MSCRM Get the description text value from optionset field in c#

public static string GetoptionsetDescription(string entityName, string attributeName, int optionSetValue, IOrganizationService service)

        {

            string AttributeName = attributeName;

            string EntityLogicalName = entityName;

            RetrieveEntityRequest retrieveDetails = new RetrieveEntityRequest

            {

                EntityFilters = EntityFilters.All,

                LogicalName = EntityLogicalName

            };

            RetrieveEntityResponse retrieveEntityResponseObj = (RetrieveEntityResponse)service.Execute(retrieveDetails);

            Microsoft.Xrm.Sdk.Metadata.EntityMetadata metadata = retrieveEntityResponseObj.EntityMetadata;

            Microsoft.Xrm.Sdk.Metadata.PicklistAttributeMetadata picklistMetadata = metadata.Attributes.FirstOrDefault(attribute => String.Equals

            (attribute.LogicalName, attributeName, StringComparison.OrdinalIgnoreCase)) as Microsoft.Xrm.Sdk.Metadata.PicklistAttributeMetadata;

            Microsoft.Xrm.Sdk.Metadata.OptionSetMetadata options = picklistMetadata.OptionSet;

            IList<OptionMetadata> OptionsList = (from o in options.Options

                                                 where o.Value.Value == optionSetValue

                                                 select o).ToList();

            string optionsetDescription = (OptionsList.First()).Description.UserLocalizedLabel.Label;

            return optionsetDescription;

        }