The Fascinating Design Challenges of Contact Lenses

This page was originally published as a part of Hexagon's Design and Engineering blog. Hexagon Design and Engineering is now a part of Cadence.

Contact lenses are one of the most common medical prostheses. They are so common that we don’t usually think of them in that way. If you’ve ever used contact lenses, you’ll probably have taken them for granted. Stop for a moment and consider what they do and how they work. Contact lenses are a true marvel of medical science. 

Join us for another look into our on-demand library of design and engineering presentations. This time, we’re highlighting an exceptional talk by Dr. Shahrokh Zeinali, Senior Research and Development Engineer at Johnson and Johnson. 

The link to the presentation is at the end of this blog. Don’t forget this is just one of many great talks by industry leaders covering diverse topics, from the medical sector through to energy and power generation, automotive, aerospace and more. 

Astonishingly, the basic theory behind contact lenses goes back to Leonardo da Vinci in 1508. Like many of da Vinci’s ideas, it was way ahead of its time. Scientists would take hundreds of years to arrive at the first prototype. The history and development of the contact lens is fascinating and well worth investigating. Today, more than 150 million people use contact lenses, and the industry is worth tens of billions of dollars. 

Every human eye is completely unique. That’s why iris recognition technology is so secure, and why solid contact lenses are made to measure, whereas soft lenses are flexible and will adapt to the shape of the eye. Both types have pro’s and con’s but soft contact lenses are easily damaged precisely because they are soft. This is one of the challenges that Dr. Zeinali speaks about in his presentation. They are susceptible to deformation just by handling. They can be damaged through accidental folding or depression on the user’s finger. They can even turn inside out, a situation (almost impossible to recognise) that stops the lens from working correctly. 

Those design challenges occur before the contact lens is even in position on the eye. Once it’s inserted, it needs to stay in place, unnoticed, for hours, despite the movements of the user. The average person blinks around 16 times a minute. That’s 960 times every hour. If you sleep for 8 hours a day, you’ll be blinking 15360 times during your waking hours and all the while a humble contact lens remains in place. 

If you think that’s interesting, do you know how fast a human eye can rotate? 

It takes just a tiny fraction of a second to move your eyes from one point of focus to another. It’s often an involuntary action and there’s even a word for it, saccade meaning “a brief, rapid movement of the eye from one position of rest to another”. 

It’s a reflex, and like all reflex actions it needs to be very, very quick to serve its purpose. But just how quick? Happily, science has provided an answer, and it’s incredible. The human eye can rotate 130 degrees (that’s the typical field of vision for a single eye) in less than a 0.25 of a second (according to the Encyclopaedia Britannica). Blink and you’ll miss it, literally. 

All of the above makes for some fascinating design challenges, the first of which is lens handling. The lens must arrive to the end user who then takes it out of the package. That might sound simple, but we’re talking about a very small, delicate object which is also transparent. Just seeing the thing is tricky, let alone picking it up. 

Then there’s the challenge of putting the lens onto the eye and keeping it in place while maintaining eyelid comfort. Touching the eye with a foreign object carries the risk of abrasion, irritation and occasionally infection. Needless to say, contact lens design needs to be absolutely perfect and that’s achieved with simulations. 

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