Near Response• Activation of rostral brain stem neurons(supranuclaear input) which relay toEdinger-Westphal to activate nearresponse.• Light-Near dissociation.
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 ).
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).
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).
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.
Efferent Arm ofPupillary Response• EW nucleus send fibers to III CN andPreganglionic accomodative Neurons innearby nuclei.
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.
Accomodation• Convergence , accomodation , and miosis.• Mechanism synchronized by supra-nuclearconnections.• Cortical areas around visual cortex andfrontal eye field.
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.
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.