Original Open Access
Klaus W Neuhaus*, Philippe Perrin, Adrian Lussi
Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland.
Background: e use of magnication devices is widely recommended in surgical disciplines, but a validation of the respective
optical aids, i.e., medical loupe systems, is lacking. e aim of this study was to objectively assess dierent medical loupe systems,
including their declared magnication.
Methods: Six Galilean binocular loupes (Zeiss 2.5×, SurgiTel 2.5×, Merident DCI 2.5×, Orascoptic 2.8×, SwissLoupes 2.5× and
3.2×) and three Keplerian binocular loupes (Zeiss 3.6×, SurgiTel 3.5×, Orascoptic 3.8×) were compared with regard to their optical
characteristics. e working distance was 350 mm for all loupe systems except for Orascoptic (370 mm). e magnication factor,
eld size and distortion were assessed and compared in an independent optical laboratory (NTB, Buchs, Switzerland).
Results: e following magnications (declared/measured) and eld sizes (in mm) were obtained: Zeiss (2.5×/2.7×; 50), SurgiTel
(2.5×/2.0×; 80), Merident DCI (2.5×/2.6×; 45), Orascoptic (2.8×/2.2×; 85), SwissLoupes (2.5×/2.3×; 50 and 3.2×/3.1×; 30
respectively), Zeiss (3.6×/3.8×; 40), SurgiTel (3.5×/3.6×; 30), and Orascoptic (3.8×/4.2×; 40 [le] and 3.8×/3.8×; 45 [right]). Most
loupe systems showed a vertical and horizontal distortion less than 1°.
Conclusions: A great variance of magnication and eld sizes could be measured in Galilean loupe systems. A lower real
magnication than declared is most likely not a problem of manufacturing quality but based on commercial reasons: lower
magnication correlates with bigger eld size and wider focal range, both of which are good selling points. Keplerian loupe
systems showed more consistency, although one loupe system diered between le and right ocular. A test for instant assessment
of the eective magnication is desirable and proposed. Recommendations of medical Galilean loupes with certain declared
magnication factors and studies based on them up to now must be regarded as biased with respect to the technical details
Keywords: Optical devices, visual aids, ocular vision, vision test
© 2013 Neuhaus et al; licensee Herbert Publications Ltd. is is an open access article distributed under the terms of Creative Commons Attribution License
(http://creativecommons.org/licenses/by/3.0), is permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The use of loupes has been recommended in several surgical
medical disciplines. Obviously, medical loupes enhance vision
and make it easier to identify small structures. A recent article
recommended a 2.5× magnification for surgery with 8-0
sutures in plastic eyelid surgery . Furthermore, a 2.5× loupe
magnification has also been recommended for emergency
departments and found to be a valuable and inexpensive
tool that aids foreign body identification and wound closure
. The identification of small structures might result in a
benefit for the patient; a retrospective study with two cohorts
of parathyroid gland removals with and without 2.5× loupe
magnification found that the patients treated with loupes
showed significantly less postoperative hypocalcaemia and a
trend towards less damage to the recurrent laryngeal nerve [
In dental medicine, the use of magnification systems is generally
recommended to support operative treatments , to support
visual caries detection [
], and to enhance ergonomics [
Greater magnifications (i.e., operating microscope) have been
proven to be useful in root canal treatments and are standard
devices in endodontic specialist training .
Apart from professional purposes, it is known that the
contrast sensitivity [
] and accommodation [
with increasing age due to presbyopia. Dentists 40 y and older
can compensate for their presbyopic deficiencies with a 2.5×
magnification and achieve a visual acuity that is comparable
to younger persons without visual deficiencies [12,13].
For general dentistry purposes, Galilean loupes with 2.5×
magnification are usually recommended . This rather low
magnification factor is a compromise between visual acuity
and ergonomics, for which a relatively large field of vision and
focal range are beneficial. For higher magnifications, Keplerian
(synonym: prismatic) loupe systems are required. They offer
greater magnifications due to their sophisticated optical system.
However, there is a dilemma one is faced with between vision
and ergonomics: the higher the magnification, the smaller the
field of vision and range of focal distance. This dependence
is implied by optical laws in physics. It could therefore be a
selling point by manufacturers to proclaim a false (i.e., too high)
magnification factor in order to achieve a larger working field
and a wider range of focal distance than comparable loupes.
This study aimed at assessing objectively the optical
properties of different medical loupe systems. The purpose was
to verify if the indicated magnification factors were credible
or not and if loupes with nominally equal optical properties
can be regarded as equal.
Neuhaus et al. Medical Instrumentation 2013,
Materials and methods
A literature search was carried out in PubMed in May 2013,
using the terms “magnifying loupes” and “magnification
loupes”. One hundred twenty-five different articles were
obtained, out of which most were personal recommendations
or explanatory articles with low external validity. Objective
comparisons between different medical loupes have not been
made so far. Due to an increasing number of available medical
loupes on the market and due to costs of a laboratory setup, a
selection had to be made. Widely distributed medical loupes
from European and US American producers were chosen
for further comparisons. We aimed at testing 10 different
medical loupes and obtained consent to include 9 medical
loupes in our study.
