Accommodation reflex opthamalogy mbbs pptx slides

1. ACCOMMODATION REFLEX By MANIKANDAN.M Roll no : 68 2nd year MBBS

2. SYNOPSIS • Accommodation • Terms related to accommodation • Mechanism of Accommodation • Light reflex and Visual pathway • Accommodation reflex • Pathway for Accommodation reflex • Anomalies of Accommodation

3. WHAT IS ACCOMMODATION ? Accommodation refers to the ability of the eye to alter it’s focus So that clear images of either close or distant objects can be formed on the retina.

5. Far point • The far point or punctum remotum is the position of an object such that its image falls on the retina in the relaxed eye i.e. in the absence of Accommodation. • In emmetropic eye , the far point is at infinity.

6. Near point • The near point or punctum proximum is the nearest point at which an object can be clearly seen when maximum accommodation is used. For a young adult with normal vision, the near point is about 25 cm. • It increases with age > 40 years.

7. Range of Accommodation . It is the distance between far point and near point.

8. Amplitude of Accommodation • The difference between the dioptric power needed to focus at near point (P) and far point (R) is called amplitude of accommodation(A). A = P-R • For example, In a normal eye, if the near point is 10 cm , . P = 1/10 cm = 100/10 m = 10 D. . In a normal eye , since the far point is at infinite distance , R = 0. Amplitude of accommodation (A) = 10D.

9. MECHANISM OF ACCOMODATION

10. Mechanism of Accommodation

12. Light Reflex • 1. When light is focused on one eye, the pupils of both eyes constrict; this is called light reflex. The pupillary constriction occurring in the stimulated eye is called direct light reflex and in the other eye is called consensual light reflex. • Afferent pathway: The first order neurons from the retinal ganglion cells project to the pre-tectal nucleus; from here the second order neurons start and proceed to the mid-brain Edinger-Westphal nucleus.

13. Efferent pathway: The parasympathetic fibers of the oculomotor nerve form the first order neurons that originate from mid-brain Edinger-Westphal nucleus and project to the ciliary ganglion. The second order neurons start from here and innervate the sphincter pupillae.

14. VISUAL PATHWAY

15. DIRECT AND CONSENSUAL LIGHT REFLEX

16. Accommodation Reflex • When sudden shift of gaze from distant to near object,the reflex changes observed in the eye is called Accommodation reflex . • 3 components in the accommodation reflex are : onvergenceof the eyeballs – image forms in the corresponding points of retina. onstrictionof the pupil– increase depth of focus. urvatureof the lens increased anteriorly- increases power of lens of the eye . C

17. Pathway for Accommodation reflex Afferent pathway • Visual impulses from retina pass through the optic nerve,optic chiasma, optic tract, lateral geniculate body and optic radiation to visual cortex (area 17) of occipital lobe.

18. Pathway for Accommodation reflex Center • From occipital lobe, the association fibres carry impulses to frontal lobe. • The center for accommodation lies in frontal eye field that is situated in the frontal lobe of cerebral cortex.

19. Pathway for Accommodation reflex Efferent pathway Efferent fibres to ciliary muscle and sphincter pupilae • From area 8, the corticonuclear fibres pass via internal capsule to Edinger-Westphal nucleus. • From here, the preganglionic fibres pass through the third cranial nerve to ciliary ganglion. • Postganglionic fibres from ciliary ganglion pass via the short ciliary nerves and supply the ciliary muscle and the constrictor pupilae.

20. OCCULOMOTOR NERVE DISTRIBUTION

21. Pathway for Accommodation reflex Efferent pathway Efferent fibres to medial rectus • Some of the fibres from frontal eye field terminate in the somatic motor nucleus of occulomotor nerve. • The fibres from motor nucleus supply medial rectus.

22. ACCOMMODATION REFLEX PATHWAY

23. ACC.REFLEX IN SHORT

24. Pathway for Accommodation reflex

25. AnomaliesofAccommodation Classification Decreased Accommodation Increased Accommodation Ill-Sustained Accommodation Insufficiency Inertia Paralysis Excess Spasm

26. Presbyopia Presbyopiaisaconditionofphysiological insufficiencyofaccommodationleading toaprogressivefallinnearvision.

27. Causes • Decreaseinaccommodativepoweroflens withincreasingage,leadsto • presbyopia,occursdueto: • Age-relatedchangesin lens: • Decreaseinelasticityoflenscapsule,and • Progressive, increase in size and hardness (sclerosis)oflens substancewhichisnoteasily moulded. • Agerelateddeclineinciliarymusclepower.

28. Symptoms • Difficultyinnearvision. • Patientscomplaintofdifficultyinreading smallprints • Symptomsoffatigueof theciliarymusclearealsocomplained afterreadingordoinganynearwork.

29. AccommodationInsufficiency • The accommodative amplitude is distinctly below the lowerlimitof theexpectedamplitudeinrelationtothe ageof theindividual • Similartopresbyopia • Can result from systemic conditions such as diabetes mellitus, multiple sclerosis, anemia, general physical fatigue, myasthenia gravis, trauma, malnutrition,chronic alcoholism,etc....

30. AccommodationInsufficiency • Specificsymptoms: • Blurred vision/eyestrainwithNEARvisual tasks • Intermittentdiplopiaduetoassociated disturbancesof convergence

31. Ill-sustainedAccommodation • Initialstageoftrueinsufficiency • Rangeisnormal • During prolonged near work, accommodative power weakens, the near point gradually recedes and vision becomesblurred

32. InertiaofAccommodation • Rarecondition • Difficultyin alteringthe range of accommodation • Requires time and effort to focus a near object after lookinginto distance • Treatment: • Correction of refractiveerror • AccommodativeExercises

33. ParalysisofAccommodation • Causes: • Druginducedcycloplegia –atropine,homatropine • Internal opthalmoplegia [paralysis of cilliary muscle & sphincterpupillae] • Neuritisassociatedwithchronicalcoholism, diabetes • CNSinfections • HeadInjury • SpecificSymptoms: • Blurringofnearvision • Photophobia[glare]

34. Treatment:ParalysisofAccommodation • Selfrecoveryoccursindruginducedparalysis • Darkglassesareeffectiveinreducingtheglare • Convexlensesfornear vision maybeprescribed

35. Excessiveaccommodation • Accommodativeresponseisgreater thantheaccommodativestimulus. • Thereisfunctionalincreaseintonusof ciliarymuscle,resultsinaconstant accommodativeeffect.

36. Precipitatingfactors • Excessivenearworkdone,especially indimorexcessiveillumination. • Generaldebility,physicalormentalill health

37. Symptoms • Blurredvisionatnear isuncommon • Blurredvisionatdistance • Headaches • Eyestrain • Photophobia • Difficultychangingfocusfromdistanceto near • Diplopia

38. Treatment • Ithasagoodprognosis. • Refractiveerrorshouldbecorrected aftercarefullyperformedcycloplegic refraction. • Nearworkshouldbestoppedforsome time,afterthat itshouldbedonewith properilluminationconditions.

39. SpasmofAccommodation • Abnormally excessive accommodation which is out of voluntary controlof theindividual • Causes: • Drug induced spasmafteruseofstrongmiotics • Spasmofnearreflex • Specificsymptoms: • Blurredvisionat DISTANCEafterperformingnearvisual tasks

40. Treatment: SpasmofAccommodation • Relaxation of ciliary muscle: the most effective method of treatment iscompleteciliary paralysiswithatropine

41. THANK YOU