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Substantial difference between declared and real magnification in medical loupes

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

Klaus W Neuhaus*, Philippe Perrin, Adrian Lussi
*Correspondence: klaus.neuhaus@zmk.unibe.ch
Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland.
Abstract
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
reported here.
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.
Introduction
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 [1]. 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
[2]. 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 [
3
].
In dental medicine, the use of magnification systems is generally
recommended to support operative treatments [4], to support
visual caries detection [
5
], and to enhance ergonomics [
6
].
Greater magnifications (i.e., operating microscope) have been
proven to be useful in root canal treatments and are standard
devices in endodontic specialist training [7].
Apart from professional purposes, it is known that the
contrast sensitivity [
8
,
9
] and accommodation [
10
,
11
] decreases
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 [14]. 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.
Medical Instrumentation
Neuhaus et al. Medical Instrumentation 2013,
http://www.hoajonline.com/journals/pdf/2052-6962-1-2.pdf
2
doi: 10.7243/2052-6962-1-2
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
vision
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 (
Figure 1
). 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).
Results
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).
Discussion
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
optical impairment.
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,
http://www.hoajonline.com/journals/pdf/2052-6962-1-2.pdf
3
doi: 10.7243/2052-6962-1-2
real magnification factor would be desirable. An example for
such a fast and inexpensive test can be downloaded at [15].
Conclusion
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.
Competing interests
The authors declare they have no competing interests.
Authors’ contributions
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.
Publication history
Received: 24-Apr-2013 Revised: 16-May-2013
Re-Revised: 17-May-2013 Accepted: 21-May-2013
Published: 24-May-2013
Table 1. Comparison of dierent loupe systems.
* Obviously dierent loupes were mounted in the loupe system.
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. J
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. 
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
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... It is known that contrast sensitivity and visual adjustment decreases with increasing age due to presbyopia. Dentists 40 years of age and older can compensate for their deficiencies in presbyopia at a 2.5-fold magnification and achieve visual acuity that is compared to younger people without any visual impairment [11] . ...
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Magnification is the amplification of the real image of an object that allows a better visual acuity for the professional. It was considered a support applied in the health area, its use grew, gained significance in the dentistry field and promoted the improvement of operative techniques for a safer and more accurate procedure. Magnifying glasses and clinical microscopes stand out the most among the devices used for this purpose. The present work aims to review the literature, in a narrative way, about the magnification technologies used in aesthetic dentistry, showing its benefits and limitations.
... There was no difference in sensitivity, specificity or AUC, irrespective of the clinical experience, when a Galilean loupe with 2.5Â magnification was used as a diagnostic aid. The declaration of the level of magnification in Galilean loupes can be misleading, as the values often are only approximately correct [22]. In fact, the true magnification level of the loupes in the latter study was 2.2Â instead of 2.8Â, and the loupe used in our study was 2.0Â instead of 2.5Â [21]. ...
Chapter
The detection of occlusal lesions is difficult because of the morphology of molars and premolars. Deep fissures are often plugged with organic material that can be stained over time or that can promote the beginning of the caries process. Deep fissures also often hamper direct sight of an existing incipient caries lesion that might therefore be detected at a relatively advanced stage. While meticulous visual-tactile caries detection is the first and most important method to detect and diagnose occlusal caries lesions, hidden caries can be detected with greater sensitivity by other means such as bitewing radiography and laser fluorescence. However, because there is a great variation between the diagnostic decisions made by different clinicians, additional caries detection aids also help to decrease this variation and help to promote more consistent clinical decision-making.
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Purpose: To assess the visual performance of Swiss hand surgeons in an environment similar to their workplace. The influence of Galilean (lenses only) and Keplerian loupes (lenses and prisms), the surgeon's age, and the credibility of a self-assessment of his or her own optical performance were evaluated. Methods: Sixty-three hand surgeons between 29 and 68 years of age with 70 loupes were included in the study (Galilean n = 35, Keplerian n = 35). The visual performance as surgeons was self-assessed on a modified visual analog scale and objectively measured with miniaturized visual tests in a simulated clinical setting. We evaluated the influence of the optical device by comparing Galilean and Keplerian loupes and the influence of the surgeon's age by comparing 2 subgroups: < 40 years and ≥ 40 years. Results: The correlation between self-assessment and objective visual performance was weak, with a Spearman rank correlation coefficient of 0.25. The near visual acuity with habitual optical aids showed considerable variability, with a range of 300% in the dimension of the smallest detected structure. The near visual acuity was significantly lower in the older group ≥ 40 years than in the younger group < 40 years with both Galilean and Keplerian loupes. Keplerian loupes allowed a significantly higher visual performance than Galilean loupes. Surgeons 40 years or older using Keplerian loupes had a similar visual acuity to surgeons younger than 40 years with Galilean loupes. Conclusions: The magnified near vision of hand surgeons showed an important individual variability. Self-assessment was not a valuable instrument for surgeons to estimate their own near vision. Hand surgeons older than 40 years should use higher magnification loupes. Type of study/level of evidence: Diagnostic III.
