twenty - eight post mortem lower eyelids ( 14 right , 14 left ) from 16 japanese cadavers were examined and divided into 2 groups . one group of 14 lower eyelids of 7 cadavers ( 7 right , 7 left ; 3 males , 4 females ) with an average age at death of 80.4 years ( range : 73~97 ) , were sagittally incised from the lower lacrimal punctum ( figure 1 ) . the other 14 lower eyelids of 9 cadavers ( 7 right , 7 left ; 4 males , 5 females ) with an average age at death of 76.3 years ( range : 69~95 ) were incised from the lower lacrimal punctum with 5 degrees lateral inclination to the sagittal plane ( figure 1 ) . all cadavers were registered in the cadaveric service of aichi medical university , with proper consent from our institutional review board and approval to use them for educational purposes and studies . all methods for securing human tissue were humane and complied with the tenets of the declaration of helsinki . in the first group , which underwent a strict sagittal incision , 10 canaliculi of 7 cadavers ( 6 right , 4 left ; male 5 eyelids , female 5 eyelids ) were interrupted at the halfway point of the vertical portion and so the distal part of the canaliculi were not included ( figures 2a , b ) . however , 4 canaliculi of 4 cadavers ( 1 right , 3 left ; male 1 eyelids , female 3 eyelids ) did include the whole length of the vertical portion . in the second group with 5 degrees laterally inclined incision , all specimens included the whole length of the vertical portion ( figures 3a , b ) . most vertical portions of the lower lacrimal canaliculus examined here demonstrated a laterally inclined course of approximately 5 degrees ( figure 4 ) . the course of the laterally directed vertical portion of the lacrimal canaliculus should be considered not only in lacrimal probing , syringing , and trephining but also in eyelid surgeries . the 5 degrees lateral inclination of the vertical portion significantly emphasizes the need of a laterally directed insertion and lateral lid traction during the passage of a lacrimal probe , syringing needle or trephine to accord with the true course of the vertical portion . as well , since the vertical portion takes its lateral course within 1 mm laterally from the lacrimal punctum ( whitnall 1979 ; hwang et al 2005 ) , surgeons , during eyelid surgery , need to recognize the area within 1 mm laterally from the punctum as being a zone with a potential for serious lacrimal canalicular injury . the vertical portion changes its direction medially because of the inward eyelid movement ( kakizaki et al 2005 ) caused by the contraction of horner s muscle . at this time , the closure of the vertical portion may become insufficient , because the relative angle of the muscle of riolan and the vertical portion of the lacrimal canaliculus becomes milder . to maintain the relative perpendicular angle to each other , although all the cadavers were in an eye - closed state , and the muscle tonus of the orbicularis oculi had been completely lost , this state would have been similar to the eye - opening state in live humans whose muscle tonus of the orbicularis oculi is little . as the lacrimal probing syringing and trephining is usually performed in eye - opening state , the present result is reasonable for the true clinical situations . first , as the study samples were all taken from elderly cadavers , we may not be able to apply the results to younger generations . confirming our results in a younger patient population through clinical procedures such as lacrimal probing is possible . our experience is that the lateral inclination of a probe usually enables easy lacrimal probing , even in young generations . second , as we did not examine samples of caucasians or blacks , we can not conclude that they have the same inclination . however , to date , racial variations have not been reported with regard to the lacrimal drainage system ; therefore , we may be able to speculate that they have the same inclination . in conclusion , most vertical portions of the lower lacrimal canaliculus are directed laterally at approximately 5 degrees . surgeons need to recognize the true course so as not to cause injury to the vertical portion of the lower lacrimal canaliculus . this anatomical view will be helpful for a better understanding of the lacrimal drainage system .
the nomenclature of each part of the lacrimal canaliculus , for example the vertical portion , does not always reflect the true course . since we have sometimes observed findings suggesting the so called vertical portion of the lower lacrimal canaliculus inclined laterally , we re - examined the course of the vertical portion . 
 twenty - eight postmortem lower eyelids in 16 japanese were examined and divided into 2 groups . 
 the first group was 14 lower eyelids of 7 cadavers . 
 eyelids were incised sagittally from the lower lacrimal punctum . 
 the second group was 14 lower eyelids of 9 cadavers ; these were incised from the lower lacrimal punctum with 5 degrees lateral inclination to the sagittal plane . in the first group , 
 10 canaliculi of 7 cadavers were interrupted at the halfway point of the vertical portion . 
 four canaliculi of 4 cadavers included the whole length of the vertical portion . in the second group , 
 all specimens included the whole length of the vertical portion . 
 most vertical portions of the lower lacrimal canaliculus demonstrated a laterally inclined course of approximately 5 degrees , although some took a completely vertical course .