- Email: [email protected]
Focusing the surgical microscope
s u r v e y o f o p h t h a l m o l o g y 6 0 ( 2 0 1 5 ) 3 7 3 e3 7 7
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/survophthal
Refractions and reflections
Focusing the surgical microscope Sergiu D. Socea, MD, Yoreh Barak, MD, Eytan Z. Blumenthal, MD* Department of Ophthalmology, Rambam Health Care Campus, Haifa, Israel
article info
abstract
Article history:
A well-focused operating microscope addresses several needs that are all secondary to the
Received 13 May 2014
surgeon’s need to see clearly at all times. These needs include: the assistant; the sharpness
Received in revised form
of the video and monitor; as well as field of view, asthenopia, and focusing issues related to
19 October 2014
zoom, accommodation, and presbyopia. We provide a practical approach to achieve
Accepted 31 October 2014
optimal focus that we call the sloping paper calibration method. ª 2015 Elsevier Inc. All rights reserved.
Available online 10 November 2014 Joseph M. Miller, Editor Keywords: focusing focus microscope surgical microscope
1.
Introduction
We take as axiomatic that clear focus is a prerequisite for successful surgical outcome. Focus enables the surgeon to appreciate finer detail, but also allows stereopsis. Unfocused equipmentdbe it a pair of glasses, the slit-lamp, an indirect ophthalmoscope, or the operating microscopedis also likely to create fatigue over time. Operating through a partially opaque cornea or fogged eye-pieces simulates the downside of working with inadequate focus. What might occur when a surgeon fails to focus the microscope? Although the surgeon will usually not notice any immediate interference during surgery, both the assistant and the video/TV monitor may be blurred. Changes in zoom will require the surgeon to refocus (an unnecessary step when
the microscope is correctly focused), and all involved may experience asthenopia over time.
2.
Methods
2.1.
Focus as it relates to changes in the zoom setting
Although the surgeon can easily attain focus at any given zoom setting via the foot pedal, this should not be lost each time the zoom setting is changed. Only at one specific diopter setting on the oculars will the microscope maintain focus. When the oculars are set to this sweet spot, the surgeon can move the zoom setting throughout its full range without ever losing focus. At all other ocular settings, a change in the zoom
* Corresponding author: Eytan Z. Blumenthal, MD, Department of Ophthalmology, Rambam e Health Care Campus, P.O.B 9602, Haifa 31096, Israel. E-mail address: [email protected] (E.Z. Blumenthal). 0039-6257/$ e see front matter ª 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.survophthal.2014.10.005
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setting will result in the need to refocus. The more distant the ocular eye-piece setting is from the ideal value and the larger the change in zoom, the greater the resultant blur.
2.2.
The zoom-calibration test
How then, can this sweet-spot be found? Place any target in front of the microscope and focus it with the foot-pedal. Then shift the zoom to the highest setting and focus again using the foot-pedal at that same target. Lastly, shift the zoom to the lowest setting. Without refocusing the foot-pedal focus the microscope using only the eye-piece oculars. Now you are well-focused. To test that this has actually been achieved, shift the zoom up and down between its extremes and ascertain that you maintain perfect focus throughout. Note the ocular settings. These are the settings that you should operate with from now on, even if they do not match your refraction. Skeptics can now dial in a wrong setting (say, 2 or 3 diopters off in either direction) and verify that now it becomes impossible to zoom throughout the entire range without losing focus. Of note, it is possible to over-minus oneself during this test. When rotating the ocular setting, dial it from plus diopters towards minus, seeking the first clear view.
2.3.
The sloping paper calibration test
Focusing the surgical microscope is not just about seeing a clear image, but also makes the plane of interest coincide with the plane of focus. The sloping paper calibration test enables the team to align three planes of interest (surgeon/assistant/video camera) with the microscope’s plane of focus. The order of calibration must be: first the camera, next the surgeon, and last the assistant. The sloping calibration test is performed as follows: 1. Construct a sloping piece of paper, either fixing it to a hard supporting surface (Fig. 1), or merely folding any sheet of paper in half, into a tent-like shape. The steeper the slope of the paper and the higher the zoom (by providing a shallower depth of focus2,4), the more accurate the test. 2. Note that the paper may contain a line perpendicular to and running down the slope. Bisecting the line should be a shorter line (or dot), marking the plane of interest along the sloping paper. Alternatively, three rows of dots may be drawn on the paper. 3. Place the sloping paper on a tray at a height allowing comfortable viewing through the microscope while sitting. 4. Focus the video monitor by moving the microscope head up and down with the foot-pedal until the plane of interest (the bisected line or the central row of dots) is in perfect focus. Importantly, at this stage do not look through the microscope, look at the monitor. Note that occasionally it may be difficult to fine-focus using the foot-pedal unless the focusing speed (controlled by a button or digitally in the microscope’s set-up panel) is slowed. 5. Without moving the microscope or touching the foot-pedal, the surgeon should now look through the surgeon’s oculars and focus on the plane of interest using only the diopter rings on the eye-pieces. After this, take a close look again
Fig. 1 e The sloping paper used to focus the surgical microscope embedded in cardboard.
