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An FYidoctors Optometrist Explains How Optical Illusions Work

Posted on April 19th, 2022

Optical illusions, explained

We recently shared an optical illusion on our social media channels, and the image was definitely a doozy for some people. The concept of optical illusions is fascinating, and our perception of them can reveal important information about our ocular health.

One of our FYidoctors optometrists, Dr. Rajan Mistry, shares interesting insight on the subject of optical illusions—and what it might mean for our eyes.

What is an optical illusion?

Before we delve into the details, it’s important to understand what an optical illusion—sometimes referred to as visual illusion—really is. An optical illusion is an image that triggers visual deception. In simple terms, it’s a photo that plays tricks on your eyes and mind by appearing to be something other than what it is.

There are three main types of optical illusions, including literal illusions, physiological illusions and cognitive illusions. 

A literal illusion occurs when a person sees an image that differs from other images within the illusion. Physiological illusions, meanwhile, are triggered by excessive stimulation (including through the inclusion of brightness, colour and dimension) which confuses the brain and can make a static scene appear to be moving. Finally, cognitive optical illusions result from previous conceptions of the world, which are then imposed on visual stimuli.

Generally speaking, as Dr. Mistry explains, visual illusions mainly fool your mind, at least much more so than your eyes.

“The eyes are sort of like a camera for your body, and your brain does most of the processing,” he says, adding that optical illusions demonstrate the way in which our eyes and brains communicate with each other. 

Interestingly, Dr. Mistry points out the act of “seeing” is rather subjective: “There’s a lot of background processing that works in order to fuse images that both eyes are receiving and make sure that we can interpret the world around us.” 

Part of that background processing is determined by “historical experiences” which inform how our world appears. For instance, the way in which individuals view the widely popular optical illusion featuring a dress—which some people see as white and gold while others view as black and blue—is determined by “how your brain assumes the lighting in the area is going to be,” Dr. Mistry says. “So if your brain assumes that the dress was sitting in the shadow, which tends to be typically how our brain loves seeing the lighting in the room, it will actually filter out or focus on certain aspects of lighting that will change your perception of how you see things.” 

In sum, what we’ve seen in the past determines how we see things in the present.

How does an optical illusion work?

As mentioned above, optical illusions are all about how the brain and eyes communicate. Our eyes gather data from the outside world as light falls within our eyes, and sensors send information back to the brain. 

In the case of optical illusions, they are specifically designed to confuse communication between our eyes and brains. Our brain then mixes up the signals from the eyes with our past life experiences and it can actually interfere with our ability to interpret what we are seeing.

Dr. Mistry believes a person’s ability to spot an optical illusion depends on the type of illusion itself. In some cases, being able to interpret a trick is all about getting your eyes to position properly.

“A lot of optical illusions rely on your eyes’ ability to either converge or diverge,” he says. “If you’re able to easily accomplish those eye movements, you’re able to get to that picture very quickly.” 

Other illusions rely on taking two disparate images to each eye, and using the brain to fuse the separate visions together. If both eyes are not working in tandem, “it can shatter the effects of an illusion,” Dr. Mistry says.

Some people have a more natural ability to focus their eyes together, which is one reason why some individuals interpret illusions differently than others. Over time and with practice, Dr. Mistry says, a person can hone their ability to position their eyes, and “it gets easier and easier.” 

What can optical illusions tell us about our eye health?

Although optometrists generally do not use optical illusions as a diagnostic tool, “there’s a lot of tests we can do that apply the same concepts of sending a different image to each eye, and using the brain to build it together,” Dr. Mistry says, explaining that such tests can be used to detect a lazy eye and other ocular issues. “From a clinical perspective, we use these on a regular basis to determine how well the eyes are working together and how well the brain is receiving information.” 

The bottom line, however, is that not being able to see an optical illusion is usually not a concerning sign that something is wrong with someone’s eyes. 

“They’re meant to play tricks on you,” Dr. Mistry says. “Have fun with it.” 

Rather than using an optical illusion to determine the status of your eye health, he continues, “it’s really, really important to go in and see your doctor. They can check and make sure that the eyes are processing information correctly, and that there’s no issues going on.” 

Book your annual eye exam today at an FYidoctors clinic near you! 

Different eyes, different world

More broadly, optical illusions “give a cool insight into how we view the world around us,” Dr. Mistry says. “What optical illusions reveal, in a lot of cases, is that our brains work off what we’re used to, and with the experiences that we’ve been through.” 

Humans tend to believe that what we see is “set in stone,” and the same for everyone, but optical illusions highlight that “we have our own ability to inject our personal experiences into how we view the world around us, and I think that’s a beautiful concept in itself,” Dr. Mistry says.