How to properly implement snake style controls for android?

I'm making a game that is snake but with added content. I've made the controls work in MIT app inventor so I know my logic should be correct. I think the problem comes from converting screen coordinates to world coordinates. I've tried offsetting the y coordinate by screen.height in both directions but still get unpredictable behavior of controls.

EDIT: It appears ScreenToWorldPoint is not the right way to do this. How can I implement the controls so that touch.position.x and touch.position.y translate directly to what they are from screen to world?

Here is my code:

//gesture recognition

 var touch : Touch;
 var worldTouchPos : Vector3;

 for (var i = 0; i < Input.touchCount; ++i) {

     touch = Input.GetTouch(i); ~~~~

     worldTouchPos = camera.main.ScreenToWorldPoint(touch.position);

     if(touch.phase == TouchPhase.Began)
     {
         if(direction == 0  || direction == 2)
         {
             if(transform.position.y < (worldTouchPos.y)) // Go up or down
             {
                  direction = 1;
             }
             else
             {
                 direction = 3;

             }
         }
         else // go right or left
         {
             if(transform.position.x > (worldTouchPos.x))
             {
                 direction = 2;
             }
             else
             {
                 direction = 0;
             }
         }

     }

 }//end for


 if(direction == 0)//right
 {
    transform.Translate(Time.deltaTime, 0, 0); 
 }
 else if (direction == 1)//up
 {
     transform.Translate(0, Time.deltaTime, 0); 
 }
 else if (direction == 2)//left
 {
     transform.Translate(-(Time.deltaTime), 0, 0); 
 }
 else if (direction == 3)//down
 {
     transform.Translate(0,-(Time.deltaTime), 0); 
 }