on the monitor to ascertain that the camera is still in perfect focus. Again, to avoid over-minusing, choose the first occurrence of clear focus while rotating the ring starting from a higher plus diopter setting. 6. Last, the assistant focuses their ocular setting on the plane of interest. If the assistant scope has a focusing knob, it can be set to a neutral position. If a neutral position doesn’t exist, they cannot directly determine the correct eye-piece setting, since for each setting of the focusing knob a different setting will be found. If this is the case, either dial in the distance refraction or else the setting on the surgeon’s oculars. Thereafter, fine-focus using the assistant’s focusing knob. 7. Note, previously we described a different approach to determining the surgeon’s correct eye-piece diopter setting utilizing the zoom calibration. What should a surgeon do if the diopter setting found with the zoom-calibration technique differs from the diopter setting found on the sloping paper test? Two explanations may underline this discrepancy: The tests might need repeating (as would occur if the surgeon had a change of accommodation between the two tests) or else the microscope is not properly aligned and calibrated (for instance, if the camera is not properly mounted or the mount used is not original). If repeating the tests still results in a discrepancy, the surgeon must choose one or the other. We favor having a perfectly focused video and refocusing whenever changing the zoom setting rather than the other way around.
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Fig. 2 e The sloping paper test: While on casual observation the central line of black dots appears in focus in both images, in (A) the depth of field straddles the line, whereas in (B) the depth of field is superior (left) of the black dot line, such that it is barely in focus (see double-ended arrow, above). Figure 2 demonstrates the sloping paper test. On casual inspection both black-dot-lines appear in focus, although in Figure 2A the depth of field is perfectly straddling the line of black dots, as the adjacent lines of blue dots on both sides of the black-dot-line are similarly blurred. The depth of field, which is the anteroposterior range of clear focus appreciated from the paper grid, extends similar distances to the left (up) and right (down) of the black dot line (depth of focus illustrated by the double-ended arrow). In contrast, in Figure 2B the depth of field is mostly above (left) of the black-dot-line, as evident in the area marked by the double-ended arrow, as well as in the asymmetry of focus of the blue dot lines (the blue dots to the left of the black-dot-line are more in focus than the blue dots to the right).
2.4.
The assistant’s focus
Although the surgeon can easily refocus his/her view multiple times during a case, the assistant is then often left with a blurred view. This may occur even when both surgeons have dialed in their distance refraction or when both wear their prescription glasses and have set both eye-pieces to zero. This happens for two reasons: accommodation and the fact that not all microscopes are perfectly calibrated. The former is far more influential. How can this be rectified? Once the surgeon dials in their correct ocular setting, the assistant then proceeds to perform the sloping paper calibration method. During this calibration method both the surgeon and assistant should pay particular attention to avoid over-minusing. The practical way to avoid over-minusing is to dial the eye-pieces from plus to minus and to stop at the first point of clear focus. Once the assistant is well-focused, the assistant’s ocular setting found should remain constant for future surgeries, but only as long as the same surgeon-assistant-microscope triad is maintained, and provided that the surgeon’s accommodation and eye piece setting are constant. Changes in accommodation often occur when younger surgeons reach difficult and/or stressful portions of the surgery. A younger, less experienced surgeon has a much larger accommodative reserve and is also more prone to experience stress,3,5 which may drive unneeded accommodation. Some newer microscopes provide a separate knob that enables the assistant to adjust their focus independently. This
knob does not exist on all microscopes and to be used during surgery must be covered with a sterile cap.
2.5.
