ACCOMMODATIONACCOMMODATION

AccommodationAccommodation

It is the ability to see It is the ability to see the near object the near object clearly by increasing clearly by increasing the converging the converging power of the eye.power of the eye.

This is by increasing This is by increasing the refractivity of the the refractivity of the lens by increasing lens by increasing the curvature of its the curvature of its anterior surface.anterior surface.

AccommodationAccommodation

Mechanism of accommodationMechanism of accommodation

There is contraction of the ciliary There is contraction of the ciliary musclemuscle

Reduction of the circle formed by the Reduction of the circle formed by the ciliary processes ciliary processes

Suspensory ligament relaxes Suspensory ligament relaxes Elastic capsule of the lens actsElastic capsule of the lens acts

Mechanism of accommodationMechanism of accommodation

Mechanism of accommodationMechanism of accommodation

TypesTypes

Physical accommodationPhysical accommodation Physiological accommodationPhysiological accommodation Range of accommodationRange of accommodation Amplitude of accommodationAmplitude of accommodation

ClassificationClassification

Insufficiency of accommodationInsufficiency of accommodation Paralysis of accommodationParalysis of accommodation Spasm of accommodationSpasm of accommodation

Insufficiency of accommodationInsufficiency of accommodation

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

CausesCauses

Early PresbyopiaEarly Presbyopia Weakness of the ciliary muscle- due Weakness of the ciliary muscle- due

to general debility, anemia or to general debility, anemia or toxemiatoxemia

Open- angle glaucoma ( due to Open- angle glaucoma ( due to impairment of the effectivity of the impairment of the effectivity of the ciliary muscle by the increased ciliary muscle by the increased intraocular pressure.intraocular pressure.

SymptomsSymptoms

Eye strainEye strain Difficulty with near workDifficulty with near work

TreatmentTreatment

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

Paralysis of accommodationParalysis of accommodation

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

CausesCauses

1. Unilateral1. 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)2. Bilateral: ( Paresis is more common) *Diphtheria *Diphtheria *Syphilis*Syphilis *Diabetes*Diabetes *Alcoholism *Alcoholism

TreatmentTreatment

Treatment of the causesTreatment of the causes If the paralysis is permanent- If the paralysis is permanent-

suitable convex glasses may be suitable convex glasses may be prescribedprescribed

Miotics are seldom usefulMiotics are seldom useful

Spasm of accommodationSpasm of accommodation

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

CausesCauses

Found mainly in children, Who attempt Found mainly in children, Who attempt to compensate his refractive errorto compensate his refractive error

Myopes are more affected than Myopes are more affected than hypermetropeshypermetropes

May occur artificially by instillation of May occur artificially by instillation of miotics (Ex- with pilocarpine in young miotics (Ex- with pilocarpine in young glaucoma patients)glaucoma patients)

Neurotic individuals who converge Neurotic individuals who converge excessivelyexcessively

Symptoms Symptoms

AsthenopiaAsthenopia Blurring for distant vision (due to Blurring for distant vision (due to

variable degrees of artificial myopia)variable degrees of artificial myopia)

TreatmentTreatment

Atropinisation for a few days or Atropinisation for a few days or weeksweeks

Assurance, and if necessary, Assurance, and if necessary, psychotherapy.psychotherapy.

ConvergenceConvergence

ConvergenceConvergence

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

Types of Convergence Types of Convergence

Voluntary convergenceVoluntary convergence Involuntary convergence Involuntary convergence

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

Reflex ConvergenceReflex Convergence

Tonic convergenceTonic convergence Fusional convergenceFusional convergence Accommodative convergenceAccommodative convergence Proximal convergenceProximal convergence

Tonic ConvergenceTonic Convergence

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

Fusional ConvergenceFusional Convergence

It is the Convergence that is It is the Convergence that is produced to ensure that similar produced to ensure that similar retinal images are projected onto retinal images are projected onto corresponding retinal areas.corresponding retinal areas.

The normal fusional convergence The normal fusional convergence amplitude for distance is about 18D amplitude for distance is about 18D and for near it is 35D.and for near it is 35D.

Accommodative ConvergenceAccommodative Convergence

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

Proximal ConvergenceProximal Convergence

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

Angle of convergenceAngle of convergence

It refers to the angle that is formed between It refers to the angle that is formed between the primary lines of sight during convergence. the primary lines of sight during convergence. Its size depends on the fixation distance, Its size depends on the fixation distance, becoming smaller with increasing distance becoming smaller with increasing distance (IPD), becoming larger with increasing IPD(IPD), becoming larger with increasing IPD

The effect of IPD on the angle of convergence The effect of IPD on the angle of convergence is usually negligible and so practically not is usually negligible and so practically not taken into consideration while measuring the taken into consideration while measuring the convergence angle. Convergence angle can be convergence angle. Convergence angle can be measured in metre angle or in prism dioptres measured in metre angle or in prism dioptres

Near point, Range and Amplitude Near point, Range and Amplitude of convergenceof convergence

Near point of ConvergenceNear point of Convergence Far point of Convergence Far point of Convergence Range of ConvergenceRange of Convergence Amplitude of ConvergenceAmplitude of Convergence

Near pointNear point

NPC is the closest point at which an NPC is the closest point at which an object can be seen singly during object can be seen singly during bifoveal vision bifoveal vision

Normal NPC – less than 8cmNormal NPC – less than 8cm

Far point Far point

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

Range of convergenceRange of convergence

RC is the distance between far point of RC is the distance between far point of convergence and near point of convergence.convergence and near point of convergence.

The part of the range of convergence The part of the range of convergence between the eye and infinity is called between the eye and infinity is called

Positive convergence, Positive convergence, and the part and the part beyond infinity beyond infinity

When eyes are in slight divergence is called When eyes are in slight divergence is called negative convergence or divergence.negative convergence or divergence.

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