PPO: Pupils

Pupil definition

Dynamic aperture within anterior chamber that controls the amount of light entering the globe

Muscles of the iris

Sphincter

Dilator

Sphincter of iris

Circular, smooth muscle

Courses circumferentially (Around the pupil in a circle)

Constricts the eye

Parasympathetic activation

Dilator

Myoepithelial cells

Courses radially (Limbus → pupil)

Dilates the eye

Sympathetic activation

Pupil size

1.1 - 8.5 mm

What does pupil size depend on

Light intensity

Accommodation

Convergence

Emotional state

Age

Hippus

“Pupilary unrest”

Oscillations of the iris 

Independent of illumination, convergence, psychological state

Function of pupils

Control retinal illumination

Reduce optical aberrations (Pinhole effect)

Indicate emotional state

Why do we check pupils?

One of the most important data points in an EE

Performed on every patient

Abnormal result may indicate life-threatening medical issue

Shining light into one will eye cause…

Both pupils to constrict

Mydriasis

Dilation of the pupil

Sympathetic

Miosis of the pupil

Parasympathetic

Constriction of the pupil

Parasympathetic funciton of pupil

Coordinates the pupillary light reflex

Responsible for constricting the pupil

Three pathways for the pupillary light reflex

Afferent

Interneural

Efferent

Afferent pathway

Path of light

Retina → brain

Begins at retinal ganglion cells

Ends in upper midbrain at the Pretectal olivary nuclei (PON)

Pretectal olivary nuclei (PON)

End of afferent pathway

Synpase with interneurons on both R and L side of brain

Entire afferent pathway

Ganglion cells (Retina) → Optic nerve → Chiasm → Optic tract → PON

Interneauronal pathway

PON → Edinger-westphal nuclei

Connects afferent and efferent pathway

Entire efferent pathway

Edinger-westphal nucleus → Ciliary ganglion → Iris

Parasympathetic fibers travel with CN III

Terminate at the ciliary ganglion

Synketic triad

Eye’s response to a near target

-Constriction

-Convergence

-Accomodation

All related, but not dependent on eachother

Accomodative system’s relationship to pupillary system

Both follow the same course (CN III)

Accomodative fibers out number pupillary fiber’s 30:1

Sympathetic pupil innervation

Three neuron chain

-Hypothalamus

-Cliliospinal center of budge

-Superior cervical ganglion

Effects of sympathetic pupil innervation

1. Eyelids → open

2. Iris → dilates

3. Glands → sweat

Parasympathetic antagonist drugs

Stop the parasympathetic pathway from constricting the pupil

Tropicamide

Cycopentolate

Sympathetic agonists

Helps the sympathetic system to dilate the pupil

Phenylephrine

Hydroxyamphetamine

Paremyd

Eye drop that contains parasympathetic antagonists and sympathetic agonists

Anisocoria

Inequality in pupil size

Defect in the pupillary pathway from brain → Iris

May be harmless or a life-threatening medical issue

Physiological anisocoria

Difference in pupil size in absence of pathology

Long standing

Difference in size remains the same in bright/dim lighting

May switch eyes

Pathological anisocoria

Significant change of anisocoria in bright v. dim illumination

Concern about life-threatening if:

-Newly noted

-Ptosis

-EOM abnormalities

-Pain

If pathological anisocoria is greater in bright light, which eye is affected?

The larger pupil → Trouble with constriction

Parasympathetic defect

If pathological anisocoria is greater in dim light, which eye is affected

Smaller pupil →Trouble with dilation

Sympathetic defect

Parasympathetic causes of anisocoria

-Adie’s tonic pupil

-Trauma → Damage to iris sphincter

-CN III Palsy

CN III Palsy and anisocoria

Parasympathetic defect

Concern is raised if there is a large ptosis the same side as dilated pupil

Neurological emergency

Adie’s tonic pupil

Lesion of the ciliary ganglion

Pupil doesnt respond to illumination

Pupil does respond when converging

Parasympathetic deffect

-Benign

-Young females

-Diminished deep tendom reflexes

Sympathetic causes of anisocoria

• Horner’s syndrome

• Trauma to iris dilator

Horner’s syndrome

Sympathetic defect

Ptosis (Eyelid closure)

Miosis (Pupil constricted)

Anhidrosis (Lack of sweating on that side of face)

New DX is neurological emergency

Relative Afferent Pupillary Defect (RAPD or APD)

Prescence of unilateral or asymmetric pathology

Indicates inhibition anterior to the optic chiasm

Shining light into one eye constricts both pupils, while shining it into the other  does nothing

Conditions that CAN cause RAPD

Conditions that DO NOT CAUSE RAPD

Why catarcts do not cause RAPD

Cataracts scatter light, do not block it from reaching the retina

Makes things blurry, but does not constrict light

Drugs that dilate the pupil

• MDMA

• LSD

• Cocain

• Methamphetamine

Drus that constrict the pupils

• Heroin

• Oxycodone

• Morphine

• Methadone

Static pupllary measurements

Measurement of pupil size under constant stimulus

Quantitative

Dynamic measurement of pupils

Measurement of pupils with changes in stimulus condition

Qualititave

Achieved using either light or accomodation

How to prevent induving a pseudo APD?

Shine light slightly temporally to avoid stray light hitting opposite eye

What do you do to measure pupils if there is no PD ruler?

Use the iris’s measurements

Iris diamete = 12 mm

What if you are unsure if RAPD is present?

Ask patient if one light is dimmer than the other

Neutral density filters

Objective way to quantify RAPD

Hold ND filter over normal eye and perform swinging flashlight test

As you go up in the density, you will reach a point where pupillary reaction is equal OD and OS