Why does light falling on portions of the retina where there are many receptors packed closely together?

Question

Why does light falling on portions of the retina where there are many receptors packed closely together (such as the fovea) produce sharp images? Why are no images recorded in the blind spot?

Answer 1

Images are sharper when the light is traveling straight into your eye as appose to an angle.  There are no images from your blind spot because the blind spot is where the optic nerve (carrying all the information about what you are seeing) is leaving your eye preventing any receptors from being located there.  But no worries, because we have two eyes are brains are able to fill in what goes there so we don't even notice unless we do one of those tests to find your blind spot.

Answer 2

More photoreceptors means greater resolution.  Think about your eye like a digital camera and photoreceptors as pixels.    A camera with a 10 megapixel sensor would take images 10 times sharper than a camera with a 1 megapixel sensor.  So the more densly packed your photoreceptors are the greater the resolution and sharper the image will be.

The area of the eye where the optic nerve enter the eyeball  has no photoreceptors on it.  This is caused by a quirk of evolution of the human eye and retina.  The photoreceptors are located on the lowest layer of the retina closest to the sclera and transmit the signal up to the top of the retina nearer the interior of the eyeball.  The optic nerve is simply the bundle of neurons from the top layer that in order to exit the eyeball must pass through the layer that would contain photoreceptors.  Interestingly an octopuses eye does not contain this flaw since the photoreceptors intheir eye are on the top layer of the retina with the signal passing to neurons below them in the retina.  Hope that makes sense.  It would be easier to discribe with a picture.