an operating microscope ( om ) has been considered as the mainstay in modern neurosurgery . it produces magnified images on the retina stereoscopically while providing detailed views of surgical anatomy . during the last two decades , neuroendoscopes are increasingly used in neurosurgery for intraventricular lesions , spine , hematoma and predominantly for trans - sphenoidal skull base surgery . an endoscope is sometimes used as an adjunct to microsurgery with om . . an endoscope can be useful by means of providing a better overview of the operating field and also revealing detailed structures with fine illumination . surgeons visualize the operative field from a display connected to the camera with usage of an endoscope . on the other hand , compared with om , the target is viewed only through right and left eyepieces . in 2008 , an exoscope system i.e. the video telescope operating monitor ( vitom ) was introduced as an alternative to both om and endoscope . the exoscope serves for observing and illuminating an object field on a patient from a position set apart from the patient s body . it enables surgeons to complete the operation under assistance by visualizing magnified images with high resolution on a display4,5 ) . therefore stereopsis was required to improve hand and eye coordination for microsurgical procedures with usage of the exoscope . subsequently novel three - dimensional and high - definition operating scopes have been developed according to recent high - tech innovations in a digital surgical technology . the standard neuroendoscope can only provide a short focal distance of approximately 3 to 20 mm . therefore , vitom allows abundant space to insert and manipulate the instruments according to this specification ( table 1 ) . usually the vitom is placed at regular interval of 25 cm from the operative field at first . an illustrative case of spinal lipoma surgery with usage of vitom was shown on fig . the main manipulations in this surgery were as follows ; drilling the vertebral arches , cutting dura and arachnoid membrane with scissors , making suspending stitches , separating adherent arachnoid , resection of the lipoma along the white plane , forming circular arc by sawing the pia matter to make a neural cord and closure of dura at last . these operative techniques were completed under 2d motion images with a visual perception through dynamic cue and stereoscopically viewing corresponding to the motion parallax . but lacking the stereoscopic vision made it difficult to manipulate required hand - eye coordination such as taking hold the needle and stitch up . according to my clinical experiences , three - dimensional ( 3d ) motion images must be necessary in a case with complete resection of deep seated lesions or vascular anastomosis for exoscopic surgery . the emphasizing advantages of exoscope were regarded as the wide field of view ( fov ) and deep focus . vitom provides the ability to maintain 35 mm depth of field ( dof ) under 50 mm fov . it minimized the need for repositioning and refocusing during the procedure . on the other hand , only 50 mm fov is possible under minimum wd , however , less than 20 mm fov is easily available under 200 mm wd with om ( table 1 ) . from this point of view , further refinements in high resolution imaging under strong magnification , such as digital zooming would be a welcome to the vitom . in the field of laparoscopic surgery , 3d laparoscopes with various mechanical designs are currently used successfully . those prevent signs of fatigue while shortening the operating time and facilitate various procedures inside the body , especially in performing precise suturing . 3d endoscope provides enhancing subject depth perception and spatial orientation . according to the recent reports , 3d images improve surgical dexterity in the field of neuroendoscope3,10 ) . for example , clinical application of 3d - neuroendoscope for trans - sphenoidal surgery is regarded as an effective assistive technique and supports the feasibility and safety9,10 ) . surgeons sometimes observe an intracranial object field from a position set apart from the sphenoid sinus during this procedure . vsiii system ( visionsense , philadelphia , pa , usa ) is one of the valuable one . it is based on  insect - eye technology  , which involves the incorporation of a single objective lens that splits light along two paths , reconstructing a 3d image9 ) . on the other hand , it incorporates information from two distinctive perspectives to render a single 3d view , similar to human vision with binocular depth perception . exoscopic microsurgery with usage of the einstein vision , 3d and high - definition ( hd ) laparoscope system which is designed based on dual optical technology . they concluded that the image quality was found to equal to that of the om , but suitability for minimally invasive neurosurgical operations is inadequate . yoshimoto et al.10 ) reported their clinical experience of endonasal surgery with usage of dual optical channel 3d endoscope ( developed by shinko optical corporation and commercialized by machida endoscope corporation , tokyo , japan ) and compared stereoscopic images with vsiii system . according to that , the stereoscopic effect of dual optical channel 3d endoscope is stronger . in other words , dual optical channel 3d endoscope exhibits greater magnitude of binocular disparity , which is translated into the sense of extrusion and depth of structures . in 2014 , a novel 3d and hd flexible scope called 3d - eye - flex was developed to visualize the operative field as a 3d digital image and support more accurate microsurgery6 ) . it was introduced with an enhanced 3d - hd laparo - thoraco videoscope system ( ltf- y009 , olympus medical systems ) . 3d - eye - flex has two miniature - sized charge coupled device ( ccd ) chips at the distal end of the scope . consequently , regardless of rigid or flexible , placing the imaging device at the tip has made  on site  processing of images without interruption possible , while maintaining consistent image quality . a 15 mm - long rigid 3d and hd scope with a 15 mm outer diameter is attached to a 615 mm - long flexible bellows . the focus distance , which is the same as the wd , is 18100 mm . the illumination is not as bright as that of om , however , the ccds help to enhance the image . a circular polarizing filter system is used for the 3d display to deliver life - like images ( fig . exoscope , an alternative to om , by means of capturing the 3d magnified images using digital signals from the outside of the body . the wide angle of view and large dof inherent in the endoscope should be emphasized as advantages just like vitom system . the large dof of 3d - eye - flex drastically minimizes the need for repositioning and refocusing during a surgical procedure . moreover , neurosurgeons feel more comfortable when using stereoscopic vision , especially in cases of deep seated lesions . on the other hand , placing the scope close to the operative area should be required for magnifying objects . it is more likely to be stained by blood or bone dust , fogging the lens and narrowing operative space . as described above , recently developed operative scopes visualize the operative field as digital images and make it possible to verify the images according to application . for example , narrow - band imaging ( nbi ) while changing the light wavelength , i.e. autofluorescence , is easily applicable with 3d - eye - flex , and can be integrated with the information obtained from white light7 ) . an optical color separation filter narrows the bandwidth for spectral transmittance , lets only two narrow wavelengths through . these two specific wavelengths are strongly absorbed by hemoglobin and allow a better understanding of superficial and subependymal vasculature in the ventricle ( fig . 4 ) . in another example , a fluorescent dye injected into the body leaks out of the tumor blood vessels due to the disrupted blood - brain barrier . it is excited with an ordinary light wavelength and the yellow color - stained tumor is visible even to the naked eye . with further refinement , an ultra - high magnified image captured by endo - cytoscopy may be possible . currently these images of the operative field are projected onto a display adjacent to navigation images or functional images . it may be coregistered on the identical display in the near future . in state - of - the - art neurosurgery , neurosurgeons could highly benefit from a new surgeon s eye that visualizes the operative field with integration of the medical information received by the senses and interpreted by surgeon s brain on demand . the novel operative scopes including exoscope system have potential for being developed to this new application . it will set the stage for the next generation in digital image based neurosurgery .