155 Differences in the biometric components of the eye between men and women Diferencias en los componentes biométricos oculares entre hombres y mujeres Diana Rey-Rodríguez1,*, Cristina Álvarez-Peregrina2, José Moreno-Montoya3, Diana P. Ramírez-Arcos4, and Luisa F. Tovar-Oviedo1 1Universidad El Bosque, Bogotá, Colombia; 2Universidad Europea de Madrid, Madrid, Spain; 3Subdirección de estudios clínicos, Fundación Santafé de Bogota, Colombia; 4Colegio Federación Colombiana de Optómetras, Bogota, Colombia ORIGINAL ARTICLE Abstract Objective: To evaluate the differences in ocular biometric components such as axial length (AL), anterior chamber depth (ACD), lens thickness (LT), corneal curvature (CC), and central corneal thickness (CT) between men and women. Methods: Cross-sec- tional, analytical, and observational study conducted in 106 university with students aged 18-36 years. All subjects underwent refraction under cycloplegia and were assessed through autorefractometry. The refractive error was measured after the appli- cation of 1% cyclopentolate. For the identification of biometric components, assessment was performed using the Aladdin equipment (Topcon Corporation, Equipos Oftalmológicos Colombia). Results. A total of 71.7% (76) of the 106 participants inclu- ded were women aged between 18 and 36 years. The mean AL was 23.3 mm ± 0.88 mm in women and 23.9 mm ± 0.99 mm in men. The ACD was 3.5 mm ± 0.26 mm in women and 3.6 mm ± 0.22 mm in men. LT in women was 3.47 mm ± 0.22 mm and 3.53 mm ± 0.20 mm in men. CT was 538.65 µm ± 0.36 in women and 542.43 µm ± 32.73 in men. The mean keratometry was 43.54D ± 1.35 in women and 42.76D ± 1.79 in men. There were statistically significant differences between CC (−0.78D; p values were 0.01 and 0.03 for men and women, respectively) and AL (0.63 mm; p values were 0.02 and 0.04 for men and women, respectively). Conclusion: There are differences in CC of up to 0.75D that happens to be more curved in women. However, the size of the eyeball is larger in men. These anatomical characteristics are involved in the prevalence of refractive errors. Keywords: Axial length. Sex. Cornea. Crystalline lens. Refractive errors. Resumen Objetivo: Evaluar las diferencias en los componentes biométricos oculares como longitud axial (AL), profundidad de cámara anterior (ACD), espesor del lente (LT), Curvatura corneal (CC) y espesor corneal central (ECC) entre hombres y mujeres. Mé- todos: Estudio observacional analítico de corte transversal, en 106 estudiantes universitarios en edades entre 18-36 años. Todos los sujetos fueron sometidos a refracción bajo cicloplejia y valorados a través de autorefractometría. El error refractivo fue medido después de la aplicación de ciclopentolato al 1%. Para la identificación de componentes biométricos se realizó una valoración con el equipo Aladdin (Topcon Corporation, Equipos Oftalmológicos Colombia). Resultados. De los 106 participan- tes el 71.7% (76) correspondían al sexo femenino, en edades entre 18 a 36 años. En mujeres el promedio de longitud axial fue de 23.3 mm ± 0.88 y en hombres 23.9 mm ± 0.99. La profundidad de cámara anterior fue de 3.5 mm ± 0.26 en mujeres y en *Correspondence: Diana Rey-Rodríguez E-mail: reydiana@unbosque.edu.co Available online: 26-01-2023 Rev Mex Oftalmol (Eng). 2022;96(4):155-161 www.rmo.com.mx Date of reception: 26-10-2021 Date of acceptance: 28-10-2022 DOI: 10.24875/RMOE.M22000239 2604-1731 / © 2022 Sociedad Mexicana de Oftalmología. Published by Permanyer. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). mailto:reydiana%40unbosque.edu.co?subject= www.rmo.com.mx http://dx.doi.org/10.24875/RMOE.M22000239 http://creativecommons.org/licenses/by-nc-nd/4.0/ http://crossmark.crossref.org/dialog/?doi=10.24875/RMOE.M22000239&domain=pdf Rev Mex OftalMOl (eng). 2022;96(4) 156 Introduction The growth and development of the eyeball are pro- gressive since the moment that we are born. When we are 3, it nearly reaches its entire size, and from 3 to 13, it only grows 1  mm to eventually reach a maximum axial length (AL) of 24 mm. This length will remain in the coming years if everything goes well. Furthermore, the power of the cornea and the crystalline lens de- crease after we are 3 years old.1,2 Biometrical values are considered the most signifi- cant factors that can induce the appearance of refrac- tive errors. AL is the most variable measurement during development and is strongly associated with the size of ametropia.3 Meanwhile, the thickness and power of the crystalline