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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 20  |  Issue : 1  |  Page : 158-161

Prevalence of pathological myopia in Upper Egypt


Department of Ophthalmology, Al-Azhar University, Assiut, Egypt

Date of Submission20-Dec-2021
Date of Decision08-Jan-2022
Date of Acceptance17-Jan-2022
Date of Web Publication4-Mar-2022

Correspondence Address:
Mohamed E Ahmed
Assistant Professor, Department of Ophthalmology, Faculty of Medicine, Al-Azhar University, Assiut, 71524
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/azmj.azmj_143_21

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  Abstract 


Background and aim Pathological myopia (PM) is one of the main causes of blindness globally, and its prevalence continues to increase rapidly over time. The aim of this study was to investigate the prevalence of PM in the clinical population in Assiut City, Upper Egypt, during a period of 1 year.
Patients and methods This cross-sectional study was carried out on a clinical population attending a large ophthalmology center in Assiut City, Upper Egypt, during the period from January to December 2018. All patients were subjected to full ophthalmologic examination. The noncycloplegic refraction was measured using an autorefractometer. The examined eyes were diagnosed as PM if they had refraction of more than or equal to −6 D spherical equivalent or an axial length of more than or equal to 25.5 mm.
Results The study included 1548 eyes of 812 patients. Pathologically myopic eyes represented 152 eyes, with a prevalence of 9.82%. Of the total included patients, 102 (12.6%) patients had at least one pathologically myopic eye. Patients with bilateral PM represented 73 (71.6%) cases. Their refractive error ranged from −6.0 to −26.0 D, with a mean of −13.24±4.13 D, and their mean axial length was 28.2±2.14 mm and ranged from 26.1 to 35.2 mm.
Conclusion The prevalence of PM in the studied sample was 9.82%, which was obviously higher compared with studies on other populations. Further large community-based studies are warranted to determine its prevalence as a step to overcome this true burden.

Keywords: Assiut, clinical population, pathological myopia


How to cite this article:
Ahmed ME. Prevalence of pathological myopia in Upper Egypt. Al-Azhar Assiut Med J 2022;20:158-61

How to cite this URL:
Ahmed ME. Prevalence of pathological myopia in Upper Egypt. Al-Azhar Assiut Med J [serial online] 2022 [cited 2022 Jun 29];20:158-61. Available from: http://www.azmj.eg.net/text.asp?2022/20/1/158/339067




  Introduction Top


Myopia poses a significant health concern globally with a rapidly increased prevalence over time [1]. Pathological myopia (PM) is an ocular condition with serious visual implications, and it forms one of the major causes of blindness worldwide. It is clinically characterized by continuous eye elongation due to scleral thinning and posterior staphyloma [2]. To date, there has not been a standard definition for PM. It was originally characterized as myopia along with degeneration of the sclera, choroid, and retinal pigment epithelium as well as visual impairment, or it was defined as the progressive elongation of the axial length, whereas others defined it by a refraction of more than or equal to −6 D spherical equivalent or an axial length of more than or equal to 25.5 mm [2],[3].

In the past five decades, the prevalence of myopia has increased rapidly in some developed Asian countries such as Singapore, China and, Taiwan. It was estimated that ∼80–90% of high school children are myopic and ∼10–20% of those had high myopia [4],[5]. A previous study in Taiwan reported that the rate of high myopia increased from 23.5% in 1988 to 38.4% in 2005 [6]. Moreover, in USA, the prevalence of myopia increased significantly from 25.0% in 1971–1972 to 41.6% in 1999–2004 [7]. In addition, a study in USA revealed that myopia causes a significant economic burden (∼2 billion dollars were spent per year on correcting refractive errors associated with myopia in 1983 and increased to 4.6 billion dollars per year in 1994) [8].

