how many cells are in your eyeballs?

Question: how many cells are in your eyeballs?

Asked by n0tty1997 to Daniel, Jon, Louise, Sharon, Zoe on 22 Jun 2010 in Categories: General.
- Louise Dash answered on 22 Jun 2010:
  
  I have no idea! But we can use physics to guesstimate it:
  
  If an average cell is 50 micrometres (50 x 10^-6 m)long and we assume it’s spherical, then it has a volume of 4/3 x pi x (25 x 10 ^-6)^2 = 2.6×10^-9 cubic metres.
  
  If your eyeball has a diameter of 3 cm and is also spherical, then its volume is 4/3 x pi x (0.015)^2 = 9.4 x 10^-4 cubic metres.
  
  If we now assume that the eyeball is full of cells, and that the cells can squish up so that they fill all the space (which I don’t think they do, there’s lots of water and stuff in there too!) then we can fit
  
  9.4 x 10^-4 / 2.6 x 10^-9 = 360,000 cells into an eyeball.
  
  It must be less than this, because the eyeball doesn’t consist completely of cells (hopefully a biologist can tell us what’s in there!) so this is my guesstimate of the upper limit of the number of cells in an eyeball.
- Sharon Sneddon answered on 22 Jun 2010:
  
  Wow, that’s a tricky one. I don’t know for definite about all the parts of the eye. Thinking logically tho, it should be easy to estimate.
  
  There are 3 main parts to the eye, The external layer, formed by the sclera and cornea. The intermediate layer, divided into the, iris and ciliary body and choroid and then the the internal layer, or the sensory part of the eye, the retina
  
  The rest of the eyeball is made up from fluid filled chambers, and these don’t tend to have blood vessels and cells, as we need the fluid to be clear so we can see!
  
  I know that there are about 1.2 million nerve cells in the optic nerve and there are 6 million cone cells in the retina, and 120 million rod cells.
  The retinal pigment epithelium (RPE) is a single layer of cells, and there is thought to be 1 million cells. We also need to factor in blood cells and other epithelial cells as well as all the muscle cells in the eye, so I’d guesstimate that at being another 10 million ish.
  
  so my guess would be about 140 million cells ( I may be way out here, will get back to you if I find I’m wrong!!)
- Jon Copley answered on 22 Jun 2010:
  
  I have no idea, but let’s try a guess…
  
  The eye is made of three layers of tissue (and then the bit in the middle is jelly, or watery stuff in the bit at the front, so that light can pass through it to the rod cells and cone cells at the back).
  
  The eyeball is around two-thirds the size of a ping-pong ball, so it has a surface area of roughly 2000 mm2. The density of cells in tissue is something like 4000 cells per mm2. So if we assume that cell density for each layer of tissue in the eye, then that’s at least 8 million cells in each layer, and three layers then gives us at least 24 million cells in each eyeball. And I imagine that it’s probably a lot more than that, because some of the cells are quite small (so the 4000 cells per mm2 may not be quite right), and there are some other tissues connected to them as well.
- Daniel Richardson answered on 22 Jun 2010:
  
  Not sure how many cells in total. But the interesting ones are the photoreceptors – the ones that sense light and turn it into brain signals. There are roughly 150 million of them. Your phone might be around 5 megapixels – perhaps you can think of your eye like a 150 megapixel camera then. But the really interesting stuff is why you eye is not at all like a camera….

Question: how many cells are in your eyeballs?

Comments