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Accommodation and convergence

Accommodation is the process by which the eye adjusts its lens shape to focus on objects at varying distances, involving the ciliary muscles and several related mechanisms. Factors such as age can affect the range of accommodation and lead to conditions like presbyopia, where near vision progressively worsens. Various assessments and treatments, including optical aids and surgical procedures, can address different types of accommodation anomalies.

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Dr. Sameeksha Agrawal
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 Our eyes have been provided with a unique mechanism by which we can even focus the diverging rays coming from a near object on the retina. This special mechanism is called ACCOMMODATION.
MECHANISM OF ACCOMMODATION • Normally the crystalline lens is held under tension by the suspensory ligament (zonules) which attaches it to the ring of ciliary muscle and keep the lens flat. • Ciliary muscle contraction reduces the tension on the suspensory ligament and lens, allowing the lens to assume a more globular shape.
MECHANISM OF ACCOMMODATION • The curvature of the lens surfaces (mainly the anterior surface of the lens) increases. • Axial thickness of the lens increases. • Anterior pole of the lens moves slightly forwards carrying the iris with it, thus making the anterior chamber shallow. • All these changes lead to increase in the diopteric power of the lens.
OTHER CHANGES • Pupils constrict and the eyes converge in a bid to achieve clear vision for near objects. • Choroid is stretched forwards by the ciliary muscle contraction. • The ora serrata moves forward about 0.05mm with each dioptre of accommodation.
• Far point: Position of an object when its image clearly falls on retina with no accommodation. Also called as punctum remotum • Near point: Nearest point clearly seen with maximum accommodation. Also called as punctum proximum. • Range of accommodation: Distance between far point and near point.
VARIATION WITH STATIC REFRACTION OF EYE Hypermetropic eyes: far point is virtual and lies behind the eyes Myopic eyes: far point is real and lies in front of the eyes Emmetropic eye: far point is at infinity and near point varies with age. 07cm at 10 years 25 cm at 40 years 33 cm at 45 years Thus, amount the eye can alter its refraction is greatest at childhood and slowly decreases until its lost in middle age
• Depth of field: The range of distance from the eye in which an object appears clear without change of accommodation. It is inversely proportional to pupil size. • Depth of focus: The range in retina in which an optical image may move without impairment of clarity. It is directly proportional to pupil size
STIMULUS FOR ACCOMMODATION • Image blur • Apparent size and distance of object • Chromatic aberrations • Oscillation of accommodation • Scanning movements of the eye
ASSESSMENT OF ACCOMMODATION • This includes: 1. Assessment of NPA and amplitude of accommodation 2. Assessment of accommodative response 3. Assessment of dynamics of accommodation
ASSESSMENT OF NPA AND AMPLITUDE OF ACCOMMODATION • It is the difference in dioptric power needed to focus at near point and far point • Can be done by measuring NPA or using minus lenses. TO MEASURE NPA a) RAF rule or Prince’s rule • Patient wears full refractive correction • Sliding target with 6/9 letters is moved towards or from the eye till the closest point is found at which it is still seen clearly. • Done for each eye separately and the for both eyes • Measured in centimeters marked on one side and the side of the bar marked in dioptres will indicate amplitude.
RAF RULE:
• Amplitude of accommodation is low: near point lies beyond the length of instrument • Plus lenses added to refractive correction to bring near point within range and the dioptric power of these lenses is deducted from the measured value of accommodation. • Amplitude of accommodation is high: young patients • minus lenses added to distance correction to move near point away from eyes and the dioptric power of these lenses is added to the measured value of accommodation.
b) Using minus lenses • Performed for each eye separately. • Patient wears full refractive correction. • Patient is asked to fixate the best corrected near vision target at 40 cm. • Minus lenses of progressively increasing power are added till patient reports the first sustained blur. • Power of the minus lens plus +2.5D(for 40 cm) gives amplitude. c) Pushup test • Can be done both monocularly or binocularly. • Patient wears full refractive correction. • Near vision target is fixed at a point where it is seen clearly. • Moved closer till the patient reports first sustained blur • Linear distance measured between the target and the patient’s spectacle plane gives NPA.
ASSESSMENT OF ACCOMMODATIVE RESPONSE • Assessed with dynamic retinoscopy • Monocular Estimation Method (MEM) Patient is asked to fixate the near target at a distance of 40 cm. Retinoscopy is performed using streak retinoscope and the lens power required to attain neutrality is noted. • Nott Retinoscopy Dynamic retinoscopy is performed as in MEM except that the retinoscopic reflex is neutralized by moving the retinoscope. ‘With’ movements: retinoscope moved away from patient ‘Against’ movements: retinoscope moved towards patient
MEM:
• Lag of accommodation: Accommodative response is less than accommodative demand. Lag of > +1.00D is seen in accommodative insufficiency or infacility • Lead of accommodation: Accommodative response is more than accommodative demand. Lead of > +0.50D is seen in accommodative excess
ASSESSMENT OF DYNAMIC ACCOMMODATION • Assessed by testing accommodative facility. • An accommodative flipper of +2.00 DS with -2.00 DS is used by rapidly flipping the lenses Difficulty with + lenses: Accommodative excess Difficulty with - lenses: Presbyopes
TYPES OF ACCOMMODATION • 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. • Proximal accommodation – Is induced by the awareness of the nearness of a target. This is independent of the actual dioptric stimulus.
• Reflex accommodation – Is an automatic adjustment response to blur which is made to maintain a clear and sharp retinal image. • 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.
ACCOMMODATION REFLEX
• The afferent – Retina (with the retinal ganglion axons in the optic nerve, chiasm and tract), – Lateral geniculate body (with axons in the optic radiations) – Visual cortex. • Ocular motor control neurons are interposed between the afferent and efferent limbs of this circuit and include the visual association cortex
• It determines the image is "out-of-focus” & sends corrective signals | internal capsule and crus cerebri | supraoculomotor nuclei (generates motor control signals) | oculomotor complex.
• The efferent – Edinger-Westphal nucleus - oculomotor nerve - ciliary ganglion - short ciliary nerve - iris sphincter and the ciliary muscle/zonules/lens of the eye – oculomotor neurons - oculomotor nerve - medial rectus, converge the two eyes.
ANOMALIES OF ACCOMMODATION • Classification (by Duane with some modification): – Accommodative insufficiency • Ill-sustained accommodation- • Paralysis (or paresis) of accommodation • Unequal accommodation – Accommodative excess. – Inertia of accommodation
• Diminished or deficient accommodation – Physiological : Presbyopia – Pharmacological : Cycloplegia – Pathological » Insufficiency of accommodation » Ill sustained accommodation » Inertia of accommodation » Paralysis of accommodation • Increased accommodation
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 of accommodation is called presbyopia.
CAUSES • Decrease in accommodative power of lens with increasing age, leads to presbyopia, occurs due to: –Age-related changes in lens: oDecrease in elasticity of lens capsule, and oProgressive, increase in size and hardness (sclerosis) of lens substance which is not easily moulded. –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. • Intermittent diplopia at near may develop because of interrelation between accommodation and convergence. • All symptoms of presbyopia are aggravated by fatigue, illness, fever etc
PRESBYOPIA TREATMENT
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. What we follow: +1.00: 40 years. +1.25: 41-44 years. +1.50: 45 years. +1.75: 46-49 years. +2.00: 50 years. +2.25: 51-54 years. +2.50: 55 years. +2.75: 56-59 years. +3.00: 60 years and beyond.
BASIC PRINCIPLES OF PRESBYOPIC CORRECTION • Refractive error for distance is corrected first. • Correction needed in each eye should be tested separately and then 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 • Corneal procedures – Non ablative corneal procedure • Monovision CK – Laser based corneal procedure • Laser thermal keratoplasty (LTK) • Monovision LASIK. • Presbyopic bifocal LASIK • Presbyopic multifocal LASIK
