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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 113  |  Issue : 3  |  Page : 97-117

The prevalence of different refractive errors in the Delta region of Egypt


1 Benha Teaching Hospital, Egypt
2 Department of Ophthalmology, Faculty of Medicine, Ain Shams University, Egypt

Date of Submission22-Mar-2020
Date of Acceptance26-Jun-2020
Date of Web Publication07-Sep-2020

Correspondence Address:
MSc, MD, PhD Mervat Salah Mourad
Professor of Ophthalmology, Faculty of Medicine, Ain Shams University, 27 Zaker Hussien St Nasr city, Flat 4, Cairo, 11471
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ejos.ejos_13_20

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  Abstract 

Introduction Epidemiologic research on the types and the distribution of refractive errors (REs) enable efficient planning to improve access to care.
Aim The aim was to fill the informational gap concerning the prevalence of REs in different age groups in the Delta region of Egypt and to introduce recommendations and key points for researchers.
Patients and methods This is a cross-sectional descriptive study for the prevalence of REs in the Delta region of Egypt among different age groups. The population-based study included 800 eyes of 400 patients from different age groups, 400 eyes in the child age group and 400 eyes in adult age group.
Results and discussion The prevalence of myopia was higher than the prevalence of hyperopia. The prevalence of astigmatism was higher than myopia, but also higher than other studies. The prevalence of myopia was higher in the adult age group than in the child age group, which was consistent with that of other East Asian countries. The prevalence of hyperopia was higher in the child age group than in the adult age group. The prevalence of astigmatism was very high and slightly similar in both groups.
Conclusion Correcting REs can reduce ophthalmic problems. Improving family awareness and promoting screening programs can be effective in identifying these errors and preventing visual impairment.

Keywords: Egypt Delta, errors of refraction, prevalence


How to cite this article:
Ali FA, Mourad MS, Rehan RA, Seleet MM. The prevalence of different refractive errors in the Delta region of Egypt. J Egypt Ophthalmol Soc 2020;113:97-117

How to cite this URL:
Ali FA, Mourad MS, Rehan RA, Seleet MM. The prevalence of different refractive errors in the Delta region of Egypt. J Egypt Ophthalmol Soc [serial online] 2020 [cited 2020 Sep 22];113:97-117. Available from: http://www.jeos.eg.net/text.asp?2020/113/3/97/294443


  Introduction Top


Refractive error (RE) may be defined as a state in which the incident parallel rays of light do not focus on the fovea in the nonaccommodating eye [1].

Epidemiologic research on the types and the distribution of REs will help more efficient planning for their correction, including glasses and other methods of treatment and follow-up [2].

According to the WHO, uncorrected REs such as myopia, hyperopia, and astigmatism are the second leading cause of blindness after cataract and the main cause of low vision [3].

In children, REs are the leading cause of amblyopia [4].

Worldwide, there are about 2.3 billion persons who have REs. Out of these, only 1.8 billion can afford correction of their errors [5].

Children are the most vulnerable group, because uncorrected REs can result in a dramatic impact on the learning process and educational capacity [6].


  Aim Top


The aim of this study was to fill the informational gap concerning the prevalence of REs (myopia, hyperopia, and astigmatism) in different age groups in the Delta region in the Arab Republic of Egypt.

Furthermore, the study compared between the prevalence of REs among other studied samples and similar studies performed.

The study also aimed at introducing recommendations for a new suggested screening program and citing some key points for researchers.


  Patients and methods Top


Patients

A cross-sectional descriptive study was carried out to study the prevalence of REs in the Delta region of Egypt among different age groups. The adult patients and the children parents, included in this study were clearly informed about the purpose of the study, the steps of examination and had to sign an informed consent before inclusion. Data collection was following the laws of Egypt and was compliant with the principles of the Declaration of Helsinki.

The population-based study included 800 eyes of 400 patients from different age groups; 200 patients in the child age group and 200 patients in the adult age group attending the outpatient clinic of Benha Teaching Hospital.