Focusing the video camera
The video camera is perhaps the most difficult to maintain in focus for three reasons: The camera has no accommodative reserve that both the surgeon and assistant may possess. The camera’s depth of field is relatively shallow, such that targeting the precise plane of interest is crucial. The team often pays little attention to the video until the case is over, and the recording is reviewed, at which time little can be done to improve quality. When watching the videotaped case, both modern computer and TV monitors, and more so overhead projectors at meetings, present a large picture up to 30 feet across in which even the slightest amount of blur becomes extremely noticeable and disturbing. How can the video camera be correctly focused? Because of the camera’s lack of flexibility, the only valid approach is to first focus the video camera and only thereafter focus the surgeon and then the assistant as described earlier. Be aware that any excess accommodation by the surgeon will instantly throw the video out of focus. Each surgeon should focus the video camera. There is no single setting that will work for all. Of note, it is possible to acquire an attachment that connects the video camera to the microscope and provides a separate focusing knob, xey capabilities, and even zoom. When such devices are incorporated, the video camera can be controlled independently of the surgeon. Such devices are relatively expensive, and demand attention, usually in the form of an additional person in the operating room, a designated videographer. This device, when used appropriately, will improve video output.
2.6. field
The video field is merely a portion of the surgeon’s
While not a focusing issue, discrepancies between the surgeon’s field of view and the camera’s field of view may undermine the quality and value of the video. The video
376
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camera captures only a portion of what the surgeon sees. This is because: The surgeon’s view is circular; the camera captures a rectangular field of view. The corners of the video image often do not extend out to the edge of the surgeon’s circular view. This is designed to avoid darkened corners of the video image. For optical reasons the camera often is not able to capture the most peripheral image. Fluctuations in zoom may vary the relative field of view that the camera captures compared to the surgeon’s field of view. The surgeon should recognize what portion of the microscope’s circular field of view is actually captured on video. A simple way to determine this is the following: 1. Place a blank piece of paper in focus under the microscope. 2. While looking through the microscope, draw the largest circle that can still be seen through the microscope. 3. Now, without moving either the paper or the microscope, shift your view from the microscope to the video monitor, and while only looking at the monitor, draw the largest rectangle that can still be seen on the video monitor. 4. Compare the rectangle to the circle. Figure 3 demonstrates a video field of view as compared to the microscope’s field of view. Much can be learned from this figure: The video view shows some rotational misalignment (a camera mounting issue) and is not centered within the surgeon’s view. Most important, this figure demonstrates how little of the surgeon’s view is captured by the video.
Fig. 3 e A hand-drawn comparison of the surgeon’s view (the larger circle) and the video view (the inner rectangle). Note that for this particular system, the video view was found not to be centrally aligned, nor rotationally aligned.
2.7.
Surgeon’s accommodation
Any changes in the surgeon’s accommodative state demand an identical change (same magnitude, opposite sign) in the ocular eye-pieces in order to avoid throwing both the assistant and video camera out of focus. If the assistant possesses enough accommodative reserve, however, they can compensate for the change in surgeon’s accommodation. The video camera, on the other hand, will always suffer loss of focus proportional to the accommodation applied by the surgeon. Similarly, when the surgeon calibrates the system while accommodating, if at any later stage the accommodation relaxes, both the assistant and video camera will be out of focus. A common and potentially disruptive scenario occurs when a young resident surgeon is assisted by an experienced senior surgeon. During the more demanding and stressful portions of the case the young surgeon may involuntarily accommodate excessively,1 blurring the senior surgeon. If the microscope is a newer model, the assistant’s focusing knob allows the senior surgeon to compensate, but this may throw the video out of focus. If, however, the microscope lacks this adjustment, one solution is to ask the younger surgeon to focus up until the senior surgeon sees clearly and then verify they still have a clear image, implying that the excessive accommodation is relaxed.
2.8.
Surgeon’s presbyopia
Presbyopia is a problem for surgeons. Surgeons under age 45 years or so can operate with or without their distance glasses, provided that they do not have much astigmatism. As long as sphere is the only issue, even in anisometropia, the correct refraction can be easily dialed into the eye-pieces, replacing the need for glasses. This also eliminates the occasional fogging of glasses, and it is usually more comfortable to operate without glasses, as the eyes can be placed closer to the oculars. Those having meaningful amounts of cylinder should operate with their glasses on as no spherical correction can provide them with crisp vision. The surgeon may need to be able to see the instrument tabledfor example, to trephine a donor corneal graftdand also to read the phaco/vitrectomy machine screen. Even if a perfect view can be achieved without glasses through the microscope, these additional requirements of near and midrange vision may convince the surgeon to wear glasses while operating. When presbyopia becomes an issue, low to moderate myopes can continue operating without glasses while emmetropes and high myopes may find that wearing glasses allows them to see clearly around the microscope. Some may prefer bifocals (as opposed to multifocals), or even half-frame reading glasses, for viewing the instrument table. It may not be easy to change one’s practice at the age of 45 if glasses were never previously worn during surgery. If a presbyopic surgeon wearing bifocal or multifocal glasses unconsciously shifts from looking through the distance portion of the lens to the intermediate or near portion, a dramatic, unwanted change in focus will occur for both the assistant and the video camera.
s u r v e y o f o p h t h a l m o l o g y 6 0 ( 2 0 1 5 ) 3 7 3 e3 7 7
2.9.
