Written by Gregori M. Kurtzman, DDS Monday, 30 November 2009 19:00
Many of us practice without magnification and rely on the operatory chair light for our illumination. Until we try using magnification in treating our patients, we don’t realize the details that we are missing. Furthermore, as we age and become more farsighted, focusing on the small details becomes more difficult thus potentially decreasing the quality of care provided.
Illumination is also important in proper visualization. If the field of view is poorly illuminated, magnification will not be effective since the details will be lost. As magnification increases, achieving visual clarity requires higher levels of light to permit the eye to focus on the object.
IMPORTANT FACTORS TO CONSIDER
When choosing a set of loupes, we need to consider several important factors: resolution, field of view, and depth of field. These factors will vary between the various manufacturers, and they will be directly related to the quality of the optics and lenses used.
Resolution is the ability to distinguish one small object from another, and is related to the quality of the optical design, precision of the lenses used, and the convergence of focus. The design and quality of the lenses used in manufacturing the loupes will influence the resolution. When superior optics are employed, the loupes will be able to focus the viewed image as a sharp image with no blurring, thus preventing eye fatigue. As we know, quality usually costs more. Lower cost loupes typically use lower quality lenses, which will provide lower resolution and result in greater degrees of eye strain.
Loupes that transmit light will allow the practitioner to work with less added light. An important aspect of resolution is 2 types of aberrations that affect loupe performance: spherical and chromatic. Spherical aberrations can be detected by looking at straight lines. If the lines are not straight when viewed through the loupes, the loupes display spherical aberration. On the other hand, chromatic aberration refers to color distortion and recognition; a critical consideration for diagnosing tissue health. The best way to check for chromatic aberration is to view black lines on white paper, looking for any blurry, blue lines adjacent to the sides of the lines. High quality loupes show no signs of spherical or chromatic aberration.
Field of View
Figure 1. Image at zero magnification.
Figure 2. Image at 2.5x magnification (Galilean loupes).
Figure 3. Image at 3.0x magnification (Galilean loupes).
Figure 4. Image at 3.5x magnification (Galilean loupes).
Figure 5. Image at 4.0x magnification (Prismatic loupes).
Figure 6. Image at 5.0x magnification (Prismatic loupes).
Field of view refers to how much of the object can be viewed at one time. As magnification increases, we see a decrease in the field of view. This needs to be matched with the specific procedure that is being performed. Restorative and periodontal procedures require a larger field of view so that several teeth may be viewed at a time, without having to move the head to see more of the object. However, when performing endodontic procedures, the practitioner typically only needs to view one tooth at a time. So, higher magnification would usually be more beneficial in an endodontic procedure than in other procedures.
High quality optics will also show edge-to-edge clarity in the field of view with no loss at the periphery. This is linked to the diameter of the loupes, the optical design, and the magnifying power. The rule is: the higher the power, the smaller the field of view. The wider the field of view, the less eye fatigue results for the practitioner. Figures 1 to 6 demonstrate the field of view at a set distance from the object, starting at zero magnification (the naked eye) through 5 times magnification.
Depth of Field
Depth of field is also an important factor to consider when choosing magnification loupes. This refers to the range of focus between what is closest to the practitioner, to what is farthest away, in the field being viewed. The longer the depth that is in focus at one time, the less the eye strain and the easier it is to render treatment. The depth of field is dependent of the design of the optics, the magnifying power, the available lighting, and the eye’s ability to focus on the objects.
TYPES OF LOUPES
Magnification allows us to see greater detail than is possible with the unaided eye. Until we use magnification in our clinical work, we are not really aware of what we are missing. From a practical clinical standpoint, magnification allows for better procedural precision.
As mentioned previously, we must decide what magnification will best suit our general needs based on the types of procedures being performed. Beginning loupe users will find it easier to adapt to lower levels of magnification rather than jumping immediately into higher magnification. To better understand magnification, we should understand the types of loupes employed in dentistry. These are divided into Galilean loupes and prismatic loupes.
Galilean loupes are named after the 17th century astronomer, Galileo Galilei. These consist of 3 lenses, and are Class II lenses with magnification between 2.0 and 2.9 power; or some are Class III lenses, with magnification between 3.0 and 3.9 power. By their design, it is not possible to achieve a high quality image with Galilean loupes above 3.5x magnification. In general, Galilean Loupes are lightweight, affordable, and easy to use.
Prismatic loupes, also referred to as Keplerian loupes, after the 17th century astronomer, Johannes Kepler, are Class IV lenses providing magnification in the range of 4.0 and higher. These consist of a compound system of several lenses. The advantage of prismatic lenses is superior resolution over Galilean equivalents throughout the field of vision. Since there are more lenses in prismatic loupes, they have longer telescopes and tend to be slightly heavier.
Figure 7. Flip-up Galilean loupes (through the lens on left, flip-up on right) (Brasseler VE [Brasseler]).
Figure 8. Flip-up prismatic loupes (Brasseler VE).
