How to collect Int textField input and use as variable

I am trying to make an app that takes the textField input, checks to see if it is within a range, then display the answer in a Label

Im having trouble defining my variable as an Integer. The code below gives me a

Value of optional type 'UITextField?' must be unwrapped to a value of type 'UITextField'

error.

@IBOutlet weak var depthTextField: UITextField!
@IBOutlet weak var pressureGroupLabel: UILabel!
@IBAction func enterButtonPressed(_ sender: Any) {

    var Depth = Int(depthTextField)

    if Depth < 40 {
        pressureGroupLabel.text = "less than 40"
    } else {
        pressureGroupLabel.text = "more than 40"
    }

Am I doing something wrong in regards to defining my variable as an Integer or is there a different problem I dont know about?