Joel Hunter, MD Refractive Surgeon, Hunter Vision Updated 10/31/18 12:10 PM
The human lens is the best it will ever be at eight years old. This fun fact—more of just a regular fact, really—is one I end up sharing with people multiple times a day. It’s because it is so relevant to the troubles people are having with their vision as they progress through their 40s and beyond. It helps to know the lens doesn’t just have a “become dysfunctional” switch that gets flipped one day after 40 years of perfection. It explains why an eight-year-old can read in almost total darkness and why they decide to hold their face six inches from the paper they’re writing on. It also explains why those tasks slowly become impossible over time.
First the lens loses enough flexibility for it to lose autofocus for near vision. This starts in teenage years but since the lens is so amazingly good at first, it takes a long time for the loss in autofocus to become noticeable. Namely, it takes losing autofocus past where our hands hold reading material. And so at that point, we need reading glasses or bifocals or to start lifting up our glasses to read. Sadly, that is only the first stop on the way to cataracts. Fortunately, that second stop—cataracts—also takes an incredibly long time to become noticeable.
The lens first becomes stiff and inflexible, but as it gets more and more dense over time, it also starts to become less transparent. It starts to steal light by filtering too much of it out. It also starts to diffuse and scatter light because it becomes less clear.
These two specific phenomena of increased lens density are the cause of the two main symptoms of cataracts.
• First, a lens that steals light will only get caught doing so when there isn’t enough light to push through the lens. That’s rarely a problem when driving on a bright, sunshiny day. It’s often a problem when trying to read under any lighting condition that isn’t perfect. If you’ve ever said, “I can read fine, I just need a lot of light,” then it’s almost certain you’ve uttered those words because of the cloudiness of the lens inside your eye. Difficulty reading in low light is one of the number one symptoms of cataracts.
• Second, a lens that scatters light will get caught doing so when there are distinct, singular lights to scatter against a dark background. This is the situation we face when we are driving at night and have streetlights and headlights cast against a pitch-black background. The glare, starbursts, and halos of night driving are almost always because of increased cloudiness and light scatter in the lens. This is the other number one symptoms of cataracts.
Low-light reading and difficult driving at night are usually how you know you’re getting cataracts. The reason for this article’s long journey of explanation to get there is how important the gradual nature is in understanding cataract symptoms. If you told an eight-year-old kid to try and notice when he’s getting taller over the next ten years, hopefully he’ll ignore you because his parents taught him to avoid adults with weird riddle questions. But the point is no kid can tell he’s getting taller. It is imperceptibly slow.
The same is true with cataracts. No day is different from the day before, but each year is absolutely different from the one before it. So, if you keep in mind the idea of difficulty with low-light reading and night driving, it may at least help you notice before it gets more frustrating than it needs to. And the same way no teenager thinks to say, “today, I have become tall,” you’ll not find a day you declare the same of your cataracts becoming terrible. You just have to look for the day when you realize there are things you’d like to do that you can’t do as well as you’d like because of your vision. The good news is the moment you’ve declared the problem is the same moment that you’re ready for the cure!