I have many unpleasant memories of dealing with a scope outfitted with an improper focal length and of trying to find the nurse who knows where all the correct lenses are hidden. Not my idea of a good time. Here are 10 factors to consider so that the new or refurbished ENT operating microscope you buy will please your surgeons and serve your surgical center well for years to come.

1 Cost vs. need.
Even though Dr. BMW would love to have a $100,000 electromagnetically controlled sports car red operating microscope to do BMTs (bilateral myringotomy tubes), you need to weigh the cost of the equipment against how you plan to use the scope. Although there are some crossovers among the different specialties, many scopes are specialty-specific. For example, the OPMI Movena/S7 from Carl Zeiss and the JEDMED/Kaps V-Series are ENT-specific scopes. The Leica M520 F40 is an example of a crossover scope, suitable for neurosurgery, otolaryngology or spine cases.

2 Floor or ceiling?
Once you've decided to purchase a scope, the next factor to think about is how you're going to get the thing into the operating room. Should it be on the floor or should you mount it on the ceiling? The advantage of ceiling-mounted scopes: If your OR is very small, it saves on floor space. The drawback: The scope can't be used elsewhere, even when it's not in use. A portable scope affords the maximum flexibility, but don't forget to take into account the size and the weight of the scope. Is it easy to move? Can one person bring it through the doors? Will it even fit through the OR doors?

3 Positioning issues.
Is the arm long enough, and is the base of the device far enough away from the operative field to make room for the table and the instruments? Can the scope be positioned easily? Once the base is in place, how easy is it for the surgeon to position the actual microscope head?

Positioning the microscope head involves moving the joints that connect the head to the arm. The most basic joints are mechanical. To move the scope in the X, Y and Z axes, you simply move the scope into position with your hands and tighten the joints to fix the scope in position.

The more sophisticated scopes have electromagnetically controlled joints. A push of a button electrically releases the magnets to allow positioning of the scope. The advantage here is the ease with which you can move the scope. In my experience, however, electromagnetically controlled joints are harder to move when you only want small changes in position, such as in ear surgery. Motorized positioning units are more expensive, but you can move them with greater precision.

4 Balancing act.
The balancing mechanism is another important scope feature. In order to keep the microscope in position, you must balance it in such a way that there's no excessive tension. The balancing can be achieved mechanically - a simple matter of your tightening the knobs to keep the scope in place - or it can be as complicated as a sophisticated triple- or dual-access automatic balancing. On many high-end models, the scope will automatically follow the surgeon's motions so that he hardly has to take his eyes off the field.

Here's a feature you probably won't need. Some of the larger and more expensive scopes (such as the neurosurgical scopes) are meant to be positioned behind the surgeon. The scope then extends up and over the surgeon's head and hangs in front of the surgeon. This keeps the scope out of the way in the best possible fashion, but it's not necessary for most ENT surgery.

5 Light source.
A good scope will have a backup light source that you can readily activate. The bulb should be easy (for anybody) to change, easy to obtain (meaning you don't have to special order it) and relatively inexpensive. A xenon lamp, which gives a brighter, clearer illumination, can cost as much as $500 and a halogen lamp as little as $35. You also want to stock the bulbs on site. It might make sense to keep several halogen bulbs in stock, but just a few of the more expensive xenon lamps.

6 Lenses.
The lenses are the heart of the microscope. The quality of the lenses varies. Generally speaking, you get what you pay for. The focal length is the distance from the lens to where the view is in focus. With ENT, you're constantly changing the focal length of the lens. For otologic cases, you'd typically use a 250mm focal length. For laryngoscopy, you might use a 400mm focal length. The less expensive scopes will require you to unscrew the lens in order to replace it with a different focal length lens. Although this is easy to do, the lenses need to be carefully stored, organized and kept in a place in which everybody knows they can find what's needed, when it's needed. A variety of focal length lenses are built into some of the newer and higher-end scopes. This way, you only need to flip a lever to change a focal length. This is a surgeon-friendly feature to have.

7 Foot pedals.
These let the surgeon adjust the balance, zoom and focus without removing his hands from the instruments. This way, he maintains proper orientation in the field. This is really a matter of ease for the surgeon.

8 Observation arm.
Many scopes offer this feature, which could be a mechanical eyepiece or a video camera. In my experience, the mechanical observation arm is not optimal. It tends to be cumbersome and cause a relative imbalance to the scope. The observer has to stand very close to the surgical field to truly observe the procedure. For best visualization of the procedure, I'd recommend hooking up a video camera to a monitor.

9 Handling.
This is more a matter of personal preference. Does the surgeon grab the body of the scope itself or the handgrips? Are the handgrips in the front, on the top or on the side of the scope?

10 Sterile draping.
Before you purchase the scope, make sure that you know how to sterilely drape it. Line up a source of reasonably priced drapes.

From my personal experience
I've used all sorts of scopes, from the short-armed, old-style scopes you could only adjust in the X and Y position to the electromagnetically controlled neurosurgery scope at our hospital that only disappoints when it's time to make small adjustments. My preference? A hand-controlled positioning scope. I believe in the KISS principle (keep it simple, stupid). The more electronics, magnets and pedals on the scope, the more there is to break. I'd rather have a user- and tech-friendly scope than a scope no one, myself included, knows how to use.