Why are my iPhoto pics suddenly displayed as thumbnails?

[Keukasmallie]

When I opened iPhoto this AM I was greeted with a screen full of thumbnails that are practically unusable in that format. How do I change back to the previous format?

 

[MCAsan]

You might want to ask photo app related questions in the Photography forum.

 

[Dave Braine]

How do I change back to the previous format?

What was the previous format? Does double clicking on the thumbnails not open that photo?