This document discusses the pathways of light reflex and near reflex in the eye. It begins by explaining how light reflex causes both pupils to constrict when light is shone in one eye. It then describes the pathway from the retina through the optic nerve, chiasm, and tract to the pretectal nucleus. It further explains how fibers from the pretectal nucleus connect to the Edinger-Westphal nucleus and travel along the oculomotor nerve to constrict the sphincter pupillae muscle. Abnormalities of the pathways such as afferent and efferent defects are also summarized, along with Adie's tonic pupil. In short, the document provides an overview of the neural pathways and functions of

1. PATHWAY OF LIGHT
REFLEX AND NEAR
REFLEX
DR. SURABHI DEKA

2. LIGHT REFLEX
 WHEN LIGHT IS SHONE TO ONE EYE,BOTH PUPILS CONSTRICT.
 CONTRICTION OF THE PUPIL TO WHICH LIGHT IS SHONE IS CALLED
“ DIRECT LIGHT REFLEX”.
 THE OTHER PUPIL IS CALLED “CONSENSUAL(INDIRECT) LIGHT REFLEX”.
 LIGHT REFLEX IS INITIATED BY RODS AND CONES.
 IN NORMAL SUBJECTS,DIRECT AND CONSENSUAL REFLEX ARE ALMOST,ALWAYS
IDENTICAL IN TIME,COURSE AND MAGNITUDE.

3. PATHWAY OF LIGHT REFLEX
“THE AFFERENT FIBRES” EXTEND FROM RETINA TO PRETECTAL NUCLEUS IN
THE MIDBRAIN.
RODS AND CONES
GANGLION CELLS
OPTIC NERVE TO
CHIASMA

4. FIBRES FROM NASAL
RETINA DECUSSATE
TRAVEL ALONG
OPPOSITE OPTIC
TRACT
TO TERMINATE IN THE
CONTRALATERAL
PRETECTAL NUCLEUS

5. FIBRES FROM TEMPORAL
RETINA REMAIN
UNCROSSED
TRAVEL ALONG OPTIC
TRACT OF SAME SIDE
TO TERMINATE IN
IPSILATERAL PRETECTAL
NUCLEUS

6. “INTERNUNCIAL FIBRES”CONNECT EACH PRETECTAL
NUCLEUS WITH EDINGER-WESTPHAL NUCLEUS OF BOTH SIDES
AS FOLLOWS:
HALF OF
POSTSYNAPTIC FIBRES
FROM PRETECTAL
AREA
CURVE AROUND
PERIAQUEDUCTAL
GREY MATTER

7. TO TERMINATE IN
IPSILATERAL EDINGER-
WESTPHAL NUCLEUS
OTHER HALF CROSS VIA
POSTERIOR COMMISSURE
TO CONTRALATERAL
EDINGER-WESTPHAL
NUCLEUS
IT FORMS BASIS OF
CONSENSUAL LIGHT
REFLEX

8.  EFFERENT PATHWAY
CONSISTS OF
PARASYMPATHETIC FIBRES.
THEY ARISE FROM EDINGER-
WESTPHAL NUCLEUS IN THE
MIDBRAIN.
TRAVEL ALONG 3RD CRANIAL
NERVE(OCCULOMOTOR).

9. PREGANGLIONIC FIBRES
ENTER INF DIVISION OF 3RD
NERVE
INFERIOR OBLIQUE REACH
CILIARY GANGLION TO
RELAY
POSTGANGLIONIC FIBRES
TRAVEL ALONG SHORT
CILIARY NERVES
TO INNERVATE THE
SPHINCTER PUPILLAE

10. FUNCTIONS OF LIGHT REFLEX
 PUPILLARY CONSTRICTION ASSOCIATED WITH LIGHT
REFLEX PROTECTS AGAINST EXCESSIVE BLEACHING
OF VISUAL COMPONENTS BY REDUCING THE AMOUNT
OF LIGHT ENTERING THE EYE.
 IT HELPS IN LIGHT AND DARK ADAPTATION THUS IT
PLAYS A ROLE IN MAXIMIZING VISUAL ACUITY AT
DIFFERENT LEVELS.

11. NEAR REFLEX
 IT OCCURS ON LOOKING AT NEAR OBJECTS. IT CONSISTS OF
TWO COMPONENTS:
a) CONVERGENCE REFLEX WHICH COMPRISES CONVERGENCE
OF VISUAL AXES OF THE EYES AND ASSOCIATED
CONSTRICTION OF THE PUPIL.
b) ACCOMMODATION REFLEX WHICH INCLUDES INCREASED
ACCOMMODATION AND ASSOCIATED CONSTRICTION OF THE
PUPIL. THE TRIAD IS
 INCREASED ACCOMMODATION
 CONVERGENCE OF VISUAL AXES
 CONSTRICTION OF THE PUPILS

12. PATHWAY OF CONVERGENCE REFLEX
AFFERENT PATHWAY:-
AFFERENTS FROM MEDIAL
RECTI TRAVEL CENTRALLY
VIA THIRD NERVE
TO MESENCEPHALIC
NUCLEUS OF 5TH NERVE
TO CONVERGENCE CENTRE
IN THE PRETECTAL REGION

13. INTERNUNCIAL FIBRES
FROM CONVERGENCE
CENTRE
EDINGER-WESTPHAL
NUCLEUS
EFFERENT PATHWAY OF
CONVERGENCE REFLEX IS
ALONG 3RD NERVE
FROM 3RD NERVE THEY RELAY
IN THE ACCESSORY GANGLION
THEN REACHES THE
SPHINCTER PUPILLAE

