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Abstract
Purpose To evaluate blink rate effects by a novel light-emitting diode (LED) timer device (PISC) on non-dry eye (DE) subjects and DE patients during a reading task on liquid crystal display (LCD) screens, in different environmental conditions.
Methods This was a case–control study that included 15 DE patients and 15 non-DE subjects as controls. Participants had their blink rates measured while they read an electronic format text. These tasks were performed in four different conditions: with and without a LED timer device in two visits, and with and without air conditioning. All participants completed the Ocular Surface Disease Index and were examined by best spectacle-corrected visual acuity exam, biomicroscopy, Schirmer test 1, fluorescein staining and break-up time and lissamine green staining (Oxford scale grading).
Results Outcomes between reading tasks conditions were compared independently for each group and blink rate frequency was higher in tasks with LED timer device, with and without air conditioning, for the DE group (p<0.0001), and with air conditioning for the control group (p<0.05).
Conclusions An LED timer device increased blink frequency for DE and control groups. Further studies need to be carried out in order to evaluate long-term effects of this new device, as well as its assessment with different reading scenarios.
- Ocular surface
- Tears
- Eye Lids
- Imaging
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Introduction
The blink rate in normal behaviour varies between 2 and 50/min1 and can be affected by many factors: age, gender,2 daily fluctuation,3 reading activities and dry eye (DE),4 ,5 environment and air conditioning.6 ,7
Video display terminal (VDT) use can result in a decrease of spontaneous eye blinking rate (SEBR) and alternating lower and higher inter-eye blinking intervals (IEBIs).8–10 DE disease can result from decreased blinking and consequent increase in tear evaporation, most specially in visual display terminal11 or VDT12 workers. Increased ocular surface risk can be calculated by the Ocular Protection Index (OPI), which is represented by tear film break-up time divided by the IEBI. Patients who present OPI values lower than 1 are more prone to develop symptoms and signs of DE.13 Additionally, DE symptoms’ impact upon life quality is associated with limitations for reading, working and using the computer.14
The orbicularis oculis muscle contracts in response to a variety of stimuli, including light flashes.15 ,16 Light-evoked blinking reflex is present in normal subjects, but not auditory blinking reflex. In addition, light intensity and distance between light and the eye were shown to influence latency until blinking and contraction through electromyographic evaluation; however, a distance of less than 200 mm was reported to disturb test subjects.17
PISC is a battery supplied electronic device (figure 1) that features a PIC10 micro-controller electronic circuit, an on–off switch, a red light-emitting diode (LED) which is frequency-controlled by a 4 MHz crystal oscillator and a microprocessor with a multi-functional clamp fit for liquid crystal display (LCD) screens of laptops or desktop computers. PISC flashes a red light every 4 s (15 times/min).
Light-emitting timer device (PISC). Top left button: ON switch; top right button: OFF switch; centre: light-emitting diode light. Access the article online to view this figure in colour.
The aim of this study was to evaluate blink rate effects by a novel light-emitting timer device (PISC) on non- DE subjects and DE patients during a reading task on notebook LCD screens, in different environment conditions.
Methods
We recruited 15 non-DE control individuals and 15 DE patients above 18 years and none wore contact lenses or had any previous eye surgery. They had uncorrected visual acuity of 20/40 or better. The study protocol was approved by the ethics committee of the Federal University of Sao Paulo, Sao Paulo, Brazil. All subjects were submitted to eye examination, which included Schirmer 1 test and fluorescein break-up time (FBUT),18 Lissamine green staining19 and Ocular Surface Disease Index (OSDI) questionnaire.20 Patients were diagnosed as DE according to the Dry Eye WorkShop (DEWS) classification.21
Subjects were requested to read an electronic format text for 15 min22 from an LCD laptop screen (Toshiba Inc.) viewed from an 80 cm distance. Texts were different at each visit, but were always black over white background, and of the same font size (Times New Roman, 12 pt). Reading tasks were conducted in a room with temperature and humidity control. PISC device was attached on top of the LCD screen and turned on. Blink rate frequency was recorded by a built-in webcam.
In order to avoid bias induced by testing repetition, tasks were performed in two different visits, with and without PISC. Between and after reading tasks of the same visit, with and without air conditioning,20 we performed FBUT, fluorescein and lissamine staining in order to evaluate the possible PISC effects. Therefore, blink rate and ocular surface examination were carried out in all individuals from both groups in four scenarios: A, without PISC or air conditioning (Ac); B, without PISC and with Ac; C, with PISC without Ac; and D, with both PISC and Ac.
