Archivos de la categoría pildoras de ciencia

blood flow at the retina (astigmatism blurs image)

Have you though on what happens if want to image the eye fundus of a person with astigmatism. The answer is that as the person sees but due to the his astigmatism, we will see bad his eye fundus. So correction of the astigmatism is important for seeing and for watching inside the eye.

I show you here two videos in order to provide you the experience of watching the difference between observing the retina without correcting the astigmatism of the subject or after correction.

In this first video , we see the the retina without astigmatism correction. The vessels are more blured in the vertical direction than in the horizontal, that is due to the astigmatism and its orientation.

In the next video I show you the same retinal area but with astigmatism correction.

You can see more defined vessels, even you can see the lood flow as a light spark in small capillars.


Pupil tracking with a Hartmann-Shack

It is now clear (it wasn’t 10 years ago) that fixational movements of the eye are important when measuring the ocular aberrations, becuase they bias the measurement (for more info read documents one and two).The easiest way to measure that movements, just by computing the displacement of the centroid of the aberrometric image.

I show you in this video an image of the aberrometric image (on the left) and an image of the pupil of the eye (right) to show you that when the eye moves the aberrometric image do the same.

The advantages of using the aberrometric image to measure the movements of the eye are:

– Cheap

– Simple (no aditional instrumentation, setups or whatever)

– synchronization (the tracking is made simultaneously with the aberrometric measurement)

So if you are looking for this characteristics, just try the Pupil tracking Hartmann-Shack

And the eye sees upside down

Geometrical optics predicts that the image formed by the eye of the retina should be inverted with respect to the real world. But then, why we don’t see things upside down? Because of the brain. Isn’t it fantastic. The brain turns the image to make easy our lifes. So, what happens with a newborn? How they see our world the first days?

In this video we show you (Ana Gargallo and me) that it is true that our eyes provides inverted images of the world. The video shows a light on the left, and an eye from a death cow. We removed part of the esclera in order to see the fundus of the eye.  If you look carefully the eye, you can see a reflex of the light on the anterior part of the eye (the cornea) and the image of the light at the back of the eye (the retina).

We move the light up and down, and look carefully what happens with the image of the lamp on the retina, it moves in the contrary sense. So the eye inverts the image, thats incredible, isn’t it?