The Online Eye Test

I work 8 to 12 hours per day at a computer screen, and I own special computer glasses in addition to my bifocals. To optimize my computer glasses, my eye doctor agreed to test me on an online, web-based eye test of my own design. He agreed to switch lenses of various strengths while I looked at a computer screen in his office. Since I design web pages for a living, I thought that designing an online eye test would be an easy task. Little did I realize there would be so many issues.

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  1. Pixel size: Web browsers currently display content at 72 pixels per inch. Ideally, the web designer needs to be able to see changes as small as a single pixel (1px). That is what I told my eye doctor - I wanted to be able to distinguish single pixels.

    The Online Eye Test uses several tests in which the objects differ by a single pixel. Seeing the single pixel is the only standard at which these tests aim. The problem is that the single pixel can vary so much across computer systems that it almost invalidates any online eye test.

  2. Screen Size: Computer screens come in different sizes. Other things being equal, a larger screen will display the same web object in a larger, easier-to-see size. That means that the same eye test will produce different results for different screen sizes.

    Note: The Online Eye Test was originally designed on a diagonally-measured 16 inch (14.8 inch viewable) monitor.

    Possible remedies include:
    • Standardize by specifying that the test is valid for only one screen size.
    • Compare eye test scores only among those with the same screen size.
    • Produce an on screen scale and some method of magnifying and reducing the screen size until the scale is equal to a specified, measured length.

  3. Screen Resolution: Computer screens display content at different screen resolutions. Other things being equal, lower screen resolutions will display the same web object in a larger, easier-to-see size.

    • This eye test was originally designed at 1024 x 768 screen resolution.

    • You can inspect and change your screen resolution.

      On the pc, click the Start menu, then Settings, Control Panel, then double-click the Display icon, click the Settings tab, and look for "Desktop area" and a slider with a label like "1024 x 768". This is your screen resolution. To change your pc screen resolution, first PLEASE write down your current screen resolution and your current Color palette. Next, slide the slider towards More or Less, and then follow the onscreen directions.

      On the Mac, the lefthand onscreen pull-tab has an icon for screen resolution. Also reachable via the Apple Menu. Select your desired screen resolution from the many options displayed.

  4. Screen Focus: Computer screens vary in quality. Some display content with pinpoint focus, but others are blurry. In fact, this Online Eye Test has revealed more bad monitors than bad eyes! Solutions: Some monitors have adjustments which will improve the focus, or you can try a new or different monitor.

  5. Screen Brightness (gamma): Computer screens vary in brightness, or a similar feature called "gamma." The action of screen brightness on an online eye test varies. Up to a point, a brighter screen is easier to see, but beyond that point, the screen becomes too bright for good contrast.

    Some monitors have controls for adjusting brightness and contrast. The Computer Eye Test assumes that the viewer has chosen the clearest available monitor settings.

  6. Viewing Distance and Viewing Angle: Variations in distance and angle of viewing will create variations in The Online Eye Test results. As it stands, the user will be choosing his or her own viewing distance and angle. Sit closer or change the monitor angle, if you want.

  7. Color: Variations in color make things easier or harder to see. To standardize the Online Eye Test, I made it completely black and white. (#000000 and #ffffff).

  8. Anti-aliased fonts: Letters and numbers displayed on modern computer screens are often anti-aliased. This means that partially transparent, grey or other intermediate colors are used to make rough edges look smoother, and to suggest small, sub-pixel features. While anti-aliasing makes fonts easier to read, up close they are actually blurrier. Thus, in my Letters test, I have invented my own small non-anti-aliased font. In the other tests, I have created non-anti-aliased symbols. This removes anti-aliasing as an issue for the Online Eye Test.

  9. Reflections, room light, peripheral distractions, fatigue: All these make a visible difference, too. There may be other relevant factors that I haven't considered.

Conclusions: The point to examining all these issues is to look at what would be required to make an online eye exam more accurate. At this time, the issues are significant. I can tell my eye doctor only about my own subjective reactions to these tests. I can say, "I need to see something this small, and I can't!"

Disclaimer: The Online Eye Exam is not a medical test. The Online Eye Exam cannot take the place of eye care by a trained professional. If you believe that you cannot see your computer screen as well as you want to, or if your computer usage is producing eye strain, headaches, back or neck aches, please see your eye doctor!

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