Verify Declination Angle Claims!

ErgoPractice News – December 2016

It has long been understood loupes with a steeper declination angle (DA) help clinicians achieve an upright, neutral posture that alleviates neck strain, pain, and injury.¹ If the DA of loupes become larger, the user declines their eyes instead of their heads and thus can work comfortably and safely with an upright posture. DA is considered as one of the important factors in selecting loupes. The only question is: how the clinician verifies the declination angle of the loupes they purchase?

Several dental professionals contacted me recently asking if I could help them review their working postures. They have started to experience the strain/neck pain even though they were told their loupes had steep declination angles. Reviewing photos of their working postures wearing loupes I found the declination angle of their loupes was significantly smaller than their manufacturers claimed. These manufacturers used the temple arm of the frames as the reference line for DA measurement. The problem with this is this reference line will change depending on the relationship of the temple arms to the lens frames.

Reference Lines

The most accurate reference line is one that does not change with frame design. The ideal reference line for defining the declination angle is a line connecting the corner of eyes to the top of ears on which temple arms sit (Figure 1).²

Figure 2 shows a loupe whose temple arms are significantly higher than the reference line. The actual declination angles of these loupes are significantly smaller than manufacturers may be claiming. As a result, users of these loupes may develop chronic neck pain and injuries.

Depending on the choice of the reference line, the declination angle claimed can be very different from the true declination angle. How can we find ergonomically correct loupes? The ultimate test for ergonomic loupes is beyond the declination angle. Simply measure the head tilt angle of the clinician using these loupes. The clinician’s head tilt should be less than 20 degrees. We may call this test “The 20° Rule.”^{3, 4}

The 20° Rule

Research has shown that tilting your head down more than 20° for an extended period of time greatly contributes to chronic pain and eventual injury.^{3, 4}

Imagine holding a bowling ball with your forearm vertical and your upper arm horizontal (at a 90° angle). This should be a relatively easy pose to hold. This simulates the weight of your head balancing on your spinal column.

Now imagine your forearm extended 30° or 40° forward. Suddenly a number of muscular systems start working overtime to keep the bowling ball up. This is what your neck and shoulders do once your neck tilt is greater than 25°.

Figure 3 shows two working postures. How many clinicians do you know work like Figure 3a? How many clinicians you know don’t believe in an ergonomic solution and work with pain? How many clinicians you know believe they have ergonomic loupes but actually work like the clinician in Figure 3a?

SurgiTel Ergonomic Loupes

SurgiTel was founded 25 years ago as a Division of General Scientific Corporation to help provide clinicians with excellent vision and ergonomics. Effective magnification is not enough if clinicians are working with chronic pain or cutting their career short due to injury. As a result of continued research and development SurgiTel is able to match ergonomic loupes to any clinician’s facial features.

Most loupe companies label their loupes “ergonomically designed” because that’s what people want to hear. But most loupes are not built to help users work with ergonomically correct postures. You can easily verify their claims by measuring the head tilt angle when wearing the loupes.⁵

Please share this article with anyone you know is suffering, or who hasn’t mentioned suffering but works like the clinician in Figure 3a and probably is!

Feel free to contact me with any questions. My e-mail is jchang@surgitel.com.

References:

1. Rucker LM, Surgical telescopes: posture maker or posture breaker? In, Murphy D, ed, Ergonomics and the dental care worker. Am Public Health Assoc, Washington DC, 1998, 191-216
2. Chang, BJ, Declination Angle: The Key Factor for Custom Loupes, Oral Health, July, 2014, 46-49.
3. Valachi B, Practice dentistry pain-free, Posturedontics Press, Portland, OR, 2008, www.posturedontics.com
4. Simmer-Beck, Melanie, BSDH, MS, and Bonnie Branson, RDH, PhD. Minimizing Work-related Injuries in the Dental Office. Belmont Publications.
5. Chang, BJ, Many Clinicians Needlessly Work with Neck Pain, ErgoPractice News, November 2016. https://surgitel.com/many-clinicians-needlessly-work-with-neck-pain/