• Intraocular refractive procedure – Refractive lens exchange – Phakic refractive lens – Monovision with IOLs • Scleral based procedures – Anterior sclerotomy with tissue barriers – Scleral spacing procedure – Scleral ablation with erbium : yag laser
INSUFFICIENCY OF ACCOMMODATION • Condition in which accommodative power is constantly less than lower limit of normal range according to patient’s age.
ETIOLOGY • Premature sclerosis of lens • Weakness of ciliary muscle due to systemic causes: Debilitating illness, anemia, toxemia, malnutrition, diabetes mellitus, pregnancy, stress etc. • Weakness of ciliary muscle due to local causes: PAOG, mild cyclitis as during onset of sympathetic ophthalmia.
CLINICAL FEATURES • Features of eye strain and asthenopia. • Headache, fatigue & irritability of the eyes, while attempting near work. • Near work is blurred & becomes difficult or impossible. • Disturbance of convergence : intermittent diplopia. • It is stable condition, if due to sclerosis of lens. • But is not stable in association with ciliary muscle weakness.
TREATMENT • Identification & treatment of any systemic cause. • 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. • If associated with convergence excess then full spherical correction is prescribed. • Convergence insufficiency is there, then base in prisms can be added. • Prismatic correction added should bring near point of convergence to same distance as near point of accommodation. • Weakest convex lenses should be prescribed, so as to exercise and stimulate accommodation. • After recovery additional correction should be made weaker from time to time.
• Accommodative exercises. – While doing exercises patient should wear correction for distance. – Should be done simultaneously in both eyes, even if associated with convergence insufficiency. – If associated 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 it cannot be sustained 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 • Blurred vision after prolonged near work. • Headaches • Eyestrain • Fatigue, sleepiness and a loss of comprehension with continued reading • 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 • Difficulty changing focus from one distance to another • Headaches • Eyestrain • Fatigue • Difficulty sustaining near tasks • Blurred vision TREATMENT: correcting any refractive error and accommodative exercises.
PARALYSIS OF ACCOMMODATION • Cycloplegia, refers to complete absence of accommodation. • Causes –Atropine, homatropine or other parasympatholytic drugs. –Internal ophthalmoplegia (paralysis of ciliary muscle and sphincter pupillae)due to neuritis associated with diphtheria, syphilis, diabetes, alcoholism, cerebral or meningeal diseases.
–Complete third nerve paralysis due to intracranial or orbital causes. –Systemic medications such as anti-hypertensive, antidepressants.
CLINICAL FEATURES • Blurred near vision • Photophobia or a 'dazzling' effect • Diplopia • Micropsia: objects may appear smaller than they are due to a false sense of distance • Dilated pupil.
TREATMENT • An effort should be made to find out the cause and try to eliminate it. • Self-recovery occurs in drug-induced paralysis and in diphtheric cases (once systemic disease is treated). • Dark-glasses effective in reducing glare. • 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 tone of ciliary muscle, results in a constant accommodative effect.
CAUSES • Young hypermetropes frequently uses excessive accommodation as a physiological adaptation • Young myopes performing excessive near work, associated with excessive convergence. • Astigmatic error in young patients • Presbyopes in the beginning • 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
SYMPTOMS • Blurred vision at near is uncommon and is due to induced pseudomyopia • Blurred vision at distance • Headaches • Eyestrain • Photophobia • Difficulty changing focus from distance to near • 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 • Spasm of accommodation refers to exertion of abnormally excessive accommodation which is out of the voluntary control of the individual
CAUSES • Drug induced spasm of accommodation is known to occur after use of strong miotics. • Spontaneous spasm of accommodation: attempt to compensate for a refractive anomaly. • Occurs when excessive near work is done with bad illumination, bad reading position, state of neurosis, mental stress or anxiety. • Iridocyclitis: ciliary spasm. • Lesions of brainstem in their irritative phase. • Toxic reactions of exogenous poisons: sulphonamides, arsenic, smoking.
CLINICAL FEATURES • Defective vision: due to induced myopia. • Asthenopic symptoms typically headache and brow ache • Near point is abnormally close. • Macropsia occurs due to optical illusion • 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.
CONVERGENCE
CONVERGENCE • It a disjugate movement in which both the eyes rotate inwards so that the line of sight intersects in front of the eyes. • Allows bifocal single vision to be maintained at any fixation distance. • Remains constant throughout life.
TYPES OF CONVERGENCE A. VOLUNTARY CONVERGENCE It is the convergence of visual axis which can be produced at will. Not a part of normal convergence movement. B. REFLEX CONVERGENCE It is the convergence of visual axis which is not under voluntary control. Has 4 components: 1. Tonic convergence 2. Fusional convergence 3. Accommodative convergence 4. Proximal convergence
A. TONIC CONVERGENCE: • Due to inherent innervational tone of the EOM when the patient is awake • Sum of excitatory and inhibitory influences from cortical subcortical centres and vestibular organs • Independent of fusion or object proximity • Strongest in childhood and decreases with age B. FUSIONAL CONVERGENCE: • It is the convergence produced to ensure that similar retinal images are projected on to corresponding retinal areas. • Occurs without change in refractive state of the eye. • It is a response to disparate stimuli lying outside the pannum’s fusional area • Important mechanism for achievement of bifoveal single vision
• Fusional convergence helps control exophoria. • Decreases in fatigue or illness converting a phoria into a tropia. C. ACCOMMODATIVE CONVERGENCE: • Occurs when eyes accommodate or when a nerve impulse to accommodate is discharged to the eyes. • Its stimulus is blurred retinal images. • Forms a part of the synkinetic near reflex complex (miosis+ accommodation+ convergence) • The quantitative relationship between accommodative convergence and accommodation is measured as the AC/C ratio. (AC is measured in prism dioptres and accommodation in lens dioptres) • It is a linear relationship and stays relatively stable throughout life. • Myopes: high AC/A ratio • Hypermetropes: Low AC/A ratio
• IPD is also considered while calculating the AC/A ratio as greater convergence is required in patients with wide IPD compared to patients with narrow IPD. • Abnormalities of AC/A ratio D. PROXIMAL CONVERGENCE • Induced by proximity of the object or the awareness of the proximity of the near object. • Initiation is by psychological factors. STABISMUS High AC/A ratio Low AC/A ratio Convergence excess Causes convergent squint On accommodating on near object Causes divergent squint On accommodating at near object
ANGLE OF CONVERGENCE • Angle that is formed between the primary lines of sight during convergence • Its size depends on fixation distance (inversely) and IPD (directly; but has negligible effect on the angle) • Can be measured in metre angle or prism dioptres Fixation point Fixation point Fixation point FIXATION DISTANCE IPD
METRE ANGLE: • 1 metre angle convergence is exerted by each eye when the eyes are directed to an object at a distance of 1 m from the meridian line between the two eyes. • The convergence in metre angle is inversely proportional to the distance of the object in front of the eyes in metres. • Emmetropic eye: number of dioptres of accommodation required is equal to number of metre angles the eye must converge to see object clearly
• PRISM DIOPTRES • The convergence required to see an object placed at 1 m distance from the eyes singly, when a prism of 1 prism dioptre is placed in front of one eye. • Base out prism (converging) is placed in front of the eye. • Deviates rays of light entering the eye outwards. • To overcome the diplopia produced the eye will turn inwards. • 1 METRE ANGLE CONVERGENCE = 3 PRISM DIOPTRES CONVERGENCE
