Teachable moment in classrooms:
- special senses chapter – layers or tunics of the eye
- special senses chapter – gross anatomical structures on the retina
- special senses chapter – microscopic layers of the retina
The news item: Recently the following report appeared online:
Eye prosthesis is the first to restore sight lost to macular degeneration
In a Stanford Medicine-led clinical trial of a wireless retinal prosthesis, people with advanced macular degeneration regained enough vision to read books and subway signs.
The article states that the PRIMA device is able to restore functional sight to people suffering from age-related macular degeneration which destroys light receptors in the retina. The article also describes that the device has a wearable camera part, and an implanted chip, and that 27 out of 32 patients have achieved 20/42 visual acuity.
So, Why Do I Care?? According to the US Centers of Disease Control age-related macular degeneration affect in the US 20 million people who are older than 40. The disorder robs the patients of their central vision, so they see everything with a blurry patch in the middle of it. Reading, using a smart phone, reading road signs, recognizing people’s faces become cumbersome. So, this disease is making life difficult for large number of people, and new electronics-based solutions are always welcome to augment the pharmaceutical-based treatments.
Plain English, Please!!! First, let’s talk about how the retina allows us to see images. The retina is the light-sensing layer inside our eyeball. Imagine a balloon that is being covered up with grape jelly, and the grape jelly is covered with a dishcloth. In that metaphor the dishcloth is the fibrous tunic, such as the sclera of the eye; the grape jelly is the vascular tunic, and the innermost layer, the balloon is the nervous tunic or retina. The retina itself has three layers to it, the deepest photoreceptor layer, and two layers of neurons on top of that. The retina is mostly a smooth layer, but there is a bump the size of a black pepper in the middle of it. The bump is called macula lutea, and in it we find a huge number of cone and rod type photoreceptors. The image focused by the lens and the cornea are projected onto the bump, and huge number of photoreceptors stimulate the neurons in the bipolar and ganglion layers to create nerve impulses. Just under the photoreceptor layer is the retinal pigment epithelium layer where oxygen and nutrients are transferred into the retina and the waste products are removed from the retina.
Second, let’s talk about what is malfunctioning in macular degeneration. Because of the very large number of photoreceptors in the macula lutea, this bump is the most sensitive part of the retina, and most visual information streams to the brain from there. In macular degeneration small