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ACCOMMODATION

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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.

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Accommodation

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

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Mechanism of accommodation

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Types Physical accommodation Physical accommodation Physiological accommodation Physiological accommodation Range of accommodation Range of accommodation Amplitude of accommodation Amplitude of accommodation

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Classification Insufficiency of accommodation Insufficiency of accommodation Paralysis of accommodation Paralysis of accommodation Spasm of accommodation Spasm of accommodation

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

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

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Symptoms Eye strain Eye strain Difficulty with near work Difficulty with near work

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

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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 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

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

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

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Spasm of accommodation Spasm of accommodation in other name is Pseudo myopia Spasm of accommodation in other name is Pseudo myopia

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

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

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

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Convergence

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

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

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Reflex Convergence Tonic convergence Tonic convergence Fusional convergence Fusional convergence Accommodative convergence Accommodative convergence Proximal convergence Proximal convergence

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

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

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

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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. 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.

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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 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 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

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Near point, Range and Amplitude of convergence Near point of Convergence Near point of Convergence Far point of Convergence Far point of Convergence Range of Convergence Range of Convergence Amplitude of Convergence Amplitude of Convergence

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

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

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Range of convergence RC is the distance between far point of convergence and near point 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 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. When eyes are in slight divergence is called negative convergence or divergence.

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