Table 4 Clinical factors associated with postoperative thinning of the average retinal nerve fibre layer thickness (µm).

	Univariate			Multivariate
	β	95% CI	p-value	β	95% CI	p-value
Age (per 1 y older)	−0.088	−0.215–0.039	0.181
Sex (male)	−1.156	−5.186–2.874	0.576
Axial length (per 1 mm longer)	0.139	−0.857–1.135	0.290
Central corneal thickness (per 1 µm thicker)	0.007	−0.077–0.091	0.509
Disc area (per 1 mm2 larger)	1.002	−2.979–4.983	0.363
Disc haemorrhage (presence)	0.135	−1.186–1.456	0.601
Preoperative severity of glaucoma
Average RNFL thickness (per 1 µm thicker)	0.180	0.092–0.268	<0.001	0.125	0.011–0.239	0.038
Average GCIPL thickness (per 1 µm thicker)	0.147	0.025–0.269	0.022
Mean deviation (per 1 dB higher)	0.283	0.083–0.483	0.008
Visual field index (per 1% higher)	0.073	0.018–0.128	0.015
IOP related parameters
Preoperative peak IOP (per 1 mmHg higher)^*	0.435	0.317–0.553	<0.001	0.338	0.175–0.501	<0.001
Postoperative mean IOP (per 1 mmHg higher)^†	−0.192	−0.688–0.304	0.451
IOP reduction (per 1 mmHg higher)^‡	0.399	0.287–0.511	<0.001
IOP fluctuation (per 1 mmHg higher)	−0.045	−0.352–0.262	0.836

CI = confidence interval, IOP = intraocular pressure, RNFL = retinal nerve fibre layer, GCIPL = ganglion cell layer plus inner plexiform layer, IOP = intraocular pressure.
Average RNFL thickness and preoperative peak intraocular pressure (IOP) remained significantly different in multivariate regression analysis (stepwise selection method). The variance inflation factor was 1.231, such that there was no collinearity between any two variables.
^*The highest IOP among those measured between 1 month and 1 day before surgery.
^†The IOP calculated as the sum of all IOPs recorded during the postoperative period commencing 1 month postoperatively divided by the total number of examinations, up until the postoperative ophthalmic examination.
^‡Preoperative peak IOP–postoperative mean IOP.

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