AL-AZHAR UNIVERSTY

FACULTY OF MEDICINE

OPHTHALMOLOGY DEPARTMENT

AccommodationUnder supervision

ofProf.dr. Ahmed shafik

Points dicussed in this research:1) Definition of accommodation.

2) Mechanism of accommodation.

3) Theories of accommodation.

4) Types of accommodation.

5) Anomalies of accommodation.

Made by all of:1) Ebtehal Abdelnaser Ahmed.2) Arwa Essam Hussein.3) Esraa Ahmed fathy.4) Esraa Elsaied Mahmoud.5) Esraa Elashry Elashry.6) Esraa Abu bakr Mohamed.7) Esraa Ahmed Mohamed.8) Esraa Gamal Eldeen Yosef.9) Esraa Arafat Ahmed.10) Esraa Abdelsamee Saied.11) Esraa Ragab Abdelkhalek.12) Esraa Salah Abdelsalam.13) Esraa Mohamed Mohamed.

Accommodation Definition : Accommodation is the mechanism by which the

eye changes refractive power by altering the shape of lens in order to focus objects at variable distances.

The mechanism of eye accommodation is not the same for all animals.

For example fish accommodates through the change of position of the lens, some types of birds accommodate through the increase of curvature of the cornea and protraction of the human eye. As far as humans are concerned accommodation is caused by the increased curvature of anterior area of the eye lens while at the same time its thickness also changes.

Accommodation is usually the same on both eyes.

Accommodation in human

it Is caused by the increased curvature of anterior area of the eye lens

Theories of mechanism of accommodation

The exact mechanism of accommodation is not known but the Principal fact is that ACCOMMODATION is a feature of increase in the curvature of the lens which affects anterior surface mainly.

Relaxation theory of HELMHOLTZ “Capsular Theory”:

He considered that lens was elastic and in normal state it is stretched and flattened by tension of the suspensory ligaments.

During accommodation, contraction of ciliary muscle shortens ciliary ring and moves towards the equator of the lens.

Relax the suspensory ligaments, relieving strain. Lens assumes more spherical form, increasing thickness and

decreasing diameter.

Relaxation theory of HELMHOLTZ

SCHACHAR’S theory Presbyopia is due to growth in equatorial diameter, leads to

decrease in peri lenticular space. Contraction of ciliary muscle cannot tense zonules and

expand lens coronally. SCHACHAR introduced use of scleral expansion bands (SEB).

TSHERNING’S theory This theory attributed increased curvature of capsule to increasing

tension of the zonules. It states that contraction of ciliary muscle pulls zonules directly and

increases tension of capsule at equator of lens, which leads to bulging of poles.

COTENARY theory COTENARY theory of accommodation was proposed by COLEMAN. The COTENARY (hydraulic suspension) theory proposes that lens,

zonules & anterior vitreous comprise a diaphragm between aqueous and vitreous.

As ciliary muscle contracts it forms a pressure gradient, causing anterior movement of lens zonules diaphragm and increasing anterior central curvature.

Presbyopia is due to increase in lens volume, results in reduced response to pressure gradient created by ciliary body contraction.

Types of Accommodation

1) Tonic accommodation :It is due to tonus of ciliary muscle and is active in absence of a stimulus. The resting state of accommodation is not at infinity but rather at an intermediate distance.

2) Proximal accommodation :Is induced by the awareness of the nearness of a target. This is independent of the actual dioptric stimulus.

3) Reflex accommodation :Is an automatic adjustment response to blur which is made to maintain a clear and sharp retinal image.

4) Convergence-accommodation :Amount of accommodation stimulated or relaxed associated with convergence. – The link between accommodation and convergence is known as accommodative convergence and is expressed clinically as AC/A ratio.

Assessment of accommodation

1. Dynamic retinoscopy.

2. Subjective measurement of accommodation amplitudes with e.g., RAF rule.

3. Facility of accommodation with "lens flippers“.

retinoscopy lens flippers

Anomalies of Accommodation1) Presbyopia.

2) Insufficiency of accommodation.

3) Ill-Sustained accommodation .

4) Inertia of accommodation.

5) Paralysis of accommodation .

6) Excessive accommodation .

7) Spasm of accommodation .

8) Accommodative esotropia

Presbyopia Presbyopia is a condition of physiological insufficiency of

accommodation leading to a progressive fall in near vision.

Pathophysiology: In emmetropic eye far point is infinity and near point

varies with age (being about 7 cm at 10 years, 25 cm at 40 years and 33 cm at 45 years).

We read from 25 cm. After 40 years, the near point recedes beyond normal reading or working range.

