What Magnification Power Does Your Work Require?

ErgoPractice News – December 2014

Most clinicians start with either 2.5x or 3.0x Galilean loupes during their training. These loupes can help students and residents learn how to use magnification and may provide users with a more ergonomic way to work (without bending over patients). Note: We say “may” since true, Total Ergonomics doesn’t just come from using any loupes.^1-4

However, these lower powers do not provide users with the true benefits of the magnification. Clinicians can actually see just as well by getting closer to patients without the use of loupes (Figures 1a and 1b). One can even improve their vision to this level with the use of strong diopter glasses (sometimes called single-lens loupes) if they are also willing to get much closer to their patients.

Young clinicians can often focus quite close and can see adequate details as they get closer to patients even without the use of diopter glasses. Some believe the only purpose of loupes is to see better, so they may continue setting themselves up for future pain and injury by ignoring the ergonomic benefits.

In order to experience true magnification benefits, one needs to use surgical microscopes or higher power prism (or Keplerian) loupes. With a microscope, a magnification setting provides the same level of detail for all users. With loupes, however, magnification depends on the custom working distance built into the loupes. If you want to purchase a high power loupe for precision procedures, the question you must ask is “How can I determine the magnification power my work requires?”

The magnification power of a loupe model is defined at a specific working distance. The user’s custom working distance is almost always different from the working distance at which the magnification was defined. As the working distance increases the magnification power of the loupes, the visual acuity of the user will significantly decrease.⁵

Rather than discussing detailed design data, which we may discuss in a future paper, let’s consider an example. A clinical instructor has been using a 4.5x prism loupe. He likes the visual acuity he can achieve with this loupe and suggests trainees to use a 4.5x loupe. The working distance of the instructor is 16″ (40cm) and the magnification power of the loupe is designed at the 16″ working distance. So the instructor in this case is, coincidently, experiencing a true 4.5x magnification. The question is “Can trainees see the same detail that the instructor can see with his loupe model with a different custom working distance?” The answer is that the trainees cannot see the same detail if their working distances are longer than 16 inches and the trainees can actually see more detail if their working distances are less than 16 inches.

Question: The working distances (WDs) of two trainees are 14″ (35cm) and 18″ (45cm). What magnification power should each trainee choose to see the same detail as the instructor above?

Answer: The magnification power of the loupe with the 14″ WD will be more than 4.5x at 16″ and it will be less than 4.5x with the 18″ WD (Figure 2). For the 14″ WD, the magnification power required to see the same detail as the instructor would be 3.9x (=4.5x x 14″/16″). For the 18″ WD, the magnification power required to see the same detail as the instructor would be 5.1x (=4.5x x 18″/16″).

From this example we learn several facts about loupe magnification:

The magnification power of loupes varies as a function of the working distance. In a strictly scientific sense, using a magnification power to describe a loupe model is incorrect. Once those loupes are made to the user’s custom working distance, the achieved magnification power may be different from the designed magnification power at a specific distance. (SurgiTel model names are not magnification powers.)
Visual acuity depends on working distance. People with shorter working distance can see better with the same loupe model than people with a longer working distance.
Utilizing this effect, we can achieve multiple magnification powers with the same loupe model by changing the working distance. The working distance of SurgiTel prism loupes can be customized by interchanging working distance caps. Users can keep different sets of working distance caps.⁶

In Conclusion

The magnification power you need to see the same detail as another person with a certain loupe model may not be the same. If your working distance is longer, you need a loupe with a higher magnification power. But if your working distance is shorter, you can use a loupe with a lower magnification power.

We advise all clinicians to experience loupes before buying. Take all claims with a grain of salt and be sure to personally experience the comfort and performance of various loupes. How these tools work for you should define your choice!

References:

Chaffin DB, Localized muscle fatigue: definition and measurement, J Occupation Med 15(4): 346-354, 1973
Valachi B, Practice dentistry pain-free, Posturedontics Press, Portland, OR, 2008, www.posturedontics.com
Chang, BJ, Key Factors for Ordering Custom Loupes: Part 1, Declination Angle as the Key Ergonomic Factor, ErgoPractice News, April Issue, 2014, https://surgitel.com/key-factors-for-ordering-custom-loupes-part-1-declination-angle-as-the-key-ergonomic-factor/
Chang, BJ, (2014, July), Declination Angle: The Key Factor for Custom Loupes, Oral Health, 46-49.
Chang, BJ, Magnification Power as the Key Vision Factor, Key Factors for Ordering Custom Loupes: Part 2, ErgoPractice News, May Issue, 2014, https://surgitel.com/magnification-power-as-the-key-vision-factor-key-factors-for-ordering-custom-loupes-part-2/
Chang, BJ, Advances in Magnification and Mounting with SurgiTel’s Patented Prism Loupe Technology, ErgoPractice News, February 2014, https://surgitel.com/advances-in-magnification-and-mounting-with-surgitels-patented-prism-loupe-technology/