the Right Microscope for Your Practice
T. Mitzner, D.V.M
veterinarians would rather do anything than look through
a microscope. I
find this somewhat alarming in light of the microscope’s
usefulness in clinical practice.
The current nature of veterinary medicine dictates
that the practitioner must use all the tools at his disposal;
so why the lack of enthusiasm?
veterinarians have methodically approached the task of
purchasing a microscope and even fewer have been properly
trained in its use. Many clinic microscopes are “carryovers” from college days
or, worse yet, hand-me-downs.
If they were purchased outright, it’s a good bet
that many selections were made on price, alone.
With regard to training, the majority of us received
our introduction to clinical microscopy back in high school
when we were handed an instrument and told to use it.
If we were lucky enough to receive any formal instruction,
it was sparse at best.
As a result, the microscope is often the most maligned
and improperly used instrument in our in-house laboratory.
is some good news, however, for the veterinarian who is
considering the purchase of a quality microscope.
During the last decade, there have been a number
of industry changes.
While microscopes have traditionally been manufactured
in Germany, Japan, and the United States, acceptable products
are now coming out of Korea, Malaysia, and especially
have also been significant strides in optical quality.
All of this translates into broader choices, higher
quality, and better value for the buyer.
change, certainly advantageous to the shopper, involves
the development of industry standards.
Most microscope tubes now have a standard length
of 160mm. The
objective length, the distance from the object to the
shoulder of the objective is also showing signs of standardization.
The sizes of slides and cover glasses are uniform,
at least in this country.
Even immersion oil must now conform to certain
recommendation I routinely make to veterinarians is that
they own two practice microscopes: a not-too-sophisticated
model for performing parasite studies, and a “better”
instrument for cytological work.
I have seen many excellent microscopes ruined by
the corrosive materials used for fecal and heartworm testing.
What’s more, having a separate microscope for high
quality work will allow the doctor to place it in a quiet
corner, away from the mainstream of activity and restrict
its use to only those individuals who will take proper
care of it.
type of microscope that the veterinarian will be purchasing
is called a compound microscope, so named because it consists
of a combination of lenses that form the image.
The stand and body of the microscope is one of
the initial considerations.
These parts need not be elaborate, but should be
strong and stable since their job is to support the delicate
nosepiece, which holds the objectives, should rotate easily
and provide ready access to objectives for easy cleaning.
I recommend purchasing a microscope with a quadruple
microscope head provides support for the oculars and can
be straight or inclined; monocular, binocular, or trinocular.
An inclined head will point the ocular back towards
the user and will prevent the individual from having to
“stand over” the microscope to look through it.
Most of us prefer a binocular head since it allows
for more comfortable viewing over a longer period of time.
Photomicrography can be interesting and can produce
excellent teaching aids for clients and staff.
If the practitioner anticipates this possibility,
than a trinocular head should be purchased at the outset
instead of a binocular head.
Camera attachments can be added later as finances
trinocular head will also allow for the later addition
of a second head for dual viewing; however, nowadays a
video set-up is a more cost effective alternative.
are by far the most important consideration in choosing
a microscope. The
objectives are responsible for forming the immediate image
that will subsequently be examined by the ocular.
There are three basic types of objectives, so named
because of their degree of correction. They are achromats, semipochromats, and apochromats.
The achromatic objectives comprise nearly all of
the objectives in common use.
The other categories are primarily for research
and high quality photomicrographic purposes.
The numerical aperture (N.A.) is a measure of the
resolving power, i.e. the higher the N.A., the greater
Achromatic objectives tend to have moderate N.A.’s
though they are still quite adequate for clinical use.
special type of achromat objective is the plano or planachromat.
These are also referred to as flatfield objectives.
They consist of a group
of lenses that essentially “flatten” the image allowing
elements at the periphery of the field to be in focus
simultaneously with those in the center of the field.
While planachromats were once necessary for rapid
scanning of blood smears and the like, many practitioners
are instead choosing high quality achromatic objectives
and achieving very good results.
Planachromatic objectives are still recommended
Veterinarians will need to have the following objective
powers: 4X for scanning, 10X, 40X high/dry, and 100X oil
ocular is used to examine the real image formed by the
most common type of ocular is the Huygenian, or negative
must be compatible with the objectives in use, so be cautious
about buying objectives and oculars from different sources.
Wide-field objectives will encompass a larger area
than the standard type and are recommended for longer
study sessions, as they tend to reduce fatigue.
High-eyepoint oculars are for individuals who need
or prefer to keep their eyeglasses on while using the
microscope; however, non-eyeglass wearers may find these
advantageous as well.
most common type of condenser is the two-lens Abbe type.
This type will be found on most microscopes offered
It is important to check the N.A. of the condenser,
as it should be equal to or greater than the N.A. of the
highest power objective. The reason for this is that the N.A. or resolving power of
the system will be no greater than the N.A. of the highest
This is especially important for objectives with
N.A. greater than 1.0.
In order to obtain the highest resolution from
these objectives, a condenser of 1.0 or greater must be
utilized and the condenser must be raised so that it contacts
the bottom of the slide.
Otherwise, air, which has an N.A. of 1.0, will
be part of the systems, relegating it to a maximum resolution
should be of the mechanical type and operate smoothly.
Left or right-handed stages are generally available.
low-voltage tungsten lamps have been used as the light
source for microscopes.
Many manufacturers have now begun replacing these
with higher quality quartz-halogen (or “white-light”)
lamps, which are recommended especially for photomicrography.
The light source can be in-base or separate and
should be of the adjustable type.
Some systems will have a separate transformer unit
allowing for even greater variation in light intensity.
that impose an image of a net, scale, or crosshairs over
the viewing area are called reticles.
Many of use know these as micrometer discs.
Depending upon the intended use of the microscope,
veterinarians may want to purchase one of these.
It is desirable to have the reticle mounted in
a separate ocular that can be removed and replaced with
a non-reticle assembly for those times when the scale
is not needed.
general tips on shopping: Consider your needs, the number
and types of samples that will be viewed, and how many
people will be using the microscope.
Take time to carefully review manufacturer’s literature
or, better yet, attend a microscope or scientific instrument
to narrow your choices down to 2 or 3 models and spend
some time working with these, utilizing your own slides.
Never, never buy on price alone.
The less expensive model with mediocre performance
will end up a chore to use and will subsequently gather
best choice will often be neither the least nor the most
you do purchase, make sure that the supplier acquaints
you with the proper care needed for your microscope and
the appropriate professional maintenance schedule.
Only high quality lens tissue should be used to
clean objectives and oculars. Recommended solvents, when needed, are methanol, or specially
formulated lens cleaners.
If xylene is used, use it sparingly as it is capable
of dissolving some of the adhesives that are used to bind
Microscopes should be kept covered when not in
use and should be protected from excessive moisture and
most clinical situations, cleaning and instrument adjustment
will be needed every six to twelve months.
clinic microscope, like your spouse, constitutes a choice
that you will live with for many years.
The informed and careful shopper will be rewarded
with an excellent and profitable investment.