Prevalence of Manifest Hyperopia among High School Students in a Ghanaian Metropolis: A Population-Based Cross-Sectional Study
Hyperopia synonymous to “hypermetropia” and “farsightedness” is an anomalous refractive condition of the eye in which light rays entering the eye converge at a point behind the retina, with accommodation fully relaxed. In other words, images of objects are not brought to a sharp focus on the retina but behind the retina. This invariably leads to blurred vision. In some cases, persons suffering from hyperopia (called “hyperopes”) have a better distance than near visual acuity[1,2].There are divergent views on the classification of hyperopia. Hyperopia however may exist as Latent, Manifest, Facultative and Absolute Hyperopia. Latent hyperopia is where all or part of a patient’s hyperopia is compensated for by a process called accommodation. For example, if a routine objective refraction reveals a 4.00 dioptre (D) of hyperopia in a patient but the subjective refraction reports on 2.00 D of hyperopia, the 2.00 D revealed in subjective refraction represents manifest hyperopia. The other 2.00D which was (hidden) compensated for by accommodation represents the latent hyperopia [1,3].
Absolute hyperopia is that hyperopia that cannot be compensated for by accommodation. If a person has 5.00D of hyperopia and 2.00 D of accommodation, the 3.00 D of hyperopia that cannot be overcome by accommodation represents absolute hyperopia and the other dioptre of hyperopia (3.00D) that can be overcome by accommodation is the facultative hyperopia [1-3].
Generally, hyperopia is common in children and young adults. The trend in prevalence could change with age, with the process of emmetropization and also the refraction technique employed . The same population could have different prevalence values if study subjects are made to undergo cycloplegic refraction at one time and non-cycloplegic refraction at another time. Studies done in different populations have reported differences in the prevalence and distribution of hyperopia [5-7].
Clinically uncorrected hyperopia could come with a myriad of oculo-visual signs and or symptoms. Hyperopia could be significant enough to cause visuomotor and sensory complications for individuals. Apart from the frequently reported blurred vision, hyperopic individuals could show accommodative esotropia and may show head turn. Hyperopia that is left uncorrected from childhood may lead to amblyopia. Other commonly reported signs and symptoms among hyperopes include red or tearing eyes, facial contortions while reading, asthenopia, frequent blinking, focusing problems, decreased binocularity and eye-hand coordination, and difficulty with or aversion to reading. The effects of uncorrected hyperopia could vary depending on the magnitude of hyperopia, the age of the individual and the status of the accommodative – convergence system [1,8-11].
Some reports show that hyperopia has an association with lower literacy standards in children . Lower intelligence quotient scores in the UK have been reported hyperopic subjects than in myopic patients . The complications of uncorrected hyperopia including but not limited to strabismus and amblyopia especially in young people can be prevented by early detection and subsequent correction of hyperopia with spectacles, contact lenses and or surgery [1, 14-16].
This study was an attempt to determine the prevalence of manifest hyperopia (MHyp), oculo-visual symptoms and the coverage of hyperopic spectacle correction among some high school students in a Ghanaian metropolis.
This was a population-based cross-sectional study in which 12 of out of the total of 23 senior high schools in the metropolis were randomly selected. Two classes were randomly selected in each of these 12 schools and the students in those particular classes examined.
Data collection/ Procedures
Participants were guided by one of the investigators to answer an interviewer – administered questionnaire which focused on gathering information on their demographic profile and ocular history (specifically oculo – visual symptoms detailed on the questionnaire) and the use of spectacle correction. Participants were free to report about their own known medical conditions. Distance visual acuity was assessed for each participant using a Snellen chart at six (6) meters backlit with luminance of 160cd/m2. We performed non-cycloplegic objective refraction (retinoscopy) in a dark room using a Welch Allyn Elite (streak) retinoscope. Subjective refraction was performed on all the participants. Plus 1 blur test was incorporated in the subjective refinement of dioptre values of the refractive error detected. Participants were diagnosed as hyperopic if they had manifest hyperopia of a spherical equivalent of at least +0.75 D in either of the eyes.
The entire study and the involved procedures were explained to all participants. Informed consent was sought from some participants (aged ≥ 18years) and from parents of some participants aged below 18 years. Permission to carry out the investigations in the selected schools was obtained from the Directorate of Education in the Metropolis and the head teachers of those schools. The study obeyed the tenets of the Declaration of Helsinki.
Data collected were analysed using GraphPad Prism version 6 (GraphPad Software, Inc., California USA). Continuous variables were expressed as mean ± standard deviation (M±SD). Descriptive statistics, Chi-square tests and Pearson correlation coefficient were performed to find significant differences between comparable categorical groups. A p-value <0.05 was considered significant.
A total of 662 students (52.0% males and 48% females) were examined during the study. The mean of these study respondents 16.9 ± 0.9 years: with an age range of 15 – 19 years. The age and sex distribution of the students is displayed in Table 1.
Table 1. Age and sex distribution of the students.
Prevalence and distribution of manifest hyperopia (MHyp) among study respondents.
The overall prevalence of MHyp recorded was ≈ 26.0% (male prevalence was 12.6% and female prevalence 13.4%). We did not detect a significant difference in the prevalence of MHhyp between sex groups (p<0.05). Table 2 shows the distribution of hyperopia among male and female respondents.
Table 2. Distribution of MHyp by gender.