Methods

Clinical examination

  1. Full history was taken:
    1. Personal data included (name, sex, job, and level of education vs age for children).
    2. Past history included (refractive surgery, squint surgery, glaucoma, cataract surgery, ocular trauma, or any other eye surgery or disease).
    3. Family history included (keratoconus, wearing glasses, squint).
  2. Full ophthalmological examination including:
    1. Slit lamp examination of the anterior segment and adnexa was done.
    2. Uncorrected visual acuity (VA) measurement. VA was measured at a distance of 6 m using the Landolt C chart.
    3. Autorefractometry was done for all cases; children had noncycloplegic autorefraction, and then cycloplegic refraction using cyclopentolate hydrochloride (1.0% solution).
    4. Best corrected visual acuity (BCVA) measurement and the final prescription were recorded.
    5. Assessment of ocular motility using a pen torch was done.
    6. The presence of ocular deviation (phoria and tropia) was determined using the cover test.
    7. Intraocular pressure (IOP) measurement by Goldmann tonometry was done for the adult age group.
    8. Indirect fundus examination was performed.


Inclusion criteria

Patients with RE without any other ocular disease were included.

Exclusion criteria

Patients with a history of eye surgery or any other ophthalmological disease that might influence refraction (e.g. keratoconus, corneal opacities, cataract, retinal detachment, etc.).

Definitions

Myopia was defined as a spherical error of more than or equal to −0.25 diopter (D).

Hyperopia was defined as a spherical error of more than or equal to +1.00 D.

Astigmatism was defined as cylinder error of more than or equal to 0.25 D.

As described by Kamiya [7], we classified astigmatism as with the rule astigmatism, when the axis of the negative correcting cylindrical power was within the range of 0–29° or 150–180°, and as against the rule astigmatism when it was in the range of 60–119°; otherwise, the astigmatism was considered to be oblique astigmatism.

Astigmatism was further classified into myopic astigmatism (compound myopic astigmatism and simple myopic astigmatism), hyperopic astigmatism (compound hyperopic astigmatism and simple hyperopic astigmatism), and mixed astigmatism.

Spherical equivalent (SE) was calculated as the algebraic sum of the spherical measurement and 0.5 times the cylindrical power.

Strabismus was defined with any child with tropia at distance or near, with or without spectacles.

Amblyopia was defined, as a more than or equal to 2-line difference in best VA, when less than 20/30 in the worse eye and with amblyogenic factors such as past or current strabismus, anisometropia (≥1.00 D difference in hyperopia, ≥3.00 D difference in myopia, or ≥1.50 D difference in astigmatism).

Statistical analysis

Data were collected, revised, coded, and entered to the Statistical Package for the Social Sciences (IBM SPSS; IBM – New York, USA) version 20. The qualitative data were presented as number and percentages while quantitative data were presented as mean, SD, and ranges when their distribution found parametric.

The comparison between two groups with qualitative data were done by using χ2 test and/or Fisher’s exact test was used instead of χ2 test when the expected count in any cell was found to be less than 5.

The confidence interval was set to 95% and the margin of error accepted was set to 5%. So, the P value was considered significant as the following:

P>0.05: nonsignificant.

P<0.05: significant.

P<0.01: highly significant.


  Results Top


Descriptive part of the all studied data

This descriptive study included 800 eyes, of them 306 were of male patients and 494 were of female patients ([Table 1] and [Figure 1]); 592 patients with negative family history of REs and 208 with positive family history of REs ([Table 1] and [Figure 2]).
Table 1 Distribution of age, sex, and family history among total study groups

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Figure 1 Sex distribution among total study groups.

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Figure 2 Family history distribution among total study groups.

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The patients were divided into two groups: a child age group of 3–18 years and an adult age group of 19–59 years ([Table 1] and [Figure 3]).
Figure 3 Age distribution among total study groups.

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The age of the study group ranged from 3 to 59 years; the mean age was 21.54 (SD±13.03) ([Table 1]).

All these patients underwent full ophthalmological examination and patients with a history of eye surgery or any other ophthalmological disease were excluded.

The mean of uncorrected visual acuity (UCVA), SE, and BCVA among the total study group was 0.23 (SD±0.26), −2.18 (SD±3.91), and 0.71 (SD±0.26), respectively ([Table 2]).
Table 2 Mean of UCVA, SE, and BCVA among total study groups

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Prevalence of REs (myopia, hyperopia, astigmatism) and emmetropia among the total study group was 21.8, 8.5, 67.4, and 2.4%, respectively ([Table 3] and [Figure 4]).
Table 3 Prevalence of refractive errors among total study groups

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Figure 4 Prevalence of refractive error among total study groups.

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The prevalence of astigmatism (with the rule, against the rule, oblique astigmatism) among the total study group was 44.9, 15.5, and 7%, respectively ([Table 4] and [Figure 5]).
Table 4 Percentage of astigmatism among total study groups

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Figure 5 Percentage of astigmatism among total study groups.

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The prevalence of amblyopia among the total study group was 10.9% ([Table 5]).
Table 5 Percentage of amblyopia among total study groups

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Comparison between the adult group and the child group regarding the studied data

The mean of UCVA among the adult age group and the child age group was 0.21±0.19 and 0.25±0.32, respectively ([Table 6] and [Figure 6]).
Table 6 Comparison between adult group and child group regarding mean of UCVA, SE, and BCVA

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Figure 6 Mean of uncorrected visual acuity among adult and child groups.

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The mean of SE among the adult age group and the child age group was −2.98±3.69 and −1.41±3.96, respectively ([Table 6] and [Figure 7]).
Figure 7 Mean of spherical equivalent among adult and child age groups.

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The mean of BCVA among the adult age group and the child age group was 0.71±0.25 and 0.72±0.27, respectively ([Table 6] and [Figure 8]).
Figure 8 Mean of best corrected visual acuity among adult and child age groups.

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The prevalence of REs (myopia, hyperopia, and astigmatism) and emmetropia among the adult group and the child age group is as shown in [Table 7] and [Figure 9].
Table 7 Prevalence of refractive errors among adult group and child age group

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Figure 9 Prevalence of refractive errors among adult and child groups.

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The prevalence of astigmatism (with the rule, against the rule, and oblique astigmatism) among the adult age group and the child age group is as shown in [Table 8].
Table 8 Percentage of astigmatism among adult and child age group

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The prevalence of amblyopia among the adult age group and the child age group was 11.5 and10.3, respectively ([Table 9]).
Table 9 Percentage of amblyopia among adult and child age group

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Adult age group

It included 400 eyes. The mean age of this group was 31.38 years, 236 less than 30 years and 164 between 31 and 59 years ([Table 10] and [Figure 10]); 264 patients were women and 136 were men ([Table 10] and [Figure 11]); 232 patients had desk jobs while 168 patients had field jobs ([Table 10] and [Figure 12]); 266 patients had negative family history for REs while 134 patients had positive family history for REs ([Table 10] and [Figure 13]).
Table 10 Distribution of sex, job and family history among adult age group

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Figure 10 Distribution of age among adult group.

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Figure 11 Distribution of sex among adult group.

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Figure 12 Distribution of job among adult group.

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Figure 13 Distribution of family history among adult group.

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The mean of UCVA among the adult age group was 0.21±0.19 while the mean of BCVA among the adult age group was 0.71±0.25 ([Table 11]).
Table 11 Mean of UCVA, SE, BCVA, and IOP among adult group

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The mean of SE among the adult age group was −2.98±3.69 while the mean of IOP among the adult age group was 15.12±2.30 ([Table 11]).

The prevalence of REs (myopia, hyperopia, astigmatism) and emmetropia among the adult age group was 25, 5.8, 67, and 2.3%, respectively ([Table 12] and [Figure 14]).
Table 12 Percentage of refractive errors among adult age group

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Figure 14 Percentage of refractive errors among the adult age group.

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The prevalence of astigmatism (with the rule, against the rule, and oblique astigmatism) among the adult age group was 36, 23.3, and 7.8%, respectively ([Table 13]).
Table 13 Percentage of astigmatism among adult group

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The prevalence of amblyopia among the adult age group was 11.5% ([Table 14]).
Table 14 Percentage of amblyopia among adult group

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The distribution of REs (myopia, hyperopia, astigmatism) and emmetropia by sex among the adult age group is as shown in [Table 15] and [Figure 15].
Table 15 Distribution of refractive errors by sex among adult age group

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Figure 15 Distribution of refractive errors by sex in adult age group.

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The distribution of REs (myopia, hyperopia, astigmatism) and emmetropia by job among the adult age group is as shown in [Table 16] and [Figure 16].
Table 16 Distribution of refractive errors by job among adult age group

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Figure 16 Distribution of refractive errors by job in the adult age group.

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The distribution of REs (myopia, hyperopia, astigmatism) and emmetropia by family history among adult age group is as shown in [Table 17] and [Figure 17].
Table 17 Distribution of refractive errors by family history among adult age group

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Figure 17 Distribution of refractive errors by family history among the adult age group.

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The mean of UCVA with different REs among the adult age group is as shown in [Table 18] and [Figure 18].
Table 18 Mean of UCVA with different refractive errors among adult age group

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Figure 18 Mean of uncorrected visual acuity with different refractive errors among adult group.

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The mean of SE with different REs among the adult age group is as shown in [Table 19] and [Figure 19].
Table 19 Mean of SE with different refractive errors among adult age group

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Figure 19 Mean of spherical equivalent with different refractive errors among the adult age group.

