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A Comparative Study Of Prevalence Of Myopia In Primary School And Secondary School Children In Owerri Municipal

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ABSTRACT

This work was aimed at finding out the prevalence of myopia in primary and secondary school children in Owerri Municipal council. One hundred children were randomly selected from two primary schools and two secondary schools in Owerri municipality, of mixed gender between the ages of 6 and 17. The prevalence of myopia was 52% and 64% for primary and secondary school respectively. The prevalence of Emmetropia, hyperopia and astigmatism were 14%, 8% and 26% for primary school and 10%, 6% and 20% for secondary school respectively. Mean, standard deviation, frequency tables and bar chart were used. The study concludes that myopia is more in secondary school than in primary school. A low uptake of eye care was also noticed in the study. The study therefore recommends that every student should go for routine eye examination, maintain the right posture when reading and use good illumination.

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

The human organ of vision, the eye, has many fascinating features like the eyelid, cornea, crystalline lens, conjunctiva, sclera, retina, vitreous, pupil and so on. I’m particularly fascinated by its ability to reflect emotions… the way it lights up when one smiles and stormy when angry; “the eyes don’t lie” they say. However, this organ is plagued or affected by many defects, structurally or physiologically, one of which is Myopia.

An eye has no refractive error when viewing an object is said to be emmetropic. Emmetropic is a state of vision where an object at infinity is in sharp focus with the eye lens in a natural or relaxed state (Saladin et al.,2012). This condition of the normal eye is achieved when the refractive power of the cornea and axial length of the eyes balance out, thereby focusing light rays exactly on the retina resulting in a clear vision. An individual who is Emmetropic would be expected to have good visual acuity at 6 meters testing distance and if accommodative amplitude in adequate, equally good visual acuity at the near testing distance of 40 centimeters (Robert Dukeman, 2006).

An eye that has refractive error when viewing an object IS said to be ammetropic. This Word ametropia can be used interchangeably with refractive error. In an ametropic eye with accommodation relaxed, parallel rays of light fail to converge to a sharp focus on the retina (Schwiegerling, 2004). Four common refractive errors include:

  • Hyperopla or hypermetropia (farsightedness): A Condition in which parallel rays of light entering the eyes are brought to focus behind the retina.
  • Myopia (nearsightedness): A condition in which parallel rays of light entering the eye are brought to focus in front of the retina.
  • Astigmatism: A type of refractive error wherein the refraction varies in different meridian of the refractive media. Consequently, the rays of light entering the eyes cannot converge to a point focus but form focal lines.
  • Presbyopia: This is not an error of refraction but a condition of physiological insufficiency of accommodation leading to a progressive fall in near vision. In this case, the eye’s lens cannot accommodate enough for very near focus. Reading glasses help converge the light before it enters the eyes to complement the refractive power of the eye lens so that near objects focus clearly on the retina. Spectacle lenses or contact lenses can usually correct these errors.

1.1.1 Background Information

Light rays from the object of regard stimulate the retina and the image is transmitted via the optic nerve to the brain. When this light is correctly focused, the eye is said to be normal. Anomalies of the eye’s optical system are by far the commonest cause of defective vision and must be looked for in any person complaining of inability to see clearly.

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Apart from a direct complaint of a child’s disability (maybe unable to see the blackboard clearly at school), examination of the optical system may be prompted by review of vision at schools and parental observation of visual inadequacy. Increase in Myopia during adolescence may be notice during routine examination.

1.1.2 Myopia

Myopia also known as near-sightedness is a condition in which parallel rays of light entering the eye are brought to focus in front of the retina (Foster & Zang, 2014). Myopia was introduced from the habit with short-sighted people frequently have of half closing the lids when looking distant subjects so that they may gain advantage of a Stenopaic opening.

Aristotle (384-322BC) was credited with first distinguishing Myopia, Galen (131-201AD) coined the term Myopia from Myelin (too close) and Ops (eye) as he observed that the individual closed the eye to see (Squint). The first satisfactory definition of the condition was stated by Kepler in 1611, and Plempius (1632) first examined the Myopic eye anatomically and attributed the condition to a lengthening of its posterior part. Donders (1866) established its pathological basis and detailed its clinical manifestation.

