
==== Front
Sci Rep
Sci Rep
Scientific Reports
2045-2322
Nature Publishing Group UK London

39261545
72426
10.1038/s41598-024-72426-8
Article
Reduced retinol (vitamin A) and α-tocopherol (vitamin E) blood levels and increased myeloperoxidase (MPO) activity in children with high myopia
Mikoluc Bozena bozenam@mp.pl

1
Sawicka-Powierza Jolanta 2
Berk Klaudia 3
Maciejczyk Mateusz 4
Powierza Katarzyna 5
Zalewska Anna 67
Szulimowska Julita 7
MacDonald Justyna 8
Koput Alicja 9
Karpinska Joanna 10
Sawczuk Roza 10
Hryniewicka Marta 10
Bakunowicz-Lazarczyk Alina 11
1 https://ror.org/00y4ya841 grid.48324.39 0000 0001 2248 2838 Department of Pediatrics, Rheumatology, Immunology and Metabolic Bone Diseases, Medical University of Bialystok, Białystok, Poland
2 https://ror.org/00y4ya841 grid.48324.39 0000 0001 2248 2838 Department of Family Medicine, Medical University of Bialystok, Białystok, Poland
3 https://ror.org/00y4ya841 grid.48324.39 0000 0001 2248 2838 Department of Physiology, Medical University of Bialystok, Białystok, Poland
4 https://ror.org/00y4ya841 grid.48324.39 0000 0001 2248 2838 Department of Hygiene, Epidemiology and Ergonomics, Medical University of Bialystok, Białystok, Poland
5 https://ror.org/04p2y4s44 grid.13339.3b 0000 0001 1328 7408 Department of Diabetology and Internal Medicine, Medical University of Warsaw, Warsaw, Poland
6 grid.48324.39 0000000122482838 Experimental Dentistry Laboratory, Medical University of Bialystok, Białystok, Poland
7 https://ror.org/00y4ya841 grid.48324.39 0000 0001 2248 2838 Department of Conservative Dentistry, Medical University of Bialystok, Białystok, Poland
8 https://ror.org/00y4ya841 grid.48324.39 0000 0001 2248 2838 Department of Foreign Languages, Medical University of Bialystok, Białystok, Poland
9 https://ror.org/00y4ya841 grid.48324.39 0000 0001 2248 2838 Department of Pediatric Laboratory Diagnostics, Medical University of Bialystok, Białystok, Poland
10 https://ror.org/01qaqcf60 grid.25588.32 0000 0004 0620 6106 Faculty of Chemistry, University of Bialystok, Białystok, Poland
11 https://ror.org/00y4ya841 grid.48324.39 0000 0001 2248 2838 Department of Pediatric Ophthalmology and Strabismus, Medical University of Bialystok, Białystok, Poland
11 9 2024
11 9 2024
2024
14 2123119 9 2023
6 9 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
The study assessed selected parameters of redox status in the plasma of patients suffering from high myopia (HM). Thirty-five children with mean age 13.7 ± 2.7 years with HM and 40 healthy children were included. Plasma redox status parameters were determined using colorimetric kits. The levels of retinol, α-tocopherol and coenzyme Q10 were determined with a high-performance liquid chromatograph. Negative correlations were observed between the concentrations of retinol and the axial length of the eye (r = − 0.514 p < 0.001). Increased myeloperoxidase (MPO) activity (p < 0.018), and decreased concentrations of retinol (p < 0.001) and α-tocopherol (p < 0.023) in patients with HM and the axial length of the eye > 26 mm compared to controls were established. Significantly lower retinol and α-tocopherol concentrations were found in patients with the axial length of the eye > 26 mm compared to those with the axial length of the eye ≤ 26 mm (p < 0.001, p < 0.021, respectively). Increased MPO activity in advanced stages of HM may confirm an inflammatory process in HM patients. Reduced retinol and α-tocopherol concentrations and their link to disease progression indicate a need for monitoring their levels and supplementation in children with HM.

Subject terms

Biomarkers
Health care
Medical research
issue-copyright-statement© Springer Nature Limited 2024
==== Body
pmcIntroduction

Myopia is now a global health issue affecting 1.4 billion people, with an anticipated 4.7 billion people (49.8% of the world population) developing myopia by 2050. As many as 163 million people suffer from high myopia (HM). In Europe, myopia prevalence is around 24.3% with an age-standardized prevalence of 30.6%1. Visual impairment, which is mainly due to retinal alterations, has been associated with longer axial length, thereby highlighting the importance of determining the axial length of the eyes in myopic children and adolescents with the use of a biometer 2–4. HM is typically described as spherical equivalent (SE) equal or lower than ( ≤) − 6.00 diopters (D) or the axial length of the eye higher than ( >) 26 mm.

Despite numerous studies on myopia, the etiopathogenesis of this condition remains unresolved. Both genetic and environmental factors, and complex interactions between them (epigenetics), as well as two major mechanisms at the cellular level oxidative stress and inflammatory processes are taken into consideration4–7. Among the causes of myopia, the significance of growth factors that influence eyeball growth, including transforming growth factor (TGF-β), basic fibroblast growth factor (bFGF), and insulin-like growth factor (IGF), is recognized 8. Genetic variants of cytokine fibroblast growth factor 10 (FGF10) have also been found to cause myopia and HM in young children 9. A relationship between three factors: myopia, oxidative stress and growth factors: vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) has been confirmed 9. The presented pathomechanisms have been identified both in animal models and in studies investigating selected parameters in the human eyeball. Apart from the above-mentioned growth factors, neurotransmitters (dopamine, serotonin, melatonin), crystallin, vasoactive intestinal peptide and enkephalins as well as glucagon, retinoic acid and retinoic acid receptors are also considered potential causes of the disease 9.

Literature data indicate that retinol (Vitamin A) and α-tocopherol (Vitamin E) play different but complementary roles in the context of myopia. Both vitamins work synergistically to enhance the overall antioxidant defense of the eyes through neutralizing free radicals, protecting cell membrane lipids and cooperating with other antioxidants. Vitamin A can prevent or slow down the development of myopia through its actions in rhodopsin regeneration, retinal protection and cell growth regulation. It also plays a crucial role in the expression of genes related to eye development, mainly through its active form, retinoic acid. 10. Vitamin E supports microcirculation in the eye, protecting retinal photoreceptor cells and regulating apoptosis, which can help in preventing and slowing the progression of myopia11.

Some studies suggest that high levels of myeloperoxidase (MPO) and the associated oxidative stress may be involved in the pathogenesis of myopia. MPO may influence myopia by inducing oxidative stress and inflammation in the eye. Reactive oxygen species (ROS) produced by MPO can damage retinal cells and other ocular structures, contributing to the development or progression of myopia. Although further research is needed to fully understand the role of MPO in myopia, current evidence suggests that controlling oxidative stress and inflammation may be an important component of myopia prevention and treatment strategies12.

Hyaluronic acid depolymerisation induced by oxygen free radicals, which occur in myopic patients with a detached retina, is also of great significance 13.

Redox imbalance and the protective effect of antioxidants have been confirmed in many eye diseases associated with high myopia 14, e.g., age-related macular degeneration 15, age-related cataract 16,17 or glaucoma 18.

Taking into consideration the established pathomechanisms of oxidative stress in myopia, we aimed to assess plasma enzymatic and non-enzymatic antioxidant parameters, oxidative damage markers of lipids, proteins and DNA as well as the MPO activity and the concentrations of coenzyme Q10, vitamins A and E in HM children compared to a healthy control group.

Material and methods

Study population

A cross-sectional study included children and adolescents suffering from HM recruited from the Department of Pediatric Ophthalmology and Strabismus, Medical University of Bialystok, Poland. The control group consisted of healthy age- and sex-matched individuals without myopia (based on ophthalmological examination) who attended the Specialist Dental Clinic (Department of Pediatric Dentistry) of the Medical University of Bialystok for standard check-ups. All the children in the study and control groups followed a similar diet (one consistent with Polish nutritional recommendations for healthy children) without any vitamin or antioxidant supplementation and spent 2 h daily outdoors.

The study excluded patients with chronic and systemic inflammatory diseases, arterial hypertension, diabetes mellitus, kidney diseases, hyperthyroidism, anterior or posterior eye segment diseases and those using systemic medication (e.g., steroids, nonsteroidal anti-inflammatory drugs, vitamins). All participants were healthy at the beginning of the study, with no signs of infection and negative health markers of inflammation (C-reactive protein, CRP; leukocytosis; erythrocyte sedimentation rate, ESR).

The following inclusion criteria for children with HM were applied: a spherical equivalent (SE) ≤  − 6.0 diopters (D) and normal intraocular pressure, and the difference in refractive error between the right and left eye no greater than − 1D.

Forty patients with HM and forty healthy children took part in the study. Five children with HM were excluded as they did not meet the eligibility criteria. Ultimately, 35 Caucasian children with HM (21 girls and 14 boys) aged 7–17 years, mean age 13.7 ± 2.7 years, with SE ≤  − 6.0 D, and 40 healthy children without HM and with hyperopia + 0.25 −  + 1.25D (21 girls, 19 boys), aged 7–17 years, mean age 13.3 ± 2.8 years, matched for age and sex were included in the study. Intraocular pressure in both the HM group and the control group (n = 75) was within the normal range, varying from 11 to19 mmHg. All participants or their legal guardians (in the case of children under 16) provided informed consent to participation in the study.

The study was conducted in accordance with the Declaration of Helsinki Guidelines for Biomedical Research Involving Human Subjects. The Ethics Committee of the Medical University of Bialystok, Poland provided their approval for this study (No: R-I- 002/395/2019).

Measurements

In patients with HM, a comprehensive ophthalmological examination that included refraction error measurement using cycloplegic 1% Tropicamidum 3 × 15 min refraction with the TONOREF™ Nidek autorefractokeratometer with a pachymeter, intraocular pressure measurement using the TonoPen, slit-lamp examination and dilated fundus examination using the + 78 D and + 90 D Volk lenses was performed. An ultrasound A scan Quantel Medical AVISO device was used to measure the axial length of both eyes. Using the contact method, ten measurements were taken for each eye to obtain an average value. The immersion method did not work due to a lack of cooperation from the child during the examination. In healthy controls, visual acuity and intraocular pressure were measured.

Blood samples

After an overnight fast, venous blood (5 mL) was collected from each participant into tubes containing ethylenediaminetetraacetic acid (S-Monovette® EDTA-K3, Sarstedt, Germany) and into tubes with clot activator (S-Monovette® Clotting Activator/Serum, Sarstedt, Germany). Following the manufacturer’s instructions, the samples were protected from light, centrifuged (2000×g for 10 min at + 4 °C), after which plasma and serum was instantly separated. Plasma and serum samples were frozen at − 80 °C until the assays were performed, for a period not exceeding 6 months.

Redox status

Commercial colorimetric kits (ImAnOx (TAS/TAC) Kit, Immundiagnostik, Bensheim, Germany and PerOx (TOS/TOC) Kit, Immundiagnostik, Bensheim, Germany, respectively) were used to determine plasma redox status parameters: total antioxidant status (TAS) and total oxidant status (TOS). We measured the resulting colored products with the colorimetric method at 450 nm. The formula: OSI = TOS/TAS was used to calculate oxidative stress index (OSI) 19.

Redox assays

The following were analyzed: antioxidant enzymes: glutathione peroxidase (GSH-Px, E.C. 1.11.1.9), catalase (CAT, E.C. 1.11.1.6), glutathione reductase (GR, EC 1.8.1.7) and superoxide dismutase-1 (SOD, E.C. 1.15.1.1); pro-oxidant enzymes: myeloperoxidase (MPO, EC 1.11.1.7); nonenzymatic markers of oxidative protein damage: advanced glycation end-products (AGE) and advanced oxidation protein products (AOPP), markers of oxidative damage of lipids: 8-isoprostanes (8-epi-PGF2 alpha) and 8-hydroxy-2’-deoxyguanosine (8-OHdG) as an oxidative DNA damage marker. Infinite M200 PRO Multimode Microplate Reader (Tecan Group Ltd., Männedorf, Switzerland) was used to measure absorbance/fluorescence. Duplicate samples were used in all assays and the results were standardized for 100 mg of total protein.

The measurement of serum GSH-Px activity was performed with a method based on the conversion of NADPH to NADP+, as described by Paglia et al. 20.

Spectrophotometry was used to determine serum CAT activity with hydrogen peroxide (H2O2) decomposition measured at 340 nm 21.

Serum GR activity was also evaluated spectrophotometrically at 340 nm by determining a decrease in NADPH absorbance 22,23.