CONVERGENCE • Near point: closest point at which an object can be seen singly during bifoveal vision i.e. the point at which the 2 foveal lines of sight intersect when maximum convergence is exerted. • Measurement of NPC: Measures all type of convergences as the object actually approaches the eye during testing. • Instruments: RAF ruler Livingstone Binocular gauge Prince rule
CONVERGENCE • Far point: relative position of eyes when they are completely at rest. • Range of convergence: Distance between the near point of convergence and far point of convergence Part of range of convergence between the eye and infinity: positive convergence Part of range of convergence beyond infinity (behind eye) when eyes are in divergence: negative convergence or divergence • Amplitude of convergence: It is the difference in the converging power needed to maintain the eye in a position of rest and a position of maximum convergence. • Measure of the amplitude of convergence can be done by: 1. Prism bar method 2. Synoptophore method
AC /A RATIO • It is a relationship between accommodative convergence expressed in prism dioptres and accommodation expressed in lens dioptres. • Normal ratio: 3 to 5 prism dioptres for 1 D of accommodation. • Defined by Fry and named by Haines • Measurement methods: Hetrophoria method Gradient method Fixation disparity method Haploscopic method
HETROPHORIA METHOD • Full optical correction is given and deviation is measured at 6 m distance and at 33 cm distance in prism dioptres and IPD is measured in centimeters • Ratio is calculated as: AC= IPD +∆n-∆d/d • IPD= interpupillary distance • ∆n = deviation at 33 cm in prism dioptres • ∆d= deviation at 6 m distance in prism dioptres • D = distance of fixation for near in dioptres • Esodeviations are denoted by positive and exodeviations by negative
GRADIENT METHOD • For a given distance of fixation, minus lenses placed in front of the eye increase accommodation and plus lenses decrease accommodation. • Calculated as ∆L - ∆O/D • ∆L is deviation with additional lenses • ∆O is original deviation without the lenses • D is the Diopteric power of the additional lens • Inaccurate as does not take the patient’s IPD into account.
ANOMALIES OF CONVERGENCE
CONVERGENCE INSUFFICIENCY • Inability to obtain and/or maintain adequate binocular convergence for any length of time without undue effort • Most common cause of ocular asthenopic symptoms. • ETIOLOGY: Primary/ idiopathic: mechanism not known Associated with wide IPD, over work, stress Refractive errors: seen with uncorrected high hypermetropia > 5 D make no effort to accommodate and hence lack accommodative convergence as well myopia do not need accommodation and hence lack accommodative convergence. Presbyopia: less use of convergence as near point of eye recedes
Muscular imbalances: EOM muscles imbalance In form of exophoria, intermittent XT and vertical muscle imbalance if neglected for long Consecutive convergence insufficiency: due to recession of MR or resection of LR
CLINICAL FEATURES A. Symptoms of muscular fatigue: due to continuous use of neuromuscular power and marked with near work. Eyestrain and a sensation of tension in and around globes Headache and eye ache after prolong near work Difficulty in changing focus from distant to near Itching/burning/soreness B. Symptoms of failure to maintain binocular vision Blurred near vision + crowding of words while reading Intermittent crossed diplopia for near vision Closure of one eye while reading to obtain relief from visual fatigue
DIAGNOSIS • Remote NPC: When NPC > 10cm from base line CI is said to exist. • Decreased fusional convergence for near: measured using synoptophore. CI is said to exist if its difficult to attain 30⁰ of convergence. • Prism convergence: low prism convergence with normal prism divergence. • Normal NPA.
CONVERGENCE INSUFFICIENCY CONVERGENCE PARALYSIS Some amount of convergence amplitude can be demonstrated Total lack of ability to overcome any amount of BO prism On receiving a converging impulse pupillary constriction occurs while converging on the approaching target which is followed by dilation of the pupil when convergence can not be maintained On receiving a converging impulse pupillary constriction occurs while the ability to converge is lost CONVERGENCE INSUFFICIENCY ACCOMMODATIVE EFFORT SYNDROME Exophoria at near Esophoria Helped by -3 D test by compensating for the lack of good fusional convergence Patient goes into tropia with this test Plus lenses worsen CI due to relaxation of accommodative convergence Plus lenses improve symptoms due to relaxation of accommodative convergence
TREATMENT • Good prognosis • Children are treated when fusional vergences are poor and patient shows signs of becoming exotropic. • Adults are treated when they show symptoms. • TREATMENT Optical treatment Orthoptic excersises Prismotherapy Surgery
A. OPTICAL TREATMENT Myopes: full correction Hypermetropes: undercorrection Stimulate accommodation which simultaneously stimulate convergence B. ORTHOPTIC TREATMENT Aim: to improve binocular convergence and to increase amplitude of fusional convergence Includes: Exercises to improve NPC Exercises to increase amplitude of fusional convergence Training of voluntary convergence Relaxation exercises
• Exercise to increase NPC Advancement exercise Jump convergence exercise: More elaborate and effective Trains patient to achieve bifoveal single vision following a sudden change in convergence requirements Done only after fourth week of convergence training when convergence has been improved using other exercises • Exercises to improve amplitude of fusional convergence Using prisms: base out prisms placed in front of the eyes Using synoptophore: The arms are slowly converged starting from the point where the patient can fuse the picture. • Exercises using convergence card • Physiologic diplopia exercise using stereogram in the uncrossed position. • Convergence exercise using diploscope.
• Training of voluntary convergence • Relaxation exercises Physiologic diplopia exercises using stereogram in crossed position Divergence exercises on synoptophore Divergence exercises with prisms C. Prism therapy: Useful when orthoptic measures fail. Base-in prism (relieving prisms) reading glasses are used. It should be avoided in young age. D. Surgery: Last resort, used when all other measures fail. Medial rectus resection is done in one or both eyes.
CONVERGENCE INSUFFICIENCY ASSOCIATED WITH ACCOMMODATIVE INSUFFICIENCY • Where convergence insufficiency is secondary to accommodative insufficiency. Etiology: - Early Adie’s syndrome. - Sequel to head injury viz posterior occipital or whiplash injury. - Subclinical viral encephalopathies. - Infectious mononucleosis. - Diphtheria. - Conversion reaction
• Clinical features: - NPC reduced - NPA reduced drastically - AC/A ratio is low or even absent. • Management: - Orthoptic exercises (alone are usually not much effective and are hence combined with reading glasses) - Plus lenses for reading along with base in prisms are the treatment of choice. - Resection of medial rectus followed by prescription of bifocal adds may be helpful in untreatable cases.
CONVERGENCE PARALYSIS • Clinical features: - Complete absence of convergence. - Exotropia and crossed diplopia on attempted near fixation only. - Normal adduction and normal accommodation. • Diagnosis: Bielschowsky’s criteria that includes: 1. Evidence of intracranial disease 2. History of sudden onset crossed horizontal diplopia at near fixation 3. Reproducible findings on subsequent examinations. 4. Preservation of accommodation and pupillary reaction on attempts to converge.
• Management: 1) Base- in prisms for near (for diplopia) 2) Plus lenses with base in prisms for weakness of accommodation. 3) Occlusion of one eye at near in patients where it is not possible to restore comfortable single binocular vision. 4) Eye muscle surgery is contraindicated.
CONVERGENCE SPASM • Intermittent episodes of maximal convergence usually associated with spasm of accommodation. • Etiology - Functional (Hysterical & Neurotic patients) - Organic (after head trauma, encephalitis, tabes dorsalis, pituitary adenomas, posterior fossa neurofibroma & Arnold-Chiari malformation)
• Clinical features: in most of the cases condition is episodic. In between the attacks patients are normal. - Eyes may be fixed in extreme convergence (like bilateral abducens palsy) - Homonymous diplopia (patient may give a history of intermittent diplopia) - Blurred vision (for near due to associated spasm of accommodation) - Miosis (due to near reflex) - Induced myopia (of 6D due to associated spasm of accommodation, resulting in decreased VA for distance)
• Management: a. Psychiatric & neurological assessment. b. Prolonged atropinization with plus lenses. c. Alternate monocular occlusion may be an alternative to atropinization. d. Psychiatric therapy.
Accommodation and convergence

