Ephron died from pneumonia brought on by acute myeloid leukaemia in a New York hospital on Tuesday (June 26).
Ryan is perhaps the actress most identified with Ephron's work, having starred in the writer's films When Harry Mat Sally, Sleepless in Seattle and You've Got Mail.
The actress reflected on Ephron's passing and her personal history with the author in a statement to ET Online.
"Nora was an era. We pictured ourselves inside her dreams and they became ours. All wisdom, wit and sparkle lights, what a treat she was... what a blessing," Ryan said.
She went on to say: "I marvel again and again, what a life... to have created a simple happiness in people, to have added to the sum of delight in the world."
Ephron's passing has also drawn tributes from Nicole Kidman, Ron Howard, Meryl Streep, Steve Martin and many others.
Ryan's Sleepless in Seattle co-star Tom Hanks credited Ephron with "so much joy to all who were lucky enough to know her".
Ephron was 71 years old at the time of her death.
Watch a Sleepless in Seattle trailer below: