AN A320 CAPTAIN DESCRIBES A CREW REQUESTED LATE RUNWAY CHANGE BECAUSE OF A BLUE HYDRAULIC SYSTEM ANOMALY. WHILE MANEUVERING FOR NIGHT TIME VFR LANDING THE FIRST OFFICER BECAME DISORIENTED. THE GREEN HYDRAULIC SYSTEM QUANTITY AND PRESSURE WERE ALSO FALLING.

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WHILE DSNDING TO ZZZ; WE NOTICED THAT THE BLUE HYD SYSTEM HAD AN ANOMALY. THE PUMP WAS SHOWING GREEN BUT WITH NO PRESSURE. WE ALSO NOTED THAT THE GREEN SYSTEM QUANTITY WAS LOW. WE WERE ASSIGNED RWY 23 AND CONTINUED THE APCH. WE DISCUSSED THE HYD SYSTEM ANOMALY AND WERE CLRED FOR THE APCH. JUST PRIOR TO ABOUT 1500 FT AGL; I CHKED THE HYD PAGE ONCE AGAIN AND NOTED THAT THE GREEN SYSTEM HAD FALLEN TO JUST ABOVE THE AMBER LINE. WE DISCUSSED QUICKLY AND DECIDED TO LAND ON A LONGER RWY. WE REQUESTED RWY 18C BUT WERE GIVEN RWY 18L INSTEAD. SINCE WE WERE SO CLOSE AND SEVERE CLEAR; WE FELT THAT THE EXTRA LENGTH AFFORDED BY RWY 18L WOULD BE SUFFICIENT; EVEN IN THE EVENT OF A HYD FAILURE. THE PNF TURNED TO A HDG TO RWY 18L AND WE WERE CLRED FOR A VISUAL FOR RWY 18L. I WENT HEADS DOWN TO RE-STRING THE APCH AND CHK THE HYD PAGE. WE HAD A CONFIGN CHANGE AND I LOOKED UP AND SAW THAT THE PNF HAD ENTERED INTO AN OBLIQUE ANGLE TO THE RWY. I THOUGHT IT WAS A LITTLE ODD BUT CONTINUED TO RE-STRING THE APCH AND LOOKED FOR THE CHKLIST TO FINISH THE LNDG PORTION OF THE CHKLIST. I LOOKED UP AND THE TWR CALLED AT THE SAME TIME TO SEE IF WE REALLY SAW THE RWY. I SAW THAT WE WERE BELOW THE GS/VASI AND TOLD THE PNF TO CLB AND/OR LEVEL IMMEDIATELY. I HAD VARIOUS THOUGHTS AT THIS TIME. A GAR WAS POSSIBLE BUT I THOUGHT THAT WITH THE GREEN SYSTEM HEADING TO NOTHING; WE WOULD EXACERBATE OUR PROBS. I THOUGHT OF TAKING CTL AND REALIGNING BUT AT THAT SECOND THE PNF SAW THE RWY AND STARTED TO PROPERLY ALIGN THE ACFT. WE FINISHED THE CHKLIST RATHER HURRIEDLY AND CONTINUED; XING THE THRESHOLD IN CONFIGN BUT SLIGHTLY L OF CTRLINE. WE LANDED IN THE FIRST 1500 FT OF THE RWY AND EXITED NORMALLY. UPON ARR AT THE GATE; THE ACFT WAS REMOVED FROM SVC DUE TO A SEVERE LEAK IN THE GREEN ENG DRIVEN PUMP. THE BLUE HYD SYSTEM ANOMALY WAS WRITTEN UP AND I DO NOT KNOW WHAT HAPPENED WITH THAT WRITE-UP. A CLASSIC CASE OF ALLOWING 1 PROB TO FIXATE AT LEAST 1 PLT AND TAKE HIM OUT OF THE LOOP. I SHOULD HAVE PAID FAR MORE ATTN TO THE APCH THAN LOOKING FOR THE CHKLIST AND RE-STRING THE APCH. I DID NOT REALIZE UNTIL LATER THAT THE PNF HAD BECOME DISORIENTED AND HAD LOST THE RWY DUE TO ALL THE LIGHTS AND NOT BEING FAMILIAR WITH THE SIGHT PICTURE NEEDED TO LAND ON RWY 18L. TAKING CTL OF THE ACFT; AT LEAST MOMENTARILY; WOULD HAVE ALLOWED THE PNF TO REORIENT HIMSELF AND PROPERLY ALIGN THE ACFT. THE PNF AND I HAD FLOWN A LOT TOGETHER AND HE IS AN EXPERIENCED PLT WITH A GREAT DEAL OF AIRBUS TIME. ANYONE CAN GET DISORIENTED AND I/WE ALLOWED OUR OTHER PROBS TO BREAK DOWN THE LINES OF COM AS TO THE PROPER ALIGNMENT OF THE ACFT. EVEN THOUGH WE LANDED SAFELY ON THE RWY IT WAS NOT THE IDEAL WAY TO FINISH THIS FLT. CONSTANTLY MONITOR ALL ASPECTS OF FLT AND DO NOT PRESUME THAT YOUR FLYING PARTNER; REGARDLESS OF EXPERIENCE OR SEAT POSITION; COULD NOT BE TASK LOADED OR DISORIENTED.