Magnification scotoma is the on-field-off-field blind zone created by your surgical magnification system.
By virtue of the fact that surgical magnification systems often magnify only a portion of the total field of vision, a certain blind zone occurs whenever an object is carried from the peripheral unmagnified field toward the magnified center of the field. In general, the greater the power of magnification, the greater the absolute size and proportion of the scotoma.
The scotoma can also be enlarged by a poor design of the telescope oculars or the device(s) on which they are suspended in the field of vision. In general, flip-up telescopes have greater potential for producing a larger scotoma than through-the-lens systems.
Non-coaxial telescope oculars can create enlarged scotomas (in addition to creating other problems, such as chromatic aberrations and diffractive viewing effects)
The greatest distress related to the magnification scotoma is related to the risk of poor control of instruments being moved into (or out of) the magnified field of view. The dangers are evident to both surgeons and patients as instruments are passed through this blind zone.
Most surgeons learn to compensate by some combination of:
1) moving the telescopes aside until their instrument is placed and established with proprioceptive fulcrum at the operating site and/or
2) guiding the instrument to the operating site with any sharp points or edges guarded with gloved finger(s) until the instrument is under visual control in the magnified field of view.
Remember: Some degree of magnification scotoma is always present except for those telescope systems which offer no view whatever of the unmagnified (peripheral) field.
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