Case study (17pts = 3% of final grade)
11 MCQ (11 pts) and 3 SA (6 pts)
Night Blindness
A patient has been admitted to the Ottawa General Hospital after an accident that happened as they
were walking home late at night. Here is what the patient reported upon admission at the hospital:
“I was walking home last night and did not see a hole on the sidewalk. It was very dark outside,
and it was as if I could not see anything. I fell on the ground and hit my head hard. In the last month this
has happened to me a few times, where I feel I am totally blind at night. I can see just fine during the
day, but not at night or if the light is dim. I have also felt pretty tired the last few days.”
Upon admission at the hospital, a blood test was performed on the patient and some of results were as
follow:
After some additional tests, the doctor confirms that the patient’s vision is altered but only in dark
conditions, a condition called nyctalopia or night blindness (see the figure below).
Page 1 of 12
, The doctor suggests a simple change in diet and recommends that the patient includes foods like fish,
cod liver, carrots, and fruits. The doctor also prescribes the following vitamin supplements:
• Vitamin A: 900 µg/day
• Vitamin C: 90 mg/day
1. Using the information above, which of the following is the most likely the cause of the patient’s night
blindness?
A. A dysfunctional liver
B. An excessive concentration of vitamins in the blood
C. A deficiency in vitamin C
D. A deficiency in vitamin A
E. The head injury caused by the fall
2. Which of the following is correct?
A. Vitamins are proteins synthesized by the human body and that are important in the cellular
metabolism
B. In humans, vitamins are essential nutrients (required in the diet) that can function as coenzyme
C. In humans, vitamins are polymers of carbohydrate that can synthesize proteins
D. Vitamins are hydrolytic enzymes that digest other proteins
E. Vitamins are electron carriers in the electron transport chain of the cellular respiration
Through a series of experiments, we will now investigate how the human eye detects light in two
conditions (in the presence of light and in the dark), in order to understand the patient impaired vision
at night.
The eye’s retina is constituted by two types of photoreceptor cells: the rods and the cones. These cells
can detect light and produce a cellular response through a specific signaling pathway. The internal
structure of these photoreceptor cells is represented in the figure below. Rods differ from cones in that
they are much taller, much thinner and have many membranous discs that play a key role in
photoreception. Light is received by a membrane receptor, which initiates a signal transduction inside
the cell. The cellular response produced consists of the release a neurotransmitter (glutamate) into a
synaptic cleft, triggering a series of action potentials in the post-synaptic neuron (not shown in the
figure). This electrical signal is then sent to (and processed by) the central nervous system to form an
image in the brain.
Page 2 of 12
11 MCQ (11 pts) and 3 SA (6 pts)
Night Blindness
A patient has been admitted to the Ottawa General Hospital after an accident that happened as they
were walking home late at night. Here is what the patient reported upon admission at the hospital:
“I was walking home last night and did not see a hole on the sidewalk. It was very dark outside,
and it was as if I could not see anything. I fell on the ground and hit my head hard. In the last month this
has happened to me a few times, where I feel I am totally blind at night. I can see just fine during the
day, but not at night or if the light is dim. I have also felt pretty tired the last few days.”
Upon admission at the hospital, a blood test was performed on the patient and some of results were as
follow:
After some additional tests, the doctor confirms that the patient’s vision is altered but only in dark
conditions, a condition called nyctalopia or night blindness (see the figure below).
Page 1 of 12
, The doctor suggests a simple change in diet and recommends that the patient includes foods like fish,
cod liver, carrots, and fruits. The doctor also prescribes the following vitamin supplements:
• Vitamin A: 900 µg/day
• Vitamin C: 90 mg/day
1. Using the information above, which of the following is the most likely the cause of the patient’s night
blindness?
A. A dysfunctional liver
B. An excessive concentration of vitamins in the blood
C. A deficiency in vitamin C
D. A deficiency in vitamin A
E. The head injury caused by the fall
2. Which of the following is correct?
A. Vitamins are proteins synthesized by the human body and that are important in the cellular
metabolism
B. In humans, vitamins are essential nutrients (required in the diet) that can function as coenzyme
C. In humans, vitamins are polymers of carbohydrate that can synthesize proteins
D. Vitamins are hydrolytic enzymes that digest other proteins
E. Vitamins are electron carriers in the electron transport chain of the cellular respiration
Through a series of experiments, we will now investigate how the human eye detects light in two
conditions (in the presence of light and in the dark), in order to understand the patient impaired vision
at night.
The eye’s retina is constituted by two types of photoreceptor cells: the rods and the cones. These cells
can detect light and produce a cellular response through a specific signaling pathway. The internal
structure of these photoreceptor cells is represented in the figure below. Rods differ from cones in that
they are much taller, much thinner and have many membranous discs that play a key role in
photoreception. Light is received by a membrane receptor, which initiates a signal transduction inside
the cell. The cellular response produced consists of the release a neurotransmitter (glutamate) into a
synaptic cleft, triggering a series of action potentials in the post-synaptic neuron (not shown in the
figure). This electrical signal is then sent to (and processed by) the central nervous system to form an
image in the brain.
Page 2 of 12
