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The Distribution Of Refractive Error Among Different Blood Groups In Imo State University, Owerri




The study investigated the distribution of refractive error among different blood groups in Imo State University, Owerri. Four research questions and hypothesis were formulated to guide the study. A cross-sectional study design was employed. The population recruited for this study are 10,000 young male and female adults subjects attending clinical and eye checkups at Imo State University eye clinic, ranging from 18 to 30 years of age. A random sampling (balloting without replacement) technique was employed to select 125 eligible subjects used for the study. Through a validated and structured questionnaire, refractive status of the subjects was taken and recorded. Their visual acuity at both far and near was taken using the Snellen visual acuity charts for distance and near vision. Blood samples were collected and stored in Ethylenediamine Tetraacetic Acid (EDTA) tubes appropriately labeled for identification. The data collected was analyzed using SPSS statistical methods version 21 (One way ANOVA) involving P and T test for the level of significance (P= 0.05) and presented in simple tables, frequency and percentages. The results revealed that the refractive error of subjects in different blood groups in both male and female irrespective of age has no significant difference with a mean value of 22.53+-2.752. In blood group o, Myopia is seen to be slightly dominant while the rest of the blood groups have similar percentage distribution. The study concludes that the distribution of refractive errors is the same in all blood groups as there is no significant difference. Although some congenital myopia and hyperopia are from birth, and ABO group system also have a genetic basis, the two genes move independently



1.1 Background of Study

The refractive state of the eyes refers to the locus within the eye conjugate with optical infinity during minimal accommodation (Bennett and Rabbet, 1998). Refractive error is known to be dependent on both local and systemic biochemical variables. Among the local variable, the axial length and refractive power of the eye (as contributed by the curvature thickness and refractive index of the cornea and lens) are known to be the primary factors on which abnormal changes may lead to refractive errors (Okorie et al., 2015).

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Emmetropia: It can be defined as a state of refraction where in the parallel rays of light coming from infinity are focused at the sensitive layer of the retina with the accommodation bring at rest (Khurana, 2012).

Ametropia is defined as a state of refraction when the parallel rays of light coming from infinity with accommodation at rest are focused either in front or behind the sensitive layer of the retina in one or both meridians (Khurana, 2012).

Factors that Affect the Refractive Error Distribution

Age: Age is an important determinant of the distribution of refractive errors. The onset and development of Myopia occur in well-established yet poorly understood pattern, only a very small proportion of infants are myopic at birth and much of this neonatal myopia is associated with prematurity, likewise babies and toddlers exhibit a powerful prevalence of Myopia. Even by the time they enter formal schooling at age 6 years, children are generally not myopic. During the ensuing 6 to 8 years, however, low to moderate myopia is first observed and progresses. For juvenile- onset myopia, onset is typically between the ages of 7 and 14 years and the cessation is 14 to 15 years for females and 15 to 16 years for males (Borish, 2006).

Gender: Myopia is more common in men than women, while hyperopia is more common in women than men

There are three basic types of refractive errors, myopia, hyperopia and astigmatism

Hypermetropia: it is an error of refraction where in parallel rays of light from infinity come to focus behind the retina when accommodation is at rest. Accommodation has a considerable influence on hyperopia. Considering accommodation, total hyperopia may be classified as; latent hyperopia (this is corrected by the physiological tone of the ciliary muscle) and manifest hyperopia. Manifest hyperopia is of two types; facultative hyperopia (the part of error which can be corrected by an effort of accommodation ) and absolute hyperopia which cannot be overcome by either accommodation or ciliary tone (Nema, 2012).

Myopia: this is an abnormal dioptric condition of the eye in which parallel rays of light from infinity come to focus in front of the retina when accommodation is at rest. It is categorically classified as developmental myopia, simple myopia, and pathological myopia. The clinical features of the myopia include the inability to see distant objects clearly and holding the book too close to the eye while reading ( Grosvenoir, 2007).

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Astigmatism: this is a refractive condition in which the eyes optical system is incapable of forming a point image for a point object. This is because the refracting power of the optical system varies from one meridian to another.  In regular astigmatism, the meridian of greatest refraction and the meridian of least refraction are 90 degree apart. The most common cause of astigmatism is the abnormalities in the curvature of the cornea (curvature astigmatism). A small amount of astigmatism occurs due to inequalities in the refractive index of different sectors of the lens (Khurana, 2012). Broadly, there are two types of astigmatism: regular and irregular.

REGULAR ASTIGMATISM The astigmatism is regular when the refractive power changes uniformly from one meridian to another (i.e., there are two principal meridian).

 1.2     Statement of Problem

Different blood groups have been shown to be associated with different diseases. Blood groups have inherited origins because of their inherited character. There may be genes responsible for eye growth and size, so the study of genetics concerned with refractive errors may allocate the treatment to prevent the series. Timely genetic detection of refractive errors with blood groups can be useful for efficient screening and also provide the pathway involved in eye development.

Refractive errors are the most common eye conditions in the world. Although most errors can be corrected by optical or surgical methods, these treatments have some drawbacks and pose a large economic burden. In the US, an estimated 12.8 billion dollars were spent on the correction of refractive errors in 1990 (Javit and Chiang, 1994). The etiologic mechanisms of refractive errors can be both genetic and environmental.  Genetics plays a role in the growth and structure of the eye, as demonstrated in twin and family studies. Close-up work, particularly reading, is generally considered as an environmental factor that may lead to myopia (Angle and Wissman, 1980).  Furthermore, other eye conditions such as cataract, glaucoma, or ocular hypertension often coexist with refractive errors (Sidon and Schwartz, 1983).  The interaction of all these factors and the underlying mechanisms of refractive errors remain unclear. In spite of the consequences of uncorrected myopia, there is a paucity of information in the literature known about the prevalence, distribution and determinants of refractive errors in the adult population of different blood groups (Zahara and Hussain, 2006). The present study was aimed at determining the prevalence of these refractive errors in the various blood groups using Imo State University, Owerri, Nigeria, in order to provide a baseline data for further studies and establishing reference values for future intervention

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1.3     Aim/Objectives of Study

The aim of this study is to determine the distribution of refractive errors among different blood groups.

Specific Objectives

  1. To determine the demographic characteristics of subjects involved in the study
  2. To identify the prevalence of refractive errors among different blood groups in Imo State University
  3. To examine and identify the distribution of different blood groups of various subjects involved in this study
  4. To carryout both objective and subjective refraction among subjects in Imo State University, Owerri

1.4 Research Questions.

  1. What is the refractive status of subjects in blood group A?
  2. What is the refractive status of subjects in blood group B?
  3. What is the refractive status of subjects in blood group AB?
  4. What is the refractive status of subjects in blood group O?

 1.5     Research hypothesis

Null Hypothesis

Ho: The distribution of refractive errors among different blood group is the same

Alternative Hypothesis

H1: The distribution of refractive errors among different blood groups is not the same

1.6     Significance of Study

This study will aid the clinician in establishing a clinical history of a patient and in assessment of refractive status of patients in different blood group.

 1.7     Scope of Study

The scope of study involves adult from 18 years to 30 years including male and female.

1.8     Limitation of Study

  1. Inability of patients complying in blood sample collection for the study
  2. Improper labelling and identification of patients’ blood samples
  3. Time frame for the collection of the sample

Pages:  69

Category: Project

Format:  Word & PDF                

Chapters: 1-5                                                      

Material contains Table of Content, Abstract and References.


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