1. Viewing Distance & Visual Discomfort While Using Handheld Displays
Yu-Chi Tai,
James Sheedy, John Hayes,
James Kundart, Hannu Laukkanen
Pacific University, Vision Performance Institute,
Vision Ergonomics Laboratory

2. Background
Handheld computer devices (e.g., PDAs, Media players, Palm-size gaming devices, etc.) have very small screens to keep them portable;
These handheld devices potentially sacrifice legibility for portability;
This has not prevented their widespread use;
Habitual working distance using handhelds for their primary purpose has not been studied.

3. Questions
Do subjects view handheld displays closer to the eyes than other reading materials?
Why might they hold such displays closer than other reading materials?
Smaller character size?
Poorer legibility?
Highly interactive operations?
Potential importance to health
Shorter viewing distances are more demanding on accommodation and convergence

4. Methods 34 subjects 19 Male & 5 Female, age 18-33 (mean=24.8);
20/20+ vision in each eye; no eyestrain history;
≥ 6 months of HCD-use experiences.
Target measurements
Viewing distance (sampled 1 frame/min)
Surface-EMG from right lower eyelid
Subjective rating of visual/body discomfort symptoms (Analog Sensation Questionnaire)

5. Experiment setup
Viewing distance was measured while performing 10 min of…
Reading hardcopy text of 5 sizes (6, 7, 8, 10, 12 pt)
5 types of handheld devices

6. Three Handheld Devices
Apple iPod
2.5” LED backlight color display
320x240 pixels, 163 ppi, weight 4.8 oz
One thumb-scroll wheel for single-hand operation
Sony PSP
4.3” TFT LCD widescreen,
480x272 pixels, 10 oz,
Two thumb-operating button area
HP iPAQ HW6945 smartphone
3” TFT LCD touch screen
w/ LED backlight & stylus, weight 6.33 oz 6

7. 10 Testing Conditions 7

8. Results

9. Finding 1:
Viewing distances differed significantly among testing conditions

10. Finding 1-1:
When reading hardcopy text, viewing distance decreased for smaller text sizes

11. While text size explains 92% variance in viewing distance, it’s NOT everything  Comparison to 3:1 acuity reserve

12. Maintaining 3:1 reserve requires more accommodation

13. Finding 1-2
With handhelds, viewing distance was closer than reading 6-pt font, depending on the nature of the task.

14. Task Analysis: Handheld viewing distance determined by task nature.

15. Finding 2
Lower blink rate when playing games
Higher blink rate when watching movies

16. Finding 3
No significant difference on subjective rating of Internal Symptoms

17. Finding 4
No significant difference on subjective rating of External Symptoms

18. Finding 4
Higher physical discomfort in most handheld use, except for watching movies

19. Conclusions
When reading hardcopies, viewing distance primarily determined by text size.
When using handhelds, viewing distance usually is closer than reading hardcopies and is affected by task nature.
Visual and body stress was observed even with as short as 10 minutes of handheld use.

20. Acknowledgement This study was supported by
Microsoft Advanced Reading Group to
Pacific University
Vision Ergonomics Laboratory.