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Abstract

Objectives:

To assess the influence of age and gender on ocular biometric values and corneal astigmatism features in individuals undergoing phacoemulsification surgery and intraocular lens implantation.

Methodology:

This retrospective study measured ocular biometrics and corneal keratometric astigmatism using the IOLMaster 700 instrument prior to phacoemulsification surgery and intraocular lens implantation.

Results:

Analysis included ocular biometric and keratometric values from 3385 eyes of 3385 patients. Lens thickness (p < 0.001, r = 0.387), mean keratometry (p < 0.001, r = 0.156), and corneal astigmatism (p < 0.001, r = 0.082) were positively correlated with age. Conversely, axial length (p < 0.001, r = −0.133), anterior chamber depth (p < 0.001, r = −0.244), and horizontal white-to-white corneal diameter (p < 0.001, r = −0.226) exhibited negative correlations with age. Increasing age led to a significant shift towards against-the-rule astigmatism (p < 0.001, r = 0.248). Mean keratometry was significantly lower in males than females (p < 0.001). Axial length, anterior chamber depth, lens thickness, and white-to-white corneal diameter were higher in males compared to females (all ps ⩽ 0.001). Corneal astigmatism types differed significantly between genders (p < 0.001), with against-the-rule being more prevalent among males (52.9%) and with-the-rule astigmatism having the highest prevalence among females (40.3%).

Conclusions:

Mean keratometry and lens thickness increased, while axial length and anterior chamber depth decreased with age. Males exhibited higher values for axial length, anterior chamber depth, and lens thickness, whereas females had steeper corneas.

Keywords

Ocular biometry corneal astigmatism cataract phacoemulsification IOLMaster

Introduction

Cataract remains a leading cause of visual impairment, particularly among elderly individuals, necessitating phacoemulsification surgery with intraocular lens (IOL) implantation. Accurate measurement of ocular axial length (AL), anterior chamber depth (ACD), and corneal parameters, including diameter and astigmatism, is crucial for precise IOL power calculation and optimal postoperative refractive outcomes.^1,2 The IOLMaster 700 (Carl-Zeiss company, Germany), based on swept-source optical coherence tomography, permits visual verification of all measurements with good repeatability and accuracy and provides precise ocular biometry for preoperative IOL power measurement, minimizing postoperative refractive surprises.^1,3–5

Previous research has shown an age-related increase in the amount of corneal astigmatism, as well as a shift toward against-the-rule (ATR) astigmatism.^6–8 In addition, AL and ACD tend to decrease with age and are generally lower in females.^9–13 However, these variations in ocular biometric values can differ across geographical regions and ethnicities, which may account for differences in the prevalence of refractive errors.¹⁴ Thus, providing region-specific reference data for ocular biometric values are essential for the clinical practice of ophthalmologists. While prior studies have examined ocular biometric values in the Iranian population,^6,15 our study specifically focuses on the Kerman province, located in southeast Iran. This study employs the IOLMaster 700 to measure ocular biometrics and corneal astigmatism features in individuals undergoing phacoemulsification surgery and IOL implantation, investigating the impact of age and gender on these measurements.

Methodology

This retrospective study was conducted using patients’ IOL power calculation data and chart reviews collected from June 2021 to July 2022 at Shafa Hospital in Kerman, Iran. The participants were selected through convenience sampling. All participants were candidates for phacoemulsification and IOL implantation, aged over 18 years, and only the right eye of each individual was included in the study. Exclusion criteria encompassed participants with corneal or ocular surface disorders, a history of previous corneal or intraocular surgery, irregular corneal astigmatism, and keratometry values <40 diopters (D) or >47 D. Prior to surgery, all participants underwent assessments including best corrected visual acuity measurement, slit lamp biomicroscopy, intraocular pressure measurement using Goldmann tonometry, and a dilated fundus examination using a hand-held 90 D lens. This study adhered to the principles of the Declaration of Helsinki, and written consent was obtained from all participants. The study protocol received approval from the ethical committee of Kerman University of Medical Sciences, Kerman, Iran (ethical code: IR.KMU.REC.1400.339).

Corneal topography imaging, performed using the Orbscan II (Bausch and Lomb, Rochester, NY, USA), was conducted for participants with corneal astigmatism ⩾2.00 D to exclude irregular corneal astigmatism. The IOLMaster 700 (Carl-Zeiss company, Germany) instrument was utilized to measure keratometry, corneal astigmatism (within the central 3 mm zone), AL, ACD, LT, and horizontal white-to-white (WTW) diameter of the cornea. The mean of three consecutive measurements was calculated for each variable, with all assessments conducted by the same experienced operator. Astigmatism was categorized into three types: with the rule (WTR: steepest meridian 90° ± 29°), ATR (180° ± 29°), and oblique (30°–60° or 120°–150°) types. In addition, the severity of corneal astigmatism was divided into three groups: <1.25, 1.25–2.00, and ⩾2.00 D. Eyes with corneal astigmatism ⩾2.00 D were considered for toric IOL implantation.⁶

Statistical analysis

Data were analyzed using SPSS software version 24 (SPSS Inc., Chicago, IL, USA). Continuous variables were presented as mean ± standard deviation, while categorical variables were presented as percentages. The Chi-square test and t-test were employed to analyze categorical and continuous variables across genders, respectively. Furthermore, Pearson’s coefficient was utilized to calculate correlation coefficients between variables and the age factor. A significance level of p < 0.05 was considered statistically significant.

