Retinitis Pigmentosa and Optic Neuritis

00:00 Alright, let's return to diseases of the posterior segment, and we're going to be talking here now about retinitis pigmentosa. Retinitis pigmentosa is actually a disease that we don't completely understand and for those of you who have a future in ophthalmology this is a really interesting disease to address. We don't have good ___ models for example and it is something that can be devastating because once it starts, we don't have any really good therapy for it. So what's going on in retinitis pigmentosa? You're looking at someone's hallucinatory way of thinking about rods, the tall, kind of rectangular ones and cones that look like a comb that's in a triangle. Those are rods and cones. And they have all the various nerves connections. There is the retinal pigmented epithelium that's up on top. So that's a kind of brown, beige layer up on top. And what happens is that there is a genetic mutation that occurs, it's germline, in the rod photoreceptors or in genes of the retinal pigmented epithelial cells and we know some of these mutations, but we don't completely understand why they drive the final product. And the final product is we start getting death or apoptosis of the rods, rods go first typically. And then we will lose the cones. So night vision will go first and then color vision will go, but there is loss of visual acuity and it's a progressive degenerative process driven by a variety of mutations and we still don't know all the mutations. But we will eventually lose the ability just to perceive light. And that's devastating because we have no way right now to replace that, even stem cell therapies can't at this stage of our understanding, reliably replace the rods and cones that we lose. So, the signs and symptoms associated with retinitis pigmentosa, loss of night vision is first. So you get night blindness. That's because you're losing the rods. And then you have glare sensitivity.

02:13 And this is because probably as the cells die, as they are dying they're undergoing apoptosis, it takes not very much to get them to fire and they may send off neuronal signals with very little kind of stimulation. So there may be an increased sensitivity even though you're losing night blindness. In the process of the cells dying, you may have a transient period of sensitivity. Once you had lost rods, you start losing cones and then you have defects in the perception of contrast and color. In the early stages, you tend to have normal central vision. So, because you have a higher density of cones in the macula and particularly in the fovea, your central vision tends to be preserved better earlier, but eventually those cells will also fall prey to whatever is driving the apoptotic death of the rods and the cones. And then there will be initially severely impaired peripheral vision, so becomes tubular in advanced stages in only the macula and fovea, but even then with time the macula and fovea will also be involved. We're looking at a fundoscopic image of what is going on or what a severe end-stage eye looks like in retinitis pigmentosa and in fact you can see why it was called pigmentosa, because of all the pigmented changes that are going around on the periphery.

03:42 So the optic disc, which is being indicated here, becomes pale and waxy and this is because we are changing not only are we losing rods and cones but we're altering slightly the vascularity too. The retinal pigmentary changes are in part because we no longer have rods and cones blocking the retinal pigmented epithelial cells, so we're beginning to see those better. And again, it's in the periphery. And then we will have thinning and atrophy of the retinal pigmented epithelium as a late stage. The arteries, again it's not just exclusively rods and cones, it's not just the neural component, but with time we will also see changes in the vasculature in the mechanisms by which this is occurring are not well understood.

04:35 Finally, we're going to talk about optic neuritis. So this is inflammation specifically of the optic nerve. We're looking from the top in an MRI of a patient who has optic neuritis and the orbits at the front, you can see the eyeballs at the front, brain at the back, brainstem right in the middle. And the very prominent whiteness behind the orbits of the eyes is inflammation, increased edema, increased water, that's how we're seeing it on MRI around the optic nerve. So the optic nerve is the thin kind of black stripe on both sides and then we have impressive inflammation. Causes for optic neuritis include multiple sclerosis. That's probably the most common cause. So a demyelinating disease of the central nervous system, in fact the optic nerve is part of the central nervous system. So, we can have inflammation that's associated with that. Infections both viral and bacterial specifically tuberculosis can be a cause of optic neuritis. And then, we can have various toxic etiologies. And ethambutol used to treat for example tuberculosis won't always cause optic neuritis in everyone who takes it, clearly, but in a subset idiopathically, idiosyncratically it will. So, you can have various causes but MS is probably the most common cause. So what are the signs and symptoms? Well, imagine that you've got all the neural input coming in to the eye and now the main highway bringing that information to the visual cortex in the back of the brain is being inflamed. We are probably not going to have perfect nervous stimulation, nervous innervation going down that highway because of that so we're going to see decreased or blurry vision. We're going to see very poor contrast vision because the discrimination from the input from various rods and cones is going to be lost to some extent. You're going to have abnormal color vision, discromatopsia kind of like saying that, but just say abnormal color vision and you can see an example of that here. And, because there are sensory nerves in that location, the more and more inflammation you get you can have ocular pain and the ocular pain will be worse with eye movement, not so much body movement but eye movement as you're moving kind of the orbit up and down and putting traction on that optic nerve.

07:09 What do we see as a result of this? What we are seeing primarily is blurring of the optic disc, this is due to edema in that location again, kind of what we expect to see with inflammation.

07:21 And the pallor is again as edema increases we're going to compress some of the vasculature that is coming in and out. So the fundoscopic exam has that appearance. And with that, we've covered 3 additional entities that affect the posterior segment of the eye and have identified at least 1 that we would love to have you solve, retinitis pigmentosa. Thanks very much.