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Objectives: This study examined the near visual acuity of dentists in relation to age and magnification under simulated clinical conditions. Materials and methods: Miniaturized visual tests were performed in posterior teeth of a dental phantom head in a simulated clinical setting (dental chair, operating lamp, dental mirror). The visual acuity of 40 dentists was measured under the following conditions: (1) natural visual acuity, distance of 300 mm; (2) natural visual acuity, free choice of distance; (3) Galilean loupes, magnification of ×2.5; (4) Keplerian loupes, ×4.3; (5) operating microscope, ×4, integrated light; (6) operating microscope, ×6.4, integrated light. Results: The visual acuity varied widely between individuals and was significantly lower in the group ≥40 years of age (p < 0.001). Significant differences were found between all tested conditions (p < 0.01). Furthermore, a correlation between visual acuity and age was found for all conditions. The performance with the microscope was better than with loupes even with comparable magnification factors. Some dentists had a better visual acuity without optical aids than others with Galilean loupes. Conclusions: Near visual acuity under simulated clinical conditions varies widely between individuals and decreases throughout life. Visual deficiencies can be compensated for with optical aids. Clinical relevance: Newly developed miniaturized vision tests have allowed, in a clinically relevant way, to evaluate the influence of magnification and age on the near visual acuity of dentists.
Article
Purpose: To describe the age-related change in contrast sensitivity seen in 35- to 80-year-old men in an Australian population. Methods: The Florey Adelaide Male Ageing Study (FAMAS) is a prospective population-based study of men aged 35–80 years randomly selected from the north-west suburbs of Adelaide. We conducted a nested ophthalmic substudy of these men. Contrast sensitivity (CS) was measured at four spatial frequencies (3, 6, 12 and 18 cycles/degree [cpd]) using the Vectorvision CSV-1000 contrast sensitivity test chart (Vectorvision, Dayton, OH, USA), and results were statistically analysed relative to age and cataract type. Results: There were 2650 eligible subjects in the FAMAS and 1195 participated (45.1%); 472 of those participated in the ophthalmic substudy. A statistically significant decrease in contrast sensitivity was seen with advancing age at each spatial frequency tested [Generalized estimating equations (GEE) multiple linear regression: p ≤ 0.01]. The decline with age was greatest in the highest spatial frequency (18 cpd) and least in the lowest spatial frequency (3 cpd). Posterior subcapsular cataract caused the greatest reduction in contrast sensitivity at all spatial frequencies, while nuclear cataract caused significant reduction only in the intermediate (12 cpd) and high (18 cpd) spatial frequencies. Cortical cataract failed to reach statistical significance in contrast sensitivity reduction at all spatial frequencies tested. Conclusion: Contrast sensitivity declines with age in all spatial frequencies tested with a greater decline occurring in the higher spatial frequencies. Age and cataracts are independently associated with contrast sensitivity decline, and posterior subcapsular cataracts caused the greatest reduction at all spatial frequencies.
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Bracket bonding has been a major advance in orthodontic treatment. However, the method of debonding can lead to diverse problems such as enamel fractures, enamel loss and enamel scratching. In this clinical investigation we aimed to evaluate the influence of wearing dental loupes on enamel damage during the debonding procedure. 22 consecutive patients were randomly assigned in a split-mouth study to evaluate adhesive removal with and without the use of dental loupes (2.5×, LED headlight). Tooth replicas in epoxy resin were made from silicone impressions. Electron microscopic images (50× magnification) of 394 buccal enamel surfaces were evaluated according to an enamel damage index (EDI), line angle grooves (LAG) and composite residues (CR) on anterior teeth, premolars and molars. The EDI revealed highly significant advantages for debonding with dental loupes, with which the EDI was significantly higher for molars, while still less than without dental loupes. We detected no differences between the tooth groups without dental loupes. We found significantly fewer LAG on anterior teeth debonded with dental loupes. CR were fewer in the dental loupes group, and we noted no significant differences between the tooth groups. Dental loupes affect the quality of the debonding procedure, resulting in less enamel damage and composite residue, as well as fewer LAG compared to the control group. We therefore strongly recommend the use of dental loupes in orthodontic debonding procedures.
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The presbyopic addition or 'add' is the (binocular) spherical positive power supplement superimposed on any distance refractive correction to counter near vision difficulties associated with the physiological age-related loss of accommodation and consequent recession of the near point: its necessity is first encountered in middle age. The continuous (linear) ascending trend in near lens power versus increasing age advocated since the seventeenth century is at odds with the twentieth-century clinical observation that there is a deceleration in add requirement beyond an individual's mid-fifties. It is shown here that this difference is reconciled--in broadly qualitative terms if not in magnitude-when typical clinical near addition data are superimposed on the accepted distance hypermetropic refractive base recorded from early middle age onwards: a continuous rising function is produced spanning most of the three decades beyond 40 years of age. This result is considered in the context of the age markings found on certain eighteenth-century antique near vision glasses and the recommendations attached to the self-selection of ready-made reading glasses in the late twentieth century.