Absolute risk and prevalence? From Wikipedia

If the absolute risk in the control group is available, conversion between the two is calculated by: 
  $$
    RR \approx \frac{OR}{1 - R_C + (R_C \times OR)}$$
  where:
RR = relative risk
OR = odds ratio
RC = absolute risk in the unexposed group, given as a fraction (for example: fill in 10% risk as 0.1)

What is the difference between absolute risk and (point) prevalence (used in rare disease assumption)? 
Thanks!
 A: The critical point, alluded to by Azula R in the comments, is that the risk reflects incident cases, while prevalence reflects both new and existing cases. Thus prevalance is a function of incidence and duration of disease. This distinction is important when trying to identify potentially modifiable causes of disease. If we identify a variable that is strongly associated with increased prevalance, intervening on that variable might do nothing to prevent future cases, because it might only be related to disease duration. 
A: From epidemiological perspective, the absolute risk is the same as incidence rate, i.e, the rate at which new cases arise in a population during a certain time period. Absolute risk is not expressed in relation to an exposure, something that distinguishes it from relative risk that is expressed as a rate of a new cases given a certain exposure. In other words, relative risk is the ratio of two incidence rates.
Prevalence is the proportion of the population that has a certain condition. Point prevalence adds the time frame to this definition, and it is the proportion of the population having the condition at a certain point of time.
Incidence can't be directly estimated from a case-control study, but if you select the controls carefully, case-control study will allow you to estimate the risk ratio, that is the relative risk.
For more information, see the following two Chapters from a book published by IARC:
http://www.iarc.fr/en/publications/pdfs-online/epi/cancerepi/CancerEpi-4.pdf
http://www.iarc.fr/en/publications/pdfs-online/epi/cancerepi/CancerEpi-9.pdf