14. PATHWAY OF ACCOMMODATION REFLEX
AFFERENT IMPULSES
EXTEND FROM OPTIC
NERVE
CHIASMA
OPTIC TRACT

15. LATERAL GENICULATE
BODY
OPTIC RADIATION
STRIATE CORTEX

16.  INTERNUNCIAL FIBRES RELAY IMPULSES FROM PARASTRIATE
CORTEX TO EDINGER-WESTPHAL NUCLEUS
 EFFERENT FIBRES :
FROM EDINGER-
WESTPHAL
NUCLEUS
TRAVEL ALONG 3RD
NERVE
REACH SPHINCTER
PUPILLAE AND
CILIARY MUSCLE

17. ABNORMALITIES OF PUPILLARY REFLEXES
 AFFERENT PATHWAY DEFECTS:
 ABSOLUTE AFFERENT PUPILLARY DEFECT(TAPD) OR
AMAUROTIC PUPIL:
 CAUSED BY COMPLETE OPTIC NERVE LESION.
 ABSENCE OF DIRECT LIGHT REFLEX ON AFFECTED SIDE AND
ABSENCE OF CONSENSUAL REFLEX ON NORMAL SIDE.
 WHEN NORMAL EYE IS STIMULATED BY LIGHT BOTH PUPILS REACT
NORMALY
 WHEN AFFECTED EYE IS STIMULATED BY LIGHT,NEITHER PUPIL
REACTS.
 NEAR REFLEX IS NORMAL IN BOTH EYES.

18. RELATIVE AFFERENT PUPILLARY DEFECT
(RAPD)
 IT IS CAUSED BY INCOMPLETE OPTIC NERVE LESION OR SEVERE
RETINAL DISEASE.
 IT IS TESTED BY SWINGING FLASH LIGHT TEST
 WHEN NORMAL LEFT EYE IS STIMULATED,BOTH PUPILS
CONSTRICT
 WHEN LIGHT IS SWUNG TO DISEASED RIGHT EYE,STIMULUS
DELIVERED TO THE CONSTRICTING MECHANISM IS REDUCED
AND BOTH PUPILS DILATE INSTEAD OF CONSTRICTING
 WHEN NORMAL LEFT EYE IS AGAIN STIMULED,BOTH PUPILS
CONSTRICT
 WHEN DISEASED RIGHT EYE IS STIMULATED,BOTH PUPILS
DILATE.

19. GRADING OF RAPD
GRADES
I. WEAK INITIAL CONSTRICTION AND GREATER
REDILATATION
II. INITIAL STALL AND GREATER REDILATATION
III. IMMEDIATE PUPIL DILATATION
IV. IMMEDIATE PUPIL DILATATION FOLLOWING
PROLONGED ILLUMINATION OF THE GOOD EYE FOR
6 SECONDS
V. IMMEDIATE PUPIL DILATATION WITH NO SECONDARY
CONSTRICTION

20. EFFERENT PUPILLARY DEFECT
 ABSENCE OF DIRECT AND CONSENSUAL LIGHT REFLEX ON
THE AFFECTED SIDE AND PRESENCE OF BOTH THE
REFLEXES ON THE NORMAL SIDE,
 COMMON CAUSES:
1. BRAINSTEM LESIONS AT THE LEVEL OF SUPERIOR
COLLICULUS
2. LESIONS OF CILIARY GANGLION OR SHORT CILIARY NERVES
3. IRIS DAMAGE SECONDARY TO PREVIOUS SURGERY
4. DRUGS-INADVERTENT EXPOSURE OF MYDRIATIC AGENT
LIKE ATROPINE(COMMON CAUSE OF FIXED DILATED PUPIL).

21. ADIE’S TONIC PUPIL
 CAUSED BY DENERVATION OF POSTGANGLIONIC SUPPLY OF
SPHINCTER PUPILLAE AND CILIARY MUSCLE
 IT IS USUALLY UNILATERAL(80%) AFFECTING HEALTHY
YOUNG WOMEN.
 THE AFFECTED PUPIL IS LARGE AND
IRREGULAR(ANISOCORIA).
 BLURRED VISION DUE TO IMPAIRED ACCOMODATION
 CONSTRICTION IS ABSENT OR SLUGGISH IN RESPONSE TO
LIGHT STIMULATION OF THE FELLOW EYE(CONSENSUAL
LIGHT REFLEX).

22.  PUPIL RESPONDS SLOWLY TO NEAR,FOLLOWING WHICH
REDILATATION IS SLOW.
 ACCOMODATION IS SLOW LEADING TO IMPAIRED FOCCUSING
FOR NEAR AND PROLONGED REFOCUSING IN DISTANCE
 PUPIL MAY BECOME SMALL IN LONG STANDING CASES.

23. CAUSES
 VIRAL CILIARY GANGLIONITIS(eg. HERPERS ZOSTER)
 ORBITAL OR CHOROIDAL TRAUMA.BLUNT TRAUMA TO GLOBE MAY INJURE
BRANCHES OF SHORT CILIARY NERVES AT IRIS ROOT.
 NEUROPATHIC TONIC PUPIL DUE TO
a) DIABETES
b) ALCOHOLISM
PHARMACOLOGICAL TESTING:
 INSTILLATION OF 0.1-0.125% PILOCARPINE IN BOTH EYES LEADS
TO CONSTRICTION OF ABNORMAL PUPIL DUE TO DENERVATION
HYPERSENSITIVITY.
 NORMAL PUPIL IS UNAFFECTED.

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