In many developed countries nowadays, PM has become one of the principal causes of blindness [9]. It is the seventh chief cause of blindness in USA [10], whereas it is the third leading cause of vision loss in Japan [11]. The prevalence of PM has also increased in most populations worldwide ‘with increase in the prevalence of myopia,’ and it is particularly high in Asian and Middle Eastern countries [6]. Moreover, the prevalence of PM differed among races. It has been reported that it was higher in the Asian population compared with the whites in the USA (9.0 vs. 2.0%) [7],[12]. Regarding the status of PM in Egypt, a previous old study found that the prevalence of PM was 0.2% [13], whereas another study reported that it was 7.4% [14]. Two almost recent studies evaluated the prevalence of PM in Egypt; the first found that it was 10.8% among university students in Upper Egypt [15] and the second reported that it was 10.9% among the general population [16]. This indicated that this prevalence continues to increase among Egyptians over time, and this calls for the importance of investigating this issue. In this study, we attempted to determine PM prevalence in clinical patients attending our ophthalmology center in Assiut City, Upper Egypt.


  Patients and methods Top


This cross-sectional study was carried out on a clinical population attending Al-Nahar Center for eye surgeries and LASIK (a large private referral ophthalmology center in Assiut City, Upper Egypt) during the period from January to December 2018. The guidelines of the Declaration of Helsinki were abided. The exclusion criteria included cases that had undergone operations for posterior segment diseases such as vitrectomy and conventional retinal detachment surgery and were taking intravitreal injections. The study is approved by the ethical standards of the Faculty of Medicine, Al-Azhar University (Assiut), Egypt. Informed written consent was obtained from all patients before the beginning of the study.

The study included 1548 eyes of 812 patients who met the inclusion criteria. All cases were subjected to full ophthalmological examination in terms of best-corrected visual acuity, intraocular pressure, anterior and posterior segment slit-lamp biomicroscopy, besides fundus examination by indirect ophthalmoscopy. Moreover, the noncycloplegic refraction was measured by an autorefractometer (Topcon Inc., Tokyo, Japan). A scan or B scan ultrasonography was done to determine the axial length for eyes that were not amenable for refraction. The examined eyes were diagnosed as pathologically myopic if they had a refraction of more than or equal to −6 D spherical equivalent or an axial length of more than or equal to 25.5 mm. The Sonomed A scan PacScan 300 A (Escalon, Ardmore, Pennsylvania, USA) was used for measuring the axial length, and the B scan was done using the Sonomed B 3000 (Escalon) model. Using the 10-MHz probe, the axial length was recorded besides the presence of staphylomata as well as vitreal opacities and retinal detachment. Each examined eye was subjected to almost five scans, and the mean value was recorded.

Statistical analysis

Data analyses were performed using SPSS software (Statistical Package for Social Sciences, version 20; IBM, New York, New York, USA) [17]. Categorical data were described by number and percentage, whereas the numerical data variables were described by mean and SD. The calculated sample size was 139 cases, and the included cases covered the calculated sample size. The sample size was calculated according to the equation of Daniel [18]: n=Z2 P (1−P)/d2, where n=sample size (139), Z= level of confidence (1.96), P=expected prevalence or proportion (0.1), and d=precision (0.05).


  Results Top


A total of 1548 eyes of 812 patients were included in this study. There were 349 (43.0%) males and 463 (57.0%) females with an age range of 15–82 years. Of the total examined eyes, the pathologically myopic eyes were 152 (9.82%) eyes ([Figure 1]), and of the total 812 patients, 102 (12.6%) patients had at least one pathologically myopic eye (45 males and 57 females) with a mean age of 39.1±12.4 (16–69 years). Patients with bilateral pathologic myopia were 73 (71.6%) cases. Their refractive error ranged from −6.0 to −26.0 D with a mean of −13.24±4.13 D, ‘calculated as the spherical equivalent of their refraction,’ and their mean axial length was 28.2±2.14 mm and ranged from 26.1 to 35.2 mm ([Table 1]).
Figure 1 Prevalence of pathological myopia in the studied cases.

