Impact of the anterior-posterior corneal radius ratio on intraocular lens power calculation errors

Figures & data

Table 1 Summary of studies reporting the AP corneal radius ratio

First author (Country)	Year	Instrument	AP ratio
Dubbelman et al^Citation2 (the Netherlands)	2006	Scheimpflug photography (Topcon SL-45)	1.23±0.02
Fam et al^Citation3 (Singapore)	2007	Slit-scan topography (Orbscan II)	1.22±0.03
Ho et al^Citation4 (Taiwan)	2008	Rotating Scheimpflug photography (Pentacam)	1.223±0.034
Tang et al^Citation6 (USA)	2010	Fourier-domain OCT (REVue)	0.836±0.016 (1.20)a
Montalban et al^Citation5 (Spain)	2012	Scheimpflug photography (Sirius: Costruzione Strumenti Oftalmici)	1.19±0.02
Savini et al^Citation7 (Italy)	2017	Scheimpflug photography (Sirius: Costruzione Strumenti Oftalmici)	1.20±0.03

Note:

a To allow comparison of our study, the result from the previous study was converted to a reciprocal value.

Abbreviations: AP, anterior–posterior; OCT, optical coherence tomography.

Table 2 Patient demographic information

Characteristics
Age (years)	72.0±11.5 (range: 17–98)
Gender	Male: 215/female: 286
Anterior corneal radius (mm)	7.60±0.25
Posterior corneal radius (mm)	6.38±0.24
Central corneal thickness (μm)	533.05±33.16
Horizontal corneal diameter (mm)	11.56±0.44
Axial length (mm)	23.71±1.51
Anterior chamber depth (mm)	2.98±0.53
Anterior posterior corneal radius ratio	1.19±0.02 (range: 1.11–1.26)
Corneal power (keratometric) (D)	44.47±1.50
Corneal power (posterior) (D)	−6.28±0.23
Corneal power (total) (D)	43.38±1.48
Corneal astigmatism (keratometric) (D)	0.96±0.71
Corneal astigmatism (posterior) (D)	0.27±0.13
Corneal astigmatism (total) (D)	1.05±0.74
Difference between the keratometric and real power (D)	1.08±0.12 (range: 0.70–1.60)

Note: Values are presented as mean ± SD.

Figure 1 Distribution of the AP corneal radius ratio in patients before cataract surgery.

Note: The mean AP ratio is 1.19±0.02, lower than that in the Gullstrand schematic eye model (1.13).
Abbreviation: AP, anterior–posterior.

Figure 2 Correlation between the anterior–posterior corneal radius ratio (AP ratio) and the following parameters: corneal thickness (A; P<0.0001, r_s =0.2233), anterior corneal radius (B; P=0.485), posterior corneal radius (C; P<0.0001, r_s =−0.465), age (D; P=0.008, r_s =−0.118), horizontal corneal diameter (E; P=0.0094, r_s =−0.1161), axial length (F; P=0.2771), anterior chamber depth (G; P=0.6733), anterior corneal astigmatism (H; P=0.6294), posterior corneal astigmatism (I; P<0.0001, r_s =0.2923), and total corneal astigmatism (J; P=0.7156).

Abbreviation: AP, anterior–posterior.

Figure 3 Correlation between the anterior–posterior corneal radius ratio and difference between the keratometric and total corneal refractive power.

Note: There was a significant correlation between the AP ratio and the difference between the keratometric and total corneal refractive power (P<0.0001, r_s =0.8809).
Abbreviation: AP, anterior–posterior.

Table 3 Patient demographic information for sub-group analysis

Characteristics
Age (years)	74.6±8.8 (range: 43–98)
Gender	Male: 69/female: 112
Anterior corneal radius (mm)	7.59±0.25
Posterior corneal radius (mm)	6.36±0.24
Corneal astigmatism (keratometric) (D)	0.82±0.54
Corneal astigmatism (posterior) (D)	0.26±0.13
Corneal astigmatism (total) (D)	0.95±0.58
Central corneal thickness (μm)	535.33±31.42
Horizontal corneal diameter (mm)	11.55±0.43
Axial length (mm)	23.27±1.34
Anterior chamber depth (mm)	2.84±0.50
Anterior–posterior corneal radius ratio	1.19±0.02 (range: 1.12–1.26)
Difference between keratometric and real power (D)	1.08±0.12 (range: 0.70–1.38)

Note: Values are presented as mean ± SD.

Table 4 The results of IOL power calculation and the correlation between the PE and AP ratio in the 4 formulas

	SRK/T	Haigis	Holladay 1	Hoffer Q
Mean PE	0.000386±0.451	0.0472±0.423	0.0822±0.425	0.0829±0.465
MedAE	0.300	0.298	0.288	0.335
P-valuea	0.523	0.751	0.565	0.478

Note:

a The correlation between the AP ratio and PE (the Spearman’s rank correlation coefficient).

Abbreviations: AP, anterior–posterior; IOL, intraocular lens; PE, prediction error; MedAE, median absolute error.

Figure 4 Correlation between the anterior–posterior corneal radius ratio and IOL power calculation error.

Notes: There was no significant correlation between the AP ratio and the IOL power calculation error. (A) SRK/T (P=0.5232); (B) Haigis (P=0.7514); (C) Holladay 1 (P=0.5646); (D) Hoffer Q (P=0.4784).
Abbreviations: AP, anterior–posterior; IOL, intraocular lens.

Table 5 Stepwise multiple regression analysis of factors influencing refractive prediction error after cataract surgery, performed with postoperative refractive prediction error as the dependent variable, and age, AP ratio, anterior/posterior corneal radius, horizontal corneal diameter, ACD, AL, and central corneal thickness as the independent variables

	Independent variables	Unstandardized regression coefficient	Partial regression coefficient	95% CI	VIFa	P-value
SRK/T	Constant	−5.911		−7.865 to −3.952		<0.001
	Corneal diameter	0.383	0.362	0.206 to 0.559	1.632	<0.001
	AL	−0.098	−0.291	−0.149 to −0.047	1.358	<0.001
	ACD	0.482	0.267	0.191 to 0.773	1.523	0.001
	Astigmatism (keratometric) R^2=0.233, P<0.001	0.133	0.16	0.023 to 0.244	1.032	0.018
Haigis	Constant	0.944		−0.628 to 3.305		0.351
	ACD	−0.514	−0.309	−0.814 to −0.233	1.455	0.001
	Corneal diameter	0.251	0.235	0.063 to 0.402	1.455	0.004
	Astigmatism (keratometric) R^2=0.096, P<0.001	0.125	0.16	0.014 to 0.237	1.014	0.028
Holladay 1	Constant	−3.912		−5.509 to −2.316		<0.001
	Corneal diameter	0.298	0.3	0.153 to 0.444	1.18	<0.001
	Astigmatism (keratometric)	0.143	0.182	0.037 to 0.294	1.013	0.009
	ACD R^2=0.180, P<0.001	0.152	0.179	0.028 to 0.276	1.168	0.017
Hoffer Q	Constant	−3.112		−4.206 to −2.017		<0.001
	AL	0.11	0.318	0.055 to 0.166	1.526	<0.001
	ACD R^2=0.245, P<0.001	0.22	0.236	0.072 to 0.368	1.526	0.004

Note:

a VIF quantifies a multicollineality of each parameters. Generally, the value exceeding 4 needs further investigation, and exceeding 10 requires correction.

Abbreviations: ACD, anterior chamber depth; AL, axial length; VIF, variance inflation factor.

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