Characteristics and prevalence of pterygium in small communities along the Solimões and Japurá rivers of the Brazilian Amazon Rainforest

1MD,Resident,Instituto Benjamin Constant Rio de Janeiro (RJ), Brasil; 2MD,Hospital Adventista de Manaus Manaus (AM), Brasil; 3PhD,Universidade Federal do Rio de Janeiro (UFRJ) Rio de Janeiro (RJ), Brasil; 4MD,Fellow, Hospital do Olho Rio de Janeiro (RJ), Brasil. 5MD,ONG Enxerga Brasil Brasil; 6PhD,Universidade Estácio de Sá (UNESA) Rio de Janeiro (RJ), Brasil; 7PhD,Instituto Benjamin Constant Rio de Janeiro (RJ), Brasil and Faculdade de Medicina de Valença – Valença (RJ), Brasil.


P
terygium is defined as a growth onto the cornea, usually nasally, of a fibrovascular tissue, often triangular in shape, that is continuous with the conjunctiva.This lesion may be clinically aggressive and occasionally threaten vision (1,2) .Recent studies suggest that pterygium is a proliferative condition instead of degenerative, highly associated with UV exposure (3)(4)(5) .The condition is common in the so-called 'pterygium zone', which is defined by a geographical latitude of 40º north and south of the equator (6) .In countries within this area prevalence of up to 22% in the general population has been reported (7) .
The pathogenesis of pterygium is very complex and the subject's genetic background is reported to be relevant
The communities evaluated in this study are located in the Amazon rain forest, in an isolated region of difficult access, near the equator.The population found in these communities is composed of Indian and whiteindians descent.Their activities are fishing, hunting and agriculture.Almost all the subjects examined have never had contact with an ophthalmologist before.To the present day, there has been no data about prevalence of pterygium in these communities.
In Brazil, there is no data about prevalence of pterygium in the whole country and even for specific regions there are few studies that cover this subject.A previous study of pterygium in Hospitals of Salvador and Manaus showed a similar frequency of the lesion in both genders (9) .Another study reported a high incidence of Characteristics and prevalence of pterygium in small communities along the Solimões and Japurá rivers of the... pterygium in an institute of ophthalmology in Manaus (10) .
Recently pterygium prevalence has been reported among indians at the Negro river region, Amazonas state.According to the reports, a pterygium prevalence of 12.8 % from total Indian population (11) and 18.4 % among elderly and adults was described.Furthermore, pterygium lesions were found mainly in Indian groups with higher UV exposure (12) .
The objective of this study is to evaluate pterygium prevalence and characteristcs in small communities of the Amazon rainforest located along the Solimões and Japurá rivers, state of Amazonas, Brazil (Figure 1).

METHODS
A cross-sectional study was developed in small communities along the Solimões and Japurá rivers, located in the countries of Tefé, Alvarães, Maraã and Fonte Boa, state of Amazonas, Brazil.Data were collected by two different evaluators in three medical expeditions.The study covered 55 local communities and 1295 patients.A total of 659 patients were above 18 years old and 636 were under 18 years old.These communities were selected because none of them had never been evaluated by an ophthalomologist before.During each visit, the examiners tried to assess the entire community.
Eyeglasses were donated to patients who needed them.Patients having pterygium lesion answered a questionnaire covering gender, age, and outdoor activity, such as fishing, hunting and agriculture.
The pterygium lesions sizes were graded clinically by slit-lamp biomicroscopy as grade 1 (lesion cover until limbus), grade 2 (lesion covers cornea by 2 mm), grade 3 (lesion surrounds the pupil) and grade 4 (lesion crosses the pupil).This graduation was used in the study of pterygium in the the Botucatu region (13) .When a individual had more than one lesion, the most severe one was analyzed, as shown in Figure 2. The type of presentation of the lesion was classified as nasal, temporal or both nasal and temporal lesion.This study was approved by the Ethics Committee of the Medical School of Valença.(protocol number 005.0.334.000-10)
Outdoor activity was referred by 89.4% (246/275) of the patients with the lesion.
Of total subjects diagnosed with pterygium, 75.6% (208/275) had it in both eyes.

DISCUSSION
The pterygium prevalence along the Solimões and Japurá rivers, of 41.1 % in individuals over 18 years old reported here, is higher than others regions previously reported, such as India, where the prevalence of pterygium in individuals above 50 years of age was 5.2% (14) .In Singapore a prevalence of 9.7% in those who were over 40 years old has been recorded (15) and in Indonesia a prevalence of 10.0% in adults over 21 years old (16) .In Nigeria there is a prevalence of 8.2% in individuals from 18 to 49 years old (17) .
In this study we showed a higher rate of pterygium than the ones previously described by others in the Amazon rainforest like in the Negro river region where a prevalence of 12.8% in the population in general (11) and of 18.4% in adults and elderly had been described (12) .The severity of the lesion is important in this study.The pterygium observed was classified mainly as grade 2 and grade 1, but lesions in grade 4, that causes a severe visual acuity disability, were found in 5 subjects, suggesting that it may still exist blindness caused by pterygium in that region.Furthermore, we showed that four patients under 18 years old and 48 patients with ages between 19 e 30 years old developed pterygium.From total subjects diagnosed with pterygium, 39.6% were under 40 years old.This data suggests that pterygium develops early in the population studied.
The outdoor activities such as fishing, hunting and agriculture were the occupation of most of the patients.This suggests the relationship between exposure to UV and the development of pterygium, already demonstrated in other articles (3,18) .

CONCLUSION
Considering the difficulty of access to the communities evaluated, this study had a large area of coverage and a larger number of inhabitants were included than in other studies in the Amazon region.In conclusion, this work described one of the highest pterygium rates in the world, in an Amazon region that had never had been studied before, showing the importance of further studies of the riverside population in the Amazon rainforest.

Figure 1 :
Figure 1: Location of the studied region, Solimões and Japurá rivers, state of Amazonas, Brazil

Figure 2 :
Figure 2: A -Nasal lesion grade 1; B-Temporal and nasal lesion grade 2; C -Temporal and nasal lesion grade 3; D-Temporal and nasal lesion grade 4

Table 1
Distribution of commited subjects according age and lesion grade

Table 2
Distribution of commited subjects with pterygium according to gender and lesion grade.F -female; M -male