Surgeon-assistant switch when tutoring
While supervising a young surgeon, the senior surgeon commonly exchanges seats several times during the case. This scenario deserves special attention and is further compounded by whether the video camera is mounted on the surgeon’s, or assistant’s, scope. If the microscope lacks an assistant focusing knob, at each exchange the oculars’ settings need to be reset on both scopes, setting aside the change in interpupillary distance. This will solve the clarity issue for all involved (including the video monitor), but poses a significant inconvenience. If, however, an assistant’s focusing knob exists, the tendency would be to rectify the focusing discrepancy using it. This will solve the problem for both surgeons, but may blur the video. If that is the case (provided, of course, that the surgeon’s and assistant’s ocular settings are different), one should decide which of the two surgeons’ work is more important to capture clearly on the TV monitor and video. Usually, the younger surgeon’s work is of more interest and should be videotaped in focus, so that after the case the residents can review his/her performance.
2.10.
A novel concept: the microscope is never out of focus
What a confusing heading! If the microscope is always in focus, wouldn’t this discussion be unnecessary? The surgical microscope is always focused and can never be out of focus. To accept this seemingly irrational statement, one needs to realize that the microscope has one specific plane of focus (plus or minus the depth of field bracketing that plane) always in perfect focus. Everything outside that specific plane is always out of focus. The surgeon’s role is to place the microscope’s plane of focus to coincide with the plane where the surgery is taking place. We can even extend this statement further and claim that the surgeon’s view is always in focus, but does not necessarily merge with the plane of interest. There are only two ways to move the microscope’s plane of focus up and down. One is by shifting the entire microscope head up or down, as routinely accomplished using the handles (gross adjustment) and foot-pedal (fine adjustment), and the other is to change the oculars’ diopter setting. The only other way we are aware of, short of replacing lenses within the microscope, is to replace the surgeon, as surgeons with different refractions and accommodative powers will have their plane of focus at varying distances from the microscope. Thus, the plane of focus for a particular microscope is not a factory preset distance, but rather takes into account the surgeon’s refractive state, as well as the oculars’ settings. Of course, another way of making the plane of interest and the microscope’s plane of focus coincide is by moving the
377
surgical bed up and down. Setting the optimal height of the surgical bed should be done before the surgery begins so as to allow the best ergonomic position for the seated surgeon. Once the height of the bed is set, the surgeon should proceed with the described maneuvers to achieve the best focus.
3.
Discussion
We discuss difficulties in fine-focusing the complex optical system on microscopes used in ophthalmic surgery. The surgical microscope, when correctly set, provides clear focus to the surgeon, the assistant, and the video camera. All three are interconnected, and satisfying all three may be difficult. We provide a practical description of one system, addressing physiological limitations and describing maneuvers that allow surgeon, assistant, and video camera to receive a sharp image throughout the operation. This is far more complex than it may at first seem because it is person-, as well as microscope-, dependent, such that each surgeon and each assistant must determine their personal settings on each microscope. Failing to adjust the oculars’ settings accordingly may result in an unhappy assistant, asthenopic surgeon, and/ or a blurred video image; this may limit staff assistance and cooperation, losing the opportunity to review and learn from past performance and to present outstanding videos at meetings.
4.
Disclosures
No funding, grants or support were received for this study. All authors claim that they have no financial disclosures to disclose.
references
1. Avetisov ES, Gundorova RA, Shakarian AA, et al. [Effects of acute psychogenic stress on the state of several functions of the visual analyzer]. Vestn Oftalmol. 1991;107:17e9 2. Hoerenz P. The operating microscope. II. Individual parts, handling, assembling, focusing, and balancing. J Microsurg. 1980;1:419e27 3. Kikuchi K, Okuyama K, Yamamoto A, et al. Intraoperative stress for surgeons and assistants. J Ophthalmic Nurs Technol. 1995;14:68e70, 2-3. 4. Serpetopoulos C. More on adjusting the slit-lamp oculars. Surv Ophthalmol. 1996;40:424 5. Yamamoto A, Hara T, Kikuchi K, et al. Intraoperative stress experienced by surgeons and assistants. Ophthalmic Surg Lasers. 1999;30:27e30
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/survophthal
Refractions and reflections
Focusing the surgical microscope Sergiu D. Socea, MD, Yoreh Barak, MD, Eytan Z. Blumenthal, MD* Department of Ophthalmology, Rambam Health Care Campus, Haifa, Israel
article info
abstract
Article history:
A well-focused operating microscope addresses several needs that are all secondary to the
Received 13 May 2014
surgeon’s need to see clearly at all times. These needs include: the assistant; the sharpness
Received in revised form
of the video and monitor; as well as field of view, asthenopia, and focusing issues related to
19 October 2014
zoom, accommodation, and presbyopia. We provide a practical approach to achieve
Accepted 31 October 2014
optimal focus that we call the sloping paper calibration method. ª 2015 Elsevier Inc. All rights reserved.
