Ametropia is the most common cause of visual impairment worldwide and the second leading cause of blindness   . Unadjusted, they can affect school performance, reduce employability, productivity and generally affect the quality of life . Its simple correction is reflected in the prescription of corrective lenses.
Countries in Africa are responsible for 1.1% to 7.9% of cases of visual impairment .
In Congo, studies have been tested on children  , but do not have data on the general population.
This study was conducted on the basis of data collected as part of a free consultation program in a region with shortage of adequate ophthalmic care.
2. Patients and Methods
We conducted a cross-sectional study in Kinkala, South Congo Brazzaville, as part of a free medical care program, in a mobile clinic.
Included in our study were patients over 5 years of age with no apparent organic disease. The study lasted one month, from 25 August to 24 September 2019.
After registration, patients were complaining of a decrease in visual acuity or asthenopia, were placed on cyclopentolate eye drops according to the following protocol: 3 applications of one drop every 5 minutes. An auto-refractometry was performed at least 45 minutes after the first instillation, allowing us to determine the objective ametropia of patients.
Only static ametropias were taken into account in this study, presbyopia was not evaluated.
Only results greater than or equal to 0.5 dioptres (D) of spherical (hyperopia and myopia) or cylindrical (astigmatism) ametropia were considered.
The patients were then examined with a slit lamp to eliminate associated organic lesions.
Data analysis was done with epi-info software 7.
Among the 2352 patients seen in ophthalmology, only 137 (5.82%) were eligible for refraction, taking into account their original complaint;
Of the 137 patients (273 eyes, one patient being monophthalmic) examined, 14 (28 eyes) were emmetropic, and 123 patients (245 eyes) had ametropia.
Among patients with ametropia 42 were men versus 81 women. Or a sex ratio of 52.
The prevalence of ametropia for all patients was 5.22%.
Astigmatism was the most common ametropia in all age groups.
Among patients with astigmatism, 150 (86.71%) had hypermetopic astigmatism, 17 (9.83) had myopic astigmatism, and 6 (3.47%) had mixed astigmatism.
The frequency of different types of ametropia was proportionally the same for both sex.
Astigmatism was direct or regular in 93 (53.75%) cases, inverse or irregular in 56 (32.36%) cases, and oblique in 24 (13.87%) cases.
Between 5 and 15, there was 71.43% of direct astigmatisms against 28.57% of inverse astigmatisms.
Between 16 and 39 years of age, there was 81.82% direct astigmatism, 10.61% inverse astigmatism and 7.58% oblique astigmatism.
Between 40 and 59 years, there was 38.55% direct astigmatism, 45.78% inverse astigmatism and 15.66 oblique astigmatism.
At age 60 and older, there was 11.76% direct astigmatism, 64.71% inverse astigmatism and 23.53% oblique astigmatism.
In spherical equivalent more than 80% of patients had hyperopia between 0 and 2.5 D.
Cycloplegia in objective refraction is one of the methods used to detect ametropia. It is a bit more expensive because of the equipment it requires. It gives reproducible ametropia values, slightly higher than those obtained in subjective refraction .
Performing refraction only in patients with complaints about ametropia probably missed other ametropia.
Among the 273 eyes that benefited from objective refraction, in addition to the complete anatomical examination, 28 were emmetropic, which corresponds to a prevalence of ametropia of 5.22%. This prevalence corresponds to African data .
The prevalence of ametropia varies from one study to another depending on the study population: children  or adults  ; or the methodology used: some authors have considered ametropia from refractive values of 0.5 diopters  , and others from the value of 0.25 diopters .
The most frequent ametropia was astigmatism, with 70.61% of cases, followed by hyperopia with 25.71%. Myopia accounted for only 3.67% of cases (Table 1). These results are close to those of Ebana  in Cameroon with 4.6% myopia and 51% hyperopia. We had a little more patients with astigmatism because of the use of the auto-refractometer which is a little more sensitive to the detection of astigmatism .
Hyperopic astigmatism accounted for 86.71% of astigmatisms versus 9.83% of myopic astigmatisms. These results are close to those of Ebana  in Cameroon with hypermetropic astigmatism at nearly 27% of all ametropia compared with nearly 9% of myopic astigmatism. Gargouri  in Tunisia had noted 59% hypermetropic astigmatism versus 41% myopic astigmatism.
There was no difference in the frequencies of different types of ametropia by sex (Table 2).
The axis of astigmatism evolved with age, between 5 and 39 years. More than 65% of patients had direct astigmatism, between 40 and 59 years of age. There was almost as much direct as there was reversed astigmatism. At 60 and over, reversed astigmatism was almost 65% of cases. This inversion of the axis of astigmatism with age had already been described in the literature . Shah  who worked on adults noted a low prevalence of direct astigmatism (14%).
Taking into account the spherical equivalent of different ametropia, 79.57% of our patients had hyperopia between 0.25 and 2.5 diopters (Table 3), which is consistent with Ebana  results in Cameroon, where hyperopia and astigmatism hyperopia accounted for 78.5% of patients.
Table 1. Distribution of patients according to the type of ametropia.
Table 2. Distribution of ametropia by sex.
Table 3. Distribution of patients according to the spherical equivalent of their ametropia.
Static ametropia in Kinkala, Congo, is dominated by astigmatism. The axis of astigmatism evolves with age, from direct astigmatism to childhood to inverse astigmatism in the elderly. Considering the spherical equivalent, hyperopia accounts for more than 80% of all ametropia encountered.
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