In this study, 641 of the 5199 subjects aged≥60 years refused to participate in the examination and 13 were excluded of the remaining due to mental retardation, deaf, and mental disorders. Thus a total of 4545 were examined with the response rate 87.42% (95% CI, 86.52%–88.32%). Among 4545 subjects, 57.96% (2635/4545) were female. The mean age of all examined subjects was 68.40±8.29 years old (SD). The age of males (68.78±8.02) was significantly higher that of females (68.12±8.48; t=2.704, P=0.007). Among the 654 non-participants, elderly (72.00±8.22 years vs.68.40±8.29 years, t=10.400, P<0.001) and male(χ2=29.12, P<0.001)were less likely to participate.
Among the 4545 subjects with presenting VA, the overall prevalence of mild, moderate and severe visual impairment was 12.59% (95% CI, 11.62%–13.55%), 8.38% (95% CI, 7.58%–9.19%) and 0.44% (95% CI, 0.25%–0.63%), respectively. The occurrence of subjects presenting blindness was 0.86% (95% CI, 0.59%–1.13%). With best-corrected VA, the prevalence of mild, moderate and severe visual impairment was 5.26% (95% CI, 4.61%–5.91%), 3.06% (95% CI, 2.56%–3.56%) and 0.09% (95% CI, 0.00%–0.17%), respectively. Blindness with best correction was 0.66% (95% CI, 0.42%–0.90%). After refractive correction, the prevalence of mild, moderate and severe visual impairment was significantly decreased(mild:χ2=150.13, P<0.001, moderate:χ2=119.46, P<0.001, severe:χ2=10.69, P=0.001), while the prevalence of blindness was not significantly changed (χ2=1.82, P=0.277). For the female subjects presenting VA, the prevalence of mild, moderate and severe visual impairment was 14.69%, 9.53% and 0.61%, respectively. For the male subjects presenting VA, the prevalence of mild, moderate and severe visual impairment was 9.69%, 6.81% and 0.21%, respectively. The prevalence of mild visual impairment in females was significantly higher than that in males (P<0.001). In other groups of visual impairment, the difference caused by gender was not significant (P>0.05). Similar results were obtained in the subjects with best-corrected VA (Table ).
Prevalence rates of blindness, SVI, Mod VI and Mild VI by age, sex, insurance, occupation and education*
According to presenting visual acuity, 973 (21.41%) of the 4545 subjects had visual impairment for a 6/12 cutoff. After refractive correction, only 374 subjects (8.23%) still had visual impairment. For a 6/18 cutoff, these values were 401 and 137, respectively. The prevalence of correctable visual impairment was 13.18% (95% CI, 12.20%–14.16%) for a 6/12 cutoff and 5.81% (95% CI, 5.13%–6.49%) for a 6/18 cutoff. Of the 599 subjects with correctable visual impairment for a 6/12 cutoff, only 98 (16.36%) wore distance spectacles, while the proportion was 18.94% (50/264) for a 6/18 cutoff (Table ). The prevalence of visual impairment and correctable visual impairment for a 6/18 cutoff was higher in the subjects with older age and less education (P<0.01). The prevalence of visual impairment and correctable visual impairment were significantly higher in females than in males (P<0.01).
Prevalence rates of VI, correctable VI and noncorrectable VI for two criteria by age, sex, insurance, occupation and education*
The subjects with older age were significantly prone to have visual impairment (≥80 years; OR, 8.31; 95% CI, 6.77–10.20 versus 60–69 years, 70–79 years; OR, 2.80; 95% CI, 2.36–3.32 versus 60–69 years). The lowest prevalence of visual impairment for a 6/12 cutoff was observed in the subjects from 60 to 69 years old (12.73%), while the highest prevalence was observed in the subjects more than 80 years old(53.08%). Females had a significant higher risk of visual impairment (OR 1.65, 95%CI 1.42-1.91) than males. A higher level of education was a protective factor for visual impairment (Junior high school or higher; OR, 0.31; 95% CI, 0.25–0.38 versus No education, Primary school; OR, 0.43; 95% CI, 0.36–0.52 versus No education). Career and the types of insurance were not significantly associated with the risk of visual impairment. In last multivariate logistic modeling, all variables, except insurance, were significantly associated with visual impairment (Table ).
Univariate and multivariate analysis of visual impairment and correctable visual impairment for a 6/12 cutoff
Table showed the association between correctable visual impairment and various independent variables. Old age (≥80 years; OR, 5.10; 95% CI, 3.98–6.54 versus 60–69 years, 70–79 years; OR, 2.32; 95% CI, 1.90–2.84 versus 60–69 years) and female gender (OR, 1.52; 95% CI, 1.27 –1.82) were significantly associated with correctable visual impairment for a 6/12 cutoff . On the other hand, a higher level of education (Junior high school or higher; OR, 0.42; 95% CI, 0.33–0.54 versus No education, Primary school; OR, 0.54; 95% CI, 0.43–0.69 versus No education) was a protective factor for correctable visual impairment.