Results

A total of 3385 eyes belonging to 3385 patients were included in this study, with 55.2% (n = 1867) of them being female. The mean age of the individuals was 66.40 ± 10.44 years, ranging from 30 to 98 years. The summarized data for participants’ demographics, as well as ocular biometrics and corneal astigmatism, are found in Tables 1 and 2.

Table 1.

Baseline demographics.

Variable	Total number (n) = 3385
Age (years), mean ± SD (range)	66.40 ± 10.44 (30–98)
Gender, n (%)	Female: 1867 (55.2)
Gender, n (%)	Male: 1518 (44.8)

Table 2.

Ocular biometric values.

Biometric value	Mean ± SD
Axial length (mm)	23.44 ± 1.30
Anterior chamber depth (mm)	3.07 ± 0.40
Lens thickness (mm)	4.43 ± 0.44
Mean keratometry (diopter)	44.68 ± 1.75
Corneal astigmatism (diopter)	1.13 ± 0.85
Horizontal white-to-white diameter of the cornea (mm)	11.73 ± 0.45

The predominant types of astigmatism were ATR at 44.3%, WTR at 34.5%, and oblique at 21.2%. The majority of participants (67.9%) exhibited corneal astigmatism of less than 1.25 D (Table 3).

Table 3.

Types and severity of corneal astigmatism.

Corneal astigmatism	N (%)
Type of corneal astigmatism	ATR: 1498 (44.3)
	WTR: 1169 (34.5)
	Oblique: 718 (21.2)
Severity of corneal astigmatism (diopter)	<1.25: 2300 (67.9)
	1.25–2.00: 670 (19.8)
	⩾2.00: 415 (12.3)

ATR: against the rule; WTR: with the rule.

Significant positive correlations were observed between age and LT, mean keratometry, corneal astigmatism, and its severity. Moreover, as age increased, a significant shift toward ATR astigmatism was noted (p < 0.001, r = 0.248). Conversely, AL, ACD, and horizontal WTW corneal diameter displayed significant negative correlations with age (Table 4). In addition, there was a significant negative correlation between mean keratometry and AL (p < 0.001, r = −0.420).

Table 4.

Correlation of ocular biometric values and corneal astigmatism features with age.

Biometric value	p	r
Axial length	<0.001	−0.133
Anterior chamber depth	<0.001	−0.244
Lens thickness	<0.001	0.387
Mean keratometry	<0.001	0.156
Horizontal white-to-white diameter of the cornea	<0.001	−0.226
Corneal astigmatism	<0.001	0.082
Severity of corneal astigmatism	<0.001	0.079

Males exhibited higher values than females for AL, ACD, LT, and WTW corneal diameter (all ps ⩽ 0.001). However, mean keratometry was significantly lower in males than in females (p < 0.001). Notably, types of corneal astigmatism exhibited significant differences between genders (p < 0.001), with ATR being the most common type among males (52.9%), while WTR had the highest prevalence among females (40.3%, Table 5).

Table 5.

Ocular biometric values and corneal astigmatism features according to gender.

Biometric value	Male (n = 1518)	Female (n = 1867)	p
Axial length (mm)	23.62 ± 1.22	23.30 ± 1.35	<0.001
Anterior chamber depth (mm)	3.11 ± 0.40	3.04 ± 0.40	<0.001
Lens thickness (mm)	4.46 ± 0.44	4.41 ± 0.44	0.001
Mean keratometry (diopter)	44.25 ± 1.74	45.04 ± 1.68	<0.001
Horizontal white-to-white diameter of the cornea (mm)	11.82 ± 0.44	11.65 ± 0.44	<0.001
Corneal astigmatism (diopter)	1.15 ± 0.86	1.10 ± 0.85	0.108
Type of corneal astigmatism, n (%)	ATR: 803 (52.9)	ATR: 695 (37.2)	<0.001
	WTR: 416 (27.4)	WTR: 753 (40.3)
	Oblique: 299 (19.7)	Oblique: 419 (22.4)
Severity of corneal astigmatism (diopter) n (%)	<1.25: 1001 (65.9)	<1.25: 1299 (69.6)	0.055
	1.25–2.00: 326 (21.5)	1.25–2.00: 344 (18.4)
	⩾2.00: 191 (12.6)	⩾2.00: 224 (12.0)

ATR: against the rule; WTR: with the rule.