Available online 10 November 2014 Joseph M. Miller, Editor Keywords: focusing focus microscope surgical microscope
1.
Introduction
We take as axiomatic that clear focus is a prerequisite for successful surgical outcome. Focus enables the surgeon to appreciate finer detail, but also allows stereopsis. Unfocused equipmentdbe it a pair of glasses, the slit-lamp, an indirect ophthalmoscope, or the operating microscopedis also likely to create fatigue over time. Operating through a partially opaque cornea or fogged eye-pieces simulates the downside of working with inadequate focus. What might occur when a surgeon fails to focus the microscope? Although the surgeon will usually not notice any immediate interference during surgery, both the assistant and the video/TV monitor may be blurred. Changes in zoom will require the surgeon to refocus (an unnecessary step when
the microscope is correctly focused), and all involved may experience asthenopia over time.
2.
Methods
2.1.
Focus as it relates to changes in the zoom setting
Although the surgeon can easily attain focus at any given zoom setting via the foot pedal, this should not be lost each time the zoom setting is changed. Only at one specific diopter setting on the oculars will the microscope maintain focus. When the oculars are set to this sweet spot, the surgeon can move the zoom setting throughout its full range without ever losing focus. At all other ocular settings, a change in the zoom
* Corresponding author: Eytan Z. Blumenthal, MD, Department of Ophthalmology, Rambam e Health Care Campus, P.O.B 9602, Haifa 31096, Israel. E-mail address: [email protected] (E.Z. Blumenthal). 0039-6257/$ e see front matter ª 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.survophthal.2014.10.005
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setting will result in the need to refocus. The more distant the ocular eye-piece setting is from the ideal value and the larger the change in zoom, the greater the resultant blur.
2.2.
The zoom-calibration test
How then, can this sweet-spot be found? Place any target in front of the microscope and focus it with the foot-pedal. Then shift the zoom to the highest setting and focus again using the foot-pedal at that same target. Lastly, shift the zoom to the lowest setting. Without refocusing the foot-pedal focus the microscope using only the eye-piece oculars. Now you are well-focused. To test that this has actually been achieved, shift the zoom up and down between its extremes and ascertain that you maintain perfect focus throughout. Note the ocular settings. These are the settings that you should operate with from now on, even if they do not match your refraction. Skeptics can now dial in a wrong setting (say, 2 or 3 diopters off in either direction) and verify that now it becomes impossible to zoom throughout the entire range without losing focus. Of note, it is possible to over-minus oneself during this test. When rotating the ocular setting, dial it from plus diopters towards minus, seeking the first clear view.
2.3.
The sloping paper calibration test
Focusing the surgical microscope is not just about seeing a clear image, but also makes the plane of interest coincide with the plane of focus. The sloping paper calibration test enables the team to align three planes of interest (surgeon/assistant/video camera) with the microscope’s plane of focus. The order of calibration must be: first the camera, next the surgeon, and last the assistant. The sloping calibration test is performed as follows: 1. Construct a sloping piece of paper, either fixing it to a hard supporting surface (Fig. 1), or merely folding any sheet of paper in half, into a tent-like shape. The steeper the slope of the paper and the higher the zoom (by providing a shallower depth of focus2,4), the more accurate the test. 2. Note that the paper may contain a line perpendicular to and running down the slope. Bisecting the line should be a shorter line (or dot), marking the plane of interest along the sloping paper. Alternatively, three rows of dots may be drawn on the paper. 3. Place the sloping paper on a tray at a height allowing comfortable viewing through the microscope while sitting. 4. Focus the video monitor by moving the microscope head up and down with the foot-pedal until the plane of interest (the bisected line or the central row of dots) is in perfect focus. Importantly, at this stage do not look through the microscope, look at the monitor. Note that occasionally it may be difficult to fine-focus using the foot-pedal unless the focusing speed (controlled by a button or digitally in the microscope’s set-up panel) is slowed. 5. Without moving the microscope or touching the foot-pedal, the surgeon should now look through the surgeon’s oculars and focus on the plane of interest using only the diopter rings on the eye-pieces. After this, take a close look again
Fig. 1 e The sloping paper used to focus the surgical microscope embedded in cardboard.
