Retrograde ejaculation is a condition where, on orgasm, semen is misdirected into the bladder rather than out through the urethra. Erection and orgasm occur as normal, but little or no ejaculate is seen. If the urine appears cloudy after orgasm without visible ejaculate being present, it is a good indicator that retrograde ejaculation may be taking place.
There are two sphincters which close off the urethra; one where it exits the bladder and one where it exits the prostate and enters the penis. In a normal ejaculation, the sphincter at the exit from the bladder closes on orgasm while the one at the exit of the prostate opens, directing the semen out of the penis through the urethra. If this doesn't happen correctly (for instance if the sphincter at the exit from the bladder doesn't close completely or is damaged) then the ejaculate can go backwards into the bladder rather than out through the penis.
Some of the causes of these sphincters not functioning correctly are:
Unless you wish to father a child, retrograde ejaculation poses no problems (except the sadness some people may feel at being unable to ejaculate normally) If you are trying to start a pregnancy, it is possible for sperm to be harvested from your bladder after orgasm.