(This is part two of a series on my vision at the start of this blog. To read the first part, see My Vision in Medical Terms.)
In the last post, I described how my photoreceptor cells are dying one by one and in turn taking with them what remains of my vision. I wrote that photoreceptors are like the “eye’s pixels,” and some of you may have imagined that a retina full of dead photoreceptors looks like an iPhone screen full of dead pixels. It would be nice if that were the case, but the truth is much more bizarre.
The Low-Res Retina
The pixel analogy holds in one important respect: fewer cones and rods mean less detail, just as fewer pixels on a screen do. In a sense, I was born with lower resolution vision than most. Think of an old, first-generation color TV from the 1950s. Broadcast resolution was low, and the images that showed up on these sets were blurry and indistinct. In this analogy, people with normal vision are like the latest generation of iPad, which have about nine times as many pixels as a broadcast TV. The difference is stark.
Comparing retinal resolution is the concept behind the common method of expressing visual acuity as “20/xx.” This method compares the distances at which two people can see the same object. The first “20” represents the patient, or more precisely, text the patient can read from 20 feet away. The second number is the distance from which a normally-sighted person can read the same text. Since people with a higher resolution can see something clearly from further away, the second number is usually higher for RP patients.
The last time I had my eyes checked, about a year ago, my right eye (which is my better eye) had an acuity of 20/250, meaning I can read at twenty feet what a normally-sighted person can see at 250 feet. To put this in more concrete terms, if there was a sign on the goal line of an American Football field, and I could read it from the 10 yard line, a normally-sighted person could still read it while sitting in the stands behind the opposite goal post. Keep in mind that this is with glasses.
Mind the Gaps
Poor resolution isn’t the only problem with my vision. There are also the gaps left by groups of dead photoreceptors. On a phone screen, dead pixels don’t give up their spot. They leave little black squares, constant reminders that there is a small part of the image you cannot see. The brain, on the other hand, doesn’t much like admitting there are gaps in your vision. It tries to fill in these gaps as best it can to create a cohesive picture of the world.
Have you ever tried that experiment where you use your finger to find your blind spot? You close your left eye and stare at a dot or letter or something on a piece of paper. Then you put a finger on the dot and slowly move it to the right, while keeping your eye on the dot. When your finger gets an inch or two away from the dot, it disappears!
This happens because everyone’s retinas have a barren spot with no photoreceptors where the optic nerve leaves the back of the eye. Your brain doesn’t like to let on that it’s missing anything, though, so usually it fills in the hole with the image from your other eye. Even when one eye is closed, you don’t see a big blank space, Your vision seems continuous; your finger is just missing.
Now imagine that, instead of one blind spot in each eye, you had a few dozen spread out across your visual field. Some are big, some are small, but your brain tries to hide them all.
I have a lot of gaps in my vision. In fact, my last visual fields exam said I had “central vision with peripheral islands,” meaning it might be more gap than vision. Most of these, my brain tries to hide from me. When I try to read long words with my eyes, some letters will often just not be there. I’ll have to look again or move my eyes slightly to see what I’m missing. The gaps across the bottom of my visual field explain my antagonistic relationship with “Wet Floor” signs, which have cause me much more grief than wet floors themselves ever have.
One hole has finally developed that my brain cannot hide. It is located near the middle of my vision in my left eye, probably spreading out from around the optic nerve. It looks like a smudge of something on my glasses, with blurry edges that fade into clearer vision. It is always there, but I think my brain still tries to hide it away. In the daytime it is white or light grey, but at night it goes dark. It’s not very good camouflage, but it still tries.
A screen with dying pixels fades into darkness, and many people think of blindness the same way, as vision fading into darkness. The Bard himself described “looking on darkness which the blind do see.”
Sorry Shakespeare, but going blind from RP is a constant chaos of color and light,
I mentioned some alarming visual phenomena in the last post, which I started to notice when I was working at an archaeological site in Israel. After a full day of digging in the blazing sun, we would go back to the air-conditioned hotel to wash up and eat. In the dim, cool room I would notice intricate, tightly-packed patterns that flashed and twinkled in my left eye. Sometimes it would look like the pattern of bumps on a basketball, sometimes like raindrops on glass. Other times it looked like a repeating tile mosaic, In every form, the pattern would flicker and flash brightly and gradually fade.
To this day, my left eye provides a near-constant psychedelic light show. The right has joined in, just a bit tamer. The patterns are still there, joined by other flashes, sparks, and twinkles. Electric whips crack across my vision. Fireworks blaze and pop, sometimes so large they blot out everything else. My entire field of vision strobes very quickly from bright red to bright blue, like I’m staring at flashing police lights from about six inches away. It must be a real party in there, because someone even turned on the smoke machine. Mist covers everything some days, like a thick morning fog.
The colors are brilliant, even beautiful, but of course it’s not a party. It is the anguished thrashing of half-dead photoreceptors, the aimless firing of bored and bereft neurons, the brain trying to synthesize an image when the signal is lost or senseless. It changes every day, every hour, every minute. I don’t know today what the world will look like tomorrow, this morning what it will look like in the afternoon, at 10 AM what it will look like at 10:05.
What I see—what I can and can’t see—is impossible to predict, difficult to communicate, and risky to trust. Vision is still useful, and many days I am grateful for what I have left, but it is not as useful as it once was, and far less dependable. I can no longer rely on my old ways of doing things. I have to change and adapt to keep moving forward through the mist and the fireworks..
Appendix A: Videos!
As I was writing this, Kristin reminded me of a video I had showed her that she found really helpful in understanding what RP looks like.
Aaron Morse made this video called “How I See the World with my RP Eyes” (bonus: cute baby!). His tunnel vision is a more classic pattern of RP than I have, but it gives a good general idea. Another YouTuber simulated some of the lights he sees in “My RP Visual Flashes.” I found it interesting that he too sees tightly-packed repeating patterns. Unlike mine, his are very angular.
(Photo credit: King-of-Herrings)