What it's like to wear custom contact lenses designed for TV and movies

Filmmakers have long used contact lenses to change actors' appearances.

But have you ever wondered where those contacts come from?

Eyeworks for Film has provided contact lenses for some of the most memorable films and TV shows of the past decade, including "Star Wars," "Wonder Woman," and "Game of Thrones."

Insider's Ju Shardlow visited the Eyeworks office in London to find out what it's like to get fitted for a pair of custom contact lenses worthy of the big screen.

The first step is doing a prescription check like you're at the eye doctor. Shardlow had her eyes checked by Eyeworks director Sinead Sweeney.

Sweeney then checked the inside of Shardlow's retinas with a device called an ophthalmoscope.

She uses a 3D scan of the retinas to ensure her lenses will fit properly atop the cornea. If done properly, the lenses will feel "very, very normal," Sweeney said.

Further tests look at the curvature of the eye …

… the diameter of the iris …

… and the front of the eye for dryness, using a yellow dye called fluorescein.

Movie contacts are bigger than normal contacts, and there's a trick to putting them in: Point your chin up, then point your eyes down to the left. "You feel like you have an entire film over your eye now," Shardlow said. "So I can picture that would really put someone into character quite quickly."

The lenses take two to three weeks to paint and manufacture. Prescription lens companies such as No7 make the lenses, and then a lens artist carefully paints them by hand using FDA-approved paint.

Luckily, Eyeworks had a pair of lenses on hand for Shardlow's visit.

As Sweeney explained, subtlety is the key in lens artwork. "Even one brushstroke too far can make a real difference," she said. "The detail is extremely fine."

Before Shardlow could try them on, the lenses needed to be sterilized. "There are a lot of safety guidelines," Sweeney said.

Finally, the moment of truth.

Her initial reaction: "Oh my goodness. I look like a fish!"

"I've really got that kind of bug-eyed, fishy look going on, but there is something really alien about it."

The lenses flatten to your eye, so it's important to get rid of air bubbles and keep putting in eye drops.

Thanks to this bit of movie magic, actors can become just about anyone — or anything.