Accommodation reflex opthamalogy mbbs pptx slides

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

4. 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.

5. 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.

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

7. 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.

8. MECHANISM OF ACCOMODATION

9. Mechanism of Accommodation

10. 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.

11. 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 .

12. VISUAL PATHWAY

13. DIRECT AND CONSENSUAL LIGHT REFLEX

14. 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 : onvergence of the eyeballs – image forms in the corresponding points of retina. onstriction of the pupil – increase depth of focus. urvature of the lens increased anteriorly - increases power of lens of the eye . C

15. 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.

16. 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.

17. 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.

18. OCCULOMOTOR NERVE DISTRIBUTION

19. 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.

20. ACCOMMODATION REFLEX PATHWAY

21. ACC.REFLEX IN SHORT

22. Pathway for Accommodation reflex

23. Anomalies of Accommodation Classification Decreased A c c o m moda t ion Insufficiency Ill-Sustained Accommodation I ne r t ia Paralysis Increased A c c o m moda t ion Ex c e s s S p a s m

24. Presbyopia Presbyopia is a condition of physiological insufficiency of accommodation leading to a pro g re s s i v e fall i n n ear v i s i on.

25. Causes D e crea s e i n a cc o m m o d at i v e po w er of l ens w i th i ncr e a s i ng ag e , lead s to pres byop i a , oc c urs d u e to: Age-related changes in lens: Decreas e i n ela s t i c i ty of lens c aps u le , and Progressive, increase in size and hardness ( s cle r os i s ) o f lens s u bsta nce wh i ch i s not eas i ly moulded. Age relat e d decli ne i n c i l i ar y m u scl e po w er.

26. Symptoms D i ff i culty i n n e a r v i s i on. Patients complaint of difficulty in reading smal l pr i nts S ymptom s of fat i gue of the c i l i ar y m u scl e ar e a l s o co m pla i ned aft e r read i ng o r d o i ng an y ne a r w o rk.

27. Accommodation Insufficiency The accommodative amplitude is distinctly below the lower limit of the expected amplitude in relation to the age of the individual Similar to presbyopia Can result from systemic conditions such as diabetes mellitus, multiple sclerosis, anemia, general physical fatigue, myasthenia gravis, trauma, malnutrition , chronic alcoholism ,etc....

28. Accommodation Insufficiency Specific symptoms: Blurred vision/eyestrain with NEAR visual tasks Intermittent diplopia due to associated disturbances of convergence

29. Ill-sustained Accommodation Initial stage of true insufficiency Range is normal During prolonged near work, accommodative power weakens, the near point gradually recedes and vision becomes blurred

30. Inertia of Accommodation Rare condition Difficulty in altering the range of accommodation Requires time and effort to focus a near object after looking into distance Treatment: Correction of refractive error Accommodative Exercises

31. Paralysis of Accommodation Causes: Drug induced cycloplegia –atropine ,homatropine Internal opthalmoplegia [paralysis of cilliary muscle & sphincter pupillae] Neuritis associated with chronic alcoholism, diabetes CNS infections Head Injury Specific Symptoms: Blurring of near vision Photophobia [glare]

32. Treatment: Paralysis of Accommodation Self recovery occurs in drug induced paralysis Dark glasses are effective in reducing the glare Convex lenses for near vision may be prescribed

33. Excessiv e accommodat i on Accommodative response is greater than the accommodative stimulus. There is functional increase in tonus of c i l i ar y muscle, r e sult s i n a consta n t accommodative effect.

34. Precipi t ating factors Exces s i v e ne a r w o rk done , es pec i ally i n d i m or e xces s i v e i l l u m i nat i on. G e n e ral deb i l i ty, phy s i cal or me n tal i ll health

35. Symptoms Bl u rr e d v i s i on a t ne a r i s uncom m on Bl u rr e d v i s i on a t d i stance Headaches Eyestrain Photophobia D i ff i cu l ty chang i ng foc u s from d i stanc e to near Diplopia

36. Treatment I t h a s a good prognos i s. R e fract i v e er r or shoul d be corrected aft e r careful l y perfor m ed cyc l op l eg i c refraction. Ne a r w o rk s hou l d be stoppe d for so m e t i me, aft e r that i t s hou l d be d o ne w i th prope r i l l um i nat i on cond i t ions.

37. Spasm of Accommodation Abnormally excessive accommodation which is out of voluntary control of the individual Causes: Drug induced spasm after use of strong miotics Spasm of near reflex Specific symptoms: Blurred vision at DISTANCE after performing near visual tasks

38. Treatment: Spasm of Accommodation Relaxation of ciliary muscle: the most effective method of treatment is complete ciliary paralysis with atropine

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