Ted’s Response:

Before I go further, you need to know that I have been away from the eye care profession since 1991, when I began pursuing other interests. As such, I am not the best source of information to answer the questions you have asked. All of this is explained on the Eye Advice and Information page at my website. Also, many of your questions can be answered by looking at the various pages of my eye site—Anatomy, Pathology, & Physiology of the Human Eye—here:

http://www.tedmontgomery.com/eye

I will go ahead, though, and try to give you some answers, although my time is very limited and I won't be as thorough as someone else might be.

<< 1. How did you come to learn about the eye or get interested in the human eye?  >>

While I was in university, my dad asked me what profession I wanted to go into. I didn't know, but I thought about it. I remembered that I enjoyed having my eyes examined a few times, and I wondered how the optometrist did all of the cool things with lenses like make me see double, move images around, make me see clearly with lenses, and other things.

I met with my optometrist, and he helped show me the process of applying to optometry schools. I had an interview at Southern California College of Optometry, and I was told all the classes and tests I had yet to take. So I finished all these requirements and went through optometry school for four years. Later, I took more classes and passed more tests that enabled me to become an optometric physician, which meant that I could prescribe medications for eye diseases.

<< 2. What, in your opinion, is the most important part of the eye and why? >>

There are numerous parts, all working together, that enable the eye to provide optimal vision. If any one of them is absent or is malfunctioning, vision can be decreased or even completely absent.

Possibly the cornea (the clear dome at the front of the eye) is the most important part. It is the first structure that begins focusing the light as it enters the eye. If it is cloudy or opaque due to some infection or injury, there may not be enough light entering the eye for proper vision to take place, even if everything else is working perfectly. Also, if the cornea were removed, much of the fluid in the eye would leak out, and the eye could collapse.

<< 3. How does the eye see and see in color? >>

There are many processes, all working together, that enable the eye to provide vision. I cannot fit all of these things into a single email, but my eye site contains information describing the processes that enable vision to occur.

Actually, the eye does not "see"; it simply picks up the light, focuses it on the retina, and sends impulses into the optic nerve that goes to the brain. It is the vision center, in the occipital lobe of the brain, that sees.

There are many cones in the retina, mostly in the macula and the fovea at the center of the retina. Cones are sensitive to color:

• "S" cones are most sensitive to short wavelengths (mostly blue),
• "M" cones are most sensitive to medium wavelengths (mostly green), and
• "L" cones are most sensitive to long wavelengths (mostly red).

<< 4. Why does the eye not recognize the blind spot in our eye? >>

The optic nerve head or optic disc contains no photoreceptors (cones or rods) that pick up the light entering the eye. Since there are no photoreceptors there, no fibers in the optic nerve are stimulated. That portion of the eye is known as the "blind spot" because it is totally blind.

When both eyes are open, light from a certain source may fall in the blind spot of one eye; but it will fall on functional retina of the other eye, so the brain will see it. However, if one eye is closed or covered, any light falling in the blind spot of the other eye is not seen by the brain.

It is even possible to cover one eye and move the other eye to a position where an entire full moon will not be seen by that eye; only the halo around the moon can be seen. More details can be found on my Optic Nerve page, in the blind spot section.

<< 5. How are the eye and brain connected? >>

The eye and the visual center of the brain are connected by the visual pathway. The pathway includes the optic nerve, optic chiasm, optic tract, and optic radiation, which extends into the visual cortex of the brain. Everything from the optic nerve on back is part of the brain. More details can be found on my Optic Nerve page, in the visual pathway section.

Also, the Parasympathetic Pathways: Pupillary Light Reflex animation shows the pathway.

<< 6. How many rods/cones are in each eye? >>

The number varies from person to person. I think a pretty reliable estimate is about 6.5 to 7 million cones, and about 120 to 130 million rods, in each retina.

<< 7. What are the main parts of the eye? >>

I would say that the main parts of the eye are those that compose the structure of the eye and those that make the eye move around. They include the following:

• cornea and sclera
• iris
• crystalline lens
• vitreous humor
• retina
• macula
• extraocular muscles

<< 8. Where can I get more sources about the human eye? >>

I have this page at my site with links to other informative sites:

Links to Eye and Health
Information on the Web

The first four links on that page are more for eye care professional, but some of the pages at those sites have good information for students of the eye.