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In this document
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Title slide and introduction to the topic of accommodation in the eye.

Accommodation is the eye's mechanism to focus at different distances by changing lens shape.

Details on the ciliary muscle's role and lens changes during accommodation affecting curvature.

Pupil constriction and eye convergence to achieve clear vision, along with choroidal stretch.

Definitions of far point and near point, and the range of accommodation explained.

Accommodation response varies with refractive errors: hyperopia, myopia, and emmetropia.

Differentiates depth of field and depth of focus in relation to pupil size.

Factors that stimulate accommodation, such as image blur, distance perception, and aberrations.

Methods for assessing near point and amplitude of accommodation using specific techniques.

Various tests used to measure NPA, modified for each eye's accommodation response.

Evaluation of accommodative response using dynamic retinoscopy techniques.

Differentiates tonic, proximal, reflex, and convergence-accommodation types.

Details of afferent and efferent pathways in the accommodation reflex.

Conditions such as insufficiency, excess, and presbyopia affecting accommodation capabilities.

Age-related changes and symptoms impacting near vision leading to presbyopia.

Optical and surgical interventions designed for managing presbyopia.

Definition and causes of accommodative insufficiency, along with clinical features.

Details symptoms and features related to accommodative fatigue.

Describes inertia of accommodation and conditions that lead to total accommodation paralysis.

Details on excessive accommodation response and methods for treatment.

Describes abnormal muscle contraction during accommodation and potential causes.

Defines convergence as a movement mechanism for maintaining single vision.

Classification of convergence types: tonic, fusional, accommodative, and proximal.

Techniques for measuring convergence angles and distances.

Defines and measures the relationship between accommodative convergence and accommodation.

Diagnosis and symptoms related to convergence insufficiency.

Describes features and management strategies for convergence paralysis.Clinical features, management, and treatment approaches for convergence spasm.