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Table 1 Baseline and clinical data of pathologically myopic patients

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  Discussion Top


Globally, PM is one of the main causes of blindness, and its prevalence continues to increase rapidly over time. In this study, we aimed to determine the prevalence of PM in patients attending a large referral ophthalmology center in Assiut City, Upper Egypt. The results showed that the prevalence of PM in the studied sample was 9.82%. This obtained prevalence was slightly lower ‘but comparable’ with that of a recent study performed in Egypt by Elnahry et al. [16] who assessed the prevalence of PM in the general population attending a Cairo University Hospital ophthalmology clinic and found that the prevalence of PM was 10.9%. Published studies have reported various prevalence of PM on different studied participants and settings. In a previous Australian study, Vongphanit et al. [19] found that the prevalence of high myopia was 2.7% in an urban population aged more than or equal to 49 years with a definition of high myopia in their study as SphEq more than or equal to −5.00 D in at least one eye. However, the obtained prevalence in our study was higher, because this study was performed on a clinical population of patients with a wide range of age (16–69 years) and with the definition of high myopia as SphEq more than or equal to −6.00 D ‘a higher cut-off value,’ and all of these factors could raise the prevalence of PM [20].

In a previous population-based study on a sample of black and white adults aged more than or equal to 40 years in USA, Katz et al. [21] found that the prevalence of high myopia in black adults was 0.8% and in white adults was 1.8%, which was obviously lower than our study, and this may be owing to the settings of their study that excluded aphakic eyes, whereas pseudophakic and aphakic patients were not excluded in our study. In addition, they added that the prevalence of high myopia differs among people of different ethnicities, and this may be attributed to genetic and behavioral differences [21], and in fact, this may support our findings regarding the higher obtained prevalence in this study. In a Chinese population-based study, Liu et al. [22] found that the prevalence of high myopia was 2.4%, and also in this study, all pseudophakic and aphakic eyes were not included in addition to patients who had undergone refractive surgery, so the prevalence of high myopia might be not accurately estimated. However, a Japanese study found that 12.1% of eyes had an axial length more than or equal to 25.00 mm and 5.5% had more than or equal to 26.00 mm [23].In an earlier study in Egypt, the prevalence of PM was found to be 0.2% [13], whereas another later study in 1976 found that this prevalence was 7.4%, which was obviously higher [14]. In line with these findings, a recent study found that the prevalence of PM among Assiut University students in Upper Egypt was 10.8%, which was almost comparable to our study [15]. However, this study included participants with lower mean age compared with our study (18.0±1.6 years). This could indicate that the prevalence of PM is continuing to rise over time in Egypt, as it is in many developing countries as a result of rising civilization and level of education.

In the present study, patients with bilateral PM represented 71.6% of the total patients. Almost similar findings were found by Elnahry et al. [16], who found that 77.4% of the included patients had bilateral PM. Moreover, a Chinese study reported that 83.7% of patients with PM had bilateral PM [24].

The obtained prevalence of PM in this study signifies the importance of reducing its burden by various methods that could prevent it and slow down its progression such as public health or lifestyle interventions, optimizing environmental influences, some pharmacological approaches, in addition to some optical devices (multifocal spectacles and multifocal contact lenses) [10].

This study had a strength point, which was diagnosing PM by including both the measurement of the axial length and the refraction, as well as lowering the exclusion criteria by including pseudophakic and aphakic patients as well as patients with media opacities. Of the study limitations, the study included a clinical population in which the prevalence of PM might be higher in addition to the lack of a standard definition of PM, which restrained our potential to compare our results with other studies.


  Conclusion Top


This study found that the prevalence of PM in the studied sample in Upper Egypt was 9.82% which was obviously higher compared with studies on other populations, and this supports our doubts. PM is a serious burden and one of the major causes of blindness globally, so further large community-based studies are warranted to determine its prevalence as a step to overcome this true burden.

Recommendations

The prevalence of PM in this study is 9.82%, which is high and may increase over time among Egyptians. We recommend further large studies to determine its prevalence as a step to overcome this true burden.

Acknowledgements

Mohamed E. Ahmed: data collection and analyses, as well as writing and publishing of the manuscript.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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