Ergonomics and Visual Acuity

Ergonomics is the scientific discipline that is concerned with the understanding of interactions among humans and their professions.¹ The desired outcome of ergonomic science is to fit the work to the worker in a manner that can help individuals achieve job performance objectives while maintaining their health and well-being. As dental hygienists strive to achieve ergonomic health, visual acuity is an important aspect that must be considered. Visual acuity is best described as the degree of clarity or sharpness of vision.² How well an individual can see is dependent on many variables and will change throughout a lifetime.

Studies have indicated a high number of dental hygienists experience some degree of musculoskeletal pain related to their occupation.^3,4 While there are many causes of this pain, an individual’s visual acuity may play a role. Optimal visual acuity is vital to the assessment of tissue conditions, accurate use of periodontal measurement instruments, and evaluating radiographs. When visual acuity is compromised, a dental hygienist may compensate in a way that could lead to a musculoskeletal disorder (MSD).^1,3,4

A group of researchers hypothesized that many in the field of dentistry are often unaware of the level of their visual acuity.⁵ In an attempt to create an accessible way to measure the degree of near vison, researchers developed a unique test for practicing dentists and dental students to evaluate their visual acuity using a $5 bill.⁵ In this test, research participants were asked to read the first five words of each line in the Lincoln Memorial frieze printed on the bill under a dental operating light at a distance of 300 mm, or approximately 12 inches. The ability to read six or more words in the memorial frieze indicated that visual acuity was within the average range of clinicians. If none of the words could be read, concurrent vision tests verified that the individual’s visual acuity was lower than the median score of research participants. The authors concluded that this was an easy manner to determine if additional aids were required when practicing dentistry.⁵

RAMIFICATIONS OF INADEQUATE VISUAL ACUITY

Pain in the neck and shoulders is commonly reported by dental hygienists.^1,2,6 There are many variables contributing to this, but bending the head closer to the patient to obtain better vision could be a contributing factor.^1,2 Studies have confirmed that tilting the head forward greater than 20° for the majority of a workday leads to an increased risk of neck pain.⁶ The forward head posture that is commonly adopted by dental hygienists often causes the muscles, ligaments, and soft tissue to permanently adapt to this posture, leading to postural deformity. The cervical spine can also be affected by this forward head posture.⁷ Dental hygienists need to be aware of the recommended positioning during treatment, which is a head tilt between 0° to no more than 20°.^1,7 It is also important to attempt to maintain that neutral posture for the majority of the workday.^6,7

Another important aspect of visual acuity is the effect of aging on eyesight. In the natural process of aging, the lens of the eye becomes thinner and less flexible, which makes it difficult to focus on nearby objects. This condition is referred to as presbyopia.⁸ In addition to changes in near vision, many individuals find that presbyopia causes an increased need for light and a heightened sensitivity to glare.⁸ A study placed dentists in a simulated dental environment to determine their near visual acuity. The results indicated a wide disparity in the quality of near vision among the research participants, with increasing age playing a major factor in the loss of acuity.⁹ This loss of vision may contribute to headaches and eye strain. Additionally, dental hygienists tend to compensate for this loss of visual acuity by adopting unhealthy working postures.^1,2 These changes in near vision may also negatively impact the ability to perform the intricate work that is required in dental hygiene.

STRATEGIES FOR IMPROVING VISUAL ACUITY

Research has indicated that magnification aids are useful in enhancing visual acuity.^9–11 A newly released study examined the visual acuity of practicing dental hygienists and dental hygiene students in their clinical settings.¹⁰ Visual acuity was measured with and without magnification aids. The authors concluded that magnification should be used to improve the visual acuity of all dental hygienists and is especially important for those older than 40.¹⁰ Other studies indicate that many dental professionals with visual deficiencies are not aware of the magnitude of their loss. These studies concluded that the use of magnification improved visual acuity and helped to minimize the effects of aging.¹¹ It was recommended that dental professionals schedule eye exams every 2 years to track any changes in vision.¹²

Illumination can be used to improve visual acuity.^13,14 The consensus is that over-illumination can be as harmful to the human eye as inadequate lighting. To evaluate products for usefulness, it is helpful to review how light affects vision. As light enters the eye through the cornea, the iris dilates or constricts, controlling the amount of light that is able to enter the pupil. The light is then refracted to the back of the eye where the image is focused. Adequate light makes it easier for the eye to focus, which improves acuity.¹³ However, if too much light is present, the eye’s natural defenses can no longer block the additional incoming light, and glare results. This leads to eye discomfort for the clinician and could be harmful in the long term.¹³

Many items are available that create greater visibility by introducing illumination into the oral cavity. For example, light sources have been attached to ultrasonic handpieces, mirrors, and suction devices. These products should be evaluated carefully to ensure they do not create additional glare. The use of retraction and isolation devices can offer enhanced access to the oral cavity and allows more light to enter in. The use of retraction devices and dental mirrors combined with high evacuation suction are helpful during ultrasonic instrumentation. Another useful product is high-definition mouth mirrors, which are available in a variety of sizes.