Figure 1.1 A diagram of the eye illustrating a normal eye and a myopic eye

A diagnosis of Myopia is typically confirmed during an eye examination by an Optometrist, Ophthalmologist or Orthoptist. Frequently an Antorefractor or Retinoscope is used to give an initial objective assessment of the refractive status of each eye, and then a phoropter is used to subjectively refine the patient’s eyeglass prescription. Myopla cannot be prevented, but some commonly attempted preventive methods include wearing glasses, eye drops and participating n some outdoor activities. For people with a high degree of Myopia, a very strong eye glasses prescription is needed to correct the focus error: however, Strong eye glasses have a negative side effect in that off-axis viewing of objects away from the center of the lens results in prismatic movement and separation or colours known as Chromatic Aberration. This prismatic distortion is visible to the wearer as colour fringe around strongly contrasting colours. The fringe moves around as the wearer’s gaze through the lenses changes, and the prismatic shifting reverses on either side, above and below the exact center of the lenses. Hong et al.,2001 and Domonsoro et al.,2003 measured aberration in contact lens wearing. Strongly near sighted wearer of contact lenses do not experience Chromatic Aberration because the lens moves with the cornea and they always stays centered in the middle of the wearer’s gaze rather it significantly reduces ocular aberration.

Atireza et al., 2004 in their studies have shown that the incidence of Myopia increase with the level of education and some studies have shown a correlation between Myopia and a higher intelligence quotient. Myopia may be corrected by Refractive Surgery, though there are cases of associated side effects. The corrective lenses have a negative optical power (that is are concave) which compensates for excessive positive dioptres of Myopia eye.

1.1.3 The Mechanism Of Accommodation

On the basis of these changes, Helmholtz (1855) hypothesized that the natural shape of the lens is the relatively spherical accommodated form, the Zonular fibres are taut (that is “on the stretch”) and therefore, hold the lens in its flattest (and thinnest) form. However, when the Cililary muscle Contracts, acting as a Sphincter Muscles, it releases the tension on the Zonular Fibres, allowing the elastic lens capsule to increase its Curvature and the lens to become thicker and more nearly spherical. Helmholtz (1855), considered the lens substance to be soft and easily moulded by the Elastic Capsule, so he proposed that Presbyopia occurs due to hardening of the lens substance with the result that it fails to respond to a relaxation of the Zonular Tension.

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Fincham (1995) studied the lens capsule and demonstrated that its thickness is greater anteriorly than posteriorly and that it is thicker at the equator (near the Zonular attachment) than near the poles. These variations in the capsule thickness cause the anterior surface of the lens to become very highly curved during accommodation-much more than would be possible if the lens capsule had the same thickness throughout. This is an important contribution to the Helmholtz theory, as otherwise there would be no completely satisfactory explanation for the large increase in refracting power of the lens that occurs when the tension of the Zonular Fibres is released.

1.1.4 Etiology

Many people have suggested different theories about Myopia. It is commonly accepted that Myopia may be caused by largeness of the eyeball (Axial Myopia) or by an increase in the strength of the refractive power of the lens or cornea (Refractive Myopia). Most cases are axial type. Heredity also plays a role in Myopia. It is presumed that heredity-linked growth of retina in the determinant in the development of Myopia. Lengthening of the posterior segment of the globe commences only during the period of active growth and probably, ends with the termination of the active growth.

Therefore, the factors (such as Nutritional deficiency, Debilitating disease and Indifferent general health) which affect the general growth process will also influence the progress of Myopia through minimally.

1.1.5 Signs And Symptoms

The following signs are observed in a Myopic patient.

  • Prominent eyeball – Exophthalmos
  • Anterior chamber slightly deeper than normal
  • Pupils are somewhat large and a bit sluggishly reacting to light
  • Myopic crescent in the fundus
  • Large Cornea

The Symptoms Include:-

  • Poor vision for distance
  • Asthenopic symptoms
  • Half shutting of the eye may complained by the child
  • Night blindness in very high Myopes

1.1.6 Classification

Borish and Duke Elder classified Myopia by cause viz:

By Cause

  • Axial Myopia is attributed to an increase in the eye’s axial length
  • Refractive Myopia is attributed to the condition of refractive element of the eye.
  • Boorish further sub classified Refractive Myopia
  1. Curvative Myopia:- Attributed is excessive or increased Curvature or one or more of the refractive surface of the eye. Especially the cornea. In those with Cohen syndrome, Myopia appears to result from high corneal and lenticular power.
  2. Index Myopia:- Attributed’ to variation in the index of refraction of one or more of the ocular media.

By Clinical Entity

Various forms of Myopia have been described by their clinical appearance.

