Posts by www.changemyeye.com
How Does The Human Eye Actually Work?
What Is Heterochromia Iridum?
Glasses or Contacts: Which are better for helping your vision?
Some people choose the convenience of glasses; depending on your prescription, you can wear them only when driving, or reading, or whatever your vision care specialist advises. But you can have different ones with the same prescription, and tailor the frames to your winter, fall, spring and summer wardrobes. Different colors and styles can make you look serious, fun or fashionable; it’s all up to you these days.
How Colored Contact Lenses Work
Blue Light, Is It Bad For Your Eyes?
Unlocking The Potential Behind Your Eyes
Does eye color affect the way you are perceived?
What does 20/20 Vision mean?
20/20 is basically defined as you can see at 20 feet what a “normal person” can see at 20 feet. 20/40 means you can see at 20 ft what a “normal person” would see at 40 ft.
If we get more in depth, 20/20 vision is actually talking about the resolution of the human eye, the 20/20 E famous on the snellen eye charts are actually very specifically sized such that each black line or white space in between is 1 arcmin of angle subtended from your eye. Therefore, resolving a 20/20 E lets you know that you can see 1 arcmin of resolution. 20/40 essentially means that the resolution you can see is 2 arcmin (smaller resolution is better).
In reality, our limit coming from the size of the rods and cones should be closer to 20/10.
Believe it or not, our eyes actually have quite a lot of optical aberrations, some (like astigmatism/defocus) which can be easily corrected with contacts or glasses, but others cannot. These difficult to correct aberrations can be known as higher order Aberrations (HOAs), which are usually relatively low compared to defocus and the larger lower order aberrations that can be corrected. For the most part, HOA really don’t affect our vision that much and lots are image processed out by your brain so you don’t really notice them, yet these with some parts of the uncorrected lower order aberrations make it so you are unable to reach 20/10 vision.
With an adaptive optics system, we are able to measure the wavefront aberration in your eye in real time and correct it with a deformable mirror which changes thousands of times a second to correct the wavefront. This effectively removes all the aberrations in your eye giving you almost perfect vision (~.01 microns rms) which enables people to see with 20/10 vision.
It is not called 100% vision because 100%, 90% ect vision would not really fit what is being measured. having “fully 100% vision” doesn’t really tell you what the resolution is, while 20/20, 20/40 ect does.
Going into stronger detail, the term 20/20 is a measure of visual acuity. This notation is now only used in North America, while Australia and New Zealand uses a 6/6 notation.
These figures are based on letter charts which are used in the standard sight test, such as the Snellen chart. The top number refers to the distance at which the chart is viewed – 20 feet (or 6 metres) – and the bottom number refers to the distance at which a person with ideal vision can see a letter clearly. Thus if you have 20/40 (or 6/12) vision then you will just be able to see something from a distance of 20 feet that a person with perfect eyesight will be able to see from 40 feet.
How the Eye Works: The Anatomy of The Human Eye
After surveying multiple people on www.changemyeye.com regarding the most important human senses — sight, hearing, taste, smell and touch — people consistently tell us that their eyesight is the mode of perception they value (and fear losing) most. However, most people don’t have a good understanding of the anatomy of the eye, how the eye works, and health problems that can affect the eye.
HOW THE EYE WORKS
In many ways, the human eye works much like a modern day camera:
- Light is focused primarily by the cornea — the clear front surface of the eye, which acts like a camera lens.
- The iris of the eye functions like the diaphragm of a camera, controlling the amount of light reaching the back of the eye by automatically adjusting the size of the pupil (aperture).
- The eye’s crystalline lens is located directly behind the pupil and further focuses light. Through a process called accommodation, this lens helps the eye automatically focus on near and approaching objects, like an autofocus camera lens.
- Light focused by the cornea and crystalline lens (and limited by the iris and pupil) then reaches the retina — the light-sensitive inner lining of the back of the eye. The retina acts like an electronic image sensor of a digital camera, converting optical images into electronic signals. The optic nerve then transmits these signals to the visual cortex — the part of the brain that controls our sense of sight.