lens increase gradually until we are 14  years old. However, this power can be reduced in near-sighted children due to an increased AL.4 AL is a determinant factor for the classification of ametropies since it indicates that minimum changes lead to major changes in refractive errors.5 It generates 6D of myopia for every 3 mm of increased AL. These biometrical values can be very different between men and women being AL and anterior chamber depth (ACD) greater, and thickness and the power of the crystalline smaller in masculine sex. De Bernardo et al. compared the biometrical data of men and women. Women have greater corneal curva- ture (CC), but the AL of their eyeball is shorter. With respect to the keratometry readings women have great- er dioptric power. We should mention that something that could account for these different characteristics is the hormonal differences between men and women.6 Therefore, the objective of this study was to investi- gate the differences that exist in the biometrical com- ponents between men and women. Methods Study population A total of 106 college students from Bogota, Colom- bia, aged between 18 and 36 were studied. Opacities in refractive means, medical history of refractive or in- traocular surgery, conditions damaging visual acuity, and contraindications for the application of cyclopento- late like a narrow iridocorneal angle were all excluded from the study. Universidad El Bosque ethics committee approved the study and the patients’ informed consent was ob- tained. The study was conducted according to the Dec- laration of Helsinki. Clinical assessment Assessment included biometrical examinations of AL, ACD, crystalline lens thickness (CLT), CC, and corneal thickness (CT) using the Aladdin corneal topographer (Topcon Corporation, Equipos Oftalmológicos Colom- bia)7 before assessing cycloplegia. Topographer calibra- tion was performed before each consultation day. Before the cycloplegia assessment, a biomicroscopy was performed using a Haag-Streit slit lamp that as- sessed the ACD using the Van Herick grading scale. During the cycloplegia assessment, a drop of cyclo- pentolate at 1% was administered to the right eye twice with a 5  min interval.8 The refraction test was per- formed using the the Potec PRK 6000 Autorefractor Keratometer through three different measurements tak- en by the same ophthalmologists considering mean data as long as the difference would not exceed 0.50D in the sphere and/or the cylinder. Spherical equivalent (SE) was defined as the spherical value plus over half of the cylindrical value. This study defined myopia as an SE < −0.50D; hypermetropia as a SE > +0.50,9 and astigmatism as a SE > 1.00D.10 Statistical analysis The Kolmogorov-Smirnov test was performed to es- tablish the type of distribution and normality of both the overall and the sex-based data. A descriptive analysis was performed. Qualitative variables were expressed as frequencies and percentages. Quantitative ones were expressed through measures of dispersion and hombres 3.6 mm ± 0.22. El espesor del cristalino en mujeres fue de 3.47 ± 0.22 y en hombres de 3.53 ± 0,20. El espesor corneal en mujeres fue de 538.65 µm ± 0.36 y en hombres de 542.43 µm ± 32.73. El promedio de la queratometría en mujeres fue de 43.54D ± 1.35 y en hombres de 42.76D ± 1.79. Existieron diferencias estadísticamente significativas entre la curvatura corneal (−0.78D valor p hombres 0.01 mujeres 0.003) y la longitud axial (0.63 mm valor p hombres 0.02 mujeres 0.04). Con- clusión: Existen diferencias en la curvatura corneal hasta de 0.75D siendo más curva en mujeres y un mayor tamaño del globo ocular en hombres, características anatómicas que intervienen en la prevalencia de errores de refracción. Palabras claves: Longitud axial. Sexo. Cornea. Cristalino. Errores de refracción. D. Rey-Rodríguez et al.: Biometric components of the eye between men and women 157 central tendency. Mean differences were identified us- ing the Student’s t test for independent samples. p < 0.05 was considered statistically significant. Linear regression was performed among the biometrical com- ponents of interest. Statistical analysis was performed using the statistical software package SPSS (ver- sion 24,0; IBM-SPSS Chicago, IL, United States). Results A total of 71.7% (76) out of the 106 participants were women. Age range was 18-36 years old. Mean age was 25 years ± 2.34. Refractive errors The percentage of patients without refractive errors, hypermetropia, astigmatism, and