Thus, the optical properties of 6 Galilean binocular
loupes (Zeiss ‘EyeMag Smart’ 2.5×, Zeiss, Jena, Germany;
SurgiTel 2.5×, SurgiTel, Ann Arbor, MI, USA; Merident DCI
2.5×, MeridentOptergo, Mölnycke, Sweden; Orascoptic 2.8×,
Orascoptic, Middleton, WI, USA; SwissLoupes 2.5× and 3.2×,
SandyGrendel, Aarburg, Switzerland) and three Keplerian
(prismatic) binocular loupes (Zeiss “EyeMag Pro” 3.6×, SurgiTel
3.5×, Orascoptic 3.8×) were assessed and compared in an
independent optical laboratory (NTB, Buchs, Switzerland). The
working distance was 350 mm for all loupe systems except
for Orascoptic (370 mm).
Measurement of the magnication factor and eld of
The loupes were mounted in an optical bench assay with a
beam splitting device in front of the tested loupe. A linear scale
was fixed at a defined distance according to the manufacturer.
A CCD camera captured a photograph both through a single
ocular of each loupe system and through a mirror closely
mounted to the dental loupe (
). In order to assess
the real magnification factor, the two captured pictures were
superimposed and the differences were calculated. The size
of the field of vision could be read directly.
Measurement of linear deviation
Additionally, in the same assay, a planar scale replaced the
Figure 1. Optical bench assay for measurement of the real
magnication factor of a medical loupe.
linear scale, and a digital image was taken through each ocular.
On each photograph, the linear deviation was measured using
the software ImageJ (NIH, Bethesda, MD, USA).
The magnification factors and field of views (in mm) are listed
in Table 1. None of the Galilean loupes showed the declared
magnification factor of 2.5× (or 2.8× for Orascoptic), with a
range from 2.0× to 2.7×. The magnification factors of the
Keplerian loupes were slightly above the declared values;
one loupe system (Orascoptic) contained two lenses with
different magnification factors. The vertical and horizontal
distortion was smaller than 1° for all loupe systems except
one (SurgiTel: 1.91°). The field size of Galilean loupes >2.5×
was severely reduced (Table 1).
This study is the first objective comparison of different medical
loupe systems. Obvious and important discrepancies were
found regarding the measured magnification among loupes
with a nominally equal level of magnification. Galilean loupes
with a nominal 2.5× magnification showed a range of 2.0×
(SurgiTel) to 2.7× (Zeiss). This difference of 0.7× magnification
makes up for a difference of 82% with respect to the optical
information of a planar object. This finding is most probably
not due to low production quality, but for concrete commercial
reasons. Maximum optical depth and size of the visual field
are attractive selling arguments with respect to dental
ergonomics. The fact that the inverse relation between depth
of field and magnification is an axiomatic physical law could
result in a misleading (i.e., too high) declaration. No Galilean
loupe system showed the magnification indicated by the
manufacturer at the working distance.
The Keplerian loupe systems showed better consistency
between nominal and measured magnification. However,
in one sample (Orascoptic) the right and left lenses showed
different magnification factors. As this manufacturer offers two
loupe systems with the respective magnifications identified, it
was assumed that this loupe was wrongly assembled during
the manufacturing process.
Galilean loupes have a physical limit of the magnification
factor, which can be extended with additional lenses. This
increases along with distortions in the outer area of the field
of view. By hiding the outer parts, most distortions can be
masked. This is the reason for the small field size found in 3.2×
SwissLoupes, as an example for this type of loupe. Keplerian
loupes are the instrument of choice for magnifications above
3.0×. They allow a free range of magnification without any
The magnification factor is crucial per se, but only one of the
features used to characterize a medical loupe (as are weight,
design, and price). The optical testing described in the present
study is expensive, demanding, and time consuming, therefore
an inexpensive and accessible device for ad hoc testing of the
Neuhaus et al. Medical Instrumentation 2013,
real magnification factor would be desirable. An example for
such a fast and inexpensive test can be downloaded at .
A great variance in magnification and field size could
be measured in Galilean loupe systems. The differences
between their declared and effective magnification are in
some cases important. A test for instant assessment of the
effective magnification is desirable and proposed. Today,
recommendations concerning medical Galilean loupes with
certain declared magnification factors and studies based on
them must be regarded as biased with regard to the technical
properties assessed in the present study.
The authors declare they have no competing interests.
KWN, PP and AL conceived and designed the study. KWN drafted
the manuscript. PP and AL critically appraised the manuscript.
Final manuscript was read and approved by all the authors.
Acknowledgement and funding
We thank Anne Seeger, ZMK Bern, for creating the figure.
This study was funded by the Department of Preventive,
Restorative and Pediatric Dentistry, University of Bern.
Received: 24-Apr-2013 Revised: 16-May-2013
Re-Revised: 17-May-2013 Accepted: 21-May-2013
Table 1. Comparison of dierent loupe systems.
* Obviously dierent loupes were mounted in the loupe system.
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