3.6). Using a foot pedal permits the surgeon to maintain a desired position with instruments in both hands without disrupting the flow of surgery (Carr and Castellucci 2010).
Preoperative Preparation of the Microscope and Operating Room
When planning a procedure using the operating microscope, preoperative preparation is essential. The surgeon must consider the interaction of numerous variables including the position and posture of the surgeon; positions of the patient, microscope, and instrument table; operating table and stool height; basic functions of the microscope and illumination system; and gross and fine focus of the microscope (Carr and Castellucci 2010; Socea et al. 2015).
Figure 3.6 Operating microscope foot pedal displaying the joystick for adjustment in an x–y plane and buttons for adjustment of level of magnification (zoom) and focus.
Figure 3.7 The surgeon should sit at the operating table with hips slightly extended and feet flat on the floor with the knees flexed slightly below the hips.
In most operative procedures of exotic animals, the surgeon and assistant surgeon sit in a face‐to‐face configuration perpendicular to the long axis of the operating table and patient. Position the operating microscope such that the stand does not interfere with normal personnel flow and allows easy manipulation of its suspension arms in and out of the surgical field (Carr and Castellucci 2010). To begin, situate the stool and operating table height with the surgeon's feet flat on the floor, knees flexed below the hips, hips slightly extended, elbows flexed 90° to the shoulders, and elbows and antebrachii resting on the operating table (Valachi and Valachi 2003; Bohan et al. 2010; Carr and Castellucci 2010; Socea et al. 2015). In such a position, the surgeon’s feet and seat create three points of contact with the floor, a very stable position that minimizes strain on the lower back during surgery (Figure 3.7). Also, resting the elbows and antebrachii on the surgical table minimizes physiologic tremor due to muscle fatigue (Figure 3.8). Next, adjust the inclinable binocular head up or down to permit the eyepieces to meet the surgeon's eyes while the surgeon maintains an erect posture with minimal slouching.
Once the table and stool height and surgeon's posture have been properly adjusted, the microscope must be focused (Socea et al. 2015). Adjustment of the microscope to maintain focus through all levels of magnification is termed “par focaling” of the microscope and must be performed prior to surgery. To par focal the scope, first adjust the eyepieces to accommodate the surgeon’s individual interpupillary distance to achieve stereopsis. Next, be sure the microscope is set to the lowest level of magnification (zoomed all the way out) and the fine focus is set to midrange (Carr and Castellucci 2010). Manually move the binocular head and objective lens up or down to rest a distance from the patient equal to the working distance of the microscope (Carr and Castellucci 2010). For example, if the working distance of the microscope is 200 mm, the part of the objective lens closest to the patient should be positioned 200 mm (8 in.) from the area of the patient to be operated. Following this step, reassess the inclination of the binocular head to be certain it does not require readjustment. Next, turn the magnification level to the highest setting (zoomed all the way in) and adjust the fine focus until the image is most clear. At this time, the surgeon should adjust the diopter settings for each eye, one eye at a time, to ensure that both eyes see a clear image (Carr and Castellucci 2010) (Figure 3.9). Surgeons with perfect vision or those wearing corrective lenses should maintain the eyepiece diopter settings at “0.” Finally, the assistant surgeon should adjust the diopter settings on the assistant binocular. Following these manipulations, the scope should be returned to the lowest magnification level (zoomed all the way out) and should remain in focus throughout all levels of magnification. The microscope is now par focaled and ready for surgery (Carr and Castellucci 2010; Socea et al. 2015).
Figure 3.8 Resting the elbows and antebrachii on the surgical table at 90° to the shoulders minimizes physiologic tremor due to muscle fatigue.
Figure 3.9 Adjust the diopter settings for each eye, one eye at a time, to ensure that both eyes see a clear image.
Surgical Loupes
Operating loupes are magnifying lenses worn by a surgeon to enhance visualization during surgery. Commercially available surgical loupes provide magnification of an image 2.5–8× the size seen by the unaided surgeon's eye (Ross et al. 2003; Carr and Castellucci 2010; Stanbury and Elfar 2011). Shortening the working distance increases magnification. Loupes are classified according to the optical system by which they provide magnification (Carr and Castellucci 2010).
Simple loupes are analogous to reading glasses and used by jewelers evaluating gems and by hobbyists. One pair of positive meniscus lenses comprises the optical system of simple loupes (Stanbury and Elfar 2011). Although inexpensive, the poor quality of the image produced by simple loupes precludes their use in exotic animal surgery. Additionally, spherical aberrations and purple or green color‐fringing along the margin of the image are serious disadvantages of this optical system (Carr and Castellucci 2010; Stanbury and Elfar 2011).
Compound loupes, also known as Galilean loupes, are the most commonly used loupes and composed of two pair of magnification lenses separated by a layer of air. Chromatic anomalies are not observed with this system, but spherical aberrations may be seen at magnification levels greater than 2.5× (Carr and Castellucci 2010; Stanbury and Elfar 2011). Compound loupes are less expensive than prismatic loupes and are widely available from numerous medical optics vendors.
Prismatic loupes, also known as Kelperian loupes, provide image amplification using Schmidt prisms. These prisms fold and lengthen paths of light through the loupes, yielding improved magnification, expanded field of view, deeper depth of focus, and longer working distance than other optical systems (Carr and Castellucci 2010; Stanbury and Elfar 2011). Although prismatic loupes are traditionally very heavy and much more expensive than compound loupes, recent innovations have permitted the development of prismatic loupes that are lighter weight and more comfortable (Chang 2014b).
Choosing Surgical Loupes
When choosing surgical loupes, exotic animal surgeons should consider numerous factors; the quality of stereopsis, level of magnification, depth of field, working distance, fit and comfort, ergonomics, and cost (Pieptu and Luchian 2003; Hart and Hall 2007). Loupes differ by level of magnification provided,