Accommodation and convergence

  • 1.
  • 2.
  • 3.
    DEFINITION Accommodation is themechanism by which the eye changes refractive power by altering the shape of lens in order to focus objects at variable distances Our eyes have been provided with a unique mechanism by which we can even focus the diverging rays coming from a near object on the retina. This special mechanism is called ACCOMMODATION.
  • 4.
    MECHANISM OF ACCOMMODATION •Normally the crystalline lens is held under tension by the suspensory ligament (zonules) which attaches it to the ring of ciliary muscle and keep the lens flat. • Ciliary muscle contraction reduces the tension on the suspensory ligament and lens, allowing the lens to assume a more globular shape.
  • 5.
    MECHANISM OF ACCOMMODATION •The curvature of the lens surfaces (mainly the anterior surface of the lens) increases. • Axial thickness of the lens increases. • Anterior pole of the lens moves slightly forwards carrying the iris with it, thus making the anterior chamber shallow. • All these changes lead to increase in the diopteric power of the lens.
  • 6.
    OTHER CHANGES • Pupilsconstrict and the eyes converge in a bid to achieve clear vision for near objects. • Choroid is stretched forwards by the ciliary muscle contraction. • The ora serrata moves forward about 0.05mm with each dioptre of accommodation.
  • 7.
    • Far point:Position of an object when its image clearly falls on retina with no accommodation. Also called as punctum remotum • Near point: Nearest point clearly seen with maximum accommodation. Also called as punctum proximum. • Range of accommodation: Distance between far point and near point.
  • 8.
    VARIATION WITH STATICREFRACTION OF EYE Hypermetropic eyes: far point is virtual and lies behind the eyes Myopic eyes: far point is real and lies in front of the eyes Emmetropic eye: far point is at infinity and near point varies with age. 07cm at 10 years 25 cm at 40 years 33 cm at 45 years Thus, amount the eye can alter its refraction is greatest at childhood and slowly decreases until its lost in middle age
  • 9.
    • Depth offield: The range of distance from the eye in which an object appears clear without change of accommodation. It is inversely proportional to pupil size. • Depth of focus: The range in retina in which an optical image may move without impairment of clarity. It is directly proportional to pupil size
  • 10.
    STIMULUS FOR ACCOMMODATION •Image blur • Apparent size and distance of object • Chromatic aberrations • Oscillation of accommodation • Scanning movements of the eye
  • 11.
    ASSESSMENT OF ACCOMMODATION •This includes: 1. Assessment of NPA and amplitude of accommodation 2. Assessment of accommodative response 3. Assessment of dynamics of accommodation
  • 12.
    ASSESSMENT OF NPAAND AMPLITUDE OF ACCOMMODATION • It is the difference in dioptric power needed to focus at near point and far point • Can be done by measuring NPA or using minus lenses. TO MEASURE NPA a) RAF rule or Prince’s rule • Patient wears full refractive correction • Sliding target with 6/9 letters is moved towards or from the eye till the closest point is found at which it is still seen clearly. • Done for each eye separately and the for both eyes • Measured in centimeters marked on one side and the side of the bar marked in dioptres will indicate amplitude.
  • 13.
  • 14.
    • Amplitude ofaccommodation is low: near point lies beyond the length of instrument • Plus lenses added to refractive correction to bring near point within range and the dioptric power of these lenses is deducted from the measured value of accommodation. • Amplitude of accommodation is high: young patients • minus lenses added to distance correction to move near point away from eyes and the dioptric power of these lenses is added to the measured value of accommodation.
  • 15.
    b) Using minuslenses • Performed for each eye separately. • Patient wears full refractive correction. • Patient is asked to fixate the best corrected near vision target at 40 cm. • Minus lenses of progressively increasing power are added till patient reports the first sustained blur. • Power of the minus lens plus +2.5D(for 40 cm) gives amplitude. c) Pushup test • Can be done both monocularly or binocularly. • Patient wears full refractive correction. • Near vision target is fixed at a point where it is seen clearly. • Moved closer till the patient reports first sustained blur • Linear distance measured between the target and the patient’s spectacle plane gives NPA.
  • 16.
    ASSESSMENT OF ACCOMMODATIVERESPONSE • Assessed with dynamic retinoscopy • Monocular Estimation Method (MEM) Patient is asked to fixate the near target at a distance of 40 cm. Retinoscopy is performed using streak retinoscope and the lens power required to attain neutrality is noted. • Nott Retinoscopy Dynamic retinoscopy is performed as in MEM except that the retinoscopic reflex is neutralized by moving the retinoscope. ‘With’ movements: retinoscope moved away from patient ‘Against’ movements: retinoscope moved towards patient
  • 17.
  • 18.
    • Lag ofaccommodation: Accommodative response is less than accommodative demand. Lag of > +1.00D is seen in accommodative insufficiency or infacility • Lead of accommodation: Accommodative response is more than accommodative demand. Lead of > +0.50D is seen in accommodative excess
  • 19.
    ASSESSMENT OF DYNAMIC ACCOMMODATION •Assessed by testing accommodative facility. • An accommodative flipper of +2.00 DS with -2.00 DS is used by rapidly flipping the lenses Difficulty with + lenses: Accommodative excess Difficulty with - lenses: Presbyopes
  • 20.
    TYPES OF ACCOMMODATION •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. • Proximal accommodation – Is induced by the awareness of the nearness of a target. This is independent of the actual dioptric stimulus.
  • 21.
    • Reflex accommodation –Is an automatic adjustment response to blur which is made to maintain a clear and sharp retinal image. • 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.
  • 22.
  • 23.
    • The afferent –Retina (with the retinal ganglion axons in the optic nerve, chiasm and tract), – Lateral geniculate body (with axons in the optic radiations) – Visual cortex. • Ocular motor control neurons are interposed between the afferent and efferent limbs of this circuit and include the visual association cortex
  • 24.
    • It determinesthe image is "out-of-focus” & sends corrective signals | internal capsule and crus cerebri | supraoculomotor nuclei (generates motor control signals) | oculomotor complex.
  • 25.
    • The efferent –Edinger-Westphal nucleus - oculomotor nerve - ciliary ganglion - short ciliary nerve - iris sphincter and the ciliary muscle/zonules/lens of the eye – oculomotor neurons - oculomotor nerve - medial rectus, converge the two eyes.
  • 26.
    ANOMALIES OF ACCOMMODATION •Classification (by Duane with some modification): – Accommodative insufficiency • Ill-sustained accommodation- • Paralysis (or paresis) of accommodation • Unequal accommodation – Accommodative excess. – Inertia of accommodation
