Ergo Practice News March 2015

Demystifying Magnification Power of Loupes: 7 Questions and Answers

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ErgoPractice News – March 2015

The largest dental industry event in the world is the International Dental Show (IDS) which takes place in Cologne, Germany every two years. 2015 IDS was host to around 138,500 visitors from 151 countries and 2,201 exhibitors from 56 countries. SurgiTel was represented and we met with many practicing dentists and distributors from all over the world. Our visitors asked many different questions about loupe magnification, such as:

  • What magnification power loupes do you have?
  • Do you have 2.5x, 3.3x, 3.5x, 3.8x, 4.5x, or 4.8x loupes or other specific magnification power loupes?
  • Do you have zoom loupes that offer multiple magnification powers?
  • Should the working distance of high magnification power loupes be kept short?
  • What is the “true magnification” of your loupes?

These questions, which seem simple to answer, are in fact quite complex. Currently, there is no standardized way to label loupe magnification. And as you will see the answers are often “it depends!”

Most manufacturers label their model’s magnifications as measured at reference working distances. Rarely though do manufacturers publish this reference point. Zeiss names their loupes with magnification powers and specific working distances. SurgiTel labels its loupes with model names based on magnifications at a reference working distance and attempts to avoid statements declaring magnifications. All these differences make it is very difficult to compare the magnification powers of various brands of loupes.

In this paper we hope to demystify magnification power and provide you with a fuller understanding of magnification and what it means for your work.

How to Specify the Magnification Power of Loupes

Loupes may seem similar to surgical microscopes and sport binoculars, but there are some very important differences. With surgical microscopes or sport binoculars, each and every user will see nearly the same level of detail. This may not be the case with loupes!

A single loupe model can be named as different magnification power loupes with different working distances. This is because the magnification power of loupe models varies as the working distance changes (Figure 1). Figure 1 shows both magnification power and relative effective magnification power of Zeiss’ two prism loupe models with respect to the magnification powers at the 16” (40cm) working distance. This technical data of Zeiss’ EyeMag Pro loupes is listed on their website.1

The relative effective magnification power curves on Figure 1 are computed by multiplying the optical magnification power of the loupe and the relative visual acuity factor of eyes which is given as a ratio of reference working distance to working distance. This relative effective magnification power is a more accurate representation of the level of detail our eyes perceive.

The level of detail our eyes perceive can be improved without the use of loupes simply by reducing working distance.2, 3 Imagine looking at your hand 16″ away from your eyes. If you move your hand to 8″ inches away from your eyes, you can suddenly see a lot more detail. If we reduce the working distance by 50%, we can double the perceived level of detail even without the use of loupes. The same effect occurs with loupes; as the working distance decreases the magnification power increases. Therefore, as working distance decreases the relative effective magnification power of loupes rapidly increases.

Zeiss’s two loupe models were designed as 4.0x and 5.0x magnification powers at a 12” (30cm) working distance. If they wished they could name these models as 4.0x and 5.0x loupes, similar to other manufacturers. But Zeiss has been selling these two models as different magnification loupes when set at their specific working distances. Since Zeiss sells the same loupe models as high power loupes with shorter working distances, many people may mistakenly come to believe that high magnification loupes need to have shorter working distances. But with different loupe designs, with inherent power differences, high magnification loupes can have any working distance.

In order to offer various magnification powers for any working distance, SurgiTel offers the most loupe model options: six Galilean models and six prism (aka Keplerian, aka expanded-field) models. This allows users to have high power magnification without compromising their working postures. All SurgiTel loupe models can be either customizable front-lens-mounted (FLM) type or custom-built through-the-lens (TTL) type.4

Questions and Answers:

During our IDS visit, we collected several of the most common questions related to loupe magnification. Below we provide answers and information which may help you understand how the magnification powers of loupes have been specified and evaluated.

Question: Loupes have been named with specific magnification powers. Are magnification powers by one brand similar to magnification powers used by another brand?

Answer: Most manufacturers have named their loupes using reference magnification powers determined at a set working distance. The actual magnification power of the loupe you use may be different from the reference magnification power if your working distance is different than the reference working distance used for measuring reference magnification powers.

Since different brand loupes may use different reference working distances to measure their reference magnification powers, it will be misrepresentative when comparing different brand loupes using only the listed magnification powers provided by manufacturers.

Question: Do 3.3x or 4.8x power loupes of one brand beat out the 3.0x or 4.5x power loupes of another brand?

Answer: Only if both brands used the exact same reference working distance for measuring their reference magnification powers. And, used those exact measurements to name and promote their loupe models. But if the 3.3x or 4.8x magnifications were determined using a shorter reference working distance, then the 3.0x or 4.5x loupes may even offer a larger magnification than the 3.3x or 4.8x loupes.

Question: Designs for Vision’s sales reps have been telling customers that only their listed magnification powers are true. Does this mean all other companies are lying?

Answer: No. Reference magnification powers used as the name of any loupes, including Designs for Vision’s loupes, is only true at a reference working distance used for measuring the reference magnification power. This is an undeniable fact. The achieved magnification power will be lower than the reference magnification power if the working distance of custom loupes is longer than the reference working distance.

