camera, and type of frame or headband. Compound loupes provide magnification from 2.5 to 3.5× and are available with frames for front‐lens‐mounted (FLM) or through‐the‐lens mounted (TTL) magnifying lenses or with an adjustable headband configuration (Pieptu and Luchian 2003; Chang 2014b). TTL loupes are configured with the magnifying lenses permanently mounted to the eyeglass lenses, customized to the exact interpupillary distance of the wearer (Figure 3.10). FLM loupes have the advantage of being repeatedly adjustable to the needs of different wearers and can be shared by several associates of a practice. FLM loupes can be adjusted by turning a dial to match the wearer’s interpupillary distance and permit individualized stereopsis. Front‐mounted lenses can be flipped out of the surgeon's line of sight to permit using magnification only when desired. This “flip‐up” ability discourages loupes wearers from looking over the top of lenses and promotes good posture and surgical ergonomics.
Prismatic loupes provide magnification from 3.5 to 8× and are available with FLM or TTL frames. Although higher magnification levels often results in smaller fields of view, technological advances have permitted development of high magnification prismatic loupes with expanded fields of view (Chang 2014a).
Ergonomics and surgeon fatigue are important considerations when purchasing and wearing surgical loupes. Loupe customizations that greatly affect ergonomics include working distance and declination angle (Chang 2014a). Determining the best working distance and declination angle of surgical loupes requires custom measurements of the surgeon positioned for work in the operating arena. Studies in clinical ergonomics have identified a number of distance and angle measurements important in selection and building of customized and adjustable loupes (Chang 2014a). All measurements are taken from a lateral view of the surgeon and operating field. First, the reference line is the line connecting the tops of the surgeon's ears with the corners of the eyes. The reference line angle (RLA) is the angle between this line and the optical axis of the eyes or loupes. The operating hand position (OHP) is the most comfortable and balanced position of the hands when standing or sitting to operate on the patient (Chang 2014a). This position will vary greatly in veterinary surgery, but the most balanced and relaxed position of the hands should be used for measurement. The body posture angle (BPA) is the angle between the vertical axis and line of sight of the eyes or loupes to the OHP. When operating ergonomically, the head tilt angle (HTA) is the angle from the horizontal axis to the reference line and should be no greater than 20°. When the head is erect with the eyes looking forward, the HTA is zero (Chang 2014a). The BPA decreases as the HTA increases, but increases in HTA should be minimized to avoid neck and shoulder strain and long‐term injury. The maximum and minimum rotation angles of the eyes should also be calculated. The rotation angle of the eyes is the angle between the reference line and the OHP. When the head is in an erect position, the rotation angle of the eyes will be greatest – the maximum rotation angle. When the head is tilted downward no more than the maximum amount of tilt without producing strain (HTA less than 20°), the rotation angle of the eyes will be least – the minimum rotation angle. The maximum rotation angle = 90° – BPA–RLA. The minimum rotation angle = 90° – BPA–RLA – HTA (Chang 2014a).
Once these values are known, the optimal declination angle for customized TTL loupes or adjustable FLM loupes can be determined. The optimal declination angle is between the minimum and maximum rotation angles of the eyes (Chang 2014a). The author prefers loupes with a large declination angle to minimize HTA. A loupe declination angle of 45° facilitates a small HTA of only 9–10° and an erect, ergonomic posture (Chang 2014a) (Figure 3.10).
Historically, wearing less optimized loupes with shorter working distances and smaller declination angles necessitated the surgeon adopt a larger HTA and slouching posture to maintain the operated tissue in focus. A shorter working distance also corresponded to a narrower field of view, and neck and back strain induced by slouching were detrimental to the surgeon. Recent innovations result in loupes with longer working distances (40–55 cm), wider fields of view, and lenses mounted at larger declination angles that permit the surgeon to adopt an erect posture and smaller HTA (<20°) (Chang 2014a).
Figure 3.10 The author's through‐the‐lens (TTL) mounted loupes. Note the steep angle of declination and LED headlamp.
First‐time wearers of loupes should adopt several practices to facilitate and encourage proper and consistent use. Begin by wearing loupes for only 1–2 hours/day the first 1–2 weeks of use, using the loupes during simple procedures in the morning that do not require exhaustive concentration. Gradually work up to longer and more complex procedures performed over the entire day during the third to fourth and subsequent weeks of use. Always adopt an erect posture during surgery, drawing the shoulder blades medially and downward, and maintaining a small HTA (<20°). Do not bend the neck to look over the lenses, but diligently look through the magnification oculars when wearing loupes or flip the lenses of FLM loupes out of the line of sight when not in use.
Do not wear loupes on the tip of the nose as this decreases field of view. Conversely, do not wear loupes too close to the eyes as this permits fogging of the lenses. Practice using loupes at the measured working distance, bringing instruments and suture into the field of view slowly at first, and gradually introduce faster movements as dexterity improves. Proper use of surgical loupes and careful observation of ergonomic principles will optimize the practice of exotic animal surgery.
Comparing the Operating Microscope and Surgical Loupes
Whether the operating microscope or surgical loupe represents the optimal magnification aid for a particular type of surgery is often debated. To date, the choice seems to be one of surgeon preference, as study findings conflict and both pieces of equipment have advantages and disadvantages (McManamny 1983; Ross et al. 2003: Eivazi et al. 2015; Al‐Benna 2011; Stanbury and Elfar 2011). The operating microscope offers greater magnification than surgical loupes, is considered the gold standard in microsurgery, and is a superior teaching tool (McManamny 1983; Pieptu and Luchian 2003; Al‐Benna 2011). However, loupe magnification has been found to achieve comparable clinical outcomes, and in some studies, resulted in shorter operative times (Ross et al. 2003; Jarrett 2004; Al‐Benna 2011). Some propose of the operating microscope always be chosen by less‐experienced microsurgeons and when operating tubular structures less than 3–4 mm in diameter (Pieptu and Luchian 2003; Ross et al. 2003; Jarrett 2004; Al‐Benna 2011; Stanbury and Elfar 2011). Others suggest that so‐called “macro‐microsurgical procedures,” those involving structures >1.5 mm in diameter, may be safely performed with loupes (Pieptu and Luchian 2003; Mungadi 2010; Stanbury and Elfar 2011). Although the operating microscope can be moved through six degrees of freedom, loupes offer the convenience of being able to change field of view simply by turning one's head (Ross et al. 2003; Stanbury and Elfar 2011; Eivazi et al. 2015). The operating microscope offers the advantage of being able to change level of magnification from low to high and high to low, a maneuver often necessary when passing the needle and tying sutures (Eivazi et al. 2015). While surgical loupes allow the surgeon and assistant surgeon to view the surgery from individual and rapidly dynamic vantage points, the operating microscope requires the surgeon and assistant to view the surgery from relatively fixed positions (Ross et al. 2003; Jarrett 2004). Whereas the operating microscope should be moved only short distances and with great caution to avoid damaging the intricate lenses and prisms within, loupes offer the advantage of portability (Jarrett 2004; Hart and Hall 2007; Stanbury and Elfar 2011). Some of the mobility issues associated with the operating microscope can be overcome by using a foot pedal programmed to permit movement of the scope in the x–y planes and by changing level of magnification and focus. Operating microscopes may offer superior illumination
