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Crystalline Lenses: Nature's Choice of Optics
Crystalline Lenses: Nature's Choice of Optics
The crystalline lens changes shape to accommodate near or far targets.
The lens in our eyes is made up of 60% protein. The tissue is transparent, which allows light to easily enter the eye. It’s also flexible, so it can change shape and bend the light to focus properly on the retina. Today, to mimic this function, scientists and experts created something called liquid lenses.
There are two main theories for how the lens changes shape.
Helmholtz theory – When the ciliary muscle contracts, all zonular tension is reduced. This permits the central lens surface lens to become rounder (increases its focusing power). When the ciliary muscle relaxes, all zonular tension is increased, causing the lens to flatten (decrease in optical power).
Schachar mechanism – When the ciliary muscle contracts, equatorial zonular tension is increased. This causes the central lens surface to become more steeply rounded (increases central optical power). When the ciliary muscle relaxes, equatorial zonular tension is reduced, causing the central lens surface to flatten (decrease in optical power).
Contact Lens Materials
Contact Lens Materials
In 1948, the first plastic contact lenses were introduced, and they were made of a material called polymethyl methacrylate. These were hard contacts similar to the modern rigid gas permeable (RGP) contact lenses available today, except that they did not allow for the transmission of oxygen.
Physics Behind Lens Technology
Physics Behind Lens Technology
Refraction:
Refraction:
Refraction is the redirection of a wave as it passes from one medium to another. It is caused by the wave's change in speed, typically because of a change in the medium.
Refractive Index:
Refractive Index:
The numerical value of the light bending ability of a substance.
1 is the refractive index of a vacuum, and lower the refractive index, the lower-density the medium is, and higher the refractive index, the medium is high-density.
Snell's Law
Snell's Law
Snell's law is a formula used to describe the relationship between the angles of incidence and refraction. The angle of incidence is the angle formed between the perpendicular line of the surface and the light ray going in. The angle of refraction is the angle formed between the same perpendicular line and the light ray that's going away from the surface. With this formula, we can either get one of the angles or the refraction index of the medium.
n1= incident index, n2= refracted index, Theta 1= incident angle, Theta 2= refracted angle
Curved Surface Refraction Formula
Curved Surface Refraction Formula
For a spherical lens especially, because when the light ray comes out, the light ray refracts one more time, it is important to run the equation 2 times.
The next equation will be
This formula is going to be used to calculate the focus point of the lens.
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