Question: Recently Orascoptic introduced the EyeZoom loupe as an adjustable magnification loupe. Orascoptic claims that with these new loupes users can achieve three (3.0x/4x/5.0x) magnification powers. Is this true?

Answer: The answer is both Yes and No. If the user’s working distance is the same as the reference working distance, users may achieve 3.0x, 4x, and 5.0x powers. But if one’s working distance is longer than the reference working distance, users cannot achieve magnification powers listed on the loupe. This results in significantly lowered visual acuity due to both the reduced magnification power and the reduced level of detail perceived by the eyes due to the increased working distance.

Question: Should higher magnification loupes have shorter working distances?

Answer: The answer is a resounding NO. As discussed earlier, the magnification power of loupes increases as the working distance decreases. So manufacturers such as Zeiss have been selling the same loupe models as different magnification loupes. In this case, the “higher magnification power” loupes are delivered with a short working distance. In order to create high-power loupes at any working distance, additional designs with increased inherent magnifications are required. SurgiTel offers many loupe models to allow customers to have the magnification powers they need at the working distance they want.

Question: Can SurgiTel loupes be used as adjustable magnification power loupes?

Answer: The answer is Yes. Zeiss makes different magnification loupes by changing the working distance. If users are able to change the working distance of loupes themselves, the same loupe model can be used as multiple magnification powers. The working distance of Zeiss’ loupes cannot be changed and thus Zeiss’s loupes can be used as their built magnification power. SurgiTel’s patented, replaceable working distance caps for both prism and Galilean loupes allow users to easily change their working distance. Thus, with a few sets of working distance caps, all SurgiTel loupes can be used as multiple magnification power loupes. But unlike Zeiss loupes, SurgiTel users can adjust their magnifications back-and-forth as often as they wish.

Question: How can users select the right loupes for their practice?

Answer: Loupes should satisfy two requirements. The 1st requirement is to support a neutral, ergonomic working posture to prevent work-related pain and injuries. The correct, ergonomic position requires the right working distance to support the correct lower back posture and a proper declination angle to support a healthy neck posture.5-11

The 2nd requirement is to provide users with the proper visual acuity to see the necessary details of their work. Using a working distance that is shorter than 15,” 2.5x loupes can be adequate as beginner’s loupes, but if the working distance is 16” or longer, 3.0x or 3.5x loupes should be the very minimum of magnification. As working distance increases, even higher power loupes should be used to achieve the necessary visual acuity.

If you have been using loupes successfully for many years, you may be tempted to recommend to new clinicians the same magnification power you have been using. But first, you should ask them for their working distance. If their working distance is shorter than yours, you may recommend the same magnification power or even less. But, if their working distance is longer than your working distance, you may need to recommend a higher power loupe than one you are using for them to see what you see.

And because of the relative nature of magnification, as discussed in this paper, the most telling of tests would be a direct comparison. Testing the loupes in question allows one to SEE the magnification they will receive.

 

References
  1. Zeiss, Technical Data: www.zeiss.com/meditec/en_us/products—solutions/dentistry/loupes/eyemag-pro.html
  2. Chang BJ, Key Factors for Ordering Custom Loupes: part 2 – Magnification Power as the Key Vision Factor, ErgoPractice News, May 2014, https://surgitel.com/magnification-power-as-the-key-vision-factor-key-factors-for-ordering-custom-loupes-part-2/
  3. Chang BJ, Are You Using Right Magnification, ErgoPractice News, September 2013, https://surgitel.com/how-to-determine-your-custom-magnification-needs/
  4. 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/
  5. Chang BJ, Key Factors for Ordering Custom Loupes: part 1 – Declination Angle as the Key Ergonomic Factor, ErgoPractice News, April 2014, https://surgitel.com/key-factors-for-ordering-custom-loupes-part-1-declination-angle-as-the-key-ergonomic-factor/
  6. 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, 191216
  7. Rucker LM, Beattie C, McGregor C, Sunell S, Ito Y, Declination angle and its role in selecting surgical telescopes, J. Am Dent Assoc 130: 1096-1100, 1999
  8. Chang BJ, Ergonomic benefits of surgical telescopes: selection guidelines, J Cal Dental Assoc, Vol.30.No2., 2002: 161-169
  9. Chaffin DB, Localized muscle fatigue: definition and measurement, J Occupation Med 15(4): 346-354, 1973
  10. Rucker LM, Sunell S, Ergonomic risk factors associated with clinical dentistry, J Cal Dental Assoc, Vol.30.No2., 2002: 139-148
  11. Valachi B, Practice dentistry pain-free, Posturedontics Press, Portland, OR, 2008, www.posturedontics.com

 

B. Jin Chang, PhD, is President and Chief Scientist of General Scientific Corporation, Ann Arbor, Michigan.

From the late 1970s to late 1980s Dr. Chang lead the development of advanced head-up display systems for fighter jets such as F15E, A10 and F4. Over the last twenty years he has been extending the ergonomic principles used for military display systems designs to clinical vision systems. This had lead to SurgiTel’s family of ergonomic loupes and illumination systems which prevent chronic neck and back pains.

Numerous patents (awarded and pending) have been applied to designs of SurgiTel’s loupes and illumination systems.