Download MBBS Ophthalmology PPT 25 Convergence And Accommodation Lecture Notes

ACCOMMODATION

AND CONVERGENCE

--- Content provided by FirstRanker.com ---

1

Revision Question

? You have gone fishing and see a fish in the water. You

--- Content provided by FirstRanker.com ---

do not have a fishing rod. The only equipment that you

have is a spear to catch the fish.

--- Content provided by FirstRanker.com ---

? Where do you throw the spear?
a. in front of the fish.
? b. behind the fish.
? c. directly at the fish.
? d. It is not possible to hit the fish as it is a virtual image.

--- Content provided by FirstRanker.com ---

2


Learning Objectives

--- Content provided by FirstRanker.com ---

At the end of the class, students shall be able to
? Understand the basic mechanism of

accommodation and clinical importance of

--- Content provided by FirstRanker.com ---

anomalies of accommodation

? Understand the pathway for near reflex and

importance of convergence insufficiency.

--- Content provided by FirstRanker.com ---

3

Looking at the pupils

--- Content provided by FirstRanker.com ---

4


Looking at the pupils

--- Content provided by FirstRanker.com ---

5

ACCOMMODATION

? Definition: Accommodation is the mechanism by which the eye

--- Content provided by FirstRanker.com ---

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

6

--- Content provided by FirstRanker.com ---

Mechanism of accommodation

? Increase in the curvature of lens affects mainly anterior

surface.

--- Content provided by FirstRanker.com ---

? Radius of curvature of anterior surface :10 mm
During accommodation

--- Content provided by FirstRanker.com ---

6 mm
This alteration in shape increases the converging power of

lens.

--- Content provided by FirstRanker.com ---

7

--- Content provided by FirstRanker.com ---