Discussion

This study aimed to assess the distribution of ocular biometric values and corneal astigmatism in a population of Iranian candidates undergoing phacoemulsification surgery. The mean age of our participants was 66.43 ± 10.46 years (range: 30–98), a figure comparable to Hashemian et al.⁶ (66.4 years) but higher than Hashemi et al.¹⁵ (50.9 years), both of which were conducted within Iranian populations. In addition, our study, like the aforementioned studies, featured a higher percentage of female participants. Notably, the mean AL in our study was 23.44 ± 1.30 mm, consistent with findings from Hashemian et al.⁶ (23.55 mm) and Hashemi et al.¹⁵ (23.14 mm). The ACD in our study, 3.07 ± 0.40 mm, closely resembled that of Hashemian et al.⁶ (3.11 mm).

Regarding corneal astigmatism, our study recorded a prevalence of ⩾2.00 D astigmatism in 12.3% of participants, lower than Hashemian et al.⁶ study (6.7%). The mean corneal astigmatism in our study was 1.13 ± 0.85 D, comparatively lower than other similar Iranian studies such as Mohammadi et al.¹⁶ (1.12 ± 1.10 D) and Hashemian et al.⁶ (0.89 ± 0.68 D). These observed variations may be due to differences in the type of measuring instrument employed for ocular biometry and corneal astigmatism assessment, as well as potential ethnic and environmental factors that may play an important role in ocular characteristics.^17,18 Understanding pre-existing corneal astigmatism is pivotal for accurate cataract surgery planning and the choice of IOL implantation.

In our study, ATR astigmatism was the most common type (44.3%), followed by WTR astigmatism (34.5%) and oblique astigmatism (21.2%). This contrasts with previous reports, where WTR astigmatism was more prevalent.^6,10,19,20 Similarly, as seen in earlier literature, corneal astigmatism’s axis shifted toward ATR with age due to the flattening of the vertical corneal meridian.^6–8 The study also identified an increase in mean keratometry and LT, while AL and ACD decreased significantly with age, consistent with prior research. According to our study, a negative correlation between mean keratometry and AL was observed, consistent with prior studies.^10,20–22 One hypothesis explaining these findings proposes a compensatory effect of AL reduction in the adult eye to counteract the increasing corneal power.^23,24

Variations in ocular biometrics across different geographical regions and ethnicities highlight the need for region-specific reference data. This information is essential for ophthalmologists to understand regional differences in refractive error prevalence, improve cataract surgery outcomes, and innovate IOL power calculations.¹⁴ For example, our study and other similar Iranian investigations reported shorter mean ACD values compared to those observed in Western research. This is in line with previous literature, which indicates greater ACD in Western populations than in Asians.^{6,9,10,17,19,25–27}

We discovered that males exhibited higher values for AL, ACD, and LT, similar to previous studies.^9–13 Furthermore, consistent with earlier literature, females exhibited steeper corneas compared to males.^10,13,28

This study is the first to evaluate ocular biometrics and corneal astigmatism among participants from southeast Iran (Kerman province) and the influence of age and gender on these parameters. However, several limitations must be noted. First, the participants were from a single center for cataract surgery, which may limit the generalizability of the findings. Nevertheless, the center is a referral hub for ophthalmic diseases in the province. In addition, convenience sampling was used without power analysis and sample size calculation, though our sample size (3385 participants) is comparable to similar studies.^6,13,15 Second, we did not account for environmental factors that could impact ocular characteristics. Previous research showed factors such as residing in urban areas, prolonged near work, extensive use of electronic screens, and higher levels of education have been correlated with axial myopia, particularly among younger individuals.^17,18 Future studies should consider these factors for a more comprehensive analysis.

Conclusions

In conclusion, this study provides valuable insights into ocular biometric values and corneal astigmatism among Iranian individuals undergoing phacoemulsification surgery, emphasizing the impact of age and gender. Our findings offer the first set of ocular biometric data from southeast Iran (Kerman province), which can assist local ophthalmologists in improving cataract surgery outcomes and innovating IOL power calculations. Notably, we observed age-related increases in mean keratometry and LT and decreases in AL and ACD. In addition, males had higher AL, ACD, and LT values, while females had steeper corneas. Age also correlated with increased corneal astigmatism and a shift toward ATR astigmatism.

Footnotes

Acknowledgements

We appreciate the Kerman University of Medical Sciences.

Authors’ contributions

A. Sharifi, M. Shafiei, and H. Sharifi designed the study. M. Shafiei and M. Sharifi collected data. A. Sharifi and A. Zand wrote the first draft of the paper, M.J. Najafzadeh, H. Sharifi, and N. Nasiri contributed to the writing and revision of the manuscript. All authors contributed to finalizing the manuscript.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Statements and declarations

The manuscript has been read and approved by all the authors. This manuscript has not been published elsewhere and it has not been submitted simultaneously for publication elsewhere.

Ethics approval

The study received approval from the Ethics Committee of Kerman University of Medical Sciences (Ethics Committee code: IR.KMU.REC.1400.339) and was conducted in compliance with the Declaration of Helsinki.

Informed consent

Although this study was retrospective, informed consent was obtained from all participants before surgery, regarding any research use of medical information without disclosing their identity.

Consent to participate

This study adhered to the principles of the Declaration of Helsinki, and written consent was obtained from all participants.

Consent for publication

Not applicable.

Trial registration

Not applicable.

ORCID iDs

Amin Zand

Mohadeseh Shafiei

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