The Pupil : Physiology and Clinical Corrleates

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The Pupil : Physiology and Clinical Corrleates

  1. 1. The Pupil : Physiologyand ClinicalApplicationsRaed Behbehani , MD FRCSC
  2. 2. Functions• Control of retinal Illumination.• Reduces optical aberrations.• Depth of focus by miosis (pinhole effect).
  3. 3. Functions• In dim light, pupil dilates maximizes thenumber of photons to enhance darkadaptation.• In light adaptation , pupil constricts andenhances light adaptation.
  4. 4. Functions• A small pupil reduces spherical andchromatic aberration.• After Refractive surgery, patient with largepupil have more bothersome symptoms( glare at night).
  5. 5. Clinical Significance ofPupil Status• Measure afferent input. (RAPD)• Indicates awakefulness.• Autonomic functions.• Pupil diameter and optical aberrations.• Pharmacological response.
  6. 6. Relative AfferentPupillay Defect• Swinging flashlight test.
  7. 7. Awakefullness• Excited individualas - larger pupil.• Sleept , on narcotivs - smaller pupil.• Central inhibition (parasympathomimetic)at level of midbrain.
  8. 8. Anisocoria• Inequality of pupils sizes.• Drugs.• Trauma.• Sympathetic lesions (Horner’s).• Parasympathetis lesions (Adie’s ,Thirdnerve Palsy).
  9. 9. Pupil Pathway
  10. 10. Near Response• Activation of rostral brain stem neurons(supranuclaear input) which relay toEdinger-Westphal to activate nearresponse.• Light-Near dissociation.
  11. 11. Afferent Arm OfPupillary Light Reflex• Same as visual perception (Rods andCones).• Under dark adaptation , rodsdominates( low-amplitude contractions ).• Under light adaptation, cones dominate( larger amplitude contractions ).
  12. 12. Melanopsin-containingRetinal Ganglion Cells• MCRGC recently discovered and fireconstantly to produce steady-statecontractions.• May mediate light input to the pupil viarods and cones.• Project to suprachiasmatic nucleus(hypothalamus - circadian rythm) andpretectal nucleus (midbrain).
  13. 13. Interneurons Arm ofPupillary Reflex• Pretectal Neurons : Summate GC input.• They send (corssed and uncrossed fibers)in PC to EW nucleus (equally).• Dorsal Mibrain Syndrome (Light-neardissociation).
  14. 14. Pupil Pathway -Pretectal Neurons• Birds and rabits have only crossed fibers inpretectal nucleus ( only ipsilateral eye willrespond to light) .• Cats - 70% crossed.• Humans - almost 50% crossed anduncrossed.
  15. 15. Efferent Arm ofPupillary Response• EW nucleus send fibers to III CN andPreganglionic accomodative Neurons innearby nuclei.
  16. 16. CN III• CN III send fibers --- ciliary ganglion(parasympathetic) -- Short Ciliary Nerve.• Post-Ganlionic accomodative fibers :Pupillary fibers = 30 : 1.• Sectoral distribution on the iris (20 clockhours)• Adies’s tonic pupil , L-N dissociation.
  17. 17. Accomodation• Convergence , accomodation , and miosis.• Mechanism synchronized by supra-nuclearconnections.• Cortical areas around visual cortex andfrontal eye field.
  18. 18. Pupil Dilataion• Iris sphincter relaxes and iris dilatormuscles contracts.• Supranuclear inhibition of EW nucleus bysympathetic class of neurons pass throughthe Periaqueductal gray area -> relaxationof iris sphincter.• Narcotics, and sleep produce miosis.
  19. 19. Oculosympathetic Flow
  20. 20. Relative AfferentPupillary Defect• RAPD correlates with amount of visualfield deficit.• Neutral density filter can measureobjectively.• If pupil does not work , look at the OTHERpupil.
  21. 21. Anisocoria• Is it worse in LIGHT (iris sphincter) orDARK (iris dilator) damage ?
  22. 22. Anisocoria
  23. 23. Anisocoria Increases inDark• Horner’s Syndrome.• Simple Anisocoria.
  24. 24. Horner’s Syndrome• Dilation Lag (pupil dilates slowly in darkroom).• Usually anisocria greatest first 4-5 secondsafter light it turned off.• Ptosis ,“up-side down ptosis”, conjunctivalinjection , ipsilateral decreased sweating.
  25. 25. Horner’s Syndrome
  26. 26. Diagnosis of Horner’s• Cocaine (prevents reuptake ofNorepinephrine) , 4% or 10%.• After application by 40-60 minutes , checkpupils.• Presence of >=1 mm aniosorocia aftercocoaine is positive test.
  27. 27. Diagnosis of Horner’s• Hydroxyamphetamine (differentiates pre-from post-ganglionic lesions).• Apraclonidine (reversal of anisocoria ,alpha-1 supersensitivity)
  28. 28. Diagnosis ?
  29. 29. Adie’s Tonic Pupil• Women.• Segmental denervation (sectoral palsy).• Light-near dissocation (chronic stage).• ? Immune-mediated damagae to ciliaryganglion.• 50% bilateral in 10 years.
  30. 30. Adies’ Tonic PupilQuickTime™ and ah264 decompressorare needed to see this picture.
  31. 31. CholinergicSupersensitivity• 0.125% Pilocarpine produces moreconstriction in the abnormal pupil.• Develops in 5-7 days.• Can occur in CN III palsy as well.
  32. 32. AnticholinergicMydriasis• 1% Pilocarpine can be used to diagnose.• Scopolamine , cyclopentolate , atropine.
  33. 33. CN III Palsy• Pupillary fibers located in medial part of theintracranial CN III.• Aberrant regeneration (Primary andSecondary)

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