Results
Demographic data, visual acuity and baseline values of Schirmer 1, FBUT, lissamine and OSDI, respectively, for DE and control subjects are presented in table 1.
Mean and SD of demographic data, BSCVA and baseline values obtained in Schirmer 1 test, FBUT, Lissamine green staining and OSDI questionnaire score, for control and DE groups
We compared outcomes between scenarios independently for each group and found that blinking was increased by PISC application, in C and D scenarios for the DE group (analysis of variance (ANOVA)_ Bonferroni's post hoc test, p<0.0001), and D scenario only for the control group (ANOVA, Bonferroni's post hoc test, p<0.05) as shown in figure 2. Mean and SD values for blinking totals in each scenario are summarised in table 2. There was no statistically significant difference for FBUT measurement and fluorescein and lissamine green staining scores after reading tasks in all scenarios for both groups.
Mean and SD values of blinking totals in 15 min measured for each reading task condition, for control and DE groups
Outcomes in eye blinking totals in 15 min after different reading task conditions for control and dry eye groups. A, without PISC, without air conditioning (Ac); B, without PISC, with Ac; C, with PISC, without Ac; D, with PISC, with Ac. *** and * indicate p<0.0001 and p<0.05, respectively, by ANOVA test with Bonferroni's post hoc test.
Discussion
By means of manual counting, Patel et al23 observed mean blink rates in 16 subjects prior to and during a video display unit game, noting an average fivefold reduction of blinking. Later, Tsubota and Nakamori12 compared the rate of blinking in 104 office workers either when they were relaxed, reading a book or viewing the text on a VDT. Mean blink rates were 22/min when relaxed, but only 10 and 7/min when viewing the book or VDT, respectively. In the present study, blinking rates found for control group using VDT on scenario A were similar (mean±SD: 4.11±2.51 blinks/min), and slightly higher for the DE group (mean±SD: 6.1±3.54 blinks/min), as observed in other studies.4 ,5
Schlote et al9 found that the reduced blink rate associated with VDT use was also accompanied by distinct patterns of blinking. For example, patients with DE symptoms exhibited alternating IEBIs for long and short durations. The authors hypothesized that change in IEBI during the course of VDT operation represented cognitive adaptation to computer tasks. Besides describing a marked decrease of SEBR during VDT use, Freudenthaler et al10 showed that there was no correlation between SEBR and ocular tear film parameters in normal eyes, which could explain why we did not find improvements for FBUT, fluorescein and lissamine staining. They also stated that SEBR is further decreased under corneal anaesthesia. This is particularly important for patients who underwent a LASIK surgery, which reduces corneal sensitivity and may lead to DE.24 Use of an LED device during VDT work could be therapeutically indicated in such cases.
Other efforts to increase blink rate during activities that demand marked visual attention were developed with success in the past, such as protective sheets for visual displays.25 Protective sheets eliminated light reflexes that could induce excessive eye strain. LCD screen position is additionally important with regard to eye gaze, as it was described previously that near horizontal (primary) gaze tasks, such as reading in a desktop VDT, can induce slower blinking rates.26 An LED timer device, therefore, might be placed on the top of the screen to stimulate blinking rate and not to disturb reading tasks.
Conclusion
PISC increased blink rate for the DE group in conditions with and without air conditioning, but only in tasks with air conditioning for the control group. Further studies need to be carried out to evaluate long-term effects of this novel LED timer device on both non-DE subjects and DE patients who routinely operate VDTs. Moreover, it should also be tested with different light frequencies and colours and diverse reading conditions such as coloured fonts and background.
Acknowledgments
Cleber José Godinho acknowledges financial interest in the subject matter of the article.
References
Footnotes
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Presented in part at the 6th International Conference on the Tear Film and Ocular Surface. Basic Science and Clinical Relevance, September 2010, Florence, Italy.
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Collaborator N G T Queiroz-Hazarbassanov.
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Contributors DLM implemented the study, examined the volunteers and drafted the paper. RMH designed data collection tools, monitored data collection for the whole study, wrote the statistical analysis plan, cleaned and analysed the data, drafted and revised the paper. CKNY implemented the study and examined participants. FBS performed the English revision of the manuscript. CJG is the inventor of the device evaluated in the study (PISC). JAPG designed the study, critically revised the manuscript and is the guarantor.
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Competing interests None.
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Ethics approval From the ethics committee of the Federal University of Sao Paulo, Sao Paulo, Brazil.
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Provenance and peer review Not commissioned; externally peer reviewed.