on the monitor to ascertain that the camera is still in perfect focus. Again, to avoid over-minusing, choose the first occurrence of clear focus while rotating the ring starting from a higher plus diopter setting. 6. Last, the assistant focuses their ocular setting on the plane of interest. If the assistant scope has a focusing knob, it can be set to a neutral position. If a neutral position doesn’t exist, they cannot directly determine the correct eye-piece setting, since for each setting of the focusing knob a different setting will be found. If this is the case, either dial in the distance refraction or else the setting on the surgeon’s oculars. Thereafter, fine-focus using the assistant’s focusing knob. 7. Note, previously we described a different approach to determining the surgeon’s correct eye-piece diopter setting utilizing the zoom calibration. What should a surgeon do if the diopter setting found with the zoom-calibration technique differs from the diopter setting found on the sloping paper test? Two explanations may underline this discrepancy: The tests might need repeating (as would occur if the surgeon had a change of accommodation between the two tests) or else the microscope is not properly aligned and calibrated (for instance, if the camera is not properly mounted or the mount used is not original). If repeating the tests still results in a discrepancy, the surgeon must choose one or the other. We favor having a perfectly focused video and refocusing whenever changing the zoom setting rather than the other way around.
s u r v e y o f o p h t h a l m o l o g y 6 0 ( 2 0 1 5 ) 3 7 3 e3 7 7
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Fig. 2 e The sloping paper test: While on casual observation the central line of black dots appears in focus in both images, in (A) the depth of field straddles the line, whereas in (B) the depth of field is superior (left) of the black dot line, such that it is barely in focus (see double-ended arrow, above). Figure 2 demonstrates the sloping paper test. On casual inspection both black-dot-lines appear in focus, although in Figure 2A the depth of field is perfectly straddling the line of black dots, as the adjacent lines of blue dots on both sides of the black-dot-line are similarly blurred. The depth of field, which is the anteroposterior range of clear focus appreciated from the paper grid, extends similar distances to the left (up) and right (down) of the black dot line (depth of focus illustrated by the double-ended arrow). In contrast, in Figure 2B the depth of field is mostly above (left) of the black-dot-line, as evident in the area marked by the double-ended arrow, as well as in the asymmetry of focus of the blue dot lines (the blue dots to the left of the black-dot-line are more in focus than the blue dots to the right).
2.4.
The assistant’s focus
Although the surgeon can easily refocus his/her view multiple times during a case, the assistant is then often left with a blurred view. This may occur even when both surgeons have dialed in their distance refraction or when both wear their prescription glasses and have set both eye-pieces to zero. This happens for two reasons: accommodation and the fact that not all microscopes are perfectly calibrated. The former is far more influential. How can this be rectified? Once the surgeon dials in their correct ocular setting, the assistant then proceeds to perform the sloping paper calibration method. During this calibration method both the surgeon and assistant should pay particular attention to avoid over-minusing. The practical way to avoid over-minusing is to dial the eye-pieces from plus to minus and to stop at the first point of clear focus. Once the assistant is well-focused, the assistant’s ocular setting found should remain constant for future surgeries, but only as long as the same surgeon-assistant-microscope triad is maintained, and provided that the surgeon’s accommodation and eye piece setting are constant. Changes in accommodation often occur when younger surgeons reach difficult and/or stressful portions of the surgery. A younger, less experienced surgeon has a much larger accommodative reserve and is also more prone to experience stress,3,5 which may drive unneeded accommodation. Some newer microscopes provide a separate knob that enables the assistant to adjust their focus independently. This
knob does not exist on all microscopes and to be used during surgery must be covered with a sterile cap.
2.5.