myopia was 36.8% (39), 23.6% (25), 21.7% (23), and 17.9% (19). A total of 42.1% (32), 23.6% (18), 17.1% (13), and 17.1% (13) of women had emmetropia, hypermetropia, myopia, and astigmatism, respectively. On the other hand, 33.3%, 23.3% (seven in each group), and 20% of men had astigmatism, hypermetropia and emmetropia, and my- opia, respectively. To assess the normality of data the statistical Kolm- ogorov-Smirnov test was used, p > 0.05 was consid- ered normal values (Table 1). Biometrical components AL Mean AL was 23.4 mm ± 0.95 with a minimum of 21.4 and a maximum of 25.97. In women, mean AL was 23.3 mm ± 0.88 mm. In men, mean AL was 23.9 mm ± 0.99 mm (Fig. 1). ACD The mean ACD was 3.54 mm ± 0.25 mm for a min- imum of 2.21 and a maximum of 4.18. In women, mean ACD was 3.5  mm ± 0.26. In men, mean ACD was 3.6 mm ± 0.22 mm (Fig. 2). CLT The population mean thickness was 3.49  mm ± 0.22 mm for a minimum of 2.49 and a maximum of 4.04. In women, mean thickness was 3.47 mm ± 0.22 mm. In men, mean thickness was 3.53  mm ± 0.20  mm (Fig. 3). CT The population mean CT was 450 µm for a minimum of 539 µm and a maximum of 628 µm. In women, mean CT was 538.65 µm ± 0.36 µm. In men, mean CT was 542.43 µm ± 32.73 µm (Fig. 4). CC Participants had a mean CC of 43.32D ± 1.2 for a minimum of 39.88D and a maximum of 47.13D. Women had a mean CC of 43.54D ± 1.35. Men had a mean CC of 42.76D ± 1.79 (Fig. 5). The statistical difference in each biometrical compo- nent between men and women was identified (Table 2). Figure 1. Axial length between men and women. A xi al le ng th Sex Men Women Astigmatism Emetrope Hypermetrope Myope Classification of refraction errors 28.00 27.00 26.00 25.00 24.00 23.00 22.00 21.00 20.00 Figure 2. Anterior chamber depth between men and women. A nt er io r c ha m be r d ep th Sex Men Women Classification of refraction errors Astigmatism Emetrope Hypermetrope Myope 4.50 4.00 3.50 3.00 2.50 2.00 Rev Mex OftalMOl (eng). 2022;96(4) 158 Table 1. Sex‑based Kolmogorov‑Smirnov normality test Components Groups Mean Standard deviation T statistic p‑value Age Men 25 3.27 0.12 0.20* Women 24.23 1.76 0.06 0.20* Total 25 2.34 0.086 0.05* Spherical component Men 0.10 2.12 0.22 0.00 Women 0.21 1.14 0.12 0.00 Total 0.17 1.48 0.14 0.00 Cylindrical component Men −1.42 1.59 0.24 0.00 Women −0.89 0.83 0.25 0.00 Total −1.00 1.12 0.26 0.00 Axial length Men 23.92 0.99 0.10 0.20* Women 23.28 0.88 0.08 0.20* Total 23.46 0.96 0.08 0.09* Anterior chamber depth Men 3.60 0.22 0.07 0.20* Women 3.5 0.26 0.14 0.00 Total 3.54 0.25 0.11 0.00 Crystalline lens thickness Hombres 3.53 0.20 0.11 0.20* Men 3.47 0.22 0.12 0.00 Women 3.49 0.21 0.08 0.06* Corneal thickness Total 542.43 32.73 0.13 0.20* Men 538.65 36.06 0.05 0.20* Women 539.73 35.0 0.06 0.20* Mean keratometry Total 42.76 1.79 0.10 0.20* Women 43.54 1.35 0.07 0.20* Total 43.32 1.52 0.05 0.20* *Variables with normal distribution. Figure 3. Thickness of crystalline lens between men and women. Th ic kn es s of c ry st al lin e le ns Sex Men Women Classification of refraction errors Astigmatism Emetrope Hypermetrope Myope 4.00 3.50 3.00 2.50 2.00 Scatter plots between the mean biometrical compo- nents of CC and AL for men and women represented a negative direction for both cases with R2 ratios of 0.26 and 0.29, respectively; p > 0.05 (Fig. 6). Discussion Differences in the biometrical components between men and women were analyzed in this study. Regard- ing the distribution of refraction errors, it was found that a 23.6% (18) of women had hypermetropia while the vast majority of men had astigmatism (33.3% [10]) un- like what Attebo et al. and Wu et al.11,12 reported who described a higher prevalence of myopia in men. D. Rey-Rodríguez et al.: Biometric components of the eye between men and women 159 Table 2. Differences in the biometrical components of men and women Components Groups Mean differences p‑value 95% CI Higher Lower Age Men 1.27 0.11 0.29 2.25 Women 0.05 −0.00 2.55 Spherical component Men −0.11 0.73 −0.74 0.52 Women 0.79 −0.94 0.72 Cylindrical component Men −0.52 0.04* −1.03 −0.22 Women 0.11 0.32 −1.20 Axial length Men 0.63 0.02* 0.24 1.02 Women 0.04* 0.21 1.05 Anterior chamber depth Men 0.08 0.11 −0.21 0.19 Women 0.09 −0.1 0.18 Crystalline lens thickness Men 0.08 0.20 −0.03 0.15 Women 0.19 −0.03 0.15 Corneal thickness Men 3.78 0.62 −11.28 18.84 Women 0.60 −10.79 18.35 Mean keratometry Men −0.78 0.01* −1.41 −0.14 Women 0.03* −1.51 −0.05 *Variables with statistically significant differences (p < 0.05). Figure 4. Corneal