Two objectives of this to lab course are to supplement and reinforce the coverage of the associated lecture. The other is to extend this coverage. Sensory physiology, optics, the eye and vision are optimal subjects for laboratory exercises, and we have assembled quite a variety for today and next week. An additional justification is that there are several specialists in vision in the biology faculty, myself and Prof Ogilvie. Also the coverage in the BIOL 454 text is somewhat limited.

Fig. 10-34

Virtually every text has a picture of the spectrum. You will look at monochromatic lights of the spectrum produced by a monochromator. Here is a photo I took of the inside of one of my monochromators demonstrating how light of a particular wavelength feeds through the slit.

"Visible" is a term applied to the portion of the spectrum between 400 and 700 nm. In this lab, we will deal with the near ultraviolet. For instance, 365 nm light causes blue fluorescence(+) of paper. Also, flies were attracted to UV in the apparatus you had demonstrated.

(*)We will also be looking at blue excited fluorescence of GFP (green fluorescent protein) later, and I think I should explain fluorescence to you in case you have not had this coverage before. Light interacts with matter through exciting electrons. (Long wavelengths vibrate the molecules and yield heat, less useful). Sometimes the excited electron loses some energy by radionless de-excitation. Then the electron may fall back down from the excited level re-emitting a photon. Having less energy, the photon is a longer wavelength. (The energy of a photon is Planck's constant times the frequency.)

I can see UV with my left eye because of a traumatic cataract removed when I was 12 years old. Here are the lens of 79 and 39 yr old donors. They look yellow and absorbs most of the UV light. We will compare your UV sensitivity with mine.

Fig. 10-28

Here is a standard picture of the anatomy of the eye as well as the view of the retina as seen through the ophthalmoscope. This coverage in your text is relevant to quite a bit of our coverage.
This week
(1) You will look through the ophthalmoscope.
(2) We have a demonstration to show you that you can see the blood vessels in front of your retina.
*(3) We have a demonstration that you can see your macular pigments.
Next week
(1) We will dissect an eye
(2) We will demonstrate the bloid spot; there are no receptors where the optic nerve exits.

*Lutein and zeaxanthin are arranged in front of your fovea. They are so neatly arranged that they polarize the light, but only slightly. Thus you can only detect polarized light if it is continuously changing as it is in our demonstration. By contrast, invertebrates can see polarized light, and it is thought that bees use polarization in the sky for navigation. Polarized sun glasses are intended to specifically block glare since reflected light favors one plane of polarization. In case you never saw polarizers, we will show you polarizing filters.

Fig. 10-29
Pupillary reflex

Actually, this figure is the anatomy of the wiring of eye to brain. Why I wrote "pupillary reflex" is that you will see the crossed pupillary reflex, an important neurological test, in your lab partner's eyes, and this diagram shows how stimulation of one eye should make the contralateral pupil constrict.

What everybody should know in eye to brain wiring is that temporal retina (nasal visual field) stays ipsilateral at the optic chiasm while nasal retina crosses to the contralateral side. There is a synapse in the lateral geniculate body of the thalamus, and the postsynaptic neurons project to the visual part of the cerebral cortex.

Figure (from my Neuroscience book

Detail of pupillary reflex

Fig. 10-35(a&c)
Anatomy of the eye

This figure shows the same anatomy you saw above but also an enlargement of the retinal cells and the fovea. What everybody should know is that the retina has several layers of cells, it is backward (so that light passes through everything before it reaches the portion of the receptor where light is absorbed), and that we see with rods and cones.


Here are standard diagrams for myopia and hyperopia as well as the lenses for correction

Fig. 10-38
Receptor spectra

Night (scotopic) vision uses rods, in very sensitive, and is in black and white. Day (photopic) vision uses 3 cones with different spectral sensitivity, has high acuity, color vision, and is localized at the fovea (point of fixation). We have two demonstrations that relate to the fact that there are very few blue cones right in the center of the fovea
(1) Small field tritanopia
(2) Difficulty reading in blue light

Fig. 10-32

The reason I included this figure here is that next week, you should have a very clear view of the ligaments in the eye dissection


What follows are a series of snapshots from the eye dissection

Exam questions from 2005 - 2006 relating to this outline and this lab

With the ciliary muscle contracted, the ligaments for the lens slacken. What is this adjustment called?


If you had a cataract and I could not test your acuity, how might I test whether your retina still functioned normally? (Hint, we did this.)

you should still see blood vessels with off-axis light

I made the blue light look the same brightness as the UV light with my normal eye (the one with an intact lens) using neutral density filters. I am 58 years old. Predict the relative amount of neutral density for you younger folk. (Alternatively, how did the data collection turn out?)

you will need less n.d. on blue light since your lens is more transparent to UV

It is thought that bees can make use of differences in the plane of polarized light much like we can see colors. Because of how well organized macular pigments are, we see through a polarizing filter. However our polarization sensitivity is so weak that I had to use a trick for you to see polarized light. What was that trick?

kept it changing (rotating)

Drosophila can see UV light. Why can't you?

lens blocks UV

I said that a 0.3 neutral density filter attenuates the light to half. To see if you understand this, you get your calculator and put 10 to the 0.3 power and the answer is 2. Resolve.

attenuation: -0.3 (negative)

Looking straight into an eye with an ophthalmoscope, you would be looking at the fovea. Off to the side is the optic disk. What is the optic disk?

where optic nerve exits (and blood vessels)

Why would it be better for a life raft to be red than yellow?

yellow disappears when it is small

Protanopia is red-blindness. Deuteranopia is green-blindness. What is the term for blue-blindness such as we demonstrated for small foveal visual fields?

small field tritanopia

What is the name of the large fluid compartment in the back of the eye with fluid having the consistency of egg white?

vitreous humor

Why would you use trigonometry in the blind spot test?

with distance from view and distance across, you determine angle off axis

If the aqueous does not drain sufficiently, pressure builds up in the eye. What is this disorder called?


What are the pigments that contribute to Haidinger's brushes?

macular pigments, zeaxanthin & lutein

When you cut the eye in half, the suspensory ligaments were conspicuous. What process are they involved in?


What is the name of the part of the thalamus where vision information is relayed?

lateral geniculate nucleus (body)

Give the parameters, roughly, in nanometers, of the visible light spectrum.


What color light does lutein absorb?


Not everyone saw the bow tie spinning during the presentation of Haidinger's
Brushes. What were we actually seeing?

macular pigments

Name the famous visual pigment associated with rods.


The eye adjusts the shape of the lens to keep objects in focus. What is this referred to


Are rods or cones more active at night, at low levels of light?


What exits at our blind spot?

optic nerve

What region of the brain does vision project to?

occipital lobe

What color light do yellow filters absorb?


Name the two macular pigments in front of the fovea that slightly polarize light.

lutein and zeaxanthin

What part of the eye gives the highest acuity or sharpest vision?


Not everyone saw the bow tie spinning during the presentation of Haidinger's
Brushes. What were we actually seeing?

Macular pigments

Does the temporal nasal retinal field (nasal visual field) stay ipsilateral or cross to the contralateral side?


Where do the left and right optic nerves first meet behind the eyes?

optic chiasm

In general, can humans see ultraviolet light?


We saw that when you shined a light on the left eye, that both pupils constricted, thus
allowing less light to enter the eye. Since it happens, or is seen on both sides, what
is this referred to as?

bilateral reflex

How many different color cones do we have?


What is the fancy word for day vision?


If you cannot see far away, what condition do you have?

myopia, near-sightedness

What is the strongest lens in the human eye?

cornea-air interface

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