Serum SOD activity was assayed spectrophotometrically by inhibiting the oxidation of epinephrine to adrenochrome 24.

Serum MPO activity was assessed by colorimetry using sulfanilamide, ortho-dianisidine dihydrochloride, hexadecyltrimethylammonium and hydrogen peroxide 25.

The method of Kalousová et al. was used to determine plasma AGE content by way of spectrofluorimetry. Plasma samples fluorescence was assessed at excitation wavelength 440 nm and emission wavelength 350 nm 19,26.

Spectrophotometry was employed to analyze plasma AOPP concentrations by measuring the oxidative capacity of the iodine ion at 340 nm 27.

Plasma 8-isop and 8-OHdG concentrations were determined using an enzyme-linked immunosorbent assay (ELISA) (Cell Biolabs, Inc. San Diego, CA, USA; Cayman Chemicals, Ann Arbor, MI, USA; USCN Life Science, Wuhan, China, respectively) 28,29.

A high-performance liquid chromatograph coupled to an MS detector equipped with a triple quadrupole (Shimadzu LCMS/MS-8040) was used to analyze plasma lipophilic antioxidants (retinol, α-tocopherol, coenzyme Q10) (Fig. 1). Plasma samples were prepared according to the previously published procedure 30.Fig. 1 Chromatogram of real sample: retinol, tR = 0.851 min, α-tocopherol, tR = 1.502 min, CoQ10, tR = 5.468 min.

Statistical analysis

Statistical analysis was performed using STATISTICA version 13. The Shapiro–Wilk test was used to check the normality of distribution of variables. Qualitative characteristics were shown as numbers and percentages. Quantitative parameters were expressed as medians and quartiles (Q1, Q3). The Pearson chi-square test was employed to compare the structure of the subgroups by gender and age. The Mann–Whitney U-test was used to assess the differences between the study group and controls. Non-parametric ANOVA (test of mean ranks for 3 groups) was used to compare controls with two subgroups of the study group (high myopia patients with the axial length of the eye equal or lower than 26 mm and higher than 26 mm). In the group of children with HM, the length of the eye in the right and left eyeball were measured. The differences between the right and left eyes were insignificant, and therefore we decided to use the variable defined as the length of the eye (the greatest selected from both eyes). Correlations between parameters were assessed using Spearman’s rank correlation coefficient. Disparities in the values of the analyzed parameters and correlations were considered statistically significant at p < 0.05.

Results

There were no significant differences in the girls-to-boys ratio between the groups.

(children with HM and the control group) (male/female, n(%): 14(40)/21(60) vs. 19(47.5)/21(52.5, p < 0.514). There were also no significant age differences between the groups (n(%),10(28.6)/25(71.4) vs 16(40)/24(60), p < 0.300). All the children from the control group had proper visual acuity. Children with the axial length of the eye higher than 26 mm (12 children) had chorio-retinal vascular atrophy at the periphery of the fundus involving 1 to 2 quadrants in the lower quadrants of the fundus, which did not require treatment. Clinical characteristics of children with HM are summarized in Table 1.Table 1 Clinical characteristics of children with HM.

Parameter	High Myopia children	High Myopia with Axial Length of Eye	
n = 35	 ≤ 26 mm, n = 23	 > 26 mm, n = 12	
Refractive error of the right eye, D	− 7.00 (− 8.50; − 6.00)	− 6.75 (− 8.0; − 5.75)	− 7.50 (− 14.00; − 6.50)	
Refractive error of the left eye, D	− 6.75 (− 8.25; − 6.00)	− 6.75 (− 7.75; − 6.0)	-8.13 (− 12.50; − 6.25)	
Axial length of the right eye, mm	25.63 (25.27; 26.11)	25.42 (25.22; 25.76)	26.34 (26.1; 28.88)	
Axial length of the left eye, mm	25.43 (25.05; 26.00)	25.19 (25.04; 25.68)	26.42 (25.99; 27.98)	
Intraocular pressure of the right eye, mm Hg	16 (15; 18)	17 (15; 18)	16 (14.5; 16.5)	
Intraocular pressure of the left eye, mm Hg	17 (14; 18)	18 (15; 19)	16.5 (14; 17)	
Data are presented as median and quartiles (Q1; Q3)- All parameters exhibit a distribution significantly different from normal.

D, diopter; mmHg, millimeter of mercury; ≤ 26 mm, equal or lower than 26 mm; > 26 mm, higher than 26 mm.

Redox Status, proteins, lipids and DNA oxidation products, enzymatic and non-enzymatic antioxidants in HM patients and the control group are shown in Table 2.Table 2 Redox Status, proteins, lipids and DNA oxidation products, enzymatic and non-enzymatic antioxidants in high myopia patients with the axial length of the eye equal or lower than 26 mm and higher than 26 mm and the control group.

Parameter	High Myopia	High Myopia with the Axial Length of the Eye	Control Group	p < Values	
	 ≤ 26 mm	 > 26 mm						
A	B	C	D	A vs D	B vs C	B vs D	C vs D	
Number, n	35	23	12	40					
Redox status	
 TASa, µmol/l	357.9

(265.2; 393.6)

	377.2

(271.7; 393.8)

	283.9

(259; 378.7)

	280.5

(253.9; 380.9)

	NS	NS	NS	NS	
 TOSb, µmol/l	394.1

(220.4; 553.2)

	415.9

(226.2; 553.2)

	335.8

(182.5; 550.6)

	405.3

(291.8; 489.2)

	NS	NS	NS	NS	
 OSIa	1.24

(0.57; 1.53)

	1.38

(0.57; 1.53)

	1.03

(0.63; 1.52)

	1.45

(0.74; 2.12)

	NS	NS	NS	NS	
Proteins, lipids and DNA oxidation products	
 AGEa, pg/mL	1758

(754; 4624)

	1778

(955; 2630)

	1349

(141; 5888)

	1338

(706; 2188)

	NS	NS	NS	NS	
 AOPPb, pg/mL	6098

(4942; 8279)

	5606

(4942; 8123)

	6583

(4512; 8295)

	6797

(5113; 8011)

	NS	NS	NS	NS	
 8-epi-PGF2 alphab, pg/mL	2.64

(2.45; 2.76)

	2.66

(2.48; 2.78)

	2.57

(2.41; 2.76)

	2.62

(2.46; 2.86)

