<ul>
 <li>
 Pupil margin is positioned more anteriorly than the iris root and gets support from the lens
 </li>
 <li>Slightly off-centre: inferonasal</li>
 <li>Varies in size from 1 to 8mm in diameter</li>
 <li>
 Physiological anisocoria (less than 0.4mm difference) is present in 25% of the population and
 may change sides!
 </li>
 <li>Physiological tremor in pupil known as hippus (or pupillary athetosis)</li>
 <li>Mydriasis occurs in low light, excitement or fear</li>
 <li>Miosis occurs in illumination, convergence/accommodation and sleep</li>
 <li>
 The strength of constriction increases with light intensity up to 9 log units above the scotopic
 threshold and then levels off
 </li>
 <li>The pupil cannot respond to stimuli of greater than 5Hz frequency</li>
 <li>Pupillary dilatation:</li>
 <ul>
 <li>Reduced depth of field</li>
 <li>Reduced depth of focus</li>
 <li>Increased Stiles-Crawford effect (see below)</li>
 <li>Reduced diffraction of light</li>
 <li>Increased chromatic aberration</li>
 </ul>
 <li>
 Stiles-Crawford effect: light entering at the edge of the pupil is less effective at stimulating
 photoreceptors than light entering centrally because it meets the receptors obliquely rather
 than head on
 </li>
 <li>Pupil size is associated with:</li>
 <ul>
 <li>Iris colour: blue irises are larger than brown</li>
 <li>Autonomic nervous system: fatigue, exercise etc.</li>
 </ul>
</ul>
## Light reflexes
<ul>
 <li>Only one functioning pupil is needed to test the anterior visual pathways</li>
 <li>The latency of the pupil light reaction is 0.2 to 0.5s</li>
 <li>Afferent impulses travel from the retina through the optic nerve, chiasma and tracts</li>
 <ul>
 <li>
 Fibres leave the tract and synapse in the pretectal olivary nucleus near the
 superior colliculus
 </li>
 <li>Each pretectal nucleus receives only an ipsilateral input</li>
 <li>
 Axons of the pretectal nerve cells synapse with the parasympathetic nuclei (Edinger-Westphal
 nuclei) of the oculomotor nerve on BOTH sides of the midbrain
 </li>
 <li>
 Preganglionic fibres travel with the oculomotor nerve ( through its inferior division to the
 inferior oblique) to the ciliary ganglion and synapse
 </li>
 <li>
 Postganglionic fibres travel in the short ciliary nerves to the sphincter pupillae muscle and
 both pupils constrict
 </li>
 <li>
 Since both Edinger-Westphal nuclei are innervated, an unilateral optic nerve lesion will not
 affect the indirect/consensual response in the ipsilateral eye
 </li>
 </ul>
 <li>
 Pupillary reflexes originate in the brainstem and are therefore unaffected by cortical lesions
 </li>
 <li>Causes of efferent pupillary defect (fixed dilated pupil)</li>
 <ul>
 <li>
 Brain stem lesions at the level of the superior colliculus and red nucleus, typically
 accompanied by so-called long tract signs
 </li>
 <li>
 Third nerve lesions, usually compressive (but 20% of microvascular palsies involve the pupil)
 </li>
 <ul>
 <li>May be false localising sign in raised ICP causing uncal herniation</li>
 </ul>
 <li>Ciliary ganglion or short ciliary nerve lesions</li>
 <li>Iris damage due to surgery or grossly elevated IOP</li>
 <li>
 Mydriatic drugs (pilocarpine will not constrict such a pupil but will constrict a pupil
 affected by a neurological lesion)
 </li>
 </ul>
</ul>
## Mydriasis
<ul>
 <li>
 Contraction of the dilator pupillae (innervated by alpha-1-adrenergic{' '}
 receptors)
 </li>
 <li>Stimulated by noradrenergic sympathetic nerves passing through the ciliary ganglion</li>
</ul>
## Miosis
<ul>
 <li>Stimulation and contraction of sphincter pupillae&nbsp;</li>
 <li>Stimulated by cholinergic postganglionic parasympathetic fibres from the ciliary ganglion</li>
</ul>
## Horner&rsquo;s syndrome
<ul>
 <li>Interruption of the sympathetic chain in the head and neck</li>
 <li>Causes:</li>
 <ul>
 <li>
 Central brain stem lesions (ie. first-neurone: the descending reticulospinal fibres within the
 medulla oblongata eg. lateral medullary syndrome -see below)
 </li>
 <li>
