Unable to cast object of type 'Microsoft.Xrm.Sdk.OptionSetValue' to type 'System.IConvertible'

Hi 

I am trying to compare the option set value in my  class. but I am getting this error "{"Unable to cast object of type 'Microsoft.Xrm.Sdk.OptionSetValue' to type 'System.IConvertible'."}." can any one please suggest to resolve this problem.please it's very urgent.

here is my code

if(new OptionSetValue(Convert.ToInt32(sa.Attributes["isr_typeofdegree"])).Value== new OptionSetValue(Convert.ToInt32(905080000)).Value)
{

//logic

}