Am I nearsighted or farsighted?
To understand vision and how it works, let’s first talk about “perfect vision”. The eye is a unique little organ that utilizes physics (or as we like to say, optics) to help us see. The eyeball is a fixed length and it has different curved surfaces that bend light. In the perfect (or “plano”) eye, light (or the image we see) enters the eye and is bent perfectly to the retina. The retina is full of receptors that receive light and then send it to the brain to analyze and enjoy. That’s a lot of weird words, right? Let me give you something to visualize this concept:
EXHIBIT A: The Plano, "Perfect" Eye
Now don't judge my artwork, I'm an eye doctor... not an artist.
Here we have a little eye looking at a flower. When our flower is seen by the eye, our eye is the perfect length and shape to bend the image of the flower directly onto the retina without effort. Thus, it sees the image of a crisp flower.
EXHIBIT B: The Myopic, Long Eye
Nearsighted = You can sight (see) near, but not far
Now, the easiest of the vision problems to relate to or conceptualize is when someone can’t see far away. Another common term that is used is myopic. In a myopic eye, the length of the eye is longer than the perfect eye, and thus the image that enters the eye is bent in front of the retina. The blurred vision is a result of the amount of defocus cast onto the retina.
The longer or more irregular the eye is, the more blurred the vision becomes:
This might seem like an obvious comment, but someone who is myopic can effortlessly see things like phone without wearing glasses, but with glasses their eye require much more effort to see closely. This is because their eye is built to see close.
EXHIBIT C: The Hyperopic, Short Eye
Farsighted = You can sight (see) far, but not near
Now the opposite of nearsighted, means that the farsighted eyeball is usually shorter than the perfect eye. Another term that is used is hyperopia or hypermetropia.
But things get a little confusing to understand when a patient walks into the exam room who has a farsighted prescription. Why? Because most people who are farsighted can see both far and near… at least until that person turns around mid 30s. Why would age matter? Well, we need to add one more component of the eye that helps us see. Enter the crystalline lens (aka the natural lens or simply the lens).
The lens in the eye is a focusing machine. It is attached to a ring of muscles (called the ciliary muscles) that help change the shape of the lens to help focus anything close to us (think: within arms length). In our fancy ray diagram, this means bringing the image length toward the retina.
P.S. This same mechanism happens when someone with perfect vision or someone nearsighted has their glasses or contacts on and is reading their phones.
This summary is a simplified description of visual problems. Add in the issue of astigmatism (which we will go into later) and we will have covered the three types of basic vision problems. To complicate things, most people's vision follow these general rules until they gets to ~40 years old and then all the rules go out the window. Remember earlier when I mentioned the age issue? Why would "too many birthdays" make farsightedness more of an issue? Well, the lens of our eye changes over time and gradually (and predictably) loses it's ability to help us focus up close. Then most people start to experience blurred vision at both near and far. Not fair, right?
What's this all about, and how does an optometrist fix these problems? As a little teaser, I'll mention one little pearl of hope. Because this is an issue that effects all eyes (plano, nearsighted, and farsighted) there is a lot of research going into this natural aging deterioration. As of May 2022, there is one prescription eye drop available in the US market that can temporarily treat near vision blur (Think: No reading glasses) and several other options in the research pipeline. But more on this in a future blog post!
For any follow up questions, reach out to us at our clinic website: Ojosdelmar.com.