Abstract
Purpose::
The purpose of this study was to use the staring method (S-TBUD)to determine the affects of near work on tear breakup dynamics.
Methods::
Two µl of 2% sodium fluorescein were instilled into the left eye of 15 control (C) and 15 dry eye (DE) subjects, who were seated behind a slit lamp biomicroscope and asked to keep the eye open as long as possible while the tear film was videotaped (S-TBUD). After the initial measurement, the subject played a computer game for 20 minutes and then the procedure was repeated. Subjects completed current symptom questionnaires before and after testing. Analysis of the changing area of breakup (AB) over time in S-TBUD trials was quantified using a custom MATLAB program. Digital movies were used to obtain the maximum blink interval (MBI) and tear breakup time (TBUT).
Results::
S-TBUD decreased in 20 (67%) and TBUT in 22 (70%) of subjects after the near task. Individual measures that increased significantly after the near task included the AB after 5 sec, the final AB (DE only), and the symptoms of discomfort and burning (p<0.05, Wilcoxon Signed Ranks test). However, DE subjects were significantly more symptomatic than C both before and after performing the near task (p<0.003, Mann-Whitney). TBUT correlated with S-TBUD measures (AB, slope, MBI), and the AB at 5 sec correlated with the symptom of discomfort (Spearman's rho r<0.52, p<0.003).
Conclusions::
Both TBUT and S-TBUD measures show that only 20 minutes of continuous near work led to a significantly destabilized tear film and increased symptoms. After performing the near task, subjects showed substantially accelerated tear breakup in only 5 sec, which may increase the risk for ocular surface exposure if the average blink rate is 12/min (once every 5 sec). This marked change in tear stability after a relatively brief near task may account for the worsening of symptoms of ocular irritation commonly noted later in the day among dry eye patients.
Keywords: cornea: tears/tear film/dry eye