	NS	NS	NS	NS	
 8-OHdGb pg/mL	72.8

(53.6; 134.0)

	68.7

(53.4; 133.7)

	89.2

(53.6; 147.1)

	130.0

(93.3; 159.5)

	0.009	NS	0.016	0.096	
Enzymatic antioxidants and pro-oxidant enzymes	
 CATb nmol/min/mg protein	0.77

(0.64; 0.90)

	0.70

(0.57; 0.90)

	0.81

(0.67; 0.93)

	0.91

(0.78; 1.05)

	0.066	NS	NS	NS	
 GSH-Pxb mU/mg protein	0.47

(0.44; 0.49)

	0.46

(0.44; 0.48)

	0.49

(0.47; 0.53)

	0.47

(0.42; 0.50)

	NS	NS	NS	NS	
 GRb mU/mg protein	51.76

(48.18; 57.65)

	50.10

(47.91; 56.14)

	52.84

(51.76; 57.80)

	51.45

(47.78; 53.91)

	NS	NS	NS	NS	
 SODb mU/mg protein	0.11

(0.04; 0.14)

	0.09

(0.01; 0.15)

	0.11

(0.09; 0.14)

	0.11

(0.08; 0.13)

	NS	NS	NS	NS	
 MPOa mU/mg protein	50.24

(47.15; 53.36)

	49.61

(46.78; 50.36)

	53.17

(49.72; 56.93)

	49.36

(47.43; 50.54)

	NS	NS	NS	0.018	
Non-enzymatic antioxidants	
 Coenzyme Q10a, µg/ml	0.09

(0.06; 0.10)

	0.09

(0.06; 0.10)

	0.08

(0.05; 0.11)

	0.08

(0.06; 0.14)

	NS	NS	NS	NS	
 α-Tocopherola, µg/ml	0.94

(0.70; 1.15)

	1.04

(0.72; 1.25)

	0.80

(0.51; 1.00)

	1.01

(0.75; 1.57)

	NS	0.021	NS	0.023	
 Retinola, µg/ml	0.09

(0.04; 0.13)

	0.12

(0.06; 0.16)

	0.04

(0.03; 0.04)

	0.12

(0.07; 0.18)

	0.028	0.001	NS	0.001	
AGE, advanced glycation end products; AOPP, advanced oxidation protein products; CAT, catalase activity; GR, glutathione reductase activity; GSH-Px, glutathione peroxidaseactivity; MPO, myeloperoxidase activity; OSI, oxidative stress index; SOD, superoxide dismutase-1activity; TAS, total antioxidant status; TOS, total oxidant status; 8-OHdG, 8-hydroxydeoxyguanosine; 8-epi-PGF2 alpha, 8-Epi-prostaglandin F2 alpha.

NS—p > 0.1

aSignificantly skewed distribution.

bApproximately normal distribution Data are presented as median and quartiles (Q1; Q3). Statistically significant < 0.05 by Mann–Whitney U-test.

The concentrations of retinol (Vitamin A), α-tocopherol (Vitamin E), and myeloperoxidase (MPO) in children with HM and with axial length of the eye equal or lower than 26 mm and higher than 26 mm compared to the control group are shown in Fig. 2.Fig. 2 Concentrations of retinol, α-tocopherol and MPO in children with HM compared to the control group. Abbreviations: D, diopter; mmHg, millimeter of mercury; <  = 26 mm, the axial length of eye equal or lower than 26 mm; > 26 mm, the axial length of eye higher than 26 mm, myeloperoxidase (MPO).

Decreased concentrations of 8-OHdG and retinol were observed in children with HM compared to controls.

In further analysis, we compared the studied parameters between two groups of patients with HM: those with the axial length of the eye equal or lower than 26 mm and those with the axial length of the eye higher than 26 mm, and then compared both to the control group.

Decreased 8-OH-dG concentrations in children with the axial length of the eye equal or lower than 26 mm in comparison to the control group were noted (p < 0.016). Other parameters did not differ between the two groups.

Increased MPO activity (p < 0.018), and decreased concentrations of retinol (p < 0.001) and α-tocopherol (p < 0.023) in patients with the axial length of the eye higher than 26 mm compared to controls were established.

Furthermore, decreased retinol and α-tocopherol levels were found in patients with HM and the axial length of eye higher than 26 mm (p < 0.001) compared to children with the axial length of eye equal or lower than 26 mm (p < 0.021).

In patients with HM, there were weak negative correlations between the concentrations of retinol and α-tocopherol, and the axial length of the eye (r = -0.588, p < 0.000; r = -0.386, p < 0.026, respectively).

No significant correlations between retinol, α-tocopherol and the refractive errors in both eyes were found. However, the analysis revealed positive correlations between the concentrations of retinol and α-tocopherol (r = 0.692, p < 0.001) (Fig. 3).Fig. 3 Correlation between retinol and α-tocopherol in HM children.

Discussion

The study demonstrated that total antioxidant status (TAS), total oxidant status (TOS) oxidative stress index (OSI) and plasma markers of oxidative damage to proteins and lipids in the group of children with HM were comparable to those of healthy children. Furthermore, antioxidant enzyme activity (CAT, SOD, GSH-Px and GR) in HM patients was comparable to healthy children.

We found a significantly decreased concentration of 8-OHdG, a product of oxidative DNA damage, in patients with HM and the axial length of the eye ≤ 26 mm. Patients with the axial length of the eye > 26 mm also showed a tendency towards lower 8-OHdG concentrations in comparison to the control group. Literature data show that 8-OHdG levels are lower in the aqueous humor of highly myopic eyes in comparison to the control group (cataractous eyes) 31. However, other studies, such as that by Micelli-Ferrari et al. (1996), report contradictory findings 17. Moreover, Zhu et al. (2018) pointed to the downregulation of antioxidant genes in highly myopic eyes due to DNA hypermethylation 32. The decreased concentration of 8-OHdG in the aqueous humor found by Kim et al. 31 and the decreased plasma concentration of this marker in our study may suggest that 8-OHdG is a sensitive indicator of redox homeostasis in HM. This bold suggestion requires further research.