Focusing the video camera
The video camera is perhaps the most difficult to maintain in focus for three reasons: The camera has no accommodative reserve that both the surgeon and assistant may possess. The camera’s depth of field is relatively shallow, such that targeting the precise plane of interest is crucial. The team often pays little attention to the video until the case is over, and the recording is reviewed, at which time little can be done to improve quality. When watching the videotaped case, both modern computer and TV monitors, and more so overhead projectors at meetings, present a large picture up to 30 feet across in which even the slightest amount of blur becomes extremely noticeable and disturbing. How can the video camera be correctly focused? Because of the camera’s lack of flexibility, the only valid approach is to first focus the video camera and only thereafter focus the surgeon and then the assistant as described earlier. Be aware that any excess accommodation by the surgeon will instantly throw the video out of focus. Each surgeon should focus the video camera. There is no single setting that will work for all. Of note, it is possible to acquire an attachment that connects the video camera to the microscope and provides a separate focusing knob, xey capabilities, and even zoom. When such devices are incorporated, the video camera can be controlled independently of the surgeon. Such devices are relatively expensive, and demand attention, usually in the form of an additional person in the operating room, a designated videographer. This device, when used appropriately, will improve video output.
2.6. field
The video field is merely a portion of the surgeon’s
While not a focusing issue, discrepancies between the surgeon’s field of view and the camera’s field of view may undermine the quality and value of the video. The video
376
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camera captures only a portion of what the surgeon sees. This is because: The surgeon’s view is circular; the camera captures a rectangular field of view. The corners of the video image often do not extend out to the edge of the surgeon’s circular view. This is designed to avoid darkened corners of the video image. For optical reasons the camera often is not able to capture the most peripheral image. Fluctuations in zoom may vary the relative field of view that the camera captures compared to the surgeon’s field of view. The surgeon should recognize what portion of the microscope’s circular field of view is actually captured on video. A simple way to determine this is the following: 1. Place a blank piece of paper in focus under the microscope. 2. While looking through the microscope, draw the largest circle that can still be seen through the microscope. 3. Now, without moving either the paper or the microscope, shift your view from the microscope to the video monitor, and while only looking at the monitor, draw the largest rectangle that can still be seen on the video monitor. 4. Compare the rectangle to the circle. Figure 3 demonstrates a video field of view as compared to the microscope’s field of view. Much can be learned from this figure: The video view shows some rotational misalignment (a camera mounting issue) and is not centered within the surgeon’s view. Most important, this figure demonstrates how little of the surgeon’s view is captured by the video.
Fig. 3 e A hand-drawn comparison of the surgeon’s view (the larger circle) and the video view (the inner rectangle). Note that for this particular system, the video view was found not to be centrally aligned, nor rotationally aligned.
2.7.
Surgeon’s accommodation
Any changes in the surgeon’s accommodative state demand an identical change (same magnitude, opposite sign) in the ocular eye-pieces in order to avoid throwing both the assistant and video camera out of focus. If the assistant possesses enough accommodative reserve, however, they can compensate for the change in surgeon’s accommodation. The video camera, on the other hand, will always suffer loss of focus proportional to the accommodation applied by the surgeon. Similarly, when the surgeon calibrates the system while accommodating, if at any later stage the accommodation relaxes, both the assistant and video camera will be out of focus. A common and potentially disruptive scenario occurs when a young resident surgeon is assisted by an experienced senior surgeon. During the more demanding and stressful portions of the case the young surgeon may involuntarily accommodate excessively,1 blurring the senior surgeon. If the microscope is a newer model, the assistant’s focusing knob allows the senior surgeon to compensate, but this may throw the video out of focus. If, however, the microscope lacks this adjustment, one solution is to ask the younger surgeon to focus up until the senior surgeon sees clearly and then verify they still have a clear image, implying that the excessive accommodation is relaxed.
2.8.
Surgeon’s presbyopia
Presbyopia is a problem for surgeons. Surgeons under age 45 years or so can operate with or without their distance glasses, provided that they do not have much astigmatism. As long as sphere is the only issue, even in anisometropia, the correct refraction can be easily dialed into the eye-pieces, replacing the need for glasses. This also eliminates the occasional fogging of glasses, and it is usually more comfortable to operate without glasses, as the eyes can be placed closer to the oculars. Those having meaningful amounts of cylinder should operate with their glasses on as no spherical correction can provide them with crisp vision. The surgeon may need to be able to see the instrument tabledfor example, to trephine a donor corneal graftdand also to read the phaco/vitrectomy machine screen. Even if a perfect view can be achieved without glasses through the microscope, these additional requirements of near and midrange vision may convince the surgeon to wear glasses while operating. When presbyopia becomes an issue, low to moderate myopes can continue operating without glasses while emmetropes and high myopes may find that wearing glasses allows them to see clearly around the microscope. Some may prefer bifocals (as opposed to multifocals), or even half-frame reading glasses, for viewing the instrument table. It may not be easy to change one’s practice at the age of 45 if glasses were never previously worn during surgery. If a presbyopic surgeon wearing bifocal or multifocal glasses unconsciously shifts from looking through the distance portion of the lens to the intermediate or near portion, a dramatic, unwanted change in focus will occur for both the assistant and the video camera.
s u r v e y o f o p h t h a l m o l o g y 6 0 ( 2 0 1 5 ) 3 7 3 e3 7 7
2.9.
