"throughthe lens loupes"which the telescope fixed dirct onto the lens of the glasses lens, and Flip-Up loupes - those where the magnification telescopes are mounted on a hinge system attached to the frame. Flip-Up loupes can be easily  flipped-up?to allow the surgeon or dentist to see through the naked eye or through their normal prescription lenses
Comparison of Flip Up and Normal TTL Loupes
two designs of loupes: Through the Lens loupes [TTL], and those with a flip-up design. With TTL loupes the telescopes are fixed directly to the lens of the glasses.
TTL loupes offer the following advantages over flip-up design:
• TTL normally weigh less than the equivalent magnification flip-up design.
• TTL offer a wider field of view than a similar magnification Flip- up design. This is because the magnification telescopes are mounted closer to the eye.
• TTL loupes are manufactured for each individual ?they are custom fit. The angle of declination is set at the factory and therefore there is no need to adjust the angle of declination. They allow the clinician to quickly adopt the most ergonomic position without having to adjust the declination angle.
• TTL loupes are generally lighter than their flip-up equivalents. Furthermore the weight is distributed more evenly.
• They fit more comfortably.
The following are the disadvantages of Nromal TTL loupes:
• They generally cost more than the equivalent magnification flip-up loupes.
• If you wear prescription glasses and choose to have the prescription incorporated into the lens of the glasses; should your prescription change, the loupes need to be sent to the manufacturer to be modified. This might involve further cost and will mean that you will be without loupes during the period in which they are being modified.
• When communicating with patients TTL loupes could do with being removed. This can be inconvenient. Alternatively it is possible to look over the telescopes.
• Can only be used for the clinician they were prescribed for.
Flip-up loupes have the magnification telescopes mounted on a hinge system. This means the telescopes can be easily flipped-up when not in use.
The advantages of the flip-up loupes include:
• They cost significantly less than TTL loupes.
• They can easily be flipped up when communicating with the patient, or carrying out other routine tasks in the surgery such as paperwork.
• Flip- up loupes are not operator specific and can be shared between multiple operators. The angle of declination is not fixed and can be modified by each user.
• If prescription lenses are incorporated into the glasses, if the clinician’s prescription changes they can be changed by an optician. Of course with prescription lenses the loupes can only be used by the operator they were customised for and not by the remainder of the dental team.
The disadvantages of flip-up loupes include:
• The angle of declination can be adjusted incorrectly, causing strain on the eyes and/or the musculoskeletal system.
• Depending upon the magnification, flip-up loupes typically weigh more than their TTL equivalents.
• Flip-up loupes have a narrower field of view than TTL loupes. This is because the telescopes are mounted further away from the eyes.