  • Simple Myopia: Characterized by an eye that is long for its optical power or optically too powerful for its axial length.
  • Degenerative Myopia (Malignant, Pathological or Progressive Myopia): Characterized by marked fundus changes associated with high refractive error and subnormal visual acuity often correction.
  • Nocturnal Myopia (Nigh Myopia or Twilight Myopia): Condition in which the eye has a greater difficulty seeing in low illumination areas.
  • Induced Myopia (Acquired Myopia): Results from exposure of various Pharmaceuticals, increase in Glucose level, Nuclear Sclerosis, Oxygen toxicity.
  • Pseudomyopia: The blurring of distant vision brought about by spasm of the Ciliary Muscle.
  • Form Deprivation Myopia (FDM): is a type or Myopia that occurs when the eyesight is deprived by limited illumination and vision range or the eye is modified with artificial lenses or deprived or clear form vision.
  • Near Work Induce Transient Myopia (NITM): 1s defined as short-term Myopia far point shifts immediately following a sustained near visual task.

By Amount/Degree

This is measured in Dioptres by the strength or optical power of CorrectiveLens

  1. Very low up to – 1.00D
  2. Low- 100D to 3-00D
  3. Medium – 3.00D to 6.00D
  4. High – 6.00D to 10.00D
  5. Very high above -10.00D

By Age

Congenital Myopia (Infantile Myopia): Present at birth and persists through infancy.

  • Youth onset Myopia occurs prior to age 20.
  1. School Myopia: Appear during children particularly the school age year. This form of Myopia is attributed to the use or the eye for close work during the school years.
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Adult onset Myopia

  1. Early onset myopia occurs between ages 20 and 40
  2. Late adult onset myopia occurs after age 40

1.2 Statement Of The Problem

A lot of research work has been conducted on the prevalence and distribution of refractive errors, surprisingly, not so much is mentioned about Myopia which is very common disorder with a variety of detrimental effects. This study is designed to:

1.3 Aim/Objective Of The Study

1.3.1 Aim

The purpose of this study is to examine and compare the prevalence of Myopia in Primary and Secondary School Children, to know if the incidence of Myopia increases with the level of education and also know if Myopia is influenced by age.

1.3.2 Objectives

  1. To determine the prevalence of myopia in primary school children in Owerri Municipal.
  2. To determine the prevalence of myopia among secondary school children in Owerri Municipal.
  3. To compare the prevalence of Myopia in Primary and Secondary School Children in Owerri Municipal.

1.4 Research Questions

The research questions that will guide this study are:

  • Does the child see distant object clearly?
  • Are asthenopic symptoms experienced?
  • Does the problem affect their academic performance?

1.5 Research Hypothesis

H0:    There is a significant prevalence of myopia among primary school

children.

H1:      There is no significant prevalence of myopia among primary school

children

H0:      There is no significant prevalence of myopia among secondary school

children.

H1:      There is significant prevalence of myopia among secondary

school children

H0:       Myopia is not more  prevalent in secondary schools than in primary schools

in Owerri municipal.

H1:       Myopia is more prevalent in secondary schools than in primary school in

Owerri Municipal.

1.6 Significance Of The Study

The medical profession requires studies that reveal the incidence of any particular condition among a group or people who are susceptible, at risk and exposed to risk factors of the disease condition. The eye care profession is not an exception.

How well students see will affect how well they learn, since education is important to every child and ignorance they say is very expensive.

Early detection and preventive care of Myopia can help avoid its interference with the children’s abilities to attain their academic potentials in schools. If the youngster does not see well to Myopia, his academic performance will be impaired.

The prevalence of Myopia when established will be useful in assessing the effectiveness of preventive optometry as well as that of Public Health in controlling the incidence of refractive errors in general and Myopia in particular among School children.

It will provide a demographic data for optometrist and other health care planners on the prevalence of Myopia in the study area, and help proffer preventive and corrective measures herein.

It will further enrich the existing literature on the subject matter.

The work when finished will constitute a modest contribution to the development of Optometry in Nigeria and will aid in a better understanding of the handicap raced by Myopes while stimulating interest in further research of Myopia thus improving the quality of services rendered.

1.7 Scope Of The Study

The research work will be limited to a cross-section of 100children in some Primary and Secondary Schools in Owerri, Municipal.

The scope of the study will cover the following: Carrying out refraction on children in some Primary and Secondary School store present a larger population. Noting the children suffering from Myopia.


Pages:  55

Category: Project

Format:  Word & PDF

Chapters: 1-5

Material contains Table of Content, Abstract and References.

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