We demonstrated that in HM children with the axial length of the eye > 26 mm, MPO activity was significantly higher compared to healthy participants. MPO is a highly sensitive marker of an ongoing inflammatory process which is not significantly related to other markers of inflammation. Numerous studies on MPO prove the universal function of this enzyme not only in inflammatory processes, but also in oxidative stress, and accordingly in the pathogenesis of many diseases 33. It should be emphasized that our study was conducted on a group of healthy children with HM, with no signs of infection. At the current level of knowledge, the enhanced activity of MPO in children with HM remains an open issue. It would be too daring to claim that increased MPO activity may be a good indicator of early inflammation and a marker of disease progression in patients with HM. Further research is required to corroborate this hypothesis. There are data in the available literature suggesting that low-grade intraocular inflammation may be a causal factor in the development and progression of HM. A significant positive association has been found between the levels of Interleukin 6 (IL-6) and matrix metalloproteinase-2 (MMP-2) in the aqueous humour, and the axial length of the eye 34.

These findings, without overinterpreting our results, contribute to the discussion on the inflammatory aspect in HM through the observed increased activity of MPO in serum. MPO values ​​are higher in patients with HM and the axial length of the eye > 26 mm.

Our study showed a reduced concentration of retinol and α-tocopherol in patients with HM and the axial length of the eye > 26 mm. In HM children, weak negative correlations between the axial length of the eye and the concentrations of retinol and α-tocopherol were also observed. The concentrations of coenzyme Q10 in children with HM were comparable to those in healthy children.

From the available literature data on the influence of vitamin A deficiency on the occurrence of myopia, studies by Ng et al. 33 confirmed its significance. The authors failed to find a relationship between vitamin A intake and refractive errors. However, based on available animal studies, they pointed to the theoretical possibility of its occurrence. They also emphasized that there is a significant link between myopia and low vitamin A status, indicating that, although a linear relationship between vitamin A and progression of myopia does not seem to exist, there may be a threshold where the risk is increased with deficient levels of vitamin A 33. This indicates that retinoic acid acts as a chemical signal that regulates eye growth. One possible pathway that the authors proposed is that vitamin A deficiency, or transcription issues of related genes for retinoic acid metabolism, may cause insufficient production of retinoic acid. Consequently, this can cause issues for the eye growth and bring about abnormal axial elongation, resulting in myopia. It should be noted that vitamin A status was assessed in our study participants while they were in a fasting state. Generally, under fasting conditions, one would have expected retinol concentrations in the serum (Retinol-binding protein 4 [RBP4] bound all-trans-retinol [ROL]) to be higher. Lower serum retinol levels, under fasting conditions, would indicate either decreased RBP4-ROL secretion or decreased Retinyl Esters/ROL concentrations in the liver 35.

We would like to emphasize that retinol concentration needs to be monitored in children with myopia as it is one of the factors that may have a potential impact on disease progression. This is even more evident in the light of the fact that vitamin A is responsible for the stabilization of cell membranes, vision processes, tissue growth and regeneration, and the proper functioning of the immune system 36. Our research results provide a basis for discussion regarding the evaluation of factors influencing the concentration of antioxidant vitamins in children with myopia. Further studies linking the concentrations of vitamin A in the plasma, retinol-binding protein and prealbumin in relation to disease duration would be needed. Although it has not been demonstrated that sufficient intake of vitamin A during adolescence is linked to a lower risk of developing myopia in early adulthood, our results confirm a negative correlation between the axial length of the eye and retinol concentration. Undetected vitamin A deficiency, which might exist in developed countries, could be linked to various pathologies 33.

Vitamin E includes eight different substances, but our body only uses one of them: α-tocopherol, which accounts for around 87% of the total pool of vitamin E. Thanks to the presence of the phenolic group, vitamin E has a strong antioxidant effect, and as the so-called "chain-breaking antioxidant" effectively prevents excessive production of free radicals in cell membranes and other lipid structures 37. Vitamin E has been known to decrease the risk of cataracts and age-related macular degeneration (AMD). Its positive role in improving vision is also recognized. However, it should be remembered that the influence of vitamin E on eye diseases is not unambiguous. There are reports in the literature which show that Vitamin E administered for four years at 500 IU daily fails to curtail the incidence or progression of nuclear, cortical or posterior subcapsular cataracts.

A systematic review and meta-analysis of ocular biometric parameters in children and adolescents confirmed that axial length is closely associated with myopia. The study demonstrated that a longer axial length correlates with a higher degree of myopia while other factors, such as central corneal thickness and anterior chamber depth, also play a role, but a less significant one. Despite its crucial role in overall eye health, direct correlations between retinol levels and axial length or refractive errors are not well-established in the literature 38.

The relationship between retinol, alpha-tocopherol, axial length and refractive errors involves complex mechanisms in which these vitamins support overall ocular health, potentially influencing factors that contribute to refractive errors. However, the direct impact of these vitamins on axial length and refractive errors requires further investigation. Understanding these relationships better could help develop strategies for preventing and managing myopia and other refractive errors.

Our study confirmed the relationship between the severity of myopia and reduced concentrations of vitamin E. This indirectly indicates the presence of redox imbalance in myopia and the need for further research on the role of vitamin E in myopia, apart from its antioxidant effect. Since vitamin E, similarly to vitamin A, belongs to the group of fat-soluble vitamins and its absorption efficiency ranges from 25 to 75% and largely depends on fat content in the diet, more attention should be paid to the type of diet consumed by patients with myopia in order to naturally supplement these vitamins. This is confirmed by the positive correlation observed in the present study between the concentrations of retinol and α-tocopherol.

In conclusion, we proved increased MPO activity in advanced stages of HM with the axial length of the eye higher than 26 mm, which may indicate an inflammatory process in these patients. Reduced concentrations of retinol (Vitamin A) and α-tocopherol (Vitamin E) in HM children with the axial length of the eye higher than 26 mm and their link to disease progression indicate a need for both monitoring their levels and supplementation in patients with HM and the axial length of the eye higher than 26 mm. The present study demonstrated a strong correlation between the concentrations of retinol and α-tocopherol in HM children and increased serum MPO activity in children with the axial length of the eye higher than 26 mm.

These findings imply the presence of redox imbalance and the potential involvement of an inflammatory process in the progression of HM. To address these issues, we recommend a collaborative approach between ophthalmologists, GPs and dietitians to monitor and manage the levels of antioxidant vitamins in HM patients. Their diet should be adjusted so that Vitamins A and E are obtained naturally, but supplemented when necessary. Monitoring patients' vitamin intake ensures that they receive optimal amounts to sustain eye health and mitigate the progression of HM.

