We appreciate comments from Rosenfield and Partello on our paper. They have carried out an interesting experiment using metronomeCitation1,Citation2 to study the effect of increased blink rate on computer vision syndrome (CVS). The aim of their experiment was similar to our study but their result was different. They found that blink rates did not reduce during computer usage but a higher percentage of incomplete blinks were detected during computer operation. They attribute this difference to the changes in cognitive demand rather than method of presentation.
In our study, we proposed that 20 min of reading task (silently) using visual display unit (VDU) caused ocular symptoms due to decreased blink rate while reading with Wink glass (WG) increased blink rate and subsequently reduced the ocular symptoms. The near task was selected based on the previous studiesCitation3–6 and our own pilot study. We feel that reading silently represents habit of majority of people who use computers in their daily life and it also encourage our subjects to give full attention and concentration on the task. When the subjects concentrate fully on the near tasks, their cognitive demand is higher and this was found to reduce the blink rateCitation7–9 during VDU usage. Therefore, our experiment aimed at investigating the effect of WG usage on blink rate and ocular symptoms.
However, we feel that if an additional experiment can be carried out to compare the blink rate during relaxed conditions (less cognitive demand) and VDU use, followed by the comparison using WG; the results of the experiment will be less influenced by the effects of different tasks that require different cognitive demand. We think this might be able to explain the discrepancy between our result and that of Rosenfield and Partello’s studies.
In our study, as long as the partial blink covers more than 3/4 of the exposed cornea area, it was considered as one eye blink. In order to find out if the usage of the WG effect the quality of blinks, we re-analyzed the video of 23 subjects and followed the classification of the incomplete blink in the study mentioned earlier.Citation1,Citation2 A blink is graded as complete (where none of the cornea was visible as the subject completed his or her blink) or incomplete (where some portion of the cornea was still visible as the blink finished) based on the video playback.
The percentage of incomplete blink (PIB), blink rate (BR) and ocular surface symptom (OSS) score were compared in the two conditions (WG and clear plastic) whereby the subjects read silently for 20 min with VDU. The results showed that the PIB is significantly different (Median PIB_clear = 12.1% (range: 0–57.1%); PIB_WG = 3.9% (0–22.8%); p = 0.003) in the two reading conditions. PIB is lower when reading with WG compared to reading with clear plastic. This indicates that the voluntary blink stimulated by WG is mostly complete blink. We also noticed that the location of the WG's sensor at the bottom of the frame might also encourage the subjects to blink fully in order to clear the view. At the same time, OSS score and blink rate were also significantly different (Median BR_WG = 15.8 blinks/min (6–33), BR-Clear = 8.00 (3–30), p = 0.001; OSS_WG = 0 (0–3), OSS-Clear = 2 (0–5), p = 0.020). WG usage appeared to have increased the blink rate and reduced the percentage of incomplete blink resulting in less discomfort during reading task. It appears that increasing overall blink rate and reducing the percentage of incomplete blinks are equally important considerations when examining discomfort associated with CVS.
We appreciated the chance given to clarify our thought and hope our experience would help in stimulating new thoughts for future studies.
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
References
- Portello JK, Rosenfield M, Chu CA. Blink rate, incomplete blinks and computer vision syndrome. Optom Vis Sci 2013;90:482–487
- Chu CA, Rosenfield M, Portello JK. Blink patterns: reading from a computer screen versus hard copy. Optom Vis Sci 2014;91:297–302
- Cho P, Cheong P, Leung K, Ma V, Lee V. Effect of reading on non-invasive tear break-up time and inter-blink interval. Clin Exp Optom 1997;80:62–68
- Himebaugh NL, Begley CG, Bradley A, Wilkinson JA. Blinking and tear break-up during four visual tasks. Optom Vis Sci 2009;86:E106–E114
- Cardona G, Garciia C, Serees C, Vilaseca M, Gispets J. Blink rate, blink amplitude, and tear film integrity during dynamic visual display terminal tasks. Curr Eye Res 2011;36:190–197
- Miyake-Kashima M, Dogru M, Nojima T, Murase M, Matsumoto Y, Tsubota K. The effect of antireflection film use on blink rate and asthenopic symptoms during visual display terminal work. Cornea 2005;24:567–570
- Bentivoglio AR, Bressman SB, Cassetta E, Carretta D, Tonali P, Albanese A. Analysis of blink rate pattern in normal subjects. Mov Disord 1997;12:1028–1034
- Karson CN, Berman KF, Donnelly EF, Mendelson WB, Kleinman JE, Wyatt RJ. Speaking, thinking and blinking. Psychiatry Res 1981;5:243–246
- Orchard LN, Stern JA. Blinks as an index of cognitive activity during reading. Integr Physiol Behav Sci 1991;26:108–116