Background We will be looking at the eye and the sense of vision as our example

Question

Background

We will be looking at the eye and the sense of vision as our example of the special senses. Use the book to look up the anatomy of the eye and then explore the following as examples of visual physiology.

Procedure

1. Blind Spot

The blind spot in our visual field occurs where the optic nerve fibers exit the retina. No vision is possible at this location because there are no rods or cones.   To find the blind spots in your eyes:

1. Print this page out then hold the figure below with the cross on the left about 30 cm from your eyes. If you wear glasses or contacts keep them on.

2. Close your left eye and stare at the cross only. You should still be able to see the circle.

3. Move your face slowly closer to the diagram until the circle disappears. Measure the distance between your eye and the diagram and record your measurement on the results section for this lab.

4. Now do the same thing with the other eye. Turn the design so the x is on the right and close your right eye and stare at the cross only. Make sure you start with the design at least 30 cm away from your eyes.

5. Now move your face slowly closer to the diagram until the circle disappears. Measure the distance between your eye and the diagram and record your measurement on the results section for this lab.

The distance of your eye to the diagram is related to the distance between the center of your visual field and your blind spot. Is the distance from your eye to the diagram the same for both eyes? Answer in the Report Pages section at the end of this

2. Astigmatism

An astigmatism is a defect in the lens and/or cornea. Look at the following chart with your right eye and focus on the middle. If all the radiating lines appear equally dark there is not distortion in your lens and cornea and you don’t have an astigmatism. If some of the lines are lighter or blurred then you have some astigmatism. Now do the same thing with your left eye. Record your results at the end of the lab.

3. Pupillary light reflex

The pupillary light reflex is one of the autonomic reflexes. The retina of the eye is the receptor and the smooth muscle of the iris is the effector (by way of several nerve pathways and central nervous system centers which integrate the signal). The purpose of the pupillary reflex is to regulate the amount of light reaching the retina. Too much light can damage the rods and cones that detect light and if too little light gets to the retina no image is formed. The absence of normal pupillary reflexes is generally an indication of severe trauma or deterioration of the brain stem. This is useful medically but not the “purpose” of the reflex.

1. Conduct this experiment in an environment which is relatively dimly lit.   Use either your metric ruler or the scale on the flashlight to measure pupil diameter. Measure the pupil diameter of each eye and record in the report section of the lab.

2. Have the subject (you?) shield one eye from the other by putting a hand vertically between the eyes.

3. Shine the flashlight in the right eye. What is the pupillary response of the right eye? Measure the diameter of the right and left eyes and record the information in the report section of the lab. Answer the rest of the questions in the report section.

4. Ciliospinal reflex

The ciliospinal reflex is a reflex in which a pupillary response is observed in response to a tactile stimulus.

1. Observe the subject’s eyes while gently stroking the skin (or even just the hairs) on the right side of the subject’s neck close to the hairline. What is the reaction of the right and left pupils? (Record these observations in the report section of this lab).

2. If you see no reaction, try the same thing using a slight pinch instead of a gentle touch.

What you should have seen is pupillary dilation of either the right or both pupils. Dilation is what happens to the pupils when the sympathetic nervous system is stimulated. Stimulation on the right side would lead to dilation of the right pupil. If both irises dilate then the two pupils are closely integrated or connected.

Report Page   Name   

1. Blind Spot –

What is the distance between your eye and the diagram when the dot disappears?

Right eye ____________________

Left eye _____________________

Is the distance between the center of your field of vision and blind spot the same for both eyes? Explain your answer.

2. Astigmatism –

Is astigmatism present in your right   eye? ____________________

Is astigmatism present in your left eye? _____________________

3. Pupillary light reflex –

Low light level

Right pupil diameter ________________   Left pupil diameter ________________

Flashlight in right eye

Right pupil diameter __________________   Left pupil diameter _________________

Does the left pupil have the same type of response as the right? _____________

It should, and this is called a consensual or contralateral response, a reflex you see on one side of the body when the other side has been stimulated. A reflex you see on the same side of the body as the stimulus (the right pupil responding to the light in the right eye) is an ipsilateral response.

What is the purpose of the pupillary light reflex?  

4. Ciliospinal reflex

Observations of the Right pupil –

Observations of the Left pupil –

Based on your observations do you think both pupils are closely integrated? Explain your answer.

Explanation / Answer

1)Blind Spot

Right Eye – 14cm

Left Eye – 13cm

Yes, it is same for both the eyes. The eye consists of inner lining and consists of sheet of nerves which helps in vision and is called as RETINA. There is an area called as the optic nerve head where the optic nerve enters the eye. The photoreceptors help in light detection and allow vision. If there are no photoceptors, it will hinder with the vision and it is called as blind spot.

Taking the test the lines looks simple and straight with no blurriness and color.

Yes, the left pupil has the same type of response as the right. It is observed that on giving flashlight, the pupil constricts a little but not much. There is no symptom for the disease.

It is a consensual response and on giving the flashlight, it leads to little constriction of the pupil inside the eye.

Ans 4) Observation of right pupil – Dilation

           Observation of left pupil – Dilation

The dilation takes place on the stimulation of the sympathetic nervous system. As the right pupil is stimulated, the left pupil is dilated. In this case the irises have dilated in both cases and hence it signifies that the pupils are integrated or closely connected to each.

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