Author contributions

B.M., J.S.-P., K.K., M.M., A.B.-L.: conception. K.B., M.M., K.P., A.Z., J.S., A.K., J.K., R.S., M.H.: investigation. B.M., J.S.-P., M.M., K.P., J.M., A.B.-L.: writing the manuscript. B.M., J.S.-P., M.M., K.P., J.M., A.B.-L.: extensive editing and revision of the manuscript.

Data availability

The original data used to support the findings of this study are available from the corresponding author upon request.

Competing interests

The authors declare no competing interests.

Ethical approval

The study was reviewed and approved by the Bioethics Committee of the Medical University of Bialystok. Written informed consent to participate in this study was provided by the participants/legal guardians/next of kin.

Publisher's note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
==== Refs
References

1. Williams KM Increasing prevalence of myopia in Europe and the impact of education Ophthalmology. 2015 122 7 1489 1497 10.1016/j.ophtha.2015.03.018 25983215
Williams, K. M. Increasing prevalence of myopia in Europe and the impact of education. Ophthalmology. 122(7), 1489–1497. 10.1016/j.ophtha.2015.03.018 (2015).25983215 10.1016/j.ophtha.2015.03.018
2. Galvis V Tello A Rey JJ Serrano Gomez S Prada AM Estimation of ocular axial length with optometric parameters is not accurate Cont. Lens Anterior Eye 2022 45 10 10.1016/j.clae.2021.101448
Galvis, V., Tello, A., Rey, J. J., Serrano Gomez, S. & Prada, A. M. Estimation of ocular axial length with optometric parameters is not accurate. Cont. Lens Anterior Eye 45, 10. 10.1016/j.clae.2021.101448 (2022).10.1016/j.clae.2021.101448
3. Mérida S Imbalance between oxidative stress and growth factors in human high myopia Front. Physiol. 2020 10.3389/fphys.2020.00463 32508679
Mérida, S. et al. Imbalance between oxidative stress and growth factors in human high myopia. Front. Physiol.10.3389/fphys.2020.00463 (2020).32508679 10.3389/fphys.2020.00463
4. Lin HJ Sclera-related gene polymorphisms in high myopia Mol. Vis. 2009 15 1655 1663 19710942
Lin, H. J. et al. Sclera-related gene polymorphisms in high myopia. Mol. Vis. 15, 1655–1663 (2009).19710942
5. Wojciechowski R Nature and nurture: The complex genetics of myopia and refractive error Clin. Genet. 2011 79 301 320 10.1111/j.1399-0004.2010.01592.x 21155761
Wojciechowski, R. Nature and nurture: The complex genetics of myopia and refractive error. Clin. Genet. 79, 301–320. 10.1111/j.1399-0004.2010.01592.x (2011).21155761 10.1111/j.1399-0004.2010.01592.x
6. Galvis V Tello A Camacho PA Parra MM Merayo-Lloves J Bio-environmental factors associated with myopia: An updated review Arch. Soc. Esp. Oftalmol. 2017 92 7 307 325 10.1016/j.oftal.2016.11.016 28162831
Galvis, V., Tello, A., Camacho, P. A., Parra, M. M. & Merayo-Lloves, J. Bio-environmental factors associated with myopia: An updated review. Arch. Soc. Esp. Oftalmol. 92(7), 307–325. 10.1016/j.oftal.2016.11.016 (2017).28162831 10.1016/j.oftal.2016.11.016
7. Swierkowska J Vishweswaraiah S Mrugacz M Radhakrishna U Gajecka M Differential methylation of microRNA encoding genes may contribute to high myopia Front. Genet. 2023 13 1089784 10.3389/fgene.2022.1089784 36685896
Swierkowska, J., Vishweswaraiah, S., Mrugacz, M., Radhakrishna, U. & Gajecka, M. Differential methylation of microRNA encoding genes may contribute to high myopia. Front. Genet. 13, 1089784. 10.3389/fgene.2022.1089784 (2023).36685896 10.3389/fgene.2022.1089784
8. Guo L Du X Lu C Zhang WH Association between insulin-like growth factor 1 gene rs12423791 or rs6214 polymorphisms and high myopia: A meta-analysis PLoS ONE 2015 10.1371/journal.pone.01297078 26720585
Guo, L., Du, X., Lu, C. & Zhang, W. H. Association between insulin-like growth factor 1 gene rs12423791 or rs6214 polymorphisms and high myopia: A meta-analysis. PLoS ONE10.1371/journal.pone.01297078 (2015).26720585 10.1371/journal.pone.01297078
9. Morgan IG The biological basis of myopic refractive error Clin. Exp. Optom. 2003 86 5 276 788 10.1111/j.1444-0938.2003.tb03123.x 14558849
Morgan, I. G. The biological basis of myopic refractive error. Clin. Exp. Optom. 86(5), 276–788. 10.1111/j.1444-0938.2003.tb03123.x (2003).14558849 10.1111/j.1444-0938.2003.tb03123.x
10. Sajovic J The role of vitamin A in retinal diseases Int. J. Mol. Sci. 2022 23 1014 10.3390/ijms23031 35162940
Sajovic, J. et al. The role of vitamin A in retinal diseases. Int. J. Mol. Sci. 23, 1014. 10.3390/ijms23031 (2022).35162940 10.3390/ijms23031
11. Edwards G Olson CG Euritt CP Koulen P Molecular mechanisms underlying the therapeutic role of vitamin E in age-related macular degeneration Front. Neurosci. 2022 16 890021 10.3389/fnins.2022.8900219 35600628
Edwards, G., Olson, C. G., Euritt, C. P. & Koulen, P. Molecular mechanisms underlying the therapeutic role of vitamin E in age-related macular degeneration. Front. Neurosci. 16, 890021. 10.3389/fnins.2022.8900219 (2022).35600628 10.3389/fnins.2022.8900219
12. Siraki AG The many roles of myeloperoxidase: From inflammation and immunity to biomarkers, drug metabolism and drug discovery Redox Biology 2021 46 102109 10.1016/j.redox.2021.102109 34455146
Siraki, A. G. The many roles of myeloperoxidase: From inflammation and immunity to biomarkers, drug metabolism and drug discovery. Redox Biology 46, 102109. 10.1016/j.redox.2021.102109 (2021).34455146 10.1016/j.redox.2021.102109
