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Physiology of eyelids and eyebrows
- 2. FARAH IFTIKHAR Bsc(Hons) Optometryand Orthoptics (Rawalpinidi Medical College Rawalpindi) Gold medalist (RMC) Bronze Medalist (UHS)
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- 4. Eyebrows • Coarse hairsoverlie the superior orbital margins • Functions include 1.Shading of eye 2.Preventing perspiration from reaching the eye
- 5. • Orbicularis muscle--depressesthe eyebrows • Corrugator muscles--moves the eyebrows medially
- 6. The Eyelids • Protectthe eye from injury and excessive light by their closure • assist in the distribution of tears over the anterior surface of eyeball • Maintains the integrity of corneal surface • Maintain the proper position of globe within the orbital contents
- 7. • Regulate theamount of light allowed to enter the eye. • Provide protection from airborne particles • Coverage of the eyes during sleep
- 8.
- 9. • Lid opening •Lid closure • Blinking • Voluntary blinking and winking • Bell's Phenomenon
- 10. Lid Opening • UpperEyelid- Elevators • Lower eyelid- Retractors
- 11. Upper lid Elevators •Levator palperbrae superioris (the primary elevator of the upper eyelid) • The superior Palpebral muscle of Muller's • Frontalis (acting as accessory elevator) (Frontalis and Muller's become important when the levator is defective)
- 13. Eyelid excrusion (duringopening movements • In adults the upper eyelid is raised some 10-15mm from extreme downward gaze to extreme upward gaze
- 14. Tone of levatorMuscle • In upward gaze, tone increases in both the superior rectus muscle and the levator, resulting in elevation of the visual axis and elevation and retraction of the upper eyelid
- 16. Lower Lid retractors •No true counterpart of the levator is present and therefore the opening movement depends upon several factors • Traction exerted by the attachment of the inferior rectus to the inferior tarsus • Inferior palpebral muscle (identical to Muller's muscle in the upper eyelid)
- 18. Dynamics of openingmovement • Opening of the upper eylid takes place against gravity • Opening movements of the upper and lower eyelids begin in phase, although the opening movement of lower eyelid is much slower than that of the upper eyelid due to lack of any direct muscular pull
- 19. • During openingMovement the upper lid moves vertically upwards, while the lower lid moves laterally in horizontal direction
- 20. Bilateral coordination andtheir basis • Opening movements of the eyelids are bilateral,symmetrical,and identical in direction and amplitude (although they may be voluntarily inhibited on either side) • So, the levator muscles of the two upper eyelids behave as YOKE MUSCLES, in that they act as a team or pair, obeys Hering's law' of equal innervation
- 21. HERING'S LAW • Thisimplies that the innervational energy reaching the one levator muscle is equal to that reaching the other.
- 22. Reciprocal innervation pattern •It exists between the levator muscle and the orbicularis oculi muscle, i-e when levator recieves maximum innervation during opening,the orbicularis oculi receives minimum innervation and vice versa. Thus these muscles follow 'SHERRINGTON'S LAW' of reciprocal innervation
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- 24. • Orbicularis oculicontrols lid closure and is supplied by the facial nerve
- 25. Upper lid versuslower lid during closing movement • Upper lid moves downwards (vertically) while the lower lid moves medially (horizontally) • Closing movement of both upper and lower eyelids occur in phase, although the movement of lower eyelid begins some 12-20 micro seconds before the movement can be detected in the upper eyelid • Gravity does not play any role in downward movement of upper eyelid during closing
- 26. Blinking • Blinking canbe devided into • voluntary and • Involuntary • The involuntary blinks are further devided into • spontaneous • Reflex blinks
- 27. Spontaneous blinking • Itis common form of blinking that occurs without any obvious external stimulus or voluntary willed efforts • Spontaneous blinking is infrequent during the first few months of life, yet the delicate infant cornea does not suffer from dryness • Average rate is 15 times per minute (12- 20)
- 28. • The blinkrate is increased in 1.Extremely dry conditions 2.Strong air currents 3.Certain emotional stress situations (surprise,anger or fight) • A decreased blink rate occurs during times of visual observations
- 29. • Present inblind, hence no retinal stimulus is required • No discontinuity of visual sensation during blinking • This helps the displacement of the tear film to the lacrimal puncta which are located on the medial side of lids
- 30. Course of events •Relaxation of levator • After 10msec relaxation of levator relaxation, a train of high frequency synchronous activity occurs in the pretarsal portion of orbicularis • As the upper lid moves vertically down, the lower lid moves medially in a horizontal direction.However when the upper eyelid touches the lower eyelid,the downward movement of othe upper lid is also transmitted to the lower lid and after contact the lower lid moves
- 31. • During eachblink, the upper eyelid covers the center of pupil for a period of 0.10sec. • Due to contraction of preseptal fibers, as the upper eyelid reaches the limit of its downward excrusion, electrical activity in the orbicularis ceases and activity appears in levator
- 32. Reflex Blinking • Reflexlyin response to a stimulus
- 33. Voluntary blinking andwinking • Is a willed coordinated closure and opening movement of the eyelids in both eyes • The voluntary blink is under the control of individual • It is produced as a protective gesture
- 34. Winking • Winking isunilateral voluntary lid closure • It is part of facial expression • Occasionally, a subject may learn to wink with one eye but not with the other • Both 'voluntary blinking and winking' are produced by simultaneous contraction of palpebral and orbital portions of orbicularis
- 35. BELL'S Phenomenon • Itis highly coordinated reflex in which eyeball is rotated upward and outward on closure of eyelids • This is a protective mechanism • On closure of eyelids,all electrical activities in the levator cease and the activity abruptly rises in the superior rectus muscle and is inhibted in the inferior rectus muscle
- 37. MCQS 1.Main Elevator ofupper eyelid is A)Frontalis B)Muller's Muscle C)Levator palpebrea superioris D)None Of these
- 38. 2)Frontalis Muscle helpsin A)Elevating the Upper eyelid B)Elevating Lower Eye lid C)Retracting Lower Eyelid D)Elevating eyeball
- 39. 3)Superior Muscle Helpsin A) Elevating Upper Eyelid B)Elevating Lower Eye lid C)Retracting Lower Eyelid D)Elevating eyeball
- 40. 4)Levator muscles oftwo eyelid follow which law A) Sherrington's Law B)Herring's Law C)Law of gravity D)All of these
- 41. 5)During closing movementwhich lid moves 12-20msec before the other one A) Upper Eylid B) Lower Eyelid C)Both Moves simultaneously