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The mean of BCVA with different REs among the adult age group is as shown in [Table 20] and [Figure 20].
Table 20 Mean of BCVA with different refractive errors among adult age group

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Figure 20 Mean of best corrected visual acuity with different refractive errors among the adult age group.

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The mean of IOP with different REs among the adult age group is as shown in [Table 21] and [Figure 21].
Table 21 Mean of IOP with different refractive errors among adult age group

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Figure 21 Mean of intraocular pressure with different refractive errors among adult group.

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The prevalence of amblyopia with different REs among the adult age group is as shown in [Table 22] and [Figure 22].
Table 22 Percentage of amblyopia with different refractive errors among adult age group

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Figure 22 Percentage of amblyopia with different refractive errors among the adult age group.

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Relations in the child age group

It included 400 eyes. The mean age of this group was 11.70 years±4.31), 166 (3–11 years), and 234 (12–18 years) ([Table 23] and [Figure 23]); 230 patients were women and 170 were men ([Table 23] and [Figure 24]); 226 patients had negative family history for REs while 174 patients had positive family history for REs ([Table 23] and [Figure 25]).
Table 23 Distribution of age, sex, and family history among child group

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Figure 23 Distribution of age among child group.

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Figure 24 Distribution of sex among child age group.

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Figure 25 Distribution of family history among child age group.

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The prevalence of REs (myopia, hyperopia, astigmatism) and emmetropia among the child age group was 18.5, 11.3, 67.8, and 2.5%, respectively ([Table 24] and [Figure 26]).
Table 24 Percentage of refractive errors among child group

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Figure 26 Percentage of refractive errors among child group.

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The mean of UCVA among the child age group was 0.25±0.32) while the mean of BCVA among the child age group was 0.72±0.27). The mean of SE among the child age group was −1.41±3.96 ([Table 25]).
Table 25 Mean of UCVA, SE, and BCVA among child group

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The prevalence of astigmatism (with the rule, against the rule, and oblique astigmatism) among the child age group was 53.8, 7.8, and 6.3%, respectively ([Table 26]).
Table 26 Percentage of astigmatism among child age group

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The prevalence of squint (esotropia and exotropia) among the child age group was 4.25 and 0.5%, respectively ([Table 27]).
Table 27 Percentage of squint among child age group

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The prevalence of amblyopia among the child age group was 10.3% ([Table 28]).
Table 28 Percentage of amblyopia among child age group

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The distribution of REs (myopia, hyperopia, astigmatism) and emmetropia by sex among the child age group is as shown in [Table 29] and [Figure 27].
Table 29 Distribution of refractive errors by sex among child age group

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Figure 27 Distribution of refractive errors by sex among the child age group.

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The distribution of REs (myopia, hyperopia, astigmatism) and emmetropia by family history among the child age group is as shown in [Table 30] and [Figure 28].
Table 30 Distribution of refractive errors by family history among child age group

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Figure 28 Distribution of refractive errors by family history among the child age group.

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The mean of UCVA with different REs among the child age group is as shown in [Table 31] and [Figure 29].
Table 31 Mean of uncorrected visual acuity with different refractive errors among child age group

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Figure 29 Mean of uncorrected visual acuity with different refractive errors among the child age group.

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The mean of SE with different REs among the child age group is as shown in [Table 32] and [Figure 30].
Table 32 Mean of spherical equivalent with different errors of refraction among child age group

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Figure 30 Mean of spherical equivalent with different refractive errors among the child age group.

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The mean of BCVA with different REs among the child age group is as shown in [Table 33] and [Figure 31].
Table 33 Mean of BCVA with different refractive errors among child age group

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Figure 31 Mean of best corrected visual acuity with different refractive errors among the child age group.

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The prevalence of amblyopia with different REs among the child age group is as shown in [Table 34] and [Figure 32].
Table 34 Percentage of amblyopia with different refractive errors among child age group

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Figure 32 Percentage of amblyopia with different refractive errors among the child age group.

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  Discussion Top


In this study, we demonstrated the prevalence of REs among different age groups in the Delta region of Egypt.

Our study was done on 800 eyes. The mean age of these patients was 21.54 years.

The patients were divided into two groups: a child age group 3–18 years and an adult age group 19–59 years.

Adult group

It included 400 eyes. The mean age of this group was 31.38 years. A total of 264 patients were women and 136 were men. Among these, 266 patients had negative family history for REs while 134 patients had positive family history for REs; 232 patients had desk jobs while 168 patients had field jobs.

