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IB Biology SL IA on Pupillary Light Reflex
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This Biology IA looks researches "Pupillary light reflex under 5 levels of light intensity exposure". It has scored full marks in 2021 year's IB session
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Pupillary light reflex under 5 levels of light intensityexposure
2019-2021
Introduction:
1
, Reflexes are involuntary and instantaneous movements of a body caused by an external
stimulus. It is an automatic defence mechanism of the body, and therefore the signal does not
go to the brain, however, is processed by local nerves. 1 The action requires a receptor,
afferent neuron, and effector to achieve a reflex on a stimulus. The ocular reflexes are the
simplest ocular motor responses. We use eyes to monitor our external environment and
depend on the ocular reflexes to protect our eyes. For example, the eye blink reflex protects
the cornea, and the pupillary light reflex (PLR) protects the retina, by adopting pupil to the
light intensity. This reflex is similar to a usual camera - as camera adjusts its light exposure,
our bodies do the same with our eyes. And it is fascinating for me how does our body adjust
to the external conditions, unnoticed, and what changes does it cause, on the example of
pupillary light reflex. Especially in the modern world, exposure to the artificial light from
phones and laptops, has a strong influence on our body in terms of physiological parameters,
such as nerve-system: alertness, cognitive responses, and as explored in this Internal
Assessment – pupillary reflex. This investigation holds scientific significance as it answers
the question on whether there is a possible correlation between external stimulus, light
intensity, and body response, pupil constriction. If there is, PLR can be seen as important
metric of autonomous nervous system function2, and positive and negative effect of digital
light on human-body should be explored further.
Background Information:
The Pupil and its reflexes are a popular and common way across medicine of diagnosing the
integrity of the sensory and motor function of the eye, by exposing to different light
intensities, swinging lights and changing accommodation. 3 The Pupillary light reflex is a
motor reflex that controls the diameter of a pupil depending on a level of light intensity, thus
assisting the eye with adapting to dim and light environments, allowing less light into the
retina.4 The pupillary light reflex thus constricts the pupil in response to light, and pupillary
constriction is achieved through the innervation of the iris sphincter muscle. In this case, the
pupil is a passive part that reacts to changes in the active iris. Dilation is controlled by the
dilator pupillae, a group of muscles in the peripheral 2/3 of the iris. The physiology behind a
1
Dowshen, Steven. What Are Reflexes? Last updated September 2010. Kids Health from Nemours. Accessed
April 16, 2013. http://kidshealth.org/kid/talk/qa/reflexes.html
2
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5872002/
3
Hal Blumenfeld, “Pupillary Responses (CN II, III),” in Neuroanatomy through Clinical Cases (New York,
NY: Sinauer Associates/Oxford University Press, 2021),
http://www.neuroexam.com/neuroexam/content19.html.
4
Alison P. Belliveau, “Pupillary Light Reflex,” StatPearls [Internet]. (U.S. National Library of Medicine, April
2, 2020), https://www.ncbi.nlm.nih.gov/books/NBK537180/.
2Figure 1. Diagram of the Pupillary Light Reflex Pathway
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