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WHAT IS ACCOMMODATION ?
• KNOWN FACT : in an emmetropic eye, parallel rays of
light coming from infinity are brought to focus on retina,
with accommodation at rest.
• WHAT ABOUT THE DIVERGING RAYS COMING FROM
NEAR OBJECT ?
• Our eyes has been provided with a unique mechanism by
which we can even focus the diverging rays coming from
near object on retina in bid to see clearly.
• IN IT THERE IS INCREASE IN LENS POWER.
• NEAR POINT OF ACCOMMODATION :
• The nearest point at which small objects can
be seen clearly is called near point of
accommodation or punctum proximum.
• the distant point is called far point off
accommodation or punctum remotum.
• RANGE OF ACCOMMODATION:
• The distance between near point and far point
is called range of accommodation.
• AMPLITUDE OF ACCOMMODATION:
• The difference between DIOPTRIC power,
needed to focus at near point (P) and to focus
at far point (R), is called amplitude of
accommodation (A). Thus, A=P-R
POINTS TO BE KNOWN...
• In HYPROPIC eye, far point is virtual and lies
behind the eye.
• In MYOPIC eye, far point is real and lies in
front of the eye.
• In an EMMETROPIC eye, far point is at infinity
and near point varies with age...
Near point in centimeters Age in years
DEPTH OF FIELD...
• The range of distance from the eye in which
an object appears clear without change in
accommodation is termed depth of field.
• It reduces the necessity for precise
DEPTH OF FOCUS...
• The range at the retina in which an optical
image may move without impairment of
clarity is termed as depth of focus.
THEORIES OF ACCOMMODATION…
• Numerous theories have been proposed on
• Few of these are as follows.
PROOF OF EXISTENCE OF
• Till 17th
century unknown that it is necessry
for eye to change its power in order to focus
• 1619 Christopher Scheiner gave proof of
existence of accommodation.
• 1801 Thomas Young demonstrated lens is
responsible for accommodation
• 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.
Relaxation theory of HELMHOLTZ
• Also known as the “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
• Lens assumes more spherical form, increasing
thickness and decreasing diameter.
GULLSTRAND mechanical model of
• It is based on HELMHOLTZ hypothesis
• GULLSTRAND devised a mechanical model to
• It shows in unaccommodated state elasticity
of choroid is stronger than lens. When
accommodation comes into play weight i.e
ciliary muscles contract to overcome elasticity
• It helps lens to take accommodated shape.
Changes in eye due to
Slackening of the zonules
Change in the curvature of lens surface
Changes in the tension of lens capsule
The lens sinks down
Change within the lens substance
Pupillary constriction and convergence of eyes
The ora serrata
• The AC/A ratio is the relationship between
accommodative convergence (AC) expressed
in prism diopetrs, and accommodation (A)
expressed in lens diopters.
• This relationship is linear one and is thought
to be relatively stable throughout life.
• Normal AC/A ratio- 3-5 prism D for 1D of
• NRA is a measure of its maximum ability to
relax accommodation while maintaining clear,
single binocular vision.
• PRA is ameasure of maximum ability to
stimulate accommodation while maintaining
clear, single binocular vision.
It refers to a time lapse between the
presentation of an accommodative stimulus and
occurrence of accommodative response.
•Average reaction time for far-to-near
accommodation is 0.64 sec and for near-to-far is
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.
– 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.
• DIMINISHED ACCOMMODATION
Presbyopia is a condition of physiological
insufficiency of accommodation leading to a
progressive fall in near vision.
• 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
• Failing near vision due to age-related decrease in
amplitude of accommodation is called
• 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.
• Uncorrected hypermetropia.
• Premature sclerosis of the crystalline lens.
• General debility causing pre-senile weakness of
• Chronic simple glaucoma.
• 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.
• Prescription of appropriate convex glasses for near
• 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
• 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
• 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
• 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
• 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.
• 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
• Features of eye strain and asthenopia.
• Head ach, fatigue & irritability of the eyes, while
attempting near work.
• Near work is blurred & becomes difficult or
• Disturbance of convergence : intermittent diplopia.
• It is stable condition, if due to sclerosis of lens.
• But is not stable in association with ciliary muscle
• 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
• If associated with convergence excess then full
• 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 and weaker from time to time.
• 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
• 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
• These symptoms are most commonly reported
at the end of the day
• Blurred vision after prolonged near work.
• Fatigue, sleepiness and a loss of comprehension
with continued reading
• A dull 'pulling' sensation around the eye.
• Near work should be curtailed during debilitating
• 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.
• Difficulty changing focus from one distance to
• Difficulty sustaining near tasks
• Blurred vision
Treatment: correcting any refractive error and
Paralysis of accommodation
• Cycloplegia, refers to complete absence of
– Atropine, homatropine or other parasympatholytic
– 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,
• Blurred vision at near
• Photophobia or a 'dazzling' effect
• Micropsia: objects may appear smaller than they
are due to a false sense of distance
• Enlarged pupil.
• 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
• Accommodative response is greater than the
• There is functional increase in tonus of ciliary muscle,
results in a constant accommodative effect.
• 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
• Excessive near work done, especially in dim or
• General debility, physical or mental ill health
• Blurred vision at near is uncommon
• Blurred vision at distance
• Difficulty changing focus from distance to near
• 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
Spasm of accommodation
• Spasm of accommodation refers to exertion of
abnormally excessive accommodation.
• 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.
• Defective vision: due to induced myopia.
• Asthenopic symptoms
• Precipitating factors like marked degree of
muscular imbalance, trigeminal neuralgia, a
dental lesion, general intoxication.
• Relaxation of ciliary muscle by atropine for 4 weeks
or more and
• Prohibition of near work allow prompt recovery from
spasm of accommodation.
• Elimination of the associated causative factors to
prevent the recurrence.
• Primary care optometry
• A.K.Khurana (optics and refraction)
• A.K.Khurana (squint and orthoptics)
• REFERENCE PPT…