science

Miosis

Miosis is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Miosis rather than just read about it. In short: Miosis, or myosis (from Ancient Greek μύειν (múein) 'to close the eyes'), is excessive constriction of the pupil. The opposite condition, mydriasis, is the dilation of the pupil.

Key takeaways

Miosis belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Miosis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Miosis from memory before moving on to harder problems.

Reference excerpt

Miosis, or myosis (from Ancient Greek μύειν (múein) 'to close the eyes'), is excessive constriction of the pupil. The opposite condition, mydriasis, is the dilation of the pupil. Anisocoria is the condition of one pupil being more dilated than the other.

Causes

Age Senile miosis (a reduction in the size of a person's pupil in old age)

Diseases Ehlers Danlos Syndrome Horner's syndrome Hemorrhage into pons (intracranial hemorrhage) Hereditary disorders Cluster headaches with ptosis Iridocyclitis Fatal familial insomnia Aphakia Hemicrania continua

Drugs Opioids such as fentanyl, morphine, heroin and methadone (the notable exception being pethidine) Products containing nicotine such as cigarettes, chewing tobacco or gum Imidazolines such as clonidine, naphazoline, oxymetazoline and tetrahydrozoline Antipsychotics, including risperidone, haloperidol, chlorpromazine, olanzapine, quetiapine Cholinergic agents such as acetylcholine Acetylcholinesterase inhibitors Serotonin antagonists, such as ondansetron (an anti-emetic) known by its brand name Zofran/ Emiston in BD Some cancer chemotherapy drugs, including camptothecin derivatives Mirtazapine, a noradrenergic and specific serotonergic antidepressant (NaSSA) Some MAO inhibitors Pilocarpine eye drops and all other parasympathomimetics In some rare cases, when exposed to mustard gas Organophosphates

Physiology of the photomotor reflex Light entering the eye strikes three different photoreceptors in the retina: the familiar rods and cones used in image forming and the more newly discovered photosensitive ganglion cells. The ganglion cells give information about ambient light levels, and react sluggishly compared to the rods and cones. Signals from photosensitive ganglion cells have multiple functions including acute suppression of the hormone melatonin, entrainment of the body's circadian rhythms and regulation of the size of the pupil. The retinal photoceptors convert light stimuli into electric impulses. Nerves involved in the resizing of the pupil connect to the pretectal nucleus of the high midbrain, bypassing the lateral geniculate nucleus and the primary visual cortex. From the pretectal nucleus neurons send axons to neurons of the Edinger-Westphal nucleus whose visceromotor axons run along both the left and right oculomotor nerves. Visceromotor nerve axons (which constitute a portion of cranial nerve III, along with the somatomotor portion derived from the Edinger-Westphal nucleus) synapse on ciliary ganglion neurons, whose parasympathetic axons innervate the iris sphincter muscle, producing miosis.

Illustrations

Worked examples

Example 1 — a first encounter with Miosis

Start with the simplest possible case. Write down what Miosis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Miosis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Miosis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Miosis

In research: Miosis appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Miosis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Miosis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Medical signs, Ophthalmology, so understanding it makes those chapters shorter.
In everyday life: Look for Miosis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Miosis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Miosis means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Miosis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Miosis in simple terms?

Miosis, or myosis (from Ancient Greek μύειν (múein) 'to close the eyes'), is excessive constriction of the pupil. The opposite condition, mydriasis, is the dilation of the pupil.

Why does Miosis matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Miosis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Miosis.