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ACCOMMODATION

ACCOMMODATION. Accommodation. It is the ability to see the near object clearly by increasing the converging power of the eye. This is by increasing the refractivity of the lens by increasing the curvature of its anterior surface. Accommodation. Mechanism of accommodation.

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ACCOMMODATION

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  1. ACCOMMODATION

  2. Accommodation • It is the ability to see the near object clearly by increasing the converging power of the eye. • This is by increasing the refractivity of the lens by increasing the curvature of its anterior surface.

  3. Accommodation

  4. Mechanism of accommodation • There is contraction of the ciliary muscle • Reduction of the circle formed by the ciliary processes • Suspensory ligament relaxes • Elastic capsule of the lens acts

  5. Mechanism of accommodation

  6. Mechanism of accommodation

  7. Types • Physical accommodation • Physiological accommodation • Range of accommodation • Amplitude of accommodation

  8. Classification • Insufficiency of accommodation • Paralysis of accommodation • Spasm of accommodation

  9. Insufficiency of accommodation • In this condition, the accommodative power is below the lower limit of normal for the patient’s age

  10. Causes • Early Presbyopia • Weakness of the ciliary muscle- due to general debility, anemia or toxemia • Open- angle glaucoma ( due to impairment of the effectivity of the ciliary muscle by the increased intraocular pressure.

  11. Symptoms • Eye strain • Difficulty with near work

  12. Treatment • Treatment of the causes • Reading spectacles (near addition) • Accommodation exercises

  13. Paralysis of accommodation • Mydriasis usually accompanies the paralysis of accommodation. The prognosis is good in cases due to drugs or diphtheria. In traumatic cases the condition may be permanent

  14. Causes • 1. Unilateral *Cycloplegics (Ex- Atropine) *Contusion of the eye *Paralysis of the third cranial nerve 2. Bilateral: ( Paresis is more common) *Diphtheria *Syphilis *Diabetes *Alcoholism

  15. Treatment • Treatment of the causes • If the paralysis is permanent- suitable convex glasses may be prescribed • Miotics are seldom useful

  16. Spasm of accommodation • Spasm of accommodation in other name is Pseudo myopia

  17. Causes • Found mainly in children, Who attempt to compensate his refractive error • Myopes are more affected than hypermetropes • May occur artificially by instillation of miotics (Ex- with pilocarpine in young glaucoma patients) • Neurotic individuals who converge excessively

  18. Symptoms • Asthenopia • Blurring for distant vision (due to variable degrees of artificial myopia)

  19. Treatment • Atropinisation for a few days or weeks • Assurance, and if necessary, psychotherapy.

  20. Convergence

  21. Convergence • Convergence is a disjugate movement in which both eyes rotate inward so that the lines of sight intersect in front of the eyes.

  22. Types of Convergence • Voluntary convergence • Involuntary convergence Voluntary convergence is thus a separate phenomenon from the reflex convergence involved in normal visual activities.

  23. Reflex Convergence • Tonic convergence • Fusional convergence • Accommodative convergence • Proximal convergence

  24. Tonic Convergence • It is that part of the convergence which results from some inherent innervational tone of the extra ocular muscles when the patient is awake.

  25. Fusional Convergence • It is the Convergence that is produced to ensure that similar retinal images are projected onto corresponding retinal areas. • The normal fusional convergence amplitude for distance is about 18D and for near it is 35D.

  26. Accommodative Convergence • It is that component of convergence which occurs when the eyes accommodate, or when a nerve impulse to accommodate is discharged to the eyes.

  27. Proximal Convergence • This component of reflex convergence is induced by the proximity of the object of regard or the awareness of the proximity of a near object.

  28. Angle of convergence • It refers to the angle that is formed between the primary lines of sight during convergence. Its size depends on the fixation distance, becoming smaller with increasing distance (IPD), becoming larger with increasing IPD • The effect of IPD on the angle of convergence is usually negligible and so practically not taken into consideration while measuring the convergence angle. Convergence angle can be measured in metre angle or in prism dioptres

  29. Near point, Range and Amplitude of convergence • Near point of Convergence • Far point of Convergence • Range of Convergence • Amplitude of Convergence

  30. Near point • NPC is the closest point at which an object can be seen singly during bifoveal vision • Normal NPC – less than 8cm

  31. Far point • FPC refers to relative position of the eyes when they are completely at rest. It is usually infinity.

  32. Range of convergence • RC is the distance between far point of convergence and near point of convergence. • The part of the range of convergence between the eye and infinity is called Positive convergence, and the part beyond infinity • When eyes are in slight divergence is called negative convergence or divergence.

  33. Thank you

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