Myopia

The prevalence of myopia among the adult age group was 25%, which was lower than that found by Gupta et al. 51% [8], Sawada et al. 41.8% [9], Wong et al. 35% [10], and Yekta et al. 34.6% [11].

Meanwhile, the prevalence of myopia was higher in the current study as compared with other studies as that conducted by Cheng et al. (19.4%) [12], Wickremasinghe et al. (17.2%) [13] but slightly equal to Katibeh et al. (25.2%) [14].

There was a difference in the prevalence of myopia across different studies. This may be due to the variability in the definition of myopia, selection of participants, inclusion criteria, and the specific age domain. Also race, sex, genes, and environmental factors may have an effect.

In our study, myopia was defined as a spherical error equal to or above −0.25 D, whereas in the studies by Gupta et al. [8], Sawada et al. [9], Wong et al. [10], Yekta et al. [11], Cheng et al. [12], Wickremasinghe et al. [13], and Katibeh et al. [14], who defined myopia as SE equals −0.5 D or more.

In this study, the prevalence of myopia was higher in women than in men; the same pattern was found by Vitale et al. [15].

Also, the prevalence of myopia was higher in patients with desk jobs than field jobs, which was also observed by Wong et al. [10].

This may be explained by lifestyle changes in the past 10 years as a result of computer use and portable computerized devices. This could be also explained by the correlation between myopia and near work activity.

The prevalence of myopia was higher in patients with positive family history of REs than patients with negative family history of REs. This relation can support the theory that the tendency toward myopia is genetically determined which was also proposed by Guggenheim et al. [16]

Hyperopia

The prevalence of hyperopia among the adult age group was 5.8%, which was slightly higher than that found by Vitale et al. 3.6% [15].

The prevalence of hyperopia reported by Saw et al. [17] was 9.2%, which was slightly higher than that in our study.

There were different studies worldwide such as those of Attebo et al. [18] and Wu et al. [19], in which the prevalence of hyperopia was considerably higher than our study, 57 and 46.9%, respectively.

Again, the difference in the prevalence of hyperopia across different studies may be due to variability in the definition of hyperopia, selection of participants, and the specific age domain.

In our study, hyperopia was defined as spherical error greater than or equal to +1.00 D or more whereas in the studies by Vitale et al. [15] hyperopia is defined as SE greater than or equal to +3.00 D, Wu et al. [19] defined hyperopia as SE greater than or equal to +0.5 D and Saw et al. [17] defined hyperopia as SE greater than or equal to +1.00 D.

The prevalence of hyperopia was slightly higher in men than in women.

The prevalence of hyperopia was slightly higher in patients with desk jobs than field jobs.

Astigmatism

The prevalence of astigmatism among the adult age group was 67%, which was higher than that found by Yekta et al. (37.5%) [11], Hashemi et al. (49%) [20], and Saw et al. (35.8%) [17].

The highest prevalence of astigmatism has been reported by Cheng et al. (74%) [12] in participants aged over 50 and 65 years, and the lowest rate has been reported by Gupta et al. (30.6%) [8] in participants over 40 years of age.

The higher prevalence of astigmatism in the current study as compared with other studies can be explained by the fact that the climate of Egypt is dry and hot. Dry weather can cause ocular reactions causing rubbing of the eye giving rise to astigmatism.

Another cause may be trachoma which is endemic in Egypt and may cause pannus which induces astigmatism. Also, the definition of astigmatism might be varied across the studies.

In our study, we defined astigmatism as a cylindrical error of greater than or equal to 0.25 D.

The prevalence of astigmatism was higher in men than women.

Our study demonstrated that the prevalence of with the rule astigmatism was higher than other forms of astigmatism.

Asano et al. [21], reported that with the rule astigmatism was the most frequent in the 40 s age group.

In other studies, the prevalence of against the rule astigmatism was higher in the elderly population such as Shahroud [20], Singapore [22] and Bangladesh [23].

IOP

The results of this study revealed that the mean IOP measured by Goldmann applanation tonometer was 15.12±2.30 mmHg, which was similar to what was found by Yassin and Al-Tamimi [24], who reported a mean IOP of 15.8±3.6 mmHg.

With respect to RE, IOP measurements did not significantly correlate to it (P=0.451).

In agreement with our finding, the study by Bonomi et al. [25], which compared the IOP between both eyes in anisometropic patients with unilateral high myopia and found no difference between the IOP of both eyes.

