Microscopes are routinely used in a variety of workplaces from medical research labs to high-tech fabrication inspection. When the task involves only sporadic use of a microscope—for a few minutes at a time, a few times a day—the risk factors associated with its use are relatively low. But, in today’s business world of high specialization, workers may be required to sit fixed at a microscope for possibly hours with very little opportunity to vary their posture or task.
Standard microscopes offer only a limited degree of adjustability, if any, usually resulting in the following:
- Excessive forward neck flexion – often measured at greater than 35°. According to Chaffin/Andersson, “… postural endurance decreases significantly when neck inclination angles exceed 30°.” Good neck posture is critical to our overall good spinal health, as often problems in other areas of the body tend to start here and work their way down. Some small amount of forward neck flexion is considered healthy, about 10°, but such forward inclination should really not exceed 15-20°.
- Static loading of the neck and shoulders. Static loading can occur in any muscle group in the body, and is defined as an absence of any movement. When a worker is in a fixed, frozen posture—such as hunched over a microscope for prolonged periods of time—static loading occurs. According to Putz-Anderson, “static muscle contraction restricts blood flow to the muscles, preventing delivery of sugar and oxygen and removal of metabolic waste products. Muscles subjected to static work require more than 12 times longer than the original contraction duration for complete recovery from fatigue.” Further, Chaffin/Andersson states that, “pain begins to occur after approximately 10 seconds of exertion at 55% of maximum strength.”
- Forward trunk flexion is another possible risk factor when microscopes are not properly adjusted to the user. If the lens pieces are located too far from the user, there will be a tendency for the user to lean forward in their chair, or even perch on the front edge of the chair. Trunk flexion, particularly when it is sustained, can cause adverse spinal disc compression, which may result in pain or even injury. Keyserling et al. 1988 created a model which predicted that a 50th percentile male, bending forward 20°, with no load in the hands, would experience spinal disc compression force equivalent to 35% of the NIOSH Action Limit (3430N).
Possible Control Measures
A short-term improvement for some of the static shoulder loading would be to use a product such as a microscope arm support device, available through distributors such as AliMed. This product is designed to provide some relief to the arms and shoulders, but cannot really address the more serious issues of forward neck flexion and trunk flexion.
A better, perhaps more long-term solution would be to modify the microscope so that the user is able to maintain a neutral posture when using it. A neutral posture would be defined as a relaxed, natural position with the body at rest, the head and neck erect, the back supported by the lumbar area of the chair’s backrest with a hip angle of at least 90° or slightly greater.
Options to consider when modifying or upgrading existing microscopes include:
- New microscope designs, such as those made in Switzerland by Leica Microsystems, incorporate features that include an adjustable bellows, angled wedges, and extender tubes. Virtually any user can achieve a comfortable, neutral seated posture with such an ergonomically designed device, allowing the back to remain upright and fully supported by the chair backrest, the neck upright, and the arms supported by the work table in a neutral position.
Where stereo viewing is not necessary, consider using video optics instead of the traditional viewing lenses, possibly the most optimal solution. In this system, the microscope itself acts like a camera and sends the image to a video monitor screen. The user is then free to locate the screen in a neutral position in relation to where they are sitting, again allowing them to maintain ideal neutral body postures while performing the task. In such a system, it is also advantageous to utilize a flat panel monitor instead of the standard CRT video monitor. The flat panel is far easier to adjust—a big advantage when the workstation is used by multiple employees—takes up less workspace, uses less energy, and is easier on the user’s eyes.
Other options include tilting the microscope towards the user with a retrofit bracket and fitting the eyepieces with fitted rubber eyecups for prolonged microscope use.