Many dental hygienists are finding that the addition of light-emitting diode (LED) headlights to magnification frames enhances illumination and improves ergonomics in many ways.¹³ The most common headlights used today are co-axial LED systems. The function of these systems is to direct a beam of light to the working area, following the head position of the operator to eliminate shadowing.^13,14 These products can vary considerably in quality and must be carefully evaluated before purchasing. A generous trial period by the manufacturer and customer follow-up are essential. When investigating different products, clinicians must be aware of several factors that will help achieve the desired outcome. It is important to evaluate the intensity of the light produced and ensure that it can be adjusted to compensate for operator preference. The light must be uniform and clear at the working distance. Lights that emit a beam with a hazy outline are not recommended. Color temperature, which is the color of light produced, is another important consideration. Light sources close in color to neutral sunlight are considered the safest options.^13,14 Batteries that control the light source can be corded or attached to the headlight. For ease of use, the power switches on the batteries should be easy to access.¹⁴ To minimize cross contamination, a good solution is to purchase lights that can be activated by motion sensors or through fabric.

CONCLUSION

Maintaining visual acuity will enable practitioners to practice dental hygiene effectively and improve body mechanics. When investigating products that claim to enhance vision, clinicians need to evaluate whether these products are improving vision without causing undue eye damage. Clinicians also need to develop an awareness of how vision needs change throughout their career and make accommodations as necessary to continue optimal clinical performance.

REFERENCES

1. Murphy DC, ed. Ergonomics and the Dental Care Worker. Washington, DC: American Public Health Association; 1998:56,
2. American Optometric Association: Visual Acuity: What is 20/20 Vision? Available at: aoa.org/patients-and-public/eye-and-vision problems/glossary-of-eye-and-vision-conditions;visual acuity. Accessed September 25, 2018.
3. Hayes M, Smith DR, Cockrell D. An international review of musculoskeletal disorders in the dental hygiene profession. Int J Dent Hyg. 2010;60:343–352
4. Morse T, Bruneau H, Michalak-Turcotte C, et. al. Musculoskeletal disorders of the neck and shoulder in dental hygienists and dental hygiene students. J Dent Hyg. 2007;81:3.
5. Perrin, Eichenberger M, Neuhaus KW, Lussi A. A near visual acuity test for dentists. Operative Dentistry November/December 2017;42:581–586.
6. Ariens GA, Bongers PM, Douwes M, et al. Are neck flexion, neck rotation, and sitting at work risk factors for neck pain? Results of a prospective cohort study. Occup Environ Med. 2001;58:200–207.
7. Valachi BS. Practicing Dentistry Pain-Free: Evidence Based Ergonomic Strategies to Prevent and Extend Your Career. Portland: Posturdontics Press; 2008:56,64.
8. Merck Manual. Eye Disorders. Available at: merckmanuals.com/professional/SearchResults?query=eye+disorders. Accessed September 25, 2018.
9. Eichenberger M, Perrin P, Neuhaus K, Bringolf U, Lussi A. Visual acuity of dentists under simulated clinical conditions. Clin Oral Invest. 2013;17:725–729.
10. Eichenberger M, Perrin P, Sieber KR, Lussi A. Near visual acuity of dental hygienists with and without magnification. Int J Dent Hyg. 2018;16:357–361.
11. Eichenberger M, Perrin P, Neuhaus K, Bringolf U, Lussi A. Influence of loupes and age on the near visual acuity of practicing dentists. J Biomed Opt. 2011;16:035003.
12. Burton JF, Bridgman GF. Presbyopia and the dentist: the effect of age on clinical vision. Int Dent J. 1990;40:303–312.
13. Chang BJ. Ergonomic benefits of surgical telescope systems: selection guidelines. J Calif Dent Assoc. 2002;30:161–169.
14. Holt E, Hoebeke R, Shine a light. Dimensions of Dental Hygiene. 2012;10(9):25–27.

From Dimensions of Dental Hygiene. October 2018;16(10):26,28.