The TV Example – “Bigger is not always better!”
Which is better? A 52-inch projection television or a 36-inch high definition television (HDTV)? If all you care about is the action of a baseball game, you may pick the projection TV – lots of action but with a fuzzy picture. However, if you want to see fine detail, like the seams on a major league curve ball, purchase a sharply detailed HDTV.

Why Field Width?
Field width is the size of the operating site when viewed through loupes. Healthcare professionals appreciate a wider field of view because it is easier and quicker to adjust when shifting from the naked eye to the loupe. A wider field also promotes less eye fatigue. Field width is linked to the diameter of the telescope, the optical design and the magnifying power – the higher the power, the smaller the field.

Field Depth - This is the range of focus delivered by the loupe. Longer field depths allow you to view the entire operating field, which means less neck and eye strain. Field depth is dependent on the available lighting, the optical design, the magnifying power and the eye’s ability to focus (accomodation).

Weight - This really represents the comfort of the complete frame and loupe system. The weight of the system has become an increasingly important feature among new magnification users. The weight of the system will increase for higher power, larger loupes.

Magnifying Power - This is the size of the image (not the clarity of the image). Optical manufacturers do not agree on the definition of magnifying power. There is no standard measurement for magnifying power in the loupe market. Even though specific labels have been used, most manufacturers actually round up to the nearest 0.5x.

“There is no accepted standard for how magnifying power is defined for surgical loupes. Different definitions give results that differ by as much as 15-percent. Because of this, the quoted magnifying power is really only a rough guide to the actual magnification of a loupe.”

John Rogers, PhD, University of Arizona Director, Photonic and Imaging Engineering Services Optical Research Associates*

Working Angle - The correct working angle (angle of declination) allows the user to work in a comfortable, ergonomically correct position, thus helping prevent neck and back pain. Choose a model that delivers the right working angle for you. Several flip-up hinge products and through-the-lens systems can be set to the required ergonomic working angles.

Superior Visualization.™

Professionals demand superior visualization. The visualization of a loupe system is truthfully governed by (in order of importance):

1. Resolution 2. Field Width 3. Field Depth 4. Magnification

CONFIRM THIS BY SAMPLING AND COMPARING

Unfortunately, some loupe manufacturers are fixated on an old convention that erroneously identifies magnifying power as the most important feature. Do not be misled by this.

“The resolution and field size of the operating site are much more relevant quality criteria than the size of the image. Regardless of the stated magnifying power, a loupe that resolves smaller features (and more of them) is superior to a loupe that provides a large but blurry image. Similarly, this is also preferable to a loupe that provides a sharp image, but only over a narrow region of space.”

John Rogers, PhD, University of Arizona

After your evaluation, choose the loupe system that provides outstanding resolution across the widest field, while simultaneously delivering a longer depth-of-field, because it will truly have superior visualization.

*Optical Research Associates, a leader in the optics industry, is the largest independent optical engineering services organization with experience in the development of high-performance optical systems for ground, aerial and space-borne applications.

Historically, loupe makers have labeled their products by exact power levels. As previously explained, this is very inaccurate.

A more realistic approach is to group products, much like automobile manufacturers group products (for example: compact, full and luxury-sized cars). For this reason, we have adapted a new and simple system to promote the professional’s clear understanding of the choices available:

Class III* - Between 3.0 & 3.9 power magnification
Class IV - Between 4.0 & 4.9 power magnification
Both of these classes are usually known as prismatic loupes and are a Keplerian design (from the 17th-century astronomer, Johannes Kepler).

*Some Class III loupes are Galilean with narrow field widths.

The diopter is a measurement of refractive power and applies to single corrective lenses. Loupe systems used by healthcare professionals contain multiple lenses, so a reference to diopters describing magnifying power is not appropriate.

Some manufacturers confuse the rule of thumb that relates diopter value to magnifying power. This technical area of optics can be difficult to understand and can be misleading. A diopter is an optometric unit of measurement that is equal to the reciprocal of the focal length of a single lens, measured in meters.** The diopter value is equivalent to refractive power (the ability to bend light) and applies only to single lenses. Loupe systems used by healthcare professionals contain multiple, positive and negative, lenses (compound loupes). Because corrective prescription lenses may also be employed, the effective diopter (or refractive) power of a loupe is not consistently related to its magnifying power.

** General Ophthalmology, Twelfth Edition, 1989. Appleton & Lange, Publisher