Failing near vision due to age-related decrease in amplitude tion is called presbyopia

CausesDecrease in accommodative power of lens with increasing age, leads to presbyopia, occurs due to:

1)Age-related changes in lens: Decrease in elasticity of lens capsule, and Progressive, increase in size and hardness (sclerosis) of lens substance which is not easily moulded.

2)Age related decline in ciliary muscle power.

Premature presbyopia Uncorrected hypermetropia.

Premature sclerosis of the crystalline lens.

General debility causing pre-senile weakness of ciliary muscle.

Chronic simple glaucoma.

Symptoms Difficulty in near vision.

Patients complaint of difficulty in reading small prints.

Asthenopic symptoms due to fatigue of the ciliary muscle are also complained after reading or doing any near work.

Optical treatment Prescription of appropriate convex glasses for near work.

A rough guide for providing presbyopic glasses in an emmetrope can be made from patient’s age.

About +1 DS is required at the age of 40-45 years,

+1.5 DS at 45-50 years,

+ 2 DS at 50-55 years,

+2.5 DS at 55-60 years.

Basic principles of presbyopic correction Refractive error for distance is corrected first.

Correction needed in each eye should be tested separately and add it to distant correction.

Near point should be fixed according to the profession of patient.

Weakest convex lens with which one can see clearly at near point should be prescribed, overcorrection will also result in asthenopic symptoms.

Presbyopic spectacles may be unifocal, bifocal or varifocal

Surgical Treatment 1)Corneal procedures:

-Non ablative corneal procedure

-Monovision CK

-Laser based corneal procedure

-Laser thermal keratoplasty (LTK)

-Monovision LASIK.

-Presbyopic bifocal LASIK

-Presbyopic multifocal LASIK C

2)Intraocular refractive procedure-Refractive lens exchange-Phakic refractive lens-Monovision with IOLs

3)Scleral based procedures -Anterior sclerotomy with tissue barriers-Scleral spacing procedure-Scleral ablation with erbium : yag laser

Insufficiency of accommodation Def: Condition in which accommodative power is

constantly less than lower limit of normal range according to patient’s age.

Etiology :

1)Premature sclerosis of lens.

2)Weakness of ciliary muscle due to systemic causes: Debilitating illness, anemia, toxemia, malnutrition, dia betes mellitus, pregnancy, stress etc.

3)Weakness of ciliary muscle due to local causes: PAOG, mild cyclitis as during onset of sympathetic ophthalmia.

Clinical features 1) Features of eye strain and asthenopia.

2) Head ach, fatigue & irritability of the eyes, while attempting near work.

3) Near work is blurred & becomes difficult or impossible.

4) Disturbance of convergence : intermittent diplopia.

5) It is stable condition, if due to sclerosis of lens.

6) But is not stable in association with ciliary muscle weakness.

Treatment1) Identification & treatment of any systemic cause.

2) Any refractive error should be corrected & if vision for near work is seriously blurred then additional near correction has to be prescribed same as presbyopia.

3) If associated with convergence excess then full spherical correction.

4) Convergence insufficiency is there, then base in prisms can be added.

5) Prismatic correction added should bring near point of convergence to same distance as near point of accommodation.

6) Weakest convex lenses should be prescribed, so as to exercise and stimulate accommodation.7) After recovery additional correction should be made weaker and weaker from time to time.8) Accommodative exercises.

– While do exercises patient should wear correction for distance.

– Should be done simultaneously in both eyes, even if associated with convergence insufficiency.

– But with convergence excess then the exercise should done with one eye alternately.

– Accommodation test card exercise.– Useless in generalized debility and sclerosis of

lens.

Ill-Sustained accommodation Accommodation fatigue.

It is a situation in which though range of accommodation is in normal range but it cannot sustain it for a sufficient period of time.

Initial stage of insufficiency of accommodation.

It occurs due to:

– Stage of convalescence from debilitating illness

– Stage of generalized tiredness

– When the patient is relaxed in the bed

Clinical features These symptoms are most commonly reported at the

end of the day:

1) Blurred vision after prolonged near work.

2)Headaches.

3)Eyestrain.

4)Fatigue, sleepiness and a loss of comprehension with continued reading .

5)A dull 'pulling' sensation around the eye.

Treatment Near work should be curtailed during debilitating illness.

General tonic measures should be taken.

The condition of illumination and posture while doing near work, should be improved.

Inertia of accommodation It is a condition in which patient faces difficulty in altering

the range of accommodation.

Amplitude of accommodation is normal.