On the contrary, several studies found higher IOP in myopic patients [26],[27].

Other studies suggested that myopia may be associated with risk of primary open-angle glaucoma [10].

Many studies on IOP in different races and geographical areas showed diversity, even though, these studies were performed on populations within similar racial groups and geographic areas; for example, studies performed on the Japanese population showed considerable variation in terms of mean IOP values and IOP association [28].

These variations can be attributed to the different methods in sample selection, criteria for exclusion of certain participants and instrumentation used to measure the IOP.

Moreover, intrinsic ocular variations such as central corneal thickness, axial length, and systemic factors such as obesity and hypertension can affect some communities [29].

Child group

This group included 400 eyes. The mean age of this group was 11.70 years.

A total of 230 patients were women and 170 were men. Among these, 226 patients had negative family history for REs, while 174 had positive family history for REs.

Myopia

Myopia was the second most common type of REs in the child age group (18.5%).

The prevalence of myopia was lower than that reported in Malaysia (20.7%) [30], Hong Kong (36.7%) [31], Ghana (27%) [32], and Singapore (36.3%) [33], but higher than that reported in Chile (5.8%) [34], Iran (4.3%), [35] and China (14.9%) [36].

In this study, the prevalence of myopia was higher in women than in men This was also found by Pärssinen and Lyyra, where the prevalence of myopia and its progression were significantly higher in women than in men among the third and fourth grade students [37].

The difference in prevalence with the latter studies can be due, in part, to the population age studied.

In addition to the age, differences between studies could also be due to ethnicities, and methodological approaches such as definitions of myopia, or methods for RE estimation.The prevalence of myopia in children with positive family history of RE was higher than children with negative family history of RE. This relation can support the theory that the tendency toward myopia is genetically determined, which was also proposed by Guggenheim et al. [16].

Hyperopia

In our study, the prevalence of hyperopia was 11.3% which is higher than that found In Baltimore (8.9%) in white children, and 4.4% in African-American children [38], Nepal (3%) [39], India (7.7%) [40], and South Africa (2.6%) [41].

The prevalence was lower than that found in Iran (16.6%) [42], Poland (13.1%) [43], and Ghana (18%) [32].

Again, prevalence findings may differ among studies due to variability in the definition of hyperopia, the refraction methods used, age, sex, location, and ethnicity.

In this study, the prevalence of hyperopia was higher in women than in men. This relationship has been shown by many studies and is explained by axial length changes with age and sex [36].

Astigmatism

Astigmatism was highly prevalent in this study, it was the most common RE among the child age group accounting for 67.8%.

The prevalence of astigmatism was higher than that reported in Ghana (55%)[32], Kampala (52%) [44], and Iran (45.3%) [45].

Astigmatism development could be resulting from incyclotorsion during near work activity, which causes the contraction of ciliary muscles for accommodation and leads to central corneal steepening and increased power as well [46].

The children also use computer devices more frequently, which could lead to increased dry eye, eye rubbing, and consequently astigmatism.

In this study, the prevalence of astigmatism was higher in men than in women.

Our study demonstrated that the prevalence of with the rule astigmatism was significantly higher than other forms of astigmatisms.

This was also reported in Korea [47] and southern India [47].

This may be explained by the action of the extrinsic ocular muscles, especially the medial rectus muscle as convergence flattens the horizontal meridian of the cornea and may also make the vertical meridian more curved, so may increase the with the rule astigmatism [21].

Amblyopia

The prevalence of amblyopia among the adult group was 11.5% and among the child group was 10.3%.

Conclusion and recommendation

  1. REs are one of the most important causes of defective vision worldwide, so recognizing and correcting these errors can reduce ophthalmic problems.
  2. Improving family awareness about the importance of correcting these errors and promoting screening programs can be effective in identifying these errors and preventing visual impairment.
  3. As a recommendation, more research is needed in Egypt regarding the recognition of the prevalence rates of REs among the population and the estimation of the extent of the problem in these age groups.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22], [Figure 23], [Figure 24], [Figure 25], [Figure 26], [Figure 27], [Figure 28], [Figure 29], [Figure 30], [Figure 31], [Figure 32]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13], [Table 14], [Table 15], [Table 16], [Table 17], [Table 18], [Table 19], [Table 20], [Table 21], [Table 22], [Table 23], [Table 24], [Table 25], [Table 26], [Table 27], [Table 28], [Table 29], [Table 30], [Table 31], [Table 32], [Table 33], [Table 34]



 

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