thickness between men and women. C or ne al th ic kn es s Sex Men Classification of refraction errors Women Astigmatism Emetrope Hypermetrope Myope The mean AL in women was lower compared to men, which is consistent with former studies.10-14 These stud- ies indicate that the mean AL values in men and the radius of curvature are greater compared to the mean values shown by women. Regarding the anterior chamber, men have greater depth, data that are consistent with the study conducted by Orucoglu et al.15 who claim that women have less deep ACDs, which can be due to the size of the female eyeball that is smaller compared to men. Similarly, the thickness of the crystalline lens and the cornea was larger in men. While the mean keratometry values show a more curved tendency in women (women, 43.54D, and men 42.76D),16,17 data that are similar to those from the study Figure 5. Corneal curvature between men and women. M ea n ke ra to m et ry v al ue s Sex Classification of refraction errors Men Women Astigmatism Emetrope Hypermetrope Myope 49.000 48.000 47.000 46.000 45.000 44.000 43.000 42.000 41.000 40.000 39.000 38.000 37.000 36.000 Rev Mex OftalMOl (eng). 2022;96(4) 160 conducted by De Bernardo et al.6 who found that that keratometry measurements were larger in women. De Bernardo et al. (2020) found differences in the CC of men and women by identifying a steeper curvature in women (44.27 ± 1.36 D) compared to men (43.54 ± 1.35 D).6 Similarly, Ferrer-Blasco et al.7 agreed on these differences being of up to 0.50D or 0.10 mm more curved the ker- atometry values measured in women. The association between AL and CC can be explained by the fact that a smaller eye will always try to compensate its size with a more inclined curvature.14-19 Several population studies have described the pos- sible association between the ACD and anthropometry, and state that there is a positive correlation between taller heights and longer ALs, deeper anterior cham- bers, greater vitreous cavity distances, flatter corneas, and thinner crystalline lenses compared to individuals of lower height, weight, age, and different sex.13,16,17,20 Similarly, the association between ametropies and biometric measurements5,9,21 has been studied reveal- ing that values change gradually with age.21,22 For ex- ample, in children between 7 and 15  years old, the biometrical values associated with ametropies are AL, ACD, and the radius of CC being the correlation stron- gest with high ametropies.9,23,24 AL is longer in men (24.57 mm ± 1.78 mm) compared to women (24.07 mm ± 1.74 mm). However, shorter ALs have been reported associated with age in both sexes.6 This study tried to reduce biases by making the same examiner assess refractive errors and calibration be- fore every examination day. Furthermore, three mea- surements were made in each case. However, there were study limitations associated with the lack of sam- ple randomization being the selection of the population of interest that of the investigator himself. We should mention that group distribution was asymmetrical with more participation from women. The future studies should take age groups into con- sideration regarding the identification of biometrical dif- ferences between men and women. Conclusion There are significant and clinical differences in AL and CC between men and women. Women have a shorter AL and a more curved CC. However, age caus- es changes in the biometrical components, which should be studied in detail. Similarly, the future studies should be performed to identify all possible associa- tions between the anthropometrical measurements and the biometrical characteristics of both sexes. Funding None. Conflict of interests None. Ethical disclosures Protection of people and animals. The authors de- clare that no experiments on humans or animals have been carried out for this experiments on human beings and animals. Confidentiality of data. The authors declare that no patient data appear in this article patients. Right to privacy and informed consent. The authors declare that no patient data appear in this article. References 1. Price MS. Corrección de la hipermetropía simple y astigmatismo hiper- metrópico en niños de 0-4 años. Cienc Tecnol Salud Vis Ocul. 2007;9: 105-15. 2. Özdemir Ö, Tunay ZO, Acar DE. Growth of biometric components and development of refractive errors in premature infants with or without retinopathy of prematurity. Turk J Med Sci. 2016;46: 468-73. 3. 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