The present study is a part of the nationwide epidemiological study on dry eye. A population-based survey performed among subjects that are ≥ 18 years old in Sanle Community, Shanghai, China was conducted between March 15, 2010 and June 30, 2010. Sanle community is located in Jing’an district, the central region of Shanghai. It was chosen as the study community on the basis of its metropolitan location, population stability, and support from local government and medical institutions. The study was approved by the ethics committee of Eye, Ear, Nose and Throat Hospital of Fudan University, and conducted according to the tenets of the Declaration of Helsinki.
Among the participants of the epidemiological study, those ≥ 40 years old were enrolled in this study. Subjects that were found to have the following abnormalities were excluded: blood pressure higher than 160/95 mmHg, diabetes mellitus, autoimmune disorder or other systemic disorders, corneal disorders that would probably affect visual acuity, such as corneal leukoma, pterygium and corneal ulcer, intraocular pressure(IOP) higher than 21 mmHg or lower than 9 mmHg, lens opacity greater than grade II according to the Lens Opacity Classification System III (LOCSIII), any abnormalities in the fundus photograph, refractive error more than +/−6D, and history of contact lens wear, allergic conjunctivitis, or ocular surgery. Those who had been diagnosed with DES before and treated with either artificial tear or punctal occlusions were excluded as well. Informed consent was obtained from all enrolled participants.
Before ocular examination, trained interviewers contacted the participants and administered a structured questionnaire, which included detailed demographic information (age, gender, educational level, occupation), history of systematic disorders and ocular diseases, life style (computer use and air conditioner), and dry eye symptoms. The questions regarding dry-eye symptoms, which had previously been used by Schein et al. , consisted of six items: (1) Do your eyes ever feel dry? (2) Do you ever feel a gritty or sandy sensation in your eyes? (3) Do your eyes ever have a burning sensation? (4) Are your eyes ever red? (5) Do you notice much crusting on your lashes? and (6) Do your eyelids ever get stuck? For each question, the participants were asked to choose among the following answers: never, rarely, sometimes, often, or all the time, which were scored as 0, 1, 2, 3 and 4 accordingly. Total DES symptom score (TDSS) was calculated by the interviewers according to the method reported previously .
All subjects underwent a complete ophthalmologic examination, including best-corrected visual acuity, slitlamp biomicroscopy, direct ophthalmoscopy, fundus photography, tonometry, and optometric examination. All pieces of equipment were transported to a local medical unit for the convenience of the participants. The best corrected visual acuity (BCVA) was evaluated with the LogMAR visual acuity chart. Noncontact tonometer rather than Goldmann applanation tonometer was used to measure IOP so as to avoid the impact on corneal epithelium and fluorescence staining.
The dry eye examinations included tear-film breakup time test (TBUT), fluorescein staining score (FSS) of the cornea, Schirmer I test (ST) and slit-lamp assessment of anterior segment. The examination was performed in conformity to the procedures described in previous report . The ophthalmologists performing the eye examinations were blinded to the dry eye information found in the questionnaire.
Diagnostic criteria of DES and division of participants
Dry eye was defined as the simultaneous presence of significant symptoms and at least one sign. Subjects were considered symptomatic when at least one of the symptoms mentioned in the questionnaire was experienced often or all the time. Objective tests were considered indicative of signs in the following instances: ST score ≤ 5 mm, TBUT ≤ 10 seconds, and FSS ≥ 1. These criteria had to be met in at least one eye. Subjects with definite dry eye were classified as group A. The asymptomatic subjects—those only with signs of DES—were defined as type I suspected DES (group B). Those who reported significant symptoms but had no signs of DES were considered as type II suspected DES (group C). The participants were classified into group D if they had neither dry eye symptoms nor signs.
Visual Function Questionnaire (VFQ-25)
A Chinese version of the VFQ-25, which was used in the previous research [13, 14], was administered to all the enrolled subjects. All subjects were requested to fill up the questionnaire by themselves. The research staff explained the questionnaire to the participants and provided assistance when required. For the illiterate participants, the research staff read the questionnaire for them in a neutral and uniform manner and recorded the patients’ choices. The completed questionnaires were reviewed by the research staff to ensure no data were missing.
NEI VFQ-25 with an additional question, being translated into Chinese, was used in the current study to evaluate the vision-specific QoL. Since the response rate of No.14 item was rather low in Chinese population , we chose item A8 from NEI-VFQ39 to serve as the appendix of No.14 item according to the instruction of the NEI-VFQ25 manual. If the statistical analysis showed a low response rate of No. 14 item in the current study, the result of its appendix would be used so as to alleviate the impact of high miss rate of No.14 item on the validity and reliability of the whole questionnaire. Each item in the questionnaire was assigned to one of the 12 subscales: general health, general vision, ocular pain, near activities, distance activities, social functioning, mental health, role difficulties, dependency, driving, color vision and peripheral vision. Answers to each question on the VFQ-25 were converted to a 100-point scale in which 100 represent the best possible score or the minimal subjective impairment, and 0 represent the worst or the maximal. The guidelines published by the NEI were adhered to when calculating the above scale conversions and subscale scores.
The mean scores and standard deviations were calculated for each VFQ-25 subscale and composite score. ANOVA and Chi-square test was used to analyze the age, gender distribution, educational level, occupation and use of computer and air conditioner among the four groups. ANOVA was used to compare each VFQ-25 subscale score and the composite score among the four groups, and Post Hoc Tests were further performed to determine the difference between every two groups. In addition, multivariate regression analysis was performed to investigate the relationship between the clinical variables and the VFQ-25 scores. The covariates tested were age, gender, educational level, occupation, BCVA of the eye with more severe DES, BCVA of the eye with less severe DES or without DES, computer use, use of air conditioner, TDSS, TBUT, ST and FSS. All tests of association were considered statistically significant at P <0.05 (SPSS for Windows, version 13.0; SPSS, Inc., Chicago, IL).