This investigation was part of a population-based study of ocular disorders among Mongolian people aged 40 years and older living in Henan County, China, the Henan Eye Survey (HES). Henan County (East longitude of 100° 53′–102° 15′ and north latitude of 34° 04′–34° 55′) is located in the eastern part of the Qinghai-Tibetan Plateau, China. The average altitude of Henan County is 3450 m, with a land area of 6997km2. It has 6 townships and 49 villages. cheap oakley sunglasses The country has a constant high altitude climate with a yearly mean temperature of －3°C, daily mean total global radiation of 625 kj/cm2, and 2650 h of sunshine per year (2005, Meteorological Service, Bureau of Environment, Qinghai, China). The socioeconomic status is at the lower end of the norm in China. Henan County was chosen as the study community after considering population stability, metropolitan areas, sea level, and local support into consideration.
Selection of subjects
According to the 2004 population census, the total population of Henan County was 32 616, with native Mongolians being 30 422 (93.3% of the total). The number of native Mongolians aged 40 and older were 6449 (21.2%) of all native Mongolians. Residents 40 years of age and older were identified by the household registration system.
The stratified, clustered, random sampling method was used for sampling drawing. For determining the sample size, the prevalence of blindness for adults 40 years and above was estimated to be 5%. We assumed a design effect of 1.5 (for cluster sampling), a confidence interval (CI) of 95%, an allowable error of 25%, and a response rate of 80%. These assumptions led to a sample size of 2426. We used the villages as the primary sampling units (PSUs)11 for the entire county. The number of native Mongolians in each PSU was within the range of 450–600. There were 47 PSUs actually involved in this survey, in 28 596 (94.0 %) of the county's total Mongolian population. The random digits table was used to draw 19 units from those PSUs to fit the needs of the sample. Two thousand four hundred and eighty-nine native Mongolians 40 years and older were eligible. All participants were native Mongolians who were born and grown up in the selected area.
The pre-survey stage and pilot study
Contacts were made from April 2006 to May 2006 with the local government and correlated constitutions to negotiate the detailed affairs of the survey, and informed the individuals who were in the selected PSUs. Before the formal survey began, 1 week's training and a pre-survey were conducted (the first 1 week of June 2006). The pilot study was conducted outside the study area and these results were excluded from this study. A total of 216 individuals from another county near by Henan County were examined. These examinations revealed weaknesses in the examination procedures and in the organization of the processes and procedures. These weaknesses were successfully addressed before implementation of the main study.
Data collection
The fieldwork of data collection was started and conducted from June 2006 to September 2006. A team of five ophthalmologists, administrative personnel from the villages, and the medical workers of the township clinics (they also acted as translators) carried out the data collection. The team was equipped with two vehicles, Snellen's E charts, two slit-lamp microscopes (Model YZ-5E, Crane, China), a stereo-ophthalmoscope (Keeler, UK) with a Volk 20 D lens. The team also was equipped with power generators for locations without electricity.
At locally established test sites (at local clinics), the participants underwent the examinations, including a personal interview, visual acuity, signs of dry eyes, slit-lamp assessment of anterior segment and lens, and fundus evaluation. Ophthalmologists conducted the eye examinations according to a standardized protocol.
A standardized interview was conducted on all participants and a structured questionnaire was used to obtain information based on demographic data (name, age, gender, locality, economic status, and education) and lifestyle (smoking, alcohol intake, wears a hat or sunglasses). Participants’ self-reported demographic data were assessed. Age was defined as the current age at the time of survey. Education level was ascertained by the question, ‘How many years have you been in school?’ cheap sunglasses We classified these answers into four categories: never, less than 3 years, 3–6 years, and more than 6 years. Family economic status was measured according to the number of yaks in the family, since yaks are one of the most important domestic animals for this group of Mongolian population. Three categories were classified: low (less than 10 yaks), middle (10–50 yaks), and high (more than 50 yaks). Symptoms of dry eye were assessed using a six-item validated questionnaire;12 presence of one or more of the six dry eye symptoms often or all the time was analyzed. People were asked to state when outdoors if they wore a hat, sunglasses, or stone spectacles (seldom or often). The participants were also asked questions about their cigarette-smoking history (smoker and non-smoker). Alcohol intake was categorized as no habit of alcohol consumption and a habit of alcohol consumption.
As part of the standardized eye examination, a slit-lamp (Model YZ) was used to examine the anterior segment for evidence of pterygium. The diagnosis of pterygium was made clinically by a single examiner (PL). The Schirmer's test was performed 1 min after instillation of a drop of 0.5% proparacaine (Alcaine, Alcon-Couveur, Belgium), and any visible fluid in the inferior fornix or lid margin was gently dried with a cotton swab. A precalibrated filter strip (Tianjin Jingming New Technological Development Co. Ltd, China) was then placed temporally in each lower fornix and left in place for 5 min. The patient was encouraged to close his/her eyes but allowed to blink normally. After 5 min, the strip was removed, and the amount of wetting was recorded. The tear-film breakup time test was repeated three times for each eye, and the average time was recorded.
Diagnostic criteria
Pterygium was diagnosed if a characteristic raised fleshy growth crossing the corneoscleral limbus and encroaching on the clear cornea was present13 or if pterygium surgery had been performed. A system of grading pterygia according to their morphology has been developed for use in pterygium studies.14, 15 Grade T1 (transparent) includes a pterygium in which episcleral vessels underlying the body of the pterygium are clearly distinguished and unobscured and grade T3 (opaque) a thick, fleshy pterygium in which episcleral vessels underlying the body of the pterygium are totally obscured. All other pterygia that do not fall into these two categories fall into grade T2 (intermediate). If a patient had bilateral pterygia, the grade was classified according to the higher grade in either eye. Age-related cataracts were assessed by use of the Lens Opacity Classification System III,16, 17 by a senior ophthalmologist (XC). Subjects with congenital or traumatic cataracts in one or both eyes were excluded from this analysis.
Data processing and statistic analysis
Fixed people for fixed items filled the results of the survey in the forms. Questions were solved by discussion with the entire team. SPSS (Statistical Package for Social Sciences Inc., Chicago, IL, USA) version 12.0 was used for statistical analysis and P<0.05 was considered statistically significant. The prevalence rates and 95% CI of pterygium for subjects were calculated. Sunglasses Hut The association between gender, age, educational level, lifestyle, and other variables and the risk of pterygia was estimated by the odds ratio (OR) and its 95% CI. The significance of visual acuity on patients with different types of pterygium was evaluated by χ2-test. The independent effect of risk factors was evaluated using logistic regression models.
This survey was approved by the Ethics Committee of the Qinghai Provincial Health Bureau and was carried out in accordance with the tenets of the Declaration of Helsinki Principal (revised in 2000). All the participants gave verbal consent and all the examinations and treatment were free of charge.
This article is quoted from http://www.nature.com/eye/journal/v23/n2/full/6703005a.html