Objective: To validate the VF-11, a vision-specific function scale and determine the relationship among vision impairment, ocular conditions, and vision-specific functioning in an Asian Malay population.
Design: Population-based cross-sectional study.
Participants: Persons aged 40 to 80 years of Malay ethnicity in Singapore.
Methods: Of the 3280 participants, 3267 answered the VF-11 scale. Participants underwent an extensive and standardized examination procedure, which included visual acuity testing. Sociodemographic and medical data were recorded using a standardized questionnaire. Rasch analysis was initially used to validate the VF-11 and determine its measurement characteristics. Analyses were performed to explore the relationship between the overall functioning score and the presenting unilateral and bilateral vision and ocular conditions using linear regression models.
Main outcome measure: Vision-specific functioning score.
Results: The mean presenting visual acuity values in the better and worse eyes were 0.21 (+/-0.23) and 0.36 (+/-0.27) logarithm of the minimum angle of resolution, respectively. Some 46.4% of participants had some form of visual impairment in either eye, and 1.8% of participants had severe visual impairment in both eyes. By using Rasch analysis, it was shown that a modified VF-11 is a unidimensional, reliable, and valid scale to assess vision-specific functioning in this population. Participants with unilateral or bilateral visual impairment had significantly lower vision functioning scores. The independent association between severe vision loss in one or both eyes and functioning was considered to be clinically meaningful. Eye conditions were not independently associated with overall visual function with bilateral visual impairment in the model with the exception of glaucoma (P<0.05 and beta = -1.08). Compared with people with normal vision, people with mild/moderate visual impairment were 1.6 (95% confidence intervals [CI], 1.2-2.2; P = 0.01) and 2.2 (95% CI, 1.6-3.0; P = 0.007) times more likely to have moderate and poor vision function, respectively. Similarly, participants with severe visual impairment were 3.5 (95% CI, 1.1-12.7; P<0.001) and 13.6 (CI, 4.0-45.4; P<0.001) times more likely to have moderate and poor vision function, respectively.
Conclusions: Presenting unilateral and bilateral vision impairment is significantly associated with poor vision-specific functioning across the spectrum of mild to severe vision impairment in this Asian Malay population.