  • 27.
    • Diminished ordeficient accommodation – Physiological : Presbyopia – Pharmacological : Cycloplegia – Pathological » Insufficiency of accommodation » Ill sustained accommodation » Inertia of accommodation » Paralysis of accommodation • Increased accommodation
  • 28.
    PRESBYOPIA Presbyopia is acondition of physiological insufficiency of accommodation leading to a progressive fall in near vision.
  • 29.
    PATHOPHYSIOLOGY • In emmetropiceye 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 of accommodation is called presbyopia.
  • 31.
    CAUSES • Decrease inaccommodative power of lens with increasing age, leads to presbyopia, occurs due to: –Age-related changes in lens: oDecrease in elasticity of lens capsule, and oProgressive, increase in size and hardness (sclerosis) of lens substance which is not easily moulded. –Age related decline in ciliary muscle power.
  • 32.
    PREMATURE PRESBYOPIA • Uncorrectedhypermetropia. • Premature sclerosis of the crystalline lens. • General debility causing pre-senile weakness of ciliary muscle. • Chronic simple glaucoma.
  • 33.
    SYMPTOMS • Difficulty innear 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. • Intermittent diplopia at near may develop because of interrelation between accommodation and convergence. • All symptoms of presbyopia are aggravated by fatigue, illness, fever etc
  • 34.
  • 35.
    OPTICAL TREATMENT • Prescriptionof 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. What we follow: +1.00: 40 years. +1.25: 41-44 years. +1.50: 45 years. +1.75: 46-49 years. +2.00: 50 years. +2.25: 51-54 years. +2.50: 55 years. +2.75: 56-59 years. +3.00: 60 years and beyond.
  • 36.
    BASIC PRINCIPLES OFPRESBYOPIC CORRECTION • Refractive error for distance is corrected first. • Correction needed in each eye should be tested separately and then 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.
  • 37.
    SURGICAL TREATMENT • Cornealprocedures – Non ablative corneal procedure • Monovision CK – Laser based corneal procedure • Laser thermal keratoplasty (LTK) • Monovision LASIK. • Presbyopic bifocal LASIK • Presbyopic multifocal LASIK
  • 38.
    • Intraocular refractiveprocedure – Refractive lens exchange – Phakic refractive lens – Monovision with IOLs • Scleral based procedures – Anterior sclerotomy with tissue barriers – Scleral spacing procedure – Scleral ablation with erbium : yag laser
  • 40.
    INSUFFICIENCY OF ACCOMMODATION •Condition in which accommodative power is constantly less than lower limit of normal range according to patient’s age.
  • 41.
    ETIOLOGY • Premature sclerosisof lens • Weakness of ciliary muscle due to systemic causes: Debilitating illness, anemia, toxemia, malnutrition, diabetes mellitus, pregnancy, stress etc. • Weakness of ciliary muscle due to local causes: PAOG, mild cyclitis as during onset of sympathetic ophthalmia.
  • 42.
    CLINICAL FEATURES • Featuresof eye strain and asthenopia. • Headache, fatigue & irritability of the eyes, while attempting near work. • Near work is blurred & becomes difficult or impossible. • Disturbance of convergence : intermittent diplopia. • It is stable condition, if due to sclerosis of lens. • But is not stable in association with ciliary muscle weakness.
  • 43.
    TREATMENT • Identification &treatment of any systemic cause. • 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. • If associated with convergence excess then full spherical correction is prescribed. • Convergence insufficiency is there, then base in prisms can be added. • Prismatic correction added should bring near point of convergence to same distance as near point of accommodation. • Weakest convex lenses should be prescribed, so as to exercise and stimulate accommodation. • After recovery additional correction should be made weaker from time to time.
  • 44.
    • Accommodative exercises. –While doing exercises patient should wear correction for distance. – Should be done simultaneously in both eyes, even if associated with convergence insufficiency. – If associated with convergence excess then the exercise should done with one eye alternately. – Accommodation test card exercise. – Useless in generalized debility and sclerosis of lens.
  • 45.
    ILL-SUSTAINED ACCOMMODATION • Accommodationfatigue. • It is a situation in which though range of accommodation is in normal range it cannot be sustained 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
  • 46.
    CLINICAL FEATURES • Thesesymptoms are most commonly reported at the end of the day • Blurred vision after prolonged near work. • Headaches • Eyestrain • Fatigue, sleepiness and a loss of comprehension with continued reading • A dull 'pulling' sensation around the eye.
  • 47.
    TREATMENT • Near workshould be curtailed during debilitating illness. • General tonic measures should be taken. • The condition of illumination and posture while doing near work, should be improved.
  • 48.
    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.
  • 49.
    CLINICAL FEATURES • Difficultychanging focus from one distance to another • Headaches • Eyestrain • Fatigue • Difficulty sustaining near tasks • Blurred vision TREATMENT: correcting any refractive error and accommodative exercises.
  • 50.
    PARALYSIS OF ACCOMMODATION •Cycloplegia, refers to complete absence of accommodation. • Causes –Atropine, homatropine or other parasympatholytic drugs. –Internal ophthalmoplegia (paralysis of ciliary muscle and sphincter pupillae)due to neuritis associated with diphtheria, syphilis, diabetes, alcoholism, cerebral or meningeal diseases.
  • 51.
    –Complete third nerveparalysis due to intracranial or orbital causes. –Systemic medications such as anti-hypertensive, antidepressants.
  • 52.
    CLINICAL FEATURES • Blurrednear vision • Photophobia or a 'dazzling' effect • Diplopia • Micropsia: objects may appear smaller than they are due to a false sense of distance • Dilated pupil.
  • 53.
    TREATMENT • An effortshould be made to find out the cause and try to eliminate it. • Self-recovery occurs in drug-induced paralysis and in diphtheric cases (once systemic disease is treated). • Dark-glasses effective in reducing glare. • Convex lenses for near vision, if the paralysis is permanent.
  • 55.
    EXCESSIVE ACCOMMODATION • Accommodativeresponse is greater than the accommodative stimulus. • There is functional increase in tone of ciliary muscle, results in a constant accommodative effect.
  • 56.
    CAUSES • Young hypermetropesfrequently uses excessive accommodation as a physiological adaptation • Young myopes performing excessive near work, associated with excessive convergence. • Astigmatic error in young patients • Presbyopes in the beginning • Use of improper and ill fitting spectacles
  • 57.
    PRECIPITATING FACTORS • Excessivenear work done, especially in dim or excessive illumination. • General debility, physical or mental ill health
  • 58.
