1. How Glasses Bend Light to Make Your Vision Sharp
Light entering your eye is bent by two lenses: the cornea and the crystalline lens. These bend the light so it forms a clear image on the retina at the back of the eye. If the bending is not perfect, the image forms in front of or behind the retina, causing blur [1].
Imagine putting a straw in a glass of water. The part of the straw under the water looks bent. This happens because light changes direction when it moves from air into water. Placing a transparent object in the path of light changes how we see things. Glasses, contact lenses, and laser surgery all use this same principle. The difference is where the transparent object is placed relative to the eye.
Glasses sit about 1 to 2 cm (less than an inch) in front of the eye. Contact lenses sit directly on the surface of the cornea. Surgery changes the shape of the cornea itself or adds a lens inside the eye. As we move from the outside to the center of the eye, the tools get closer to where the light is bent.
2. What Materials Are Glasses Lenses Made Of?
Glasses use concave lenses for nearsightedness and convex lenses for farsightedness. But what are these lenses made of? Long ago, glasses were made of glass. Glass is heavy and breaks easily. People with strong prescriptions had thick, heavy lenses [2].
In the 1940s, a plastic called CR-39 was developed in the United States. By around 1946, it was being made into glasses lenses in large numbers [2]. In 1947, a company in California made the first CR-39 lenses. These plastic lenses were about half the weight of glass and harder to break [3].
In 1972, safety standards in the United States changed, making impact-resistant lenses more necessary [2]. Today, most glasses lenses are made of plastic. This history shows how changing materials helped address the problems of weight and breakability.
3. Do Glasses Make Your Eyes Worse?
Many people worry that wearing glasses makes their eyes worse. However, glasses only change the path of light outside the eye. They do not directly change the length of the eye or the shape of the cornea and lens [1].
The International Myopia Institute (IMI) reported that there is no evidence that wearing glasses with a weaker prescription (under-correction) slows down nearsightedness. In fact, it might make it progress faster. The Japanese Society of Ophthalmology lists spending long periods looking at near objects, like smartphones or computers, as a cause of vision changes, not the act of wearing glasses itself [4].
There is no evidence that putting glasses on and off harms the eye. Glasses are just tools that bend light through a lens. When you take them off, the effect simply stops. The action of wearing or removing them does not change the shape of the eye.
4. How Contact Lenses Sit on the Eye and Help You See
The first records of contact lenses go back to the 1880s. Doctors in different places tried placing lenses directly on the eye. A Swiss doctor named Fick created a glass lens larger than the eyeball and placed it over the white part of the eye. Glass was heavy, and the cornea could not breathe, so people could only wear them for a few hours [2].
In the 1930s, a plastic called PMMA appeared. It was lighter and harder to break. However, it did not let oxygen pass through. The cornea has no blood vessels and gets oxygen from the air. Hard plastic blocked this, causing oxygen shortage [5].
A Czech chemist named Otto Wichterle [7] broke this barrier. He and his research partner Lim developed HEMA, a material that becomes soft when it absorbs water, in the late 1950s [2]. The challenge was shaping it. On Christmas Day in 1961, Wichterle used a toy construction kit and a bicycle light generator in his kitchen to build a machine. With his wife, he made the first soft lens that day [6][14]. He put it in his own eye. The prescription was wrong, but it felt comfortable [6].
These soft lenses were sold worldwide in 1972 [2]. In the late 1990s, silicone hydrogel lenses arrived. They let more oxygen through, reducing stress on the eye [2]. Contact lenses float on the thin film of tears on the cornea. Eyelids and surface tension hold them in place. Because they sit on the cornea, the light is bent right at the eye's surface [2].
5. How Special Night-Time Contact Lenses Work While You Sleep
Some contact lenses are worn only at night. This method is called orthokeratology. It uses hard lenses with a gentle curve [9]. While you sleep, the lens gently presses the center of the cornea. The cells on the cornea’s surface rearrange to match the pressure, making the center slightly flatter [8].
When you wake up and remove the lens, the shape stays for a while. During the day, you can spend time with less blurry vision, without glasses or contacts [9]. However, this change is temporary. If you stop using the lenses, the cornea returns to its original shape in a few days [8].
This method was approved in the United States in 2004 and in Japan in April 2009 [8]. It works for mild nearsightedness, usually up to about -4.00 diopters. Because it presses on the cornea, strict care is needed to prevent infections, which can affect vision [9].
6. How Laser Surgery Reshapes the Eye to Fix Vision
In the 1970s, researchers at IBM in the United States were studying an excimer laser. They found it could remove very thin layers of organic material without burning them [10]. Eye doctor Stephen Trokel from Columbia University saw a use for this. In 1983, he and IBM researchers used the laser on cow corneas, showing it could shape the cornea precisely [10].
Today, LASIK is a common method. A femtosecond laser creates a flap on the cornea surface. This flap is lifted, and an excimer laser reshapes the tissue underneath. The flap is then put back [11]. After surgery, the cornea is thinner than before [11].
A newer method is SMILE. A laser cuts inside the cornea, and a small piece of tissue is removed through a tiny 2 mm (about 0.08 inch) incision. This is much smaller than the 20 mm (about 0.8 inch) incision in LASIK. Because fewer nerves are cut, eyes may dry less [12]. It was approved in Japan in March 2023 [12].
Both LASIK and SMILE remove corneal tissue, so the change is permanent. Another option, ICL, adds a soft lens inside the eye, behind the iris and in front of the natural lens. It uses a 3 mm (about 0.12 inch) incision and the lens can be removed [13]. Whether removing tissue or adding a lens, both methods fix vision by changing different parts of the eye.
7. Experiments You Can Try at Home to See How Light Bends
You can try the straw-in-water experiment at different angles to see how the light bends. You can also look through a magnifying glass to compare how distant scenery and nearby text appear.
If you know someone who wears glasses, contacts, or had surgery, ask them about their experience. However, do not try on someone else’s glasses or lenses. The wrong prescription can put a strain on your eyes.
For more details on LASIK, SMILE, ICL, and orthokeratology, check the websites of the Japanese Society of Ophthalmology or the Japanese Society of Myopia. Always talk to an eye doctor to decide which method is right for you.