THE NORMAL EYE
A tough white covering called the sclera protects the eye. Some part of the white sclera can be seen in the front of the eye and a clear, delicate membrane called the conjunctiva covers the sclera (Glaucoma Research Foundation 2009). Figure 2.1 presents the important features of an eye.
At the front of the eye is the cornea. The cornea is the clear part of the eye’s protective covering and it allows light to enter the eye. The iris is the colored part of the eye that shrinks and expands so the pupil can let just the right amount of light into the eye. The light is directed by the pupil to the lens. The lens focuses the light onto the retina (inside the lining of the eye). Nerve fibers in the retina carry images to the brain through the optic nerve (Glaucoma Research Foundation 2009).
The front part of the eye is filled with a clear fluid called intraocular fluid or aqueous humor which is made by the ciliary body. This fluid flows out through the pupil and is then absorbed into the bloodstream through the eye’s drainage system. The drainage system is a meshwork of drainage canals around the outer edge of the iris. Proper drainage helps keep eye pressure at a normal level. The production, flow, and drainage of this fluid is an active continuous process that is needed for the health of the eye (Glaucoma Research Foundation 2009).
The inner pressure of the eye known as intraocular pressure (IOP) depends upon the amount of fluid in the eye. If the eye’s drainage system is working properly, the fluid can drain out and prevent a build-up. Likewise, if the eye’s fluid system is working properly, then the right amount of fluid will be produced for a healthy eye. IOP can vary at different times of the day, but it normally stays within a range that the eye can handle (Glaucoma Research Foundation 2009).
The glaucomas are a group of eye disorders characterised by progressive optic nerve damage at least partly due to increased IOP (The Merck manual of diagnosis and therapy 2006:903). They are categorised as open-angle or closed-angle (angle-closure). The “angle” refers to the angle formed by the junction of the iris and cornea at the periphery of the anterior chamber (see figure 2.2), and this is where >96% of the aqueous humour leaves the eye. Glaucomas are further sub-divided into primary glaucomas (cause of outflow resistance or angle closure is unknown) and secondary glaucomas (outflow resistance results from another disorder), accounting for more than 20 adult types (The Merck manual of diagnosis and therapy 2006:903).
Primary open-angle glaucoma is a syndrome of optic nerve damage associated with an open anterior chamber angle and an elevated or sometimes average IOP (The Merck manual of diagnosis and therapy 2006:906). The majority of people with glaucoma worldwide have primary open-angle glaucoma (Quigley & Broman 2006). It is also the most common glaucoma amongst Africans (Cook 2009:124). Thus, much of the discussion in this study focused on primary open-angle glaucoma.
Angle-closure glaucoma is glaucoma associated with a closed anterior chamber angle, which may be chronic or rarely acute (The Merck manual of diagnosis and therapy 2006:909). This type of glaucoma is more common in Asians and in women (Quigley & Broman 2006).
Epidemiology of glaucoma
Glaucoma is the second leading cause of blindness worldwide if undetected or untreated (Quigley 1996:389; Quigley & Broman 2006:262) and it is estimated that there will be 60.5 million people with the primary glaucomas in 2010 (Quigley & Broman 2006:262).
Most Africans in many parts of the world such as North America and Europe are disproportionately affected by primary open angle glaucoma. It is also the most common in Africa. Large population-based studies such as the Barbados Eye Study showed that 1 in 11 Afro-Caribbeans over the age of 50 years and 1 in 6 over the age of 70 years have open angle glaucoma (Leske, Connell, Schachat & Hyman 1994:295).
The prevalence of glaucoma in East, Central and Southern Africa can be conservatively estimated to be 10,000 people for every 1 million population which may be higher in West Africa (Cook 2009:124). Glaucoma in Nigeria is the second most common cause of blindness after cataract and approximately 980,000 Nigerians are blind from glaucoma (Abdul et al 2009:4114).
In 2002, 37 million individuals were blind worldwide, with glaucoma accounting for 12.3% of these individuals. Bilateral blindness from glaucoma is projected to affect 8.4 million people worldwide by 2010 and greater than 11 million in 2020 (Quigley & Broman 2006:262).
