You should pass your AccountListFilterModel to the view, either via model (which is the best solution as it's less error-prone) or using ViewBag \ ViewData (which is an anti-pattern actually, but fits the quick-fix niche).
Using the latter approach:
In your controller:
public ViewResult Index(AccountListFilterModel accountListFilter)
{
ViewBag.Filter = accountListFilter;
}
In your view (you can delete the code at the top of the view, that uses Request to get parameters.
<a style="@(ViewBag.Filter.currentSortOrder == "UserName desc" ? "" : "display:none;")" ... />
It's a general rule of thumb that your view should not contain any logic at all, your controller should supply all the data that the view needs.