    SYMPTOMS • Blurred visionat near is uncommon and is due to induced pseudomyopia • Blurred vision at distance • Headaches • Eyestrain • Photophobia • Difficulty changing focus from distance to near • Diplopia
  • 59.
    TREATMENT • It hasa 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.
  • 60.
    SPASM OF ACCOMMODATION •Spasm of accommodation refers to exertion of abnormally excessive accommodation which is out of the voluntary control of the individual
  • 61.
    CAUSES • Drug inducedspasm of accommodation is known to occur after use of strong miotics. • Spontaneous spasm of accommodation: attempt to compensate for a refractive anomaly. • Occurs when excessive near work is done with bad illumination, bad reading position, state of neurosis, mental stress or anxiety. • Iridocyclitis: ciliary spasm. • Lesions of brainstem in their irritative phase. • Toxic reactions of exogenous poisons: sulphonamides, arsenic, smoking.
  • 62.
    CLINICAL FEATURES • Defectivevision: due to induced myopia. • Asthenopic symptoms typically headache and brow ache • Near point is abnormally close. • Macropsia occurs due to optical illusion • Precipitating factors like marked degree of muscular imbalance, trigeminal neuralgia, a dental lesion, general intoxication.
  • 63.
    TREATMENT • Relaxation ofciliary 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.
  • 64.
  • 65.
    CONVERGENCE • It adisjugate movement in which both the eyes rotate inwards so that the line of sight intersects in front of the eyes. • Allows bifocal single vision to be maintained at any fixation distance. • Remains constant throughout life.
  • 66.
    TYPES OF CONVERGENCE A.VOLUNTARY CONVERGENCE It is the convergence of visual axis which can be produced at will. Not a part of normal convergence movement. B. REFLEX CONVERGENCE It is the convergence of visual axis which is not under voluntary control. Has 4 components: 1. Tonic convergence 2. Fusional convergence 3. Accommodative convergence 4. Proximal convergence
  • 67.
    A. TONIC CONVERGENCE: •Due to inherent innervational tone of the EOM when the patient is awake • Sum of excitatory and inhibitory influences from cortical subcortical centres and vestibular organs • Independent of fusion or object proximity • Strongest in childhood and decreases with age B. FUSIONAL CONVERGENCE: • It is the convergence produced to ensure that similar retinal images are projected on to corresponding retinal areas. • Occurs without change in refractive state of the eye. • It is a response to disparate stimuli lying outside the pannum’s fusional area • Important mechanism for achievement of bifoveal single vision
  • 68.
    • Fusional convergencehelps control exophoria. • Decreases in fatigue or illness converting a phoria into a tropia. C. ACCOMMODATIVE CONVERGENCE: • Occurs when eyes accommodate or when a nerve impulse to accommodate is discharged to the eyes. • Its stimulus is blurred retinal images. • Forms a part of the synkinetic near reflex complex (miosis+ accommodation+ convergence) • The quantitative relationship between accommodative convergence and accommodation is measured as the AC/C ratio. (AC is measured in prism dioptres and accommodation in lens dioptres) • It is a linear relationship and stays relatively stable throughout life. • Myopes: high AC/A ratio • Hypermetropes: Low AC/A ratio
  • 69.
    • IPD isalso considered while calculating the AC/A ratio as greater convergence is required in patients with wide IPD compared to patients with narrow IPD. • Abnormalities of AC/A ratio D. PROXIMAL CONVERGENCE • Induced by proximity of the object or the awareness of the proximity of the near object. • Initiation is by psychological factors. STABISMUS High AC/A ratio Low AC/A ratio Convergence excess Causes convergent squint On accommodating on near object Causes divergent squint On accommodating at near object
  • 70.
    ANGLE OF CONVERGENCE •Angle that is formed between the primary lines of sight during convergence • Its size depends on fixation distance (inversely) and IPD (directly; but has negligible effect on the angle) • Can be measured in metre angle or prism dioptres Fixation point Fixation point Fixation point FIXATION DISTANCE IPD
  • 71.
    METRE ANGLE: • 1metre angle convergence is exerted by each eye when the eyes are directed to an object at a distance of 1 m from the meridian line between the two eyes. • The convergence in metre angle is inversely proportional to the distance of the object in front of the eyes in metres. • Emmetropic eye: number of dioptres of accommodation required is equal to number of metre angles the eye must converge to see object clearly
  • 72.
    • PRISM DIOPTRES •The convergence required to see an object placed at 1 m distance from the eyes singly, when a prism of 1 prism dioptre is placed in front of one eye. • Base out prism (converging) is placed in front of the eye. • Deviates rays of light entering the eye outwards. • To overcome the diplopia produced the eye will turn inwards. • 1 METRE ANGLE CONVERGENCE = 3 PRISM DIOPTRES CONVERGENCE
  • 73.
    CONVERGENCE • Near point:closest point at which an object can be seen singly during bifoveal vision i.e. the point at which the 2 foveal lines of sight intersect when maximum convergence is exerted. • Measurement of NPC: Measures all type of convergences as the object actually approaches the eye during testing. • Instruments: RAF ruler Livingstone Binocular gauge Prince rule
  • 74.
    CONVERGENCE • Far point:relative position of eyes when they are completely at rest. • Range of convergence: Distance between the near point of convergence and far point of convergence Part of range of convergence between the eye and infinity: positive convergence Part of range of convergence beyond infinity (behind eye) when eyes are in divergence: negative convergence or divergence • Amplitude of convergence: It is the difference in the converging power needed to maintain the eye in a position of rest and a position of maximum convergence. • Measure of the amplitude of convergence can be done by: 1. Prism bar method 2. Synoptophore method
  • 75.
    AC /A RATIO •It is a relationship between accommodative convergence expressed in prism dioptres and accommodation expressed in lens dioptres. • Normal ratio: 3 to 5 prism dioptres for 1 D of accommodation. • Defined by Fry and named by Haines • Measurement methods: Hetrophoria method Gradient method Fixation disparity method Haploscopic method
  • 76.
    HETROPHORIA METHOD • Fulloptical correction is given and deviation is measured at 6 m distance and at 33 cm distance in prism dioptres and IPD is measured in centimeters • Ratio is calculated as: AC= IPD +∆n-∆d/d • IPD= interpupillary distance • ∆n = deviation at 33 cm in prism dioptres • ∆d= deviation at 6 m distance in prism dioptres • D = distance of fixation for near in dioptres • Esodeviations are denoted by positive and exodeviations by negative
  • 77.