In the final multiple logistic regression analysis controlling for all covariates, older age (≥80 years; OR, 4.80; 95% CI, 3.69–6.26 versus 60–69 years, 70-79 years; OR,2.24; 95% CI, 1.82–2.76 versus 60–69 years) and female gender (OR 1.56, 95%CI 1.29-1.88) were significantly associated with correctable visual impairment. A higher level of education, e.g., junior high school or higher, (OR, 0.65; 95% CI, 0.48–0.89) was a protective factor for correctable visual impairment. Career and the types of insurance showed no significant association with correctable visual impairment.
Table showed the improvement in the participants’ vision by correcting their undercorrected refractive errors. Utilization of appropriate spectacles improved the visual acuity by at least one line in 45.43% (95%CI, 43.99% to 46.88%) of the studied population and as high as four lines or more in 5.79% (95%CI, 5.11% to 6.47%). These figures were more pronounced among participants with visual impairment, especially in severe/moderate visual impairment.
Visual improvement after correcting refractive errors
Among 572 participants (12.59%) who had mild visual impairment according to the aforementioned definition with a presenting visual acuity worse than 20/40 in the better eye, only 88 subjects (15.38%) had no improvement after correction, while 12.76% (95% CI, 10.03% to 15.50%) could experience a four line improvement by wearing proper spectacles. In addition, 46.46% of Mod VI (95% CI, 41.44% to 51.56%) and 45.00% of SVI (95% CI, 23.00% to 69.00%) obtained an improvement of at least four lines with accurately prescribed spectacles. Although correctable visual impairment gained more lines of improvement than uncorrectable visual impairment, 35.29% of uncorrectable SVI and 18.22% of uncorrectable Mod VI could gain four lines of improvement after refractive correction.
Of the 4545 participants, 1129 participants gained an improvement of two or more lines in visual acuity. Thus, the overall prevalence of undercorrected refractive error was 24.84% (95% CI, 23.58% to26.01%). If stratified by visual impairment (VI) categories, the prevalence of undercorrected refractive error for mild VI, moderate VI, severe VI and no VI were 61.54%, 67.98%, 60.00% and 14.10%, respectively (Table ).
A total of 473 subjects accounting for 10.41% (95% CI, 9.52%–11.29%) were corrected for refractive error with spectacles (met need), while 599 subjects accounting for 13.18% (95% CI, 12.20%–14.16%) had unmet need. Among the unmet need, 501 subjects never wore spectacles or gave up wearing spectacles and the remaining 98 subjects wore an inappropriate spectacle. Thus spectacle coverage was 44.12%. Spectacle coverage declined with age (χ2=114.17, P<0.001), which was 56.99% in the youngest age group (60–69 years) and 15.69% in the oldest age group (≥80 years). In the contrary, the spectacle coverage was increased with education (χ2=133.18, P<0.001), which was 15.79% in the no-education group and 63.22% in the junior/high school education or higher group. Spectacle coverage was significantly lower in females (36.47%) than in males (54.51%) (χ2=34.56, P<0.001). In peasant and the subjects with insurance, the spectacle coverage was also significantly higher (χ2=62.74, P<0.001; χ2=11.51, P<0.01, respectively). The spectacle coverage in our study was significantly different in the subjects with different refractive errors (χ2=34.49, P<0.001). For example, the highest coverage was observed in myopia and the lowest coverage was in astigmatism. In myopia, spectacle coverage among moderate/high myopia was 64.62% and 53.44%, which was significantly higher than 33.96% in mild myopia (Moderate myopia vs. Mild myopia, χ2=44.39, P<0.001; High myopia vs. Mild myopia, χ2=13.81, P<0.001, respectively). In hyperopia, only mild hyperopia showed significant higher spectacle coverage than moderate hyperopia (48.66% in mild hyperopia vs.33.33% in moderate hyperopia, χ2=7.60, P = 0.006). No significant difference was observed between the coverage of the two remaining degree of hyperopia (P≥0.05) (Table ).
Spectacle coverage rate by sociodemographic variables as well as univariate and multivariate model of unmet need
Table showed the association between unmet need and the various independent variables, e.g., age, gender, career, insurance, education and type of refractive error. Univariate analyses showed that all these variables were significantly associated with the participant′s unmet need. The adjusted effect of these variables on the unmet need was assessed by multivariate logistic regression analysis. In the final model, insurance showed no significant association with unmet need, while age, career, education (except for primary school), and type of refractive error had significant correlation with unmet need. Among these variables, higher educational level, myopia and hyperopia were protective factors for unmet need, while others were risk factors.