How does drug injection into the eye save people from blindness?

TeachableMedicalNews article 05252022

Teachable moment in classrooms:

1. special senses chapter – location of macula lutea in the retina of the eye
2. special senses chapter – the photoreceptors rods and cones are in the retina
3. hemodynamics chapter – capillaries are the thinnest blood vessels
4. hemodynamics chapter – endothelial cell location in capillaries

The news item:  Recently a report appeared about a drug that restores eyesight:

New technology helps Georgetown veteran restore his eyesight

If you’re living with blurry vision, there’s a chance a new device can help you get your eyesight back without frequent visits to the doctor. The newly FDA-approved Susvimo implant helped one Georgetown veteran preserve his vision after being diagnosed with wet age-related macular degeneration.

The article states that AMD (wet, age-related macular degeneration) is the leading cause of blindness over the age 60, that this disorder is caused by growth and scarring of blood vessels under the retina, and that the drug-delivery implant has restored vision in 90% of the treated individuals.

So, Why Do I Care??  Blindness is a condition where a significant part of the eyesight is lost, and such loss has a severe negative impact on people’s lives. In the USA alone there are about a million patients with wet age-related macular degeneration, and without treatment most of them will go blind.

Plain English, Please!!!   First, let’s talk about how the structure called macula plays a role in our vision. When we say we see something, the image of that something has to be turned into a nerve impulse so our brain can tell us what the image looks like. When you take a selfie, your image is turned into electrical signal by your smartphone. In our eyes the cells called rods and cones turn any image into nerve impulses. Millions of rods and cones form a thin sheet, the retina, and that sheet is pushed against the inside of the back of the eyeball. The macula (macula lutea is the full name) is a small circle on the retina, and inside the macula very large number of cones group together. Because of the large number of cones in the macula, it gives us the sharpest, center portion of our visual field. So, when you look at your selfie, you can see the middle part of your face because of the action by the cells in the macula.

Second, let’s talk about what macular degeneration is. The rods and cones receive oxygen and nutrients from a thin sheet of cell called the retinal pigment cells. Any disruption of the retinal pigment cells means that the rods and cones will be starved of nutrients, and will die, or, in other words, degenerate. The disorder macular degeneration happens, because rods and cones in the macula die, and can not make nerve impulses about the center portion of our visual field. Patients with macular degeneration see a blurred or darkened center part of pictures. On a selfie your nose, mouth and eyes would be covered by with a grey haze.  Missing the center portion of the visual field make many activities in life, like driving a car, reading, cooking, shopping very hard.

Third, let’s talk about how the drug Susvimo works.  Wet form of macular degeneration happens when thin, unwanted blood vessels (capillaries) grow into the retinal pigment cell layer, and when those new blood vessels form a scar, that scarring disrupts the functioning of the retinal pigment cells, and causes the death of the rods and cones.  Unwanted blood vessels grow, because the endothelial cells in older blood vessels are told to divide by a protein factor called VEGF. Newly-made endothelial cells grow a new branch of a blood vessel, and that new branch grows into the retinal pigment epithelium.  The drug Susvimo sticks to VEGF, and stops it from acting on the endothelial cell. Imagine that VEGF is a running back rushing to the end zone, the endothelial cell.  Susvimo acts like defensive tackle preventing the VEGF from reaching the cell. As the result, VEGF can not instruct endothelial cell to divide, so no new branches will form. Susvimo acts best when it is injected directly into the eyeball, close to the blood vessels of the retina.