 Preganglionic lesions (second neurone: travels from T1 exit over apex of lung and around first
 rib up to carotid bifurcation)
 </li>
 <li>
 Postganglionic lesions (third neurone: travels from superior cervical ganglion to eye along
 the internal carotid and within the cavernous sinus)
 </li>
 <ul>
 <li>
 No anhidrosis since the postganglionic sympathetic fibres controlling facial sweating follow
 the external carotid artery rather than the internal. They separate from the fibres to the
 pupil approximately at the level of the carotid bifurcation
 </li>
 </ul>
 </ul>
 <li>
 Anisocoria (especially in low light conditions) due to failure of normal dilation by the
 affected pupil
 </li>
</ul>
Classic drugs tests for Horner&rsquo;s
<ul>
 <li>
 Cocaine will not dilate a Horner&rsquo;s pupil since increasing adrenergic activity by
 preventing reuptake has no effect on an interrupted neural pathway
 </li>
 <li>
 Hydroxyamphetamine (increases adrenaline release from postganglionic nerve terminals) will
 dilate a first or second neurone Horner&rsquo;s but not a third order neurone lesion (since
 there&rsquo;s no noradrenaline to release)
 </li>
 <li>
 Adrenaline, apraclonidine and phenylephrine will dilate a post-ganglionic Horner&rsquo;s due to
 denervation hypersensitivity
 </li>
 <li>Note: there is no test to distinguish a second from a first-order lesion</li>
</ul>
<ClinicalCorrelate>
 <>
 Lateral medullary syndrome
 <ul>
 <li>Infarction of the ipsilateral posterior inferior cerebellar artery</li>
 <ul>
 <li>Cerebellum: ataxia</li>
 <li>IX and X nuclei: swallowing difficulty</li>
 <li>
 Descending sympathetic tracts: Horner&rsquo;s syndrome
 </li>
 <li>
 Spinothalamic tract: contralateral (due to decussation) sensory loss of pain and
 temperature
 </li>
 <li>Trigeminal nerve (sometimes involved): ipsilateral facial sensory loss</li>
 </ul>
 </ul>
 </>
</ClinicalCorrelate>
## Light-near dissociation
<ul>
 <li>When the near response is greater than the response to light</li>
 <ul>
 <li>Implies a diminished light response</li>
 </ul>
 <li>Causes</li>
 <ul>
 <li>Retinal lesions</li>
 <li>Optic nerve lesions</li>
 <li>Pineal lesions</li>
 <li>Pretectal lesions eg. Sylvian aqueduct syndrome, Argyll-Robertson</li>
 <li>
 Third nerve lesions: secondary to aberrant regeneration of neurones to the iris sphincter
 normally supplying medial rectus
 </li>
 <li>Ciliary ganglion lesions (as above for third nerve lesions), eg. Adie&rsquo;s</li>
 </ul>
</ul>
## Argyll-Robertson pupil
<ul>
 <li>Small pupil</li>
 <li>Unresponsive to light</li>
 <li>Good near response</li>
 <li>Does not dilate with atropine</li>
 <li>Physostigmine increases constriction</li>
 <li>Associated with neurosyphilis</li>
 <li>Lesion site unknown</li>
 <li>Absent tendon reflexes and iris atrophy are common</li>
</ul>
## Adie pupil
<ul>
 <li>Sluggish light reaction: may present with blurred vision due to mydriasis</li>
 <li>Strong near response (with light-near dissociation)</li>
 <li>
 Supersensitive to cholinergics eg. pilocarpine, due to &ldquo;post-denervation phenomenon&rdquo;
 </li>
</ul>
<ClinicalCorrelate>
 <>
 Using dilute pilocarpine can aid the diagnosis of an Adie&rsquo;s pupil
 <ul>
 <li>Lesion affects the ciliary ganglion</li>
 <li>Second eye involvement may not be noticed by the patient</li>
 </ul>
 </>
</ClinicalCorrelate>

AC to Lens

Pupil

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

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Corticosteroids

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Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Vision

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Visual Acuity

Colour Vision

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Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

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Cell Growth

Neoplasia

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Genetics

Chromosomes

Mitosis

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Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance