When the ciliary muscles relax the eye lens becomes thin which ""increases"" its focal length and ""decreases"" its curvature but how is it possible because R= 2f?
Answers
I had laser eye surgery a decade ago, but in recent years my eyesight has become significantly myopic. I consulted an ophthalmologist to see if this was eye strain because I work at computers a lot, or part of a natural degradation of the eye over time, or both. My ophthalmologist seems to believe that in my case I'm youngish enough that the natural degradation with age is minimal, and that it's mostly eye strain that is my problem. She believes I can get my eyesight back to roughly 90% of my post-surgery sight ability, if I can reduce eye strain. She gave me some eye drops to help with dryness, and recommended various ways to for me to help my eyes recuperate.
I decided to look into eye strain to learn more about what conditions cause it and what can alleviate it. What I learned is that the lens of the eye needs to be flatter to accommodate focusing on far objects, and rounded to focus on near objects. The way the lens becomes flat is by using spring-like connective tissue called choroids that pull it taught. Attached to these choroids are muscles called ciliary muscles that stretch the choroids out when they contract. This action causes the choroids to stop pulling on the lens, and the lens will retract into a more rounded shape. So, when the ciliary muscles are relaxed, you can see far. When the ciliary muscles are contracted, you can see close up. This diagram from the York University website was the clearest explanation I have come across:
Thus, the reason for my current inability to focus on far objects is that so much focusing on close objects, mainly computer monitors, is straining my eyes. In order to regain the ability to focus on far objects, I need to reduce strain and allow the muscles to relax. If they relax, the choroids can pull the eye to the flatter shape needed to see far.
However, I can't reconcile that model with how I understand the mechanics of the other muscles in my body. If I go to the gym and run or lift weights, or in any way expose my muscles to work, they respond by getting stronger without sacrificing the ability to stop contracting. The muscles in my body don't lose the ability to relax, no matter how much I train them. I have never heard of anyone who worked out too hard or too long such that their bicep would remain in a permanent state of contraction.
In fact, in my experience, after a hard workout, it's impossible to prevent my muscles from relaxing and resisting doing more work. When I do a bicep curl at the gym, and I do it to the point that I can't lift the weight anymore, my muscle gives up and I drop the weight. Similarly, if I've spent a long time looking at close up objects, shouldn't my ciliary muscles give up, allowing the choroids to take over, making clear far vision the unavoidable outcome?
The idea that my ciliary muscles need to relax in order to see far also seems to contradict my personal anecdotal experience. Sometimes I am able to see far away, but I can't hold it for more than a few seconds. If I try to maintain focus on far objects for too long, I get an uncomfortable feeling in my eyes that is hard to describe, but it's a form of pain that forces me to give up. My vision goes blurry, and I can only see close objects again. If my bicep worked the same way, it would be as if it hurt to let my arm hang straight down with a weight, and the only way to alleviate it would be to raise the weight, which makes no sense. I feel like the effort is in seeing far, and that when I'm tired, I can only see close up.
It's not that the case that I think that all medical research on the eye has it backwards, it must be that there is some aspect of this that I am not seeing (pun intended).