Surgeon-assistant switch when tutoring
While supervising a young surgeon, the senior surgeon commonly exchanges seats several times during the case. This scenario deserves special attention and is further compounded by whether the video camera is mounted on the surgeon’s, or assistant’s, scope. If the microscope lacks an assistant focusing knob, at each exchange the oculars’ settings need to be reset on both scopes, setting aside the change in interpupillary distance. This will solve the clarity issue for all involved (including the video monitor), but poses a significant inconvenience. If, however, an assistant’s focusing knob exists, the tendency would be to rectify the focusing discrepancy using it. This will solve the problem for both surgeons, but may blur the video. If that is the case (provided, of course, that the surgeon’s and assistant’s ocular settings are different), one should decide which of the two surgeons’ work is more important to capture clearly on the TV monitor and video. Usually, the younger surgeon’s work is of more interest and should be videotaped in focus, so that after the case the residents can review his/her performance.
2.10.
A novel concept: the microscope is never out of focus
What a confusing heading! If the microscope is always in focus, wouldn’t this discussion be unnecessary? The surgical microscope is always focused and can never be out of focus. To accept this seemingly irrational statement, one needs to realize that the microscope has one specific plane of focus (plus or minus the depth of field bracketing that plane) always in perfect focus. Everything outside that specific plane is always out of focus. The surgeon’s role is to place the microscope’s plane of focus to coincide with the plane where the surgery is taking place. We can even extend this statement further and claim that the surgeon’s view is always in focus, but does not necessarily merge with the plane of interest. There are only two ways to move the microscope’s plane of focus up and down. One is by shifting the entire microscope head up or down, as routinely accomplished using the handles (gross adjustment) and foot-pedal (fine adjustment), and the other is to change the oculars’ diopter setting. The only other way we are aware of, short of replacing lenses within the microscope, is to replace the surgeon, as surgeons with different refractions and accommodative powers will have their plane of focus at varying distances from the microscope. Thus, the plane of focus for a particular microscope is not a factory preset distance, but rather takes into account the surgeon’s refractive state, as well as the oculars’ settings. Of course, another way of making the plane of interest and the microscope’s plane of focus coincide is by moving the
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surgical bed up and down. Setting the optimal height of the surgical bed should be done before the surgery begins so as to allow the best ergonomic position for the seated surgeon. Once the height of the bed is set, the surgeon should proceed with the described maneuvers to achieve the best focus.
3.
Discussion
We discuss difficulties in fine-focusing the complex optical system on microscopes used in ophthalmic surgery. The surgical microscope, when correctly set, provides clear focus to the surgeon, the assistant, and the video camera. All three are interconnected, and satisfying all three may be difficult. We provide a practical description of one system, addressing physiological limitations and describing maneuvers that allow surgeon, assistant, and video camera to receive a sharp image throughout the operation. This is far more complex than it may at first seem because it is person-, as well as microscope-, dependent, such that each surgeon and each assistant must determine their personal settings on each microscope. Failing to adjust the oculars’ settings accordingly may result in an unhappy assistant, asthenopic surgeon, and/ or a blurred video image; this may limit staff assistance and cooperation, losing the opportunity to review and learn from past performance and to present outstanding videos at meetings.
4.
Disclosures
No funding, grants or support were received for this study. All authors claim that they have no financial disclosures to disclose.
references
1. Avetisov ES, Gundorova RA, Shakarian AA, et al. [Effects of acute psychogenic stress on the state of several functions of the visual analyzer]. Vestn Oftalmol. 1991;107:17e9 2. Hoerenz P. The operating microscope. II. Individual parts, handling, assembling, focusing, and balancing. J Microsurg. 1980;1:419e27 3. Kikuchi K, Okuyama K, Yamamoto A, et al. Intraoperative stress for surgeons and assistants. J Ophthalmic Nurs Technol. 1995;14:68e70, 2-3. 4. Serpetopoulos C. More on adjusting the slit-lamp oculars. Surv Ophthalmol. 1996;40:424 5. Yamamoto A, Hara T, Kikuchi K, et al. Intraoperative stress experienced by surgeons and assistants. Ophthalmic Surg Lasers. 1999;30:27e30