    GRADIENT METHOD • Fora given distance of fixation, minus lenses placed in front of the eye increase accommodation and plus lenses decrease accommodation. • Calculated as ∆L - ∆O/D • ∆L is deviation with additional lenses • ∆O is original deviation without the lenses • D is the Diopteric power of the additional lens • Inaccurate as does not take the patient’s IPD into account.
  • 78.
  • 79.
    CONVERGENCE INSUFFICIENCY • Inabilityto obtain and/or maintain adequate binocular convergence for any length of time without undue effort • Most common cause of ocular asthenopic symptoms. • ETIOLOGY: Primary/ idiopathic: mechanism not known Associated with wide IPD, over work, stress Refractive errors: seen with uncorrected high hypermetropia > 5 D make no effort to accommodate and hence lack accommodative convergence as well myopia do not need accommodation and hence lack accommodative convergence. Presbyopia: less use of convergence as near point of eye recedes
  • 80.
    Muscular imbalances: EOMmuscles imbalance In form of exophoria, intermittent XT and vertical muscle imbalance if neglected for long Consecutive convergence insufficiency: due to recession of MR or resection of LR
  • 81.
    CLINICAL FEATURES A. Symptomsof muscular fatigue: due to continuous use of neuromuscular power and marked with near work. Eyestrain and a sensation of tension in and around globes Headache and eye ache after prolong near work Difficulty in changing focus from distant to near Itching/burning/soreness B. Symptoms of failure to maintain binocular vision Blurred near vision + crowding of words while reading Intermittent crossed diplopia for near vision Closure of one eye while reading to obtain relief from visual fatigue
  • 82.
    DIAGNOSIS • Remote NPC:When NPC > 10cm from base line CI is said to exist. • Decreased fusional convergence for near: measured using synoptophore. CI is said to exist if its difficult to attain 30⁰ of convergence. • Prism convergence: low prism convergence with normal prism divergence. • Normal NPA.
  • 83.
    CONVERGENCE INSUFFICIENCY CONVERGENCEPARALYSIS Some amount of convergence amplitude can be demonstrated Total lack of ability to overcome any amount of BO prism On receiving a converging impulse pupillary constriction occurs while converging on the approaching target which is followed by dilation of the pupil when convergence can not be maintained On receiving a converging impulse pupillary constriction occurs while the ability to converge is lost CONVERGENCE INSUFFICIENCY ACCOMMODATIVE EFFORT SYNDROME Exophoria at near Esophoria Helped by -3 D test by compensating for the lack of good fusional convergence Patient goes into tropia with this test Plus lenses worsen CI due to relaxation of accommodative convergence Plus lenses improve symptoms due to relaxation of accommodative convergence
  • 84.
    TREATMENT • Good prognosis •Children are treated when fusional vergences are poor and patient shows signs of becoming exotropic. • Adults are treated when they show symptoms. • TREATMENT Optical treatment Orthoptic excersises Prismotherapy Surgery
  • 85.
    A. OPTICAL TREATMENT Myopes:full correction Hypermetropes: undercorrection Stimulate accommodation which simultaneously stimulate convergence B. ORTHOPTIC TREATMENT Aim: to improve binocular convergence and to increase amplitude of fusional convergence Includes: Exercises to improve NPC Exercises to increase amplitude of fusional convergence Training of voluntary convergence Relaxation exercises
  • 86.
    • Exercise toincrease NPC Advancement exercise Jump convergence exercise: More elaborate and effective Trains patient to achieve bifoveal single vision following a sudden change in convergence requirements Done only after fourth week of convergence training when convergence has been improved using other exercises • Exercises to improve amplitude of fusional convergence Using prisms: base out prisms placed in front of the eyes Using synoptophore: The arms are slowly converged starting from the point where the patient can fuse the picture. • Exercises using convergence card • Physiologic diplopia exercise using stereogram in the uncrossed position. • Convergence exercise using diploscope.
  • 88.
    • Training ofvoluntary convergence • Relaxation exercises Physiologic diplopia exercises using stereogram in crossed position Divergence exercises on synoptophore Divergence exercises with prisms C. Prism therapy: Useful when orthoptic measures fail. Base-in prism (relieving prisms) reading glasses are used. It should be avoided in young age. D. Surgery: Last resort, used when all other measures fail. Medial rectus resection is done in one or both eyes.
  • 89.
    CONVERGENCE INSUFFICIENCY ASSOCIATEDWITH ACCOMMODATIVE INSUFFICIENCY • Where convergence insufficiency is secondary to accommodative insufficiency. Etiology: - Early Adie’s syndrome. - Sequel to head injury viz posterior occipital or whiplash injury. - Subclinical viral encephalopathies. - Infectious mononucleosis. - Diphtheria. - Conversion reaction
  • 90.
    • Clinical features: -NPC reduced - NPA reduced drastically - AC/A ratio is low or even absent. • Management: - Orthoptic exercises (alone are usually not much effective and are hence combined with reading glasses) - Plus lenses for reading along with base in prisms are the treatment of choice. - Resection of medial rectus followed by prescription of bifocal adds may be helpful in untreatable cases.
  • 91.
    CONVERGENCE PARALYSIS • Clinicalfeatures: - Complete absence of convergence. - Exotropia and crossed diplopia on attempted near fixation only. - Normal adduction and normal accommodation. • Diagnosis: Bielschowsky’s criteria that includes: 1. Evidence of intracranial disease 2. History of sudden onset crossed horizontal diplopia at near fixation 3. Reproducible findings on subsequent examinations. 4. Preservation of accommodation and pupillary reaction on attempts to converge.
  • 92.
    • Management: 1) Base-in prisms for near (for diplopia) 2) Plus lenses with base in prisms for weakness of accommodation. 3) Occlusion of one eye at near in patients where it is not possible to restore comfortable single binocular vision. 4) Eye muscle surgery is contraindicated.
  • 93.
    CONVERGENCE SPASM • Intermittentepisodes of maximal convergence usually associated with spasm of accommodation. • Etiology - Functional (Hysterical & Neurotic patients) - Organic (after head trauma, encephalitis, tabes dorsalis, pituitary adenomas, posterior fossa neurofibroma & Arnold-Chiari malformation)
  • 94.
    • Clinical features:in most of the cases condition is episodic. In between the attacks patients are normal. - Eyes may be fixed in extreme convergence (like bilateral abducens palsy) - Homonymous diplopia (patient may give a history of intermittent diplopia) - Blurred vision (for near due to associated spasm of accommodation) - Miosis (due to near reflex) - Induced myopia (of 6D due to associated spasm of accommodation, resulting in decreased VA for distance)
  • 95.
    • Management: a. Psychiatric& neurological assessment. b. Prolonged atropinization with plus lenses. c. Alternate monocular occlusion may be an alternative to atropinization. d. Psychiatric therapy.