Title : Relation between computer vision syndrome and objective binocular tests in Italian office workers
Abstract:
The prolonged use of video display units (VDU) in occupational activities can affect the visual health of workers, who can suffer from ocular and/or visual symptoms that are grouped into computer vision syndrome (CVS). Its pathophysiology seems to include changes in the ocular surface and in the balance of accommodation-convergence. The most current research has focused on ocular changes in VDU workers, but studies on accommodation and convergence are mainly old and the results are heterogeneous. Therefore, the objective was to analyze the relationship between CVS and different objective binocular tests that assess accommodation and convergence. A cross-sectional study was conducted on 42 Italian VDU workers, randomly selected from 3 different companies in Brescia (Italy). Each worker underwent an anamnesis and if they met the inclusion criteria, they completed the CVS-Q IT© (validated Italian questionnaire to study CVS symptoms), and 6 binocular optometric tests were performed (near point of convergence (NPC), cover test near and far (CTN and CVF), far positive and negative fusional vergence (PFV and NFV) and binocular accommodative facility (BAF)). The difference in medians (Mann-Whitney U test) and proportions (Chi-square or Fisher test) was analyzed in all quantitative and qualitative variables studied as a function of CVS. It was also analysed whether there was a relationship between the CVS-Q IT© score and the quantitative variables (Pearson's or Spearman's correlation coefficient). Finally, it was analyzed whether the mean CVS-Q IT© score was different in those workers who had an abnormal result in each binocular test (t-test for means comparison). Half of the sample (50.0%) was female, the median age was 40.50 (interquartile range (IQR)=12.00), with a range of 18-50 years. The median number of hours of VDU use for work was 6.50 (2.00) hours/day. 38.1% had CVS. The mean score on the CVS-Q IT© was 4.58 (standard deviation (SD)=1.47) points for those without CVS and 9.38 (1.97) for those with CVS, p-value<0.001. Differences were also observed in the total hours of VDU use between those without CVS (median=7.50, IQR=1.60 hours/day) and those with CVS (median=8.25, IQR=1.00 hours/day), p-value=0.015. Regarding the optometric tests, it was observed that of the total sample, the tests with the most abnormalities were the CTN (45.2%) and BAF (42.5%), and the least abnormalities were the NFV (0.0%), followed by the PFV and NPC (14.3% in both cases), and the CTL (28.6%). No significant relationship was observed between failing each of the individual optometric tests and having CVS. However, it was obtained that the failure of 3 of the 6 optometric binocular tests was related to CVS (p-value=0.023). No significant correlation was found between any optometric test and the CVS-Q IT©. However, when analysing whether the mean CVS-Q IT© score was different according to each of the tests, considering that the cut-off point of the questionnaire for diagnosing CVS is ≥7 points and although the value was not significant, it was observed that the mean score of the questionnaire for those who did not have an abnormal NPC test was 6.19 (2.79) points and for those who did have an altered NPC test was 7.67 (3.45) points (p-value=0.126). Furthermore, when grouped by the number of abnormal tests, it was observed that the mean CVS-Q IT© score for those who failed less than 3 tests was 5.94 (2.61) points and for those who failed 3 of the 6 tests was 9.17 (3.19) points, this difference being statistically significant (p-value=0.005). All workers who had CVS and failed 3 of the 6 binocular optometric tests had abnormal values on both the CTc and the BAF test. These 2 tests are fundamental signs for the diagnosis of some binocular dysfunctions, such as convergence insufficiency, which could be a risk factor for CVS.