13. McNeil JD Wiebkin OW Betts WH Cleland LG Depolymerisation products of hyaluronic acid after exposure to oxygen-derived free radicals. Ann. Rheumat. Diseases 1985 44 11 780 789 10.1136/ard.44.11.780 4062391
McNeil, J. D., Wiebkin, O. W., Betts, W. H. & Cleland, L. G. Depolymerisation products of hyaluronic acid after exposure to oxygen-derived free radicals.. Ann. Rheumat. Diseases 44(11), 780–789. 10.1136/ard.44.11.780 (1985).4062391 10.1136/ard.44.11.780
14. Haarman AEG The complications of myopia: A review and meta-analysis Investig. Ophthalmol. Vis. Sci. 2020 10.1167/iovs.61.4.49
Haarman, A. E. G. et al. The complications of myopia: A review and meta-analysis. Investig. Ophthalmol. Vis. Sci.10.1167/iovs.61.4.49 (2020).10.1167/iovs.61.4.49
15. Ye L Sulforaphane enhances the ability of human retinal pigment epithelial cell against oxidative stress, and its effect on gene expression profile evaluated by microarray analysis Oxid. Med. Cell Longev. 2013 10.1155/2013/413024 24187606
Ye, L. et al. Sulforaphane enhances the ability of human retinal pigment epithelial cell against oxidative stress, and its effect on gene expression profile evaluated by microarray analysis. Oxid. Med. Cell Longev.10.1155/2013/413024 (2013).24187606 10.1155/2013/413024
16. Kisic B Miric D Zoric L Ilic A Dragojevic I Antioxidant capacity of lenses with age-related cataract Oxid. Med. Cell Longev. 2012 10.1155/2012/467130 22363833
Kisic, B., Miric, D., Zoric, L., Ilic, A. & Dragojevic, I. Antioxidant capacity of lenses with age-related cataract. Oxid. Med. Cell Longev.10.1155/2012/467130 (2012).22363833 10.1155/2012/467130
17. Micelli-Ferrari T Role of lipid peroxidation in the pathogenesis of myopic and senile cataract Br. J. Ophthalmol. 1996 10.1136/bjo.80.9.840 8942384
Micelli-Ferrari, T. et al. Role of lipid peroxidation in the pathogenesis of myopic and senile cataract. Br. J. Ophthalmol.10.1136/bjo.80.9.840 (1996).8942384 10.1136/bjo.80.9.840
18. Chalasani ML A glaucoma-associated mutant of optineurin selectively induces death of retinal ganglion cells which is inhibited by antioxidants Investig. Ophthalmol. Vis. Sci. 2007 10.1167/iovs.06-0834
Chalasani, M. L. et al. A glaucoma-associated mutant of optineurin selectively induces death of retinal ganglion cells which is inhibited by antioxidants. Investig. Ophthalmol. Vis. Sci.10.1167/iovs.06-0834 (2007).10.1167/iovs.06-0834
19. Maciejczyk M Zalewska A Ładny JR Salivary antioxidant barrier, redox status, and oxidative damage to proteins and lipids in healthy children, adults, and the elderly Oxid. Med. Cell Longev. 2019 10.1155/2019/4393460 31885792
Maciejczyk, M., Zalewska, A. & Ładny, J. R. Salivary antioxidant barrier, redox status, and oxidative damage to proteins and lipids in healthy children, adults, and the elderly. Oxid. Med. Cell Longev.10.1155/2019/4393460 (2019).31885792 10.1155/2019/4393460
20. Paglia DE Valentine WN Studies on the quantitative and qualitative characterization of erythrocyte glutathione peroxidase J. Lab. Clin. Med. 1967 10.5555/uri:pii:0022214367900765 6066618
Paglia, D. E. & Valentine, W. N. Studies on the quantitative and qualitative characterization of erythrocyte glutathione peroxidase. J. Lab. Clin. Med.10.5555/uri:pii:0022214367900765 (1967).6066618 10.5555/uri:pii:0022214367900765
21. Misra HP Fridovich I The role of superoxide anion in the autoxidation of epinephrine and a simple assay for superoxide dismutase J. Biol. Chem. 1972 247 3170 3175 10.1016/S0021-9258(19)45228-9 4623845
Misra, H. P. & Fridovich, I. The role of superoxide anion in the autoxidation of epinephrine and a simple assay for superoxide dismutase. J. Biol. Chem. 247, 3170–3175 (1972).4623845 10.1016/S0021-9258(19)45228-9
22. Juchnowicz D Dzikowski M Rog J Oxidative stress biomarkers as a predictor of stage illness and clinical course of schizophrenia Front. Psychiatry 2021 10.3389/fpsyt.2021.728986 34867519
Juchnowicz, D. et al. Oxidative stress biomarkers as a predictor of stage illness and clinical course of schizophrenia. Front. Psychiatry10.3389/fpsyt.2021.728986 (2021).34867519 10.3389/fpsyt.2021.728986
23. Mize CE Langdon RG Hepatic glutathione reductase. I. Purification and general kinetic properties J. Biol. Chem. 1962 237 1589 1595 10.1016/S0021-9258(19)83745-6 14474846
Mize, C. E. & Langdon, R. G. Hepatic glutathione reductase. I. Purification and general kinetic properties. J. Biol. Chem. 237, 1589–1595. 10.1016/S0021-9258(19)83745-6 (1962).14474846 10.1016/S0021-9258(19)83745-6
24. Kruidenier L Imbalanced secondary mucosal antioxidant response in inflammatory bowel disease J. Pathol. 2003 201 17 27 10.1002/path.1408 12950013
Kruidenier, L. et al. Imbalanced secondary mucosal antioxidant response in inflammatory bowel disease. J. Pathol. 201, 17–27. 10.1002/path.1408 (2003).12950013 10.1002/path.1408
25. Choromańska B Bariatric surgery normalizes protein glycoxidation and nitrosative stress in morbidly obese patients Antioxidants 2020 10.3390/antiox9111087 33158288
Choromańska, B. et al. Bariatric surgery normalizes protein glycoxidation and nitrosative stress in morbidly obese patients. Antioxidants10.3390/antiox9111087 (2020).33158288 10.3390/antiox9111087
