Adaptive focus digital sunglasses

My grandmother always used to say, eat carrots to have sharp eyesight like Arjuna. She had good vision, but sometimes she used glasses to read the newspaper. And I wondered maybe she too did not eat enough carrots. I asked her why you are wearing these glasses. She said I could see far-off objects very clearly but have a problem in seeing nearby objects. Of course, who does not wish to have a perfect vision lifelong but unfortunately, every one of us is losing a little bit of our eyesight daily. The human eye is very dynamic and can focus both nearby and far-off objects very well. As new-born, we have the ability to see objects close to 6.5 cm, which increases to 10 cm in the mid-twenties. This distance further increases to 25 cm in the early forties, and beyond which it becomes increasingly difficult for reading. The inability of the eyes to focus close by objects with age is called presbyopia. There are 1.8 billion people with presbyopia worldwide, and it is an irreversible eye condition that typically occurs in people over the age of 45 and gets progressively worse [https://doi.org/10.1016/j.ophtha.2018.04.013]. Light enters the human eye, focused by the flexible crystalline lens, and transforms into electrochemical impulses that travel to the brain to form images. The crystalline lens is very flexible and changes its shape with the help of circular muscle surrounding it to focus on objects at far-off and nearby distances [https://doi.org/10.5772/31073]. When one looks at something at a far distance, the circular muscle relaxes. The muscle constricts when one looks at something nearby, allowing the relatively elastic lens to curve and adjust the focus.

Presbyopia is caused by a hardening of the lens of an eye and occurs naturally with aging [https://doi.org/10.1016/j.preteyeres.2004.11.001]. As the lens becomes less flexible, it can no longer change shape to focus on close-up images. There are many ways in which it can be corrected. One of them is by wearing reading glasses with a single focal power lens. It brings nearby objects in focus, but distant objects tend to go out of focus. These glasses with static focus require a person to switch appropriate glasses for near and far vision, respectively. To overcome this limitation, Benjamin Franklin invented a bifocal or progressive lens [https://doi.org/10.1046/j.1532-5415.2002.50502.x]. These lenses are placed in the top and bottom regions of the glasses. Just by changing the line of sight by moving the eye one can view both near and far-off objects. The disadvantage of the bifocal glasses is that there is a sudden jump of the image when a line-of-sight passes from the far vision region of the glasses to the near vision.

 

Image: Adaptive focus glasses with pixelated liquid crystal lenses. Image courtesy: https://www.deepoptics.com

Inspired by the human eye, Deep Optics, an Israeli startup has developed a ground-breaking novel adaptive lens, 32 ºN glasses which also serve as sunglasses (to look far-off object) by default and switch to the reading glass with a swipe. 32 ºN has an adaptive electrically switchable pixelated liquid crystal (LC) lens with a tiny processor embedded in the glasses frame [https://www.deepoptics.com]. It is a complex electro-optical system. LCs are rod-like structures exhibiting dielectric and optical anisotropy. When light propagates through an LC material its travelling speed depends on the optical anisotropy, incident angle, and polarization[https://doi.org/10.3390/cryst8010029]. The LC molecules change their orientation under an external electric field. The wavefront passing through the LC material is modulated by the orientation of the LC molecules which leads to convergence or divergence of the light leading to positive or negative focal length. By default, the glasses are transparent with no focal power. When the user swipes the side frame of glasses, the processor takes the user’s personalized prescription and electrically switches the orientation of the LC molecules to obtain the desired optical power. In these glasses, the active area is consisting of a polarization-independent LC (cholesteric), which has anisotropic refractive indices [U.S. Pat. No. 20210294162]. Its effective local refractive index is determined by the voltage applied across the active area (electro-optical layer). This reorients the LC and results in a phase modulation profile which helps one to obtain desired focal power.

These lenses are flexible and programmable, where reading magnification and power can be tuned and controlled by the mobile app via Bluetooth connection. It is power by a lithium-polymer battery which typically lasts for a day. The links given below show the working prototype of 32 ºN.

 

https://www.youtube.com/watch?v=0tKY9hBZLZ0

https://www.youtube.com/watch?v=fdTf-5QRPyc

 

Ms. Brindhu Malani
Senior Research Fellow
Group of Dr Viswanath P.
CeNS, Bengaluru