Regarding the distribution of MHyp per age of the study respondents, those aged 17 years recorded the highest percentage of 11.2%, followed by those aged 16 years. The least per age category were those aged 15 years (0.6%). Pearson correlation coefficient revealed a negative correlation between age and the prevalence of MHyp [r (3) = -0.07, p- >0.05]. Table 3 summarizes the distribution of MHyp per age of the participants.
Oculo-visual symptoms reported by the respondents.
In all, the most widely reported symptom was headache (62.8%). This was followed by teary (watery) eyes (47.1%) with the least reported symptom being blurred vision (31.4%). Some of the hyperopes in the study reported of more than one of these symptoms.
Table 3. Distribution of MHyp per age of participants.
Coverage of refractive correction of respondents.
The overall coverage of hyperopic refractive correction was low. Only 4% of the total with MHyp wore spectacle corrections. The other (96%) hyperopes had their hyperopia uncorrected (unmanaged).
Globally, there have been extensive studies on the prevalence of refractive errors (including hyperopia) in different populations and across different span of ages [5,7,17,18]. Many studies focused on younger children but our study was concerned with studying high school students who in their middle (15years) to late (19years) teenage years. This was done as an attempt to gain some insight into the trend of hyperopia in that particular span of ages in the Ghanaian population.
The overall prevalence of MHyp for this study was relatively higher than what has been reported in other studies conducted elsewhere in Ghana and South Africa (≈26% versus 1.6% and 5%) which also employed non-cycloplegic refraction technique [19,20]. On one hand, our reported prevalence value was lower than what was reported (≈26.0% versus 73.1%) in a study which also used non-cycloplegic . Other comparable studies reported prevalence values that are close to what we recorded (≈26.0% versus 22.6%, ≈26.0% versus 27.3%) [22,23].
It suffices to say that the prevalence value of hyperopia differs from one study to the other. This could be due to differences in population characteristics, sample size, age and sex of participants [20-22]. Another possible factor that could account for the differences in prevalence value is the refraction technique employed. Prevalence values have been observed to be different for studies employing cycloplegic technique and non-cycloplegic technique [5, 24, 25].
While we detected a negative and insignificant relationship between the prevalence of MHyp and age, other studies have reported otherwise. A Polish study  recorded a positive and significant correlation (p< 0.001) between the prevalence of hyperopia and age. For that study, hyperopia increased between the ages of 7 -8 years. Difference in prevalence between male respondents (12.6%) and females (13.4%) was insignificant (p->0.05). Other studies, have reported significant differences in prevalence of hyperopia between sex age groups. Hyperopia has also been found to have association with age and gender [1,2,26,27].
We would like to mention that, readers should consider the findings from this study in the light of some limitations to our study design. For example, the nature of our study sites did not allow for cycloplegic refraction; we thus are reporting only dioptric values of hyperopia from dry refraction (Manifest hyperopia) ranging from +0.75D to +1.25D. Even though these values are comparable to what is reported in other studies, it would be wrong to interpret our findings as the whole picture of hyperopia among the population studied. The latency of hyperopia common among young people would provide different results should we have employed cycloplegic/refraction (1, 3, 28-30). Studies that employed cycloplegia to unmask latent hyperopia have reported values ranging from +1.00D to >+3.00D [5,24,27,31].
Some of these participants with MHyp reported more than one oculo – visual symptom. Headache was the most frequently reported symptom (62.8%). Blur vision and watery eyes were also reported. Even though we did not focus on studying how MHyp associated with these symptoms, it is important the stress accommodative stress placed on the visual system of persons with uncorrected could be significant to trigger general asthenopia – which comprise but not limited to pain in the eye, redness, headaches, blur and sometimes double vision [1-3]. It is these unpleasant visual experiences that warrant early detection and subsequent correction of hyperopia. We also did not assess how hyperopia impacted academic performances of our study respondents but some studies have reported low literacy standards and lower intelligent quotients among hyperopes [12,13]. Reading and writing require good vision and where refractive anomalies exist proficiency in these skills could be reduced.
It was found in our study that, only 4% of the participants with MHyp wore spectacle correction. This indicates a low coverage of refractive correction in the population studied. One study reported a similarly low coverage (1.69%) of refractive correction among study subjects . On one hand, a different study reported a higher coverage of refractive correction among children with refractive error . While we neither knew nor investigated what accounts for the low coverage of refractive correction, it is reasonable to assume that many of the hyperopes did not wear a spectacle correction for reasons that may include cost, lack of awareness (and or knowledge) of their refractive status and or other personal reasons.
Socioeconomic challenges have been a barrier to uptake of refractive services in most places across the world. People may not wear a spectacle correction (or assess any form of health care) because of financial constraints or social stigma attached to wearing spectacle – spectacle wearers in certain Ghanaian communities are often tagged as having “bad eyes” [31, 33-38].
The study has attempted to provide an insight into the prevalence of manifest hyperopia among some high school population in Ghana. The overall prevalence (26.0%) is relatively high compared to what other studies have been reported. There was a low coverage of refractive correction; this suggests that the participants and other people at their age in Ghana will benefit from refractive screening and correction services. The Ghana Education Service could thus implement a policy on rolling basis to help screen, detect and correct hyperopia and other forms of ametropia in students.
We recommend future investigation in population of ages similar to the participants in this study to employ cycloplegic refraction to allow for better comparison and to give a standard picture of the hyperopia situation among people of such ages in Ghana. We have only reported on manifest hyperopia which does not provide a perfect representation of hyperopia in the study population.
Conflicts of Interests
The authors declare that they have no conflicting interests.
The authors have no financial relationships to disclose.
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