There are essentially 2 designs of loupes: flip-up and through-the-lens loupes (Figures 7 and 8). Flip-up loupes have the telescopes on a hinge system, allowing them to be easily flipped-up when not in use. With through-the-lens loupes, the telescopes are fixed to the lenses of the glasses. The benefit of flip-up lens is they are not operator specific, allowing the practitioner to alter the interpupillary distance, as well as the focal point of the right and left lenses. Through-the-lens loupes do not allow for any adjustment of the telescopes by the operator. Additionally, with flip-up loupes, should the practitioner’s regular eyeglass prescription change over time, the eyeglass lens can be changed easily by any optician. It is more costly to change the prescription of the glass lens in through-the-lens loupes because the loupes must be returned to the manufacturer for changes.
CLINICAL LOUPES IN OUR PRACTICE
In our office, we use a line of loupes that employ high-quality optical glass to provide maximum resolution, large fields of view, and outstanding depth of field (Vision Enhancement [Brasseler]). Options include a wide range of magnifications and working distances to accommodate various practitioners in both flip-up and prismatic styles. Magnifications available include 2.5x, 3.0x and 3.5x Galilean telescopes and 4.0x and 5.0x prismatic telescopes. Galilean loupes are available in through the lens design in 2.5x and 3.0x only and all magnifications are available in flip-up in both Galilean and prismatic designs.
The flip-up design incorporates a unique double-hinge system, allowing customization for the best viewing angle. A wide selection of frames are available.
Advances in Illumination
Figure 9. Comparison of the field of illumination of the various types of headlights.
The operatory chair light, to which we had become accustomed, does not provide adequate illumination and is too far from the field to provide proper illumination. Light diffuses and spreads as the distance between the light source and the item being illuminated increases. Incandescent lighting, as seen in chair lights, is generated from a bulb with a curved surface. The light leaving the bulb radiates in all directions and consequently only a small percentage of the light falls on the subject.
An alternative to this, introduced a number of years ago, is fiber-optic lighting. As the light is directed through a bundle of glass fibers, the majority of the light is concentrated on the subject being illuminated. The field of illumination is equal to the diameter of the bundle, so that a fiber-optic chair light requires a diameter of 4 to 6 inches to illuminate the full mouth. This is not practical, as the weight and bulk of this would prohibit its use in the dental operatory. The alternative is a smaller diameter light affixed to the head of the operator, taking the place the light, providing excellent illumination much closer to the subject. The downside of fiber-optic headlights is they require a powerful light source which occupies a large box and is tethered to the headlight by a long fiber-optic cable. So, maneuverability is controlled and limited to short distances from the light source.
As technology advanced, the next leap in illumination was LED lights. It became possible to place a power pack on the user’s belt and eliminate being tethered to the light source located on the counter adjacent to the practitioner. The early LED headlights unfortunately did not provide the same intensity of illumination found with the fiber-optic headlights and, although they had a relatively bright center of illumination, the lighting rapidly faded as one moved from the center of the field of illumination. This was directly related to the batteries in the power pack for the LED light. As improvements in batteries became available, not only could the LED be powered longer between charging, but the intensity of illumination was now able to surpass fiber optics (Figure 9).
Figure 10. Portable LED power pack (Brasseler VE).
|Figure 11. Galilean loupes with LED headlight (Brasseler VE).|
A recent development in illumination technology that we have introduced into our practice is a portable LED headlight (Brasseler VE LED headlight [Brasseler]). This has greatly helped us in the ability to better visualize all procedures to which it is applied. Using a state-of-the-art lithium polymer battery, the compact lightweight power pack provides 6 hours of use between charges with 5,000 foot-candle illumination, providing a bright white field (Figures 10 and 11). The unique lens design provides a beam that is focused with minimal diffusion and scatter at the borders. The unit allows for fully adjus-table beam intensity, preventing color distortion and glare, to fit any clinical situation and preferences. It is available as a clip-on for loupes, with mounts that will fit not only both Brasseler loupes and most competitors’ products, but also as a headband for standalone illumination for those who do not use loupes. An optional composite filter is available to prevent resin curing when using illumination during bonding procedures.
The cost of magnification and illumination varies with the quality of the technology offered. It is important to judge the resolution, field of view and depth of field when evaluating loupes. Magnification and illumination are a must for those seeking to do the best technical work possible. Enhanced vision and illumination is also beneficial for hygienists to employ, allowing them to perform more thorough exams, render higher quality treatment, and to contribute to optimal patient care.
Other Resources for Magnification and Illumination
The author recognizes the importance of making your own decisions in comparing and choosing a system that is right for your practice. Therefore, the following companies may be contacted as additional resources in providing magnification and illumination products and advice: Orascopic (Middleton, Wis,  369-3698), Designs for Vision (Ronkonkoma, NY,  727-6407), Perioptix (San Clemente, Calif,  360-0033), and SurgiTel (Ann Arbor, Mich,  959-0153).
Dr. Kurtzman practices general dentistry in Silver Spring, Md. He is a former assistant clinical professor at the University of Maryland, Department of Endodontics, Prosthetics, and Operative Dentistry. He has lectured internationally and has had over 160 articles published. He is on the editorial board of numerous dental publications, a consultant for multiple dental companies, a former assistant program director for a university-based implant maxi-course, and he has earned the status of Diplomat in the ICOI. He can be reached via e-mail at email@example.com.
Disclosure: Dr. Kurtzman reports no conflicts of interest.
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