Question

hiCAL_Assignment and Report 2020 QULUTUIN TU NIJVLITI TILI UM O l) Patient 1 was subjected to increased and decreased levels of light. • What is the expected effect of light changes on pupil size? • How does the autonomic nervous system control pupil size? • 2) In Patient 2, the pupil of one eye did not constrict as expected with light changes. • Provide your hypothesis as to whether this defect arises in the sympathetic or parasympathetic nervous system. Explain your rationale. Which 3 drugs would you choose from the agents available to test your hypothesis? Explain your rationale. o 2) For Patient 3, a decision was made to test phenylephrine, cocaine and amphetamine to investigate a defect in pupil size. • What previous analysis of pupil size is likely to have led to this decision? • Explain how these 3 drugs could help distinguish if the underlying problem is a defect in neurotransmitter synthesis, storage or release. ich

Answer 1

The eye is an organ in the human body that has a function to detect light. When a particular light source hits the eye, the optic nerve carries the message forward to the brain which allows us to visualize the object.

1. The question provides us the scenario of a patient who has been subjected to increased and decreased levels of light.

• The pupil is a special structure that resembles a hole, which is located at the centre of the eye, and its function is to allow light to come and strike the retina. The pupil looks black in colour because of its absorbtion of light. The pupil size changes with change in the light intensity. When there is an exposure to dim light, the pupil of the eye undergoes expansion such that maximum amount of light enters into the eye. On the other hand, when there is an exposure to bright eye, the pupil constricts. In this way the pupil regulates the amount of light which is allows to pass through itself and strike the retina.
• The autonomous nervous system has two branches which are sympathetic nervous system and parasympathetic nervous system. The dilation of the pupil is caused due to the result of the sympathetic nervous system and the constriction is caused due to the parasympathetic nervous system

2. This question provides us with the scenario of a patient whose pupil does not undergo constriction as expected with light changes.

• Normally it is expected that when the eye is exposed to bright light , the pupils undergo constriction as to regulate the amount of light which is optimum for visualization. As already stated in the previous answer, pupil constriction is controlled by the parasympathetic nervous system. The inability to cause constriction in the pupil can occur due to various reasons. One such reason can be a physical trauma in the eye, which results in the tissue of iris being damaged. Another reason can be a diseased condition called Adie's tonic pupil syndrome which generally affects young females.
• In such a condition when the pupil of the eye fails to constrict, several drugs are used to revert the diseased condition. Cholinergic agonists is the class of drug which is used in this case. Drugs which fall under this category is Pilocarpine hydrochloride.

3. The question provides us with the scenario of a patient whose defect in pupil is tested with the help of three drugs which are-phenylephrine, cocaine and ampethamine respectively.

• The action of the three drugs on eye are written as follows. First, phenylephrine is used as an ophthalmic drug to constrict the blood vessels present in the eye, which causes the pupil to be dilated. Second, cocaine is a stimulant drug that is used illegally. The effect of cocaine on the eye again causes it to dilate. Third, amphetamine is used as an ophthalmic drug to stimulate the sympathetic nervous system which causes dilation of the pupils. After studying that the patients's pupil do not constrict nor dilate, we can infer that iris tissue of the eye has been subjected to some sort of physical trauma.
• The above mentioned three drugs have specific mechanisms of action which are different from each other. They all target the same problem and they all focus on causing dilation in the pupil.