In order to view specimens and record data, microscope operators must assume an unusual but exacting position, with little possibility to move the head or the body. They are often forced to assume an awkward work posture such as the head bent over the eye tubes, the upper part of the body bent forward, the hand reaching high up for a focusing control, or with the wrists bent in an unnatural position. This tutorial explores proper posture for microscope observations and demonstrates how new ergonomic microscope designs can lead to a reduction of associated musculoskeletal disorders.
The tutorial initializes with the operator stationed at an older upright microscope developed without basic ergonomic conveniences. Use the Swap Microscopes slider to morph the applet between the older microscope and a newer design featuring lowered focus knobs and observation tubes that are adjustable to the operator's height. When the ergonomic microscope is in place, the Change Height slider is automatically activated, and can then be utilized to change the operator's height between a simulated range of 4' 10" and 6' 4". As the slider is translated, both the microscope and operator change to demonstrate how the microscope can accommodate users of varying heights. A set of radio buttons can be employed to toggle between upright, inverted, stereo, and industrial semiconductor microscopes. Each class of microscope can then be explored with respect to operator height variations and microscope ergonomic design.
Poor posture and awkward positioning are the primary risk factors for MSDs that can affect full-time microscopists, who often experience pain or injury to the neck, wrists, back, shoulders, and arms. Eyestrain, leg, and foot discomfort have also been documented with long-term microscope use. In the semiconductor industry, the second leading cause of work-related medical problems is found in microscope technicians, trailing only maintenance workers who traditionally have high injury rates. A regional survey of cytotechnologists, heavy users of microscopes, found that slightly over 70 percent reported having neck, shoulder, or upper back symptoms, while 56 percent had an increased incidence of hand and wrist symptoms. Other studies have indicated that around 80 percent of microscopists in all fields have experienced job-related musculoskeletal pain and that 20 percent have missed work because of medical problems related to microscope use. The rather high 5- to 10-year drop out rate for cytotechnologists is attributed, in part, to physical discomfort associated with long hours examining specimens through the microscope. Table 1 lists the range of percentages reported in the literature for medical complaints associated with long-term microscope use. A majority of reported problems occur with the neck, back, shoulders, and arms, with a smaller percentage of microscopists reporting discomfort or injury to the wrists, hands, legs, feet, and eyes.
Many of these conditions can be avoided or at least mitigated. Two studies at Duke University Medical Center during the 1990s suggested that people suffered fewer discomforts when using new ergonomically designed microscopes or even conventional microscopes modified to better accommodate the user. In either case, adaptability was the key. Microscopes that could be adapted to an individual user, rather than forcing the user to adapt to the microscope, were more comfortable and caused fewer problems.
Factors believed to be causing these problems are head inclinations up to 45 degrees and upper back inclination at angles up to 30 degrees, awkward positioning of the arms and hands, and repetitive motions. An unaccommodating workstation that requires a microscopist to sit in awkward positions for long periods can also cause fatigue and MSDs.
The major factor with using conventional microscopes is that viewing specimens requires users to maintain a flexed neck posture while the hands are in a relatively fixed position. From the viewpoint of biomechanics, having to maintain even a slight incline of 30 degrees from the vertical can produce significant muscle contractions, muscle fatigue, and pain. In fact, it has been documented that nerves can often be pinched when the neck is overextended by this amount. Repetitive motions of the hands and the contact stress of arms resting on a hard surface can cause pain and nerve injury, leading to repetitive stress injuries and/or carpal tunnel syndrome.
Later studies have suggested that to permit a more neutral erect working posture, the optical path (distance from the ocular lenses to the specimen being viewed) should range between 45 and 55 centimeters (18 to 21.5 inches). The eyepieces should be no more than 30 degrees above the horizontal plane of the desktop. A majority of older microscopes, however, have much shorter optical path dimensions (25 to 30 centimeters or 10 to 12 inches) with the eyepieces angled at 60 degrees above horizontal.
John C. Long, Kathleen E. Carr, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.