Risk Factors for open – angle glaucoma
Elevated intraocular pressure is an important risk factor for open – angle glaucoma (American Academy of Ophthalmology 2008:85). Large, population based epidemiologic studies have revealed a mean IOP of 15.5 mm Hg, with a standard deviation of 2.6 mm Hg. This led to the definition of “normal IOP” as approximately 10 – 21 mm Hg. Other risk factors for POAG other than IOP include race, advanced age and positive family history (American Academy of Ophthalmology 2008:85). The Baltimore Eye Survey (Tielsh et.al 1991:369-374) found the prevalence of glaucoma to increase dramatically with age, particularly among blacks, exceeding 11% in those aged 80 years or older. Black race is another important risk factor. Prevalence of POAG is 3 to 4 times greater in blacks than in others. Blindness from glaucoma is at least 4 times more common in blacks than in whites (Tielsh et al 1991:369). The Baltimore Eye Survey (Tielsh et al 1991:369-374) found that the relative risk of having POAG is increased about 3.7-fold for individuals who have a sibling with POAG, thus highlighting the role of a positive family history. Omoti and Edema (2007:79) in a study in Benin, Nigeria report risk factors for open angle glaucoma to include increased age, African ethnicity, family history of glaucoma, increased IOP, myopia and decreased corneal thickness. Some other possible risk factors for glaucoma include diabetes, hypertension, eye injury or surgery, history of steroid use, migraine headaches, sleep-related breathing disorders and male gender (The Eye Digest 2009).
Table of contents :
CHAPTER 1 ORIENTATION TO THE STUDY
1.2 BACKGROUND INFORMATION ABOUT THE RESEARCH PROBLEM
1.2.1 The source of the research problem
1.3 RESEARCH PROBLEM
1.4 AIM OF THE STUDY
1.4.1 Research purpose
1.4.2 Research objectives
1.5 SIGNIFICANCE OF THE STUDY
1.6 DEFINITIONS OF KEY CONCEPTS
1.7 FOUNDATION OF THE STUDY
1.7.1 Theoretical framework
1.8 RESEARCH DESIGN AND METHODOLOGY
1.9 VALIDITY AND RELIABILITY
1.10 ETHICAL CONSIDERATIONS
1.11 LAYOUT OF THE STUDY
CHAPTER 2 LITERATURE REVIEW
2.2 THE NORMAL EYE
2.3.1 Epidemiology of glaucoma
2.3.2 Clinical features of glaucoma
2.3.3 Diagnosis of glaucoma
188.8.131.52 Vision tests
184.108.40.206 Slit-lamp examination
220.127.116.11 Corneal thickness
2.3.4 Treatment of glaucoma
2.4 GLAUCOMA AWARENESS/KNOWLEDGE
2.5 DETERMINANTS OF GLAUCOMA KNOWLEDGE
2.6 THEORETICAL FOUNDATION
2.6.1 The Health Belief Model applied to knowledge about glaucoma
2.6.2 Individual perceptions
2.6.3 Modifying factors
2.6.4 Likelihood of action
CHAPTER 3 Research design and methodology
3.2 RESEARCH DESIGN
3.2.1 Research paradigm
3.3 RESEARCH METHODS
3.3.1 Research study setting
3.3.3 Sampling and sample
3.3.4 Sample size estimation
3.3.5 Data collection
18.104.22.168 Data collection instrument
22.214.171.124 Data collection process
3.4 VALIDITY AND RELIABILITY
3.5 DATA ANALYSIS
3.6 ETHICAL CONSIDERATIONS
CHAPTER 4 Data presentation, analysis and interpretation
4.2 DATA ANALYSIS
4.2.1 Section A: General information
126.96.36.199 Respondents’ age
188.8.131.52 Ethnic background
184.108.40.206 Clinic attendance of respondents
220.127.116.11 Marital status of respondents
18.104.22.168 Respondents’ level of education
22.214.171.124 Status of the respondents
126.96.36.199 Previous eye examination and knowledge about glaucoma
188.8.131.52 Respondents’ awareness of the term glaucoma
4.2.2 Section B: Assessment of glaucoma knowledge
CHAPTER 5 FINDINGS, LIMITATIONS AND RECOMMENDATIONS
5.2 OBJECTIVES OF THE STUDY
5.3 SUMMARY OF FINDINGS
5.3.1 Demographic data
5.3.2 Respondents’ knowledge of glaucoma
5.3.3 Determinants of glaucoma knowledge
5.4 SCOPE AND LIMITATION OF THE STUDY
LIST OF SOURCES