	97±21
Arithmetic magnitude (D)	2.03±1.37	1.17±0.64	0.86±0.59	0.62±0.42
95% CI	1.66–2.41	0.80–1.54	0.49–1.24	0.25–0.99
P-values^‡
Against EXP	0.0017^*	–	–	–
Against exLOT	<0.0001^**	0.2471	–	–
Against μLOT	<0.0001^**	0.0402	0.3599	–

Notes: P-values are calculated for the arithmetic means among the four glaucoma surgeries by one-way analysis of variance (^#) followed by comparison between each pair of groups using the post hoc Student t-test (^‡). In the post hoc test, based on Bonferroni’s method to correct multiple comparisons, P<0.0083 and P<0.0017 are considered significant at the probability levels of 5% (^*) and 1% (^**), respectively. Astigmatism data are expressed as the mean ± standard deviation.

Abbreviations: LEC, trabeculectomy; EXP, EX-PRESS^® shunt; exLOT, ab externo trabeculotomy; μLOT, microhook ab externo trabeculotomy; CI, confidence interval.

Table 3 Possible association between SIA magnitude, IOP, and BCVA at 3 months postoperatively (n=80)

Parameters	SIA magnitude (D)	BCVA (logMAR)	IOP (mmHg)
SIA magnitude (D)	–	P=0.0013^**	P=0.0031^**
BCVA (logMAR)	r=0.3538	–	P=0.0051^*
IOP (mmHg)	r=−0.3265	r=−0.3105	–

Notes: The correlation coefficient (r) and P-values are calculated by Spearman’s rank correlation test between parameters. Based on Bonferroni’s method to correct multiple comparisons, P<0.0167 and P<0.0033 are considered significant at the probability levels of 5% (^*) and 1% (^**), respectively.

Abbreviations: SIA, surgically induced astigmatism; IOP, intraocular pressure; BCVA, best-corrected visual acuity; logMAR, logarithm of the minimum angle of resolution.