On Cheaters: Loupes are designed for specific vision shortcomings
BY ANNE NUGENT GUIGNON, RDH, MPH
Don't you just love it when a word draws you into a conversation? You're probably wondering what kind of cheating I'm referring to: marital indiscretion, document falsification, "borrowing" other people's information, plagiarism, liberties with a new diet, or inappropriate tool use. I'm actually referring to the little reading glasses that people wear to read a book, to decipher small label print, or to thread a needle.
A very interesting online discussion I saw started out with this question: "In theory, could bifocal glasses be used instead of loupes? I'm assuming the answer is no since I haven't heard of that being done ... but why not?"
What a great question! Obviously this hygienist has heard about the benefits of magnification. As a wise consumer, she was looking for some good, honest answers to guide her decision.
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Other articles by Guignon
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Typically, online chats are full of people who mean well. Clinicians report what works well for them individually, but there is often no discussion about the science that either supports or refutes these anecdotes. And when it comes to spending money, the discussion can be even more intense. There will always be those who don't want to spend a dime on anything that involves their jobs and those who view their expenditures as a professional investment. So before you get your feathers ruffled, this discussion is about the science of optics, not a critique of personal choices.
Around age 40, the human eye loses its ability to focus on objects in close range (i.e., presbyopia). When this occurs, small objects such as newsprint become harder to see clearly, so a vision accommodation is necessary.1 Some solve the dilemma by using mono-vision contact lenses. Many start using reading glasses, commonly called readers, or have a bifocal prescription added to their current glasses. This vision correction now makes it easy to read a book, sew on a button, or apply makeup more deftly. Remember, each of these tasks involves visualizing a flat, geometric plane, not a complex, deep area like the mouth.
Back to the original question: why not just get a pair of readers (cheaters) or bifocals to function as your magnification system in the clinical setting? Inexpensive cheaters are readily available in every drugstore and in bulk packaging in some big-box stores. There are even plastic safety glasses fashioned with a diopter correction in the lower part of the lens. The diopter number indicates the strength of the cheater. Low-strength cheaters start at 1.0 and go as high as 3.5. While these inexpensive devices are perfect for short-duration tasks, there are a number of downsides to using readers as a clinical magnification system.2
Let's start with the numbers. There is a lot of confusion when it comes to readers versus loupes. A 2.5 diopter used in a pair of reading glasses improves clarity but does not magnify an image. A 2.5 pair of magnification loupes is not based on a diopter measurement. While both use the number 2.5, that is where the similarity ends, since each reflects a number that uses a different measurement scale. To further confuse the situation, one's personal reading prescription should be installed in whatever strength of magnification is chosen. If Suzy selects a 2.5 magnification system and needs a 2.5 reading correction, her custom loupes would reflect both factors.
Custom-fitted magnification loupes are made with a series of compound lenses installed in the ocular, resulting in a specified field view width and depth. The strength of the magnification affects both the field width and depth. As the strength of the magnification increases, the area in view becomes smaller and shallower. Custom-fitted loupes are also fabricated using a working distance to accommodate the user's preferred posture, while reading glasses are made to fit a standard distance of about 16 inches. In the clinical setting, the patient's head should be positioned at waist level, keeping our forearms parallel to the floor. When we hold a book, our forearms have a slight upward angle, so the distance is shorter than what is ideal in the clinical setting. When the time comes to add a reading correction to the magnification system, the working distance will also be adjusted to make sure the user can maintain a healthy posture.
The lenses found in readers from the drugstore are plastic, not high-grade optical glass. Cheaters utilize a generic geometric center, not an optical center specifically created for the user, so cheaters create a high visual demand on the eyes. High quality lenses fabricated with one's personal requirements allow the eyes to remain in neutral because the glasses do the work, reducing the potential for eye fatigue and headaches because there is less muscle strain.3
Another consideration is the frame. Cheaters are typically very small, allowing the user to peer over the top of the frame to view objects at a distance. Given the dimensions and the lack of side shields, readers do not offer sufficient eye protection for clinical work. These devices are also made with inexpensive plastic or metal components that can't be adjusted to individual facial geometry. Some with very small heads or those whose faces are very sensitive to weight are attracted to the feel of readers, but many companies now offer loupes on very lightweight frames with oculars that weigh considerably less than previous options.
Whether one purchases inexpensive readers or invests in a high quality pair of bifocals, these devices are constructed to see a one-dimensional surface.3 Since the oral cavity has depth, a clinician wearing readers or bifocals will have to constantly reposition the head to keep the images in focus. Trying to exceed one's personal vision need by using readers that are too strong is another dangerous plan. Yes, reading glasses will provide a clearer image, but the user will have to lean forward to keep in focus, resulting in a stressful, compromised posture, and increased eyestrain.
So the discussion comes full circle. Readers and bifocals are not substitutes for loupes, but the two can be combined to create synergy. Glasses are made for vision correction, not magnification, and magnification loupes are designed to enlarge images, not correct vision problems. A properly fitted custom loupe system offers enhanced visual acuity and postural protection. What you choose to do has to fit your personal comfort zone, but it is important to understand the differences between the two technologies. RDH
References
1. Diseases and conditions. Presbyopia. http://www.mayoclinic.org/diseases-conditions/presbyopia/basics/risk-factors/con-20032261
2. How to read your eyeglass prescription. http://www.cnib.ca/en/living/independent-living/pages/prescription-1007.aspx
3. Glasses. http://en.wikipedia.org/wiki/Glasses
