We, as humans, often take for granted how much we rely on vision to gather critical pieces of information. Information that allows us to properly comprehend all that is happening in the world we’re in. Neglecting its importance is a complete oversight, pun intended. We rely so much on what we see to determine our reality that we regularly fall into the trap of optical illusions (stay tuned for an upcoming post). Then, questioning what we see becomes primordial. But first, we need to establish how this sense works. It will come to you as no surprise to learn that the organs responsible for sight are the eyes. Those delicate globular organs are the product of many parts, all working together, enabling us to detect light and its many properties.
Light is a form of energy called electromagnetic radiation that travels as waves. Only a portion of electromagnetic radiation, found within the visible light spectrum, can be seen through our eyes. This spectrum includes any wavelengths between 400 nm and 700 nm, 400 nm associated with blue light and 700 nm with red. Wavelengths certainly exist beyond that range, but we are unfortunately unable to see them through our naked eyes. We consider any shorter wavelengths (10–400 nm) to produce ultraviolet lights and longer waves (700 nm-1mm) to generate infrared lights. All of the invisible light might escape our natural perception, but beware that it is far from useless.
We deal with those wavelengths every day. Ultraviolet is an aseptic agent (kills bacteria), but it is also used as a tanning agent for tanning beds. Actually, there is a logic behind this second example. The Sun is a massive emitter of ultraviolet light, commonly referred to as UV light (UV). It is that invisible light that is responsible for you getting that sun-kissed skin you so desire. However, that same light is also what is responsible for so many new cases of skin cancer. The risk associated with UV light exposure is the reason why we all need to protect against it. We must continue or, at the very least, start using proper sun-blocking agents like sunscreens covering against both UVA (UV type-A) and UVB (UV type-B).
We can find infrared light often used in night-vision cameras, remote controllers, infrared astronomy and fibre-optic cables. These application examples might make it sound as if infrared was totally harmless, but it is sadly not. Infrared is responsible for the greenhouse effect, i.e. getting the Earth warmer than it should or would be. The greenhouse gases are efficiently trapping infrared light near the Earth’s surface. The more greenhouse gases (like carbon dioxide, nitrous oxide, methane and ozone) we release, the greater the heat produced through the greenhouse effect will be.
On a more positive note, let’s come back to how our eyes can perceive all that visible light. When light reflects back into our eyes, it first hits the cornea. It is a transparent part of our eyes forming a dome, which serves as the primary and most important focusing power. However, despite being so impressive, it lacks something that only the lens has, an adjustable focus. The cornea focuses on the pupil (the dark spot at the centre of our eyes). To control the amount of light passing through the pupil, the iris (the colourful circle in our eyes) will stretch to let more light in (for darker conditions) or shrink to block some (for lighter conditions).
For the next part, if we try keeping things as simple as possible, we may say that the light goes directly to the retina. The retina is a light-sensitive layer of tissue containing photoreceptors known as cones and rods. The cones are wavelength-sensitive which means that they are in charge of colour perceptions. They are also responsible for high acuity vision, and they work best in well-lit conditions. In obscure conditions, the rods are particularly helpful as they still can provide us with a black and white vision. Once the photoreceptors detect lights, it triggers an electrical signal which will travel to the brain via the optic nerves.
So, as I said previously, this is a simplified version, so let’s complicate the matter a little more. Before reaching the retina, the light passes through a structure called the lens, which converges (or focuses) the light on the retina by refracting it. The lens connects to suspensory ligaments that can control its curvature changing its focal range. This process is called accommodation and leads to the creation of a sharper image. However, once the light gets past the lens, it is not quite yet at the retina. The light has to swim through a transparent liquid, the vitreous humour. This substance is helping to maintain the shape of the eye and protects against sudden shocks. Now that the light has finally reached the retina, it must hit a particular spot to produce a crisp image, and that spot is called the macula. In the absence of an eye disorder, the lenses will manage to focus an image onto the fovea found in the macula. The fovea is the region of the retina where the cones are at their highest confluence. Finally, there is one last eye part, and it doesn’t seem to provide as much value for sight. However, it appears to be very precious for communication. That part is the sclera, the white part of our eyes.
All these parts work in unison as do musical instruments of a symphony. Without one, the others cannot function appropriately. For its maintenance, the eye has a cleaning and lubricating agent mostly referred to as tears. Yet sometimes, tears are not sufficient to resolve some situations we may face. It is unquestionably the case of people affected by eye disorders, like nearsightedness (myopia) or far-sightedness (hypermetropia). These disorders commonly occur when the axial length of the eye is respectively too long or too short. Nonetheless, they could also result from an anomaly regarding the lenses’ shape or failure to produce suitable accommodation.
These two disorders are inducing refractive errors. Yet, they are not the only ones; presbyopia and astigmatism also produce refractive errors. Presbyopia mainly occurs when ageing, the lenses weaken and are thus less able to adjust or accommodate. As for astigmatism, I can speak from my own experience. I was first diagnosed with astigmatism three years ago. If we could all omit this slight astigmatism, my vision would be pretty much 20/20; I have no sign of near or far-sightedness, and my eyeballs are neither elongated nor short. Yet my sight is somehow blurred when I am looking from both close and far distances. This blurriness causes strain to my eye, especially when I have to focus heavily on something. My main occupation at present is reading. And thus, I am regularly using prescription reading glasses for extended reading. It is the only moment I need glasses. That blurriness comes from light not being evenly distributed on the retina. This situation can arise from an issue with the lenses or the cornea.
Luckily for us, all these disorders have the potential to be treated through laser surgery. Even though I have decided that it wasn’t necessary as my current glasses suffice me. I still keep in mind that although laser surgeries are becoming safer and safer, there will still forever remain some risks. With reading glasses, those risks naturally don’t exist. Let’s say that I’m not against reconsidering this option if my situation worsens; it is still an exceedingly attractive procedure. But right now, I have honestly no incentive to go along with it. What about you? If you had the opportunity to opt for laser surgery, would you do it?
I thank you infinitely for reading this post and if you would like to know more about the mysteries that surround us, please join my subscription list to keep up with my newest content. If you have any questions, please add them to the comment section and I’ll make sure to answer as soon as humanly possible.
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