Ability to make use of this amplitude quickly and for long periods of time is inadequate

Clinical features 1) Difficulty changing focus from one distance to another.

2) Headaches.

3) Eyestrain.

4) Fatigue.

5) Difficulty sustaining near tasks.

6) Blurred vision.

Treatment: correcting any refractive error and accommodative exercises.

Paralysis of accommodation Cycloplegia, refers to complete absence of accommodation.

Causes:

1) Atropine, homatropine or other parasympatholytic drugs.

2) Internal ophthalmoplegia (paralysis of ciliary muscle and sphincter pupillae)due to neuritis associated with diphtheria, syphilis, diabetes, alcoholism, cerebral or meningeal diseases.

3) Complete third nerve paralysis due to intracranial or orbital causes.

4) Systemic medications such as antihypertensive, antidepressants.

Clinical features 1) Blurred vision at near.

2) Photophobia or a 'dazzling' effect.

3) Diplopia.

4) Micropsia: objects may appear smaller than they are due to a false sense of distance.

5) Enlarged pupil.

Treatment1) An effort should be made to find out the cause and try

to eliminate it.

2) Self-recovery occurs in drug-induced paralysis and in diphtheric cases (once systemic disease is treated).

3) Dark-glasses effective in reducing glare.

4) Convex lenses for near vision, if the paralysis is permanent.

Excessive accommodation Accommodative response is greater than the

accommodative stimulus.

There is functional increase in tonus of ciliary muscle, results in a constant accommodative effect.

Causes1) Young hypermetropes frequently uses excessive

accommodation as a physiological adaptation.

2) Young myopes performing excessive near work, associated with excessive convergence.

3) Astigmatic error in young patients.

4) Presbyopes in the beginning.

5) Use of improper and ill fitting spectacles.

Precipitating factors Excessive near work done, especially in dim or excessive

illumination.

General debility, physical or mental ill health

Symptoms1) Blurred vision at near is uncommon.

2) Blurred vision at distance.

3) Headaches.

4) Eyestrain.

5) Photophobia.

6) Difficulty changing focus from distance to near.

7) Diplopia

Treatment It has a good prognosis.

Refractive error should be corrected after carefully performed cycloplegic refraction.

Near work should be stopped for some time, after that it should be done with proper illumination conditions

Spasm of accommodation Def: Spasm of accommodation refers to exertion of

abnormally excessive accommodation.

Causes:1) Drug induced spasm of accommodation is known to

occur after use of strong miotics.

2) Spontaneous spasm of accommodation: attempt to compensate for a refractive anomaly.

3) Occurs when excessive near work is done with bad illumination, bad reading position, state of neurosis, mental stress or anxiety.

Clinical features 1) Defective vision: due to induced myopia.

2) Asthenopic symptoms.

3) Precipitating factors like marked degree of muscular imbalance, trigeminal neuralgia, a dental lesion, general intoxication

Treatment Relaxation of ciliary muscle by atropine for 4 weeks or

more

Prohibition of near work allow prompt recovery from spasm of accommodation.

Elimination of the associated causative factors to prevent the recurrence

Anomalies of accommodation are very common and management of these anomalies is an integral part of optometric practice

Accommodative esotropia Accommodative esotropia is a condition where in excessive

effort of accommodation results in an inward deviation of the eyes.

Most often it is caused by uncorrected Hypermetropia. Acquired Esotropia in a visually immature child is a day time

emergency. The consequences are loss of Binocular vision & onset of

amblyopia. The interval between the time of onset & the treatment

determines the visual outcome. Classification:

1)Refractive Accommodative. 2) Non- Refractive Accommodative.

3)Partially Accommodative (Mixed).

Terms to remember Range of Accommodation: The distance between the far point

and near point ie the distance over which accommodation is effective.

Amplitude of Accommodation: The difference between dioptric power needed to focus at far point (at rest) and at near point (fully accommodated).

Relative amplitude of accommodation: The total amount of accommodation which the eye can exert while the convergence of the eyes is fixed.It can be positive (using concave lenses until the image blurs). This is called positive relative accommodation (PRA)..It can be negative (using convex lenses until the image blurs). This is negative relative accommodation (NRA)

Lead of Accommodation: The amount by which the accommodative response of the eye is greater than the dioptric stimulus to accommodation.

Lag of Accommodation: The amount by which the accommodative response of the eye is less than the dioptric stimulus to accommodation

References: www.Wikipedia.com.

www.slideshare.com.

Evans BJW (1997) Pickwell’s Binocular Vision Anomalies, Butterworth-Heinemann, Oxford.

Duke-Elder S (1973), System of Ophthalmology, Kimpton, London .

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