(This is Part One in a series of posts about the state of my vision at the start of this blog. The next post will deal with my personal experience of my vision. There’s a lot of technical medical information in this post, but I’ll try not to make it too boring.)
I have had very poor eyesight since birth—poor enough that I was deemed “low vision.” I got my first pair of glasses before I was two. No one could identify exactly what was wrong with my eyes, though, and not for lack of trying. My parents carted me around to practically every expert in the state of Colorado, and none of them could provide an answer. To all appearances, my eyes were perfect; I just couldn’t see well. The closest approximation of the truth was probably given by Dr. Alexander, my favorite childhood optometrist, who said “You may just have been born with fewer cones and rods [retinal photoreceptors] than other people.”
For the first thirty years of my life, this was about all that could be said about it. My vision was poor, but it seemed at least to be stable. In 2012, though, while I was working at an archaeological excavation in Israel, I started to notice strange visual phenomena that prompted me to visit an ophthalmologist when I returned home to Massachusetts. This ophthalmologist gave me a preliminary diagnosis of Retinitis Pigmentosa and referred me to the Massachusetts Eye and Ear Infirmary for confirmation.
The doctors at MEEI took high-res photographs of my retinas and subjected me to a battery of tests, including color discrimination, visual fields, dark adaptation, and the notorious ERG. The ERG, or Electroretinograph, measures the electrical activity of your retina (like an EKG for your eyeball. You put on a giant contact lens with electrodes implanted in it, and stare at a strobe light for what feels like an hour (probably five minutes). People with healthy eyes produce a graph with a nice wave of ups and downs. Mine? Flatline.
A flat ERG response is the hallmark of advanced Retinitis Pigmentosa. There’s no measurable electrical activity going on in the retina, but most of us can still see to some extent. As the doctor told me, “it’s like there are people who don’t register a pulse, but they’re still up and walking around.”
So what is this strange form of retinal zombiism known as Retinitis Pigmentosa?? There’s a boilerplate description that appears with a little variation across the internet, and goes a little something like this:
Retinitis Pigmentosa (RP) refers to a group of inherited diseases causing retinal degeneration. The cell-rich retina lines the back inside wall of the eye. It is responsible for capturing images from the visual field. People with RP experience a gradual decline in their vision because photoreceptor cells (rods and cones) die.
(I took this version from the article at http://www.blindness.org/retinitis-pigmentosa — the rest of the article is quite good also, and the Foundation Fighting Blindness is an excellent resource for learning about retinal disorders and new research)
Photoreceptor death explains the diminished ERG response. Fewer cells means less electrical activity, and a weaker signal traveling from the eyes to the brain. You can imagine these photoreceptor cells as the eyes’ “pixels”—the fewer there are the less detail there is in the image. Healthy eyes contain over 120 million photoreceptors—way too many for the optic nerve and brain to handle at once, so much of the signal is just discarded. For people with RP, vision loss only begins once the number of photoreceptors falls below the maximum number the brain can interpret at one time.
Graph of photoreceptor loss in RP
This explanation is a bit simplistic, since degradation does not occur evenly across the visual field. Most people with RP develop dead spots in some areas of their vision, while other areas remain relatively clear for much longer. In the majority of patients, degeneration happens from the outside of the retina in. They lose their peripheral vision and night vision first, and only lose their central vision in the final stage of the disease.
Since my vision has always been poor, I was probably born with a reduced number of photoreceptors across the board, as Dr. Alexander surmised so many years ago. That means my graph might look more like this:
Graph of how I imagine my photoreceptor loss
Now more of my photoreceptors are dying, but not in the usual pattern. I am losing cells from the center of my retinas outward. My detailed central vision is going first, and the periphery will follow.
It may seem strange that I stray so far from the norm, but this leads to an important point: RP is not one disease, but many.
When I first started seeing that standard description of RP four years ago, it did not mention a “group” of inherited diseases, but in the past several years it has become very clear just how many forms RP can take. It can strike at any age, progress at any speed, and carry with it a number of other symptoms. Some of the nastier varieties, like Usher’s Syndrome, cause deafness as well as blindness. They all culminate in the death of photoreceptors, but can differ substantially in how long this takes and the path they take to get there.
The variety in RP patterns probably results from the variety of its causes. It is commonly considered an inherited genetic disorder, but the details get pretty complicated. Genetic testing of RP patients has linked the disease to mutations in more than 250 genes at this time, and that number keeps growing. Certain mutations are quite common and well-understood, while others are rare and more tenuously linked to disease symptoms.
With this many genetic links identified, it is a startling fact that the genetic cause of RP cannot be determined in about 45% of patients. Almost half of patients’ RP is caused by either an unidentified genetic factor or something else entirely. This is my lot—despite the cutting-edge genetic testing I received from the Ocular Genomics Institute in Massachusetts, a genetic cause for my RP has not been found.
It is possible that an as-yet-unidentified gene mutation or combination of gene mutations is causing my vision loss, but it could also be something completely unrelated to genes. No one else in my extended family has suffered from any similar malady, which points away from an inherited cause. It could have been some accident of development in the womb, a vascular event that starved my retinas of oxygen or nutrients at a critical moment. At this point, who knows?
So have I learned anything from being diagnosed with RP? I have confirmed the suspicion that I don’t have enough photoreceptors, and have learned that more are dying every day. I’ve learned that this condition is progressive, and my vision will continue to deteriorate. I have passed the boundary into legal blindness, and without medical treatment I will end up totally blind at some point in the future. This won’t happen right away—my last photoreceptor may not blink out for another twenty or thirty years— but with the current state of technology, it is inevitable.
So it’s a good thing technology changes. This diagnosis has also clued me in to a world of exciting research on retinal deterioration and rejuvenation. There is nothing on the market right now that can halt or stop what is happening in my eyes, but research teams are working on treatments and cures using gene therapy and stem cells. All of these are still at least 5 to 10 years away from widespread deployment, but clinical trials are going strong. Hope may not be right around the corner, but it is on its way.
(Note: The information in this post comes from my research on the topic of RP and from personal conversations with retinal specialists, I am not an expert in the field, so there may be a few inaccuracies. I alone am responsible for all of them and I welcome corrections!)