Otvor na zadnjoj strani Tuohy igle u predelu krivine vrha igle (back-eye), omogućava prolazak spinalne igle bez savijanja i frikcije.

There is just the choice of presence or absence of backeye, so the options apply to the doctor choosing needle diameter, etc and whether needle will have a backeye or not, and a fixed or rotating hub.
http://www.proz.com/kudoz/english_to_french/medical:_instrum...

http://www.networkofnewengland.org/Meetings/Tech/2009/Patt R...
Allows blood to enter or exit from both the bevel and backeye.

Backeye opening to allow blood intake from both sides of needle. Arterial or Venous
Non backeye needle – Venous Only

http://images.google.com/images?hl=en&um=1&sa=1&q=needles wi...