Theories & Anomalies Of
Dr. Rohit Rao
• Duke-Elder’s practice of refraction by David
• Optics & Refraction By A K Khurana
• Textbook of Ophthalmology by E Ahmed
• Clinical Optics By A R. Elkington
• Borish's Clinical Refracfion By W J. Benjamin
• Werner L, Trindade F, Pereira F,Werner L
Physiology of Accommodation and
Presbyopia, ARQ. BRAS. OFTALMOL.
63(6), December 2000.
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
• Far point: Position of an object when its
image clearly falls on retina with no
• Near point: Nearest point clearly seen with
• Range of accommodation: Distance
between far point and near point.
• Amplitude of accommodation: Dioptric power
difference between rest and fully
– A=P-R ( A: amplitude of accommodation; P:dioptric
value of near point; and R: dioptric value of far
– To view near object: Accommodation for clear retinal
images, & convergence for binocular single vision.
– The number of prism dioptres of convergence which
accompanies each dioptre of accommodation is
– The normal range for the AC/A ratio is 3:1 to 5:1.
• The exact mechanism of accommodation is
• In year 1801 YOUNG reported lens is responsible
“Principal fact that ACCOMMODATION is a feature of
increase in the curvature of the lens which affects anterior
Relaxation theory of
• 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
• 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.
Points in favour of the
• Imaging technique showed that ciliary
muscle move anteriorly & the equatorial
edge of lens move away from sclera
• Gonio-videography show zonular fibers
extending from ciliary processes to lens
equator, are relaxed during
Points against the theory
• It is not clear how lens alters its shape
when tension in suspensory ligaments is
• what is responsible for decline in power
of accommodation with age?
model of accommodation
• 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.
• Presbyopia is due to
growth in equatorial
diameter, leads to
decrease in perilenticular
• Contraction of ciliary
muscle cannot tense
zonules and expand lens
• SCHACHAR introduced
use of scleral expansion
• 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 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
• Presbyopia is due to increase in lens
volume, results in reduced response to
pressure gradient created by ciliary
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
• Reflex accommodation
– Is an automatic adjustment response to blur
which is made to maintain a clear and sharp
– 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
• The afferent
– Retina (with the retinal ganglion axons in the
optic nerve, chiasm and tract),
– Lateral geniculate body (with axons in the
– 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
• The efferent
nucleus - oculomotor
nerve - ciliary ganglion short ciliary nerve - iris
sphincter and the ciliary
– oculomotor neurons oculomotor nerve medial rectus, converge
the two eyes.
Anomalies of Accommodation
• Classification (by Duane with some
– Accommodative insufficiency
– Ill-sustained accommodation– Paralysis (or paresis) of accommodation
– Unequal accommodation
– Accommodative excess.
– Inertia of accommodation
– Diminished or deficient
– Physiological : Presbyopia
– Pharmacological : Cycloplegia
– Insufficiency of accommodation
– Ill sustained accommodation
– Inertia of accommodation
– Paralysis of accommodation
– Increased 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
• We read from 25 cm. After 40 years, the near
point recedes beyond normal reading or
• 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:
o Decrease in elasticity of lens capsule, and
o Progressive, increase in size and hardness
(sclerosis) of lens substance which is not easily
– Age related decline in ciliary muscle power.
• Uncorrected hypermetropia.
• Premature sclerosis of the crystalline lens.
• General debility causing pre-senile
weakness of ciliary muscle.
• Chronic simple glaucoma.
• Difficulty in near vision.
• Patients complaint of difficulty in reading
• 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 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
– +1.5 DS at 45-50 years,
– + 2 DS at 50-55 years,
– +2.5 DS at 55-60 years.
Basic principles of
• 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
• 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
– 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
• Premature sclerosis of lens
• Weakness of ciliary muscle due to
systemic causes: Debilitating
illness, anemia, toxemia, malnutrition, dia
betes mellitus, pregnancy, stress etc.
• Weakness of ciliary muscle due to local
causes: PAOG, mild cyclitis as during
onset of sympathetic ophthalmia.
• 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 :
• It is stable condition, if due to
sclerosis of lens.
• But is not stable in association
with ciliary muscle weakness.
• Identification & treatment of any
• 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.
• 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
• Weakest convex lenses should be
prescribed, so as to exercise and
• 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
– But with convergence excess then the
exercise should done with one eye
– Accommodation test card exercise.
– Useless in generalized debility and
sclerosis of lens.
• 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
• 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
• General tonic measures should be
• The condition of illumination and posture
while doing near work, should be
Inertia of accommodation
• It is a condition in which patient faces
difficulty in altering the range of
• Amplitude of accommodation is normal.
• Ability to make use of this amplitude
quickly and for long periods of time is
• Difficulty changing focus from one distance
• 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
– Internal ophthalmoplegia (paralysis of
ciliary muscle and sphincter pupillae)due
to neuritis associated with
diphtheria, syphilis, diabetes, alcoholism, c
erebral or meningeal diseases.
– Complete third nerve paralysis due to
intracranial or orbital causes.
– Systemic medications such as antihypertensive, antidepressants.
• Blurred vision at
• Photophobia or a 'dazzling' effect
• Micropsia: objects may appear smaller
than they are due to a false sense of
• 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 permanent.
• Accommodative response is greater
than the accommodative stimulus.
• There is functional increase in tonus of
ciliary muscle, results in a constant
• Young hypermetropes frequently uses
excessive accommodation as a
• Young myopes performing excessive near
work, associated with excessive
• Astigmatic error in young patients
• Presbyopes in the beginning
• Use of improper and ill fitting spectacles
• Excessive near work done, especially
in dim or excessive illumination.
• General debility, physical or mental ill
Blurred vision at near is uncommon
Blurred vision at distance
Difficulty changing focus from distance to
• It has a good prognosis.
• Refractive error should be corrected
after carefully performed cycloplegic
• 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
• Drug induced spasm of
accommodation is known to occur after
use of strong miotics.
• Spontaneous spasm of accommodation:
attempt to compensate for a refractive
• Occurs when excessive near work is
done with bad illumination, bad reading
position, state of neurosis, mental stress
• Defective vision: due to induced
• Asthenopic symptoms
• Precipitating factors like marked degree
of muscular imbalance, trigeminal
neuralgia, a dental lesion, general
• Relaxation of ciliary muscle by atropine
for 4 weeks or more and
• Prohibition of near work allow prompt
recovery from spasm of
• Elimination of the associated causative
factors to prevent the recurrence.