PATHWAY OF LIGHT REFLEX AND NEAR REFLEX.pptx

OPHTHALMOLOGY

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 3 RD CRANIAL NERVE(OCCULOMOTOR).

9. PREGANGLIONIC FIBRES ENTER INF DIVISION OF 3 RD 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: CONVERGENCE REFLEX WHICH COMPRISES CONVERGENCE OF VISUAL AXES OF THE EYES AND ASSOCIATED CONSTRICTION OF THE PUPIL. 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 5 TH NERVE TO CONVERGENCE CENTRE IN THE PRETECTAL REGION

13. INTERNUNCIAL FIBRES FROM CONVERGENCE CENTRE EDINGER-WESTPHAL NUCLEUS EFFERENT PATHWAY OF CONVERGENCE REFLEX IS ALONG 3 RD NERVE FROM 3 RD 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 3 RD 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 WEAK INITIAL CONSTRICTION AND GREATER REDILATATION INITIAL STALL AND GREATER REDILATATION IMMEDIATE PUPIL DILATATION IMMEDIATE PUPIL DILATATION FOLLOWING PROLONGED ILLUMINATION OF THE GOOD EYE FOR 6 SECONDS 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: BRAINSTEM LESIONS AT THE LEVEL OF SUPERIOR COLLICULUS LESIONS OF CILIARY GANGLION OR SHORT CILIARY NERVES IRIS DAMAGE SECONDARY TO PREVIOUS SURGERY 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 DIABETES ALCOHOLISM PHARMACOLOGICAL TESTING: I NSTILLATION OF 0.1-0.125% PILOCARPINE IN BOTH EYES LEADS TO CON S TRICTION OF ABNORMAL PUPIL DUE TO DENERVATION HYPERSENSITIVITY. NORMAL PUPIL IS UNAFFECTED.

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