26. Kalousová M Škrha J Zima T Advanced glycation end-products and advanced oxidation protein products in patients with diabetes mellitus Physiol. Res. 2002 51 597 604 10.33549/physiolres.930234 12511184
Kalousová, M., Škrha, J. & Zima, T. Advanced glycation end-products and advanced oxidation protein products in patients with diabetes mellitus. Physiol. Res. 51, 597–604 (2002).12511184 10.33549/physiolres.930234
27. Niki E Assessment of antioxidant capacity in vitro and in vivo Free Radic. Biol. Med. 2010 10.1016/j.freeradbiomed.2010.04.016 20736061
Niki, E. Assessment of antioxidant capacity in vitro and in vivo. Free Radic. Biol. Med.10.1016/j.freeradbiomed.2010.04.016 (2010).20736061 10.1016/j.freeradbiomed.2010.04.016
28. Bosch-Morell F Sanz A Díaz-Llopis M Romero FJ Lipid peroxidation products in human subretinal fluid Free Radic. Biol. Med. 1996 20 899 903 10.1016/0891-5849(95)02219-8 8743976
Bosch-Morell, F., Sanz, A., Díaz-Llopis, M. & Romero, F. J. Lipid peroxidation products in human subretinal fluid. Free Radic. Biol. Med. 20, 899–903. 10.1016/0891-5849(95)02219-8 (1996).8743976 10.1016/0891-5849(95)02219-8
29. England T The steady-state levels of oxidative DNA damage and of lipid peroxidation (F2-isoprostanes) are not correlated in healthy human subjects Free Radic. Res. 2000 32 355 62 10.1080/10715760000300351 10741856
England, T. et al. The steady-state levels of oxidative DNA damage and of lipid peroxidation (F2-isoprostanes) are not correlated in healthy human subjects. Free Radic. Res. 32, 355–62. 10.1080/10715760000300351 (2000).10741856 10.1080/10715760000300351
30. Karpińska J Mikołuć B Motkowski R Piotrowska-Jastrzebska J HPLC method for simultaneous determination of retinol, α-tocopherol and coenzyme Q10 in human plasma J. Pharm. Biomed. Anal. 2006 42 232 6 10.1016/j.jpba.2006.03.037 16765550
Karpińska, J., Mikołuć, B., Motkowski, R. & Piotrowska-Jastrzebska, J. HPLC method for simultaneous determination of retinol, α-tocopherol and coenzyme Q10 in human plasma. J. Pharm. Biomed. Anal. 42, 232–6. 10.1016/j.jpba.2006.03.037 (2006).16765550 10.1016/j.jpba.2006.03.037
31. Kim EB Kim HK Hyon JY Wee WR Shin YJ Oxidative stress levels in aqueous humor from high myopic patients Korean J. Ophthalmol. 2016 30 172 179 10.3341/kjo.2016.30.3.172 27247516
Kim, E. B., Kim, H. K., Hyon, J. Y., Wee, W. R. & Shin, Y. J. Oxidative stress levels in aqueous humor from high myopic patients. Korean J. Ophthalmol. 30, 172–179. 10.3341/kjo.2016.30.3.172 (2016).27247516 10.3341/kjo.2016.30.3.172
32. Zhu XJ Epigenetic regulation of αA-crystallin in high myopia-induced dark nuclear cataract PLoS ONE 2013 10.1371/journal.pone.0081900 24391995
Zhu, X. J. et al. Epigenetic regulation of αA-crystallin in high myopia-induced dark nuclear cataract. PLoS ONE10.1371/journal.pone.0081900 (2013).24391995 10.1371/journal.pone.0081900
33. Ng FJ Mackey DA O’sullivan TA Oddy WH Yazar S Is dietary vitamin a associated with myopia from adolescence to young adulthood? Transl. Vis. Sci. Technol. 2020 10.1167/TVST.9.6.29 33244445
Ng, F. J., Mackey, D. A., O’sullivan, T. A., Oddy, W. H. & Yazar, S. Is dietary vitamin a associated with myopia from adolescence to young adulthood?. Transl. Vis. Sci. Technol.10.1167/TVST.9.6.29 (2020).33244445 10.1167/TVST.9.6.29
34. Yuan J Inflammatory cytokines in highly myopic eyes Sci. Rep. 2019 10.1038/s41598-019-39652-x 31889150
Yuan, J. et al. Inflammatory cytokines in highly myopic eyes. Sci. Rep.10.1038/s41598-019-39652-x (2019).31889150 10.1038/s41598-019-39652-x
35. Made AK Widjaja-Adhi MG The molecular aspects of absorption and metabolism of carotenoids and retinoids in vertebrates Biochim. Biophys. Acta (BBA) Mol. Cell Biol. Lipids 2020 1865 11 158571 10.1016/j.bbalip.2019.158571
Made, A. K. & Widjaja-Adhi, M. G. The molecular aspects of absorption and metabolism of carotenoids and retinoids in vertebrates. Biochim. Biophys. Acta (BBA) Mol. Cell Biol. Lipids 1865(11), 158571. 10.1016/j.bbalip.2019.158571 (2020).10.1016/j.bbalip.2019.158571
36. Mayo-Wilson E Imdad A Herzer K Yakoob MY Bhutta ZA Vitamin A supplements for preventing mortality, illness, and blindness in children aged under 5: Systematic review and meta-analysis BMJ 2011 10.1136/bmj.d5094 21868478
Mayo-Wilson, E., Imdad, A., Herzer, K., Yakoob, M. Y. & Bhutta, Z. A. Vitamin A supplements for preventing mortality, illness, and blindness in children aged under 5: Systematic review and meta-analysis. BMJ10.1136/bmj.d5094 (2011).21868478 10.1136/bmj.d5094
37. Traber MG Atkinson J Vitamin E, antioxidant and nothing more Free Radic. Biol. Med. 2007 43 4 15 10.1016/j.freeradbiomed.2007.03.024 17561088
Traber, M. G. & Atkinson, J. Vitamin E, antioxidant and nothing more. Free Radic. Biol. Med. 43, 4–15. 10.1016/j.freeradbiomed.2007.03.024 (2007).17561088 10.1016/j.freeradbiomed.2007.03.024
38. Zhang Z Correlation between refractive errors and ocular biometric parameters in children and adolescents: a systematic review and meta-analysis BMC Ophthalmol. 2023 23 1 472 10.1186/s12886-023-03222-7 37990308
Zhang, Z. et al. Correlation between refractive errors and ocular biometric parameters in children and adolescents: a systematic review and meta-analysis. BMC Ophthalmol. 23(1), 472. 10.1186/s12886-023-03222-7 (2023).37990308 10.1186/s12886-023-03222-7
