I know you're not an eye doctor, but this is the only Dr. themed birthday joke I could find:

An eye-doctor was having his 40th birthday, and gathered lots of friends and family in his house. His wife had made him a surprise cake, and led her husband blindfolded to a table where the cake was placed.

Eagerly the doctor removed the blindfold and looked down on the cake. He immediately burst into a crazed laughter, for there in front of him was a huge cake, with 40 marzipan eyes!

The guests asked him why he laughed, and after some minutes of laughing and wiping his eyes, the doctor said: "I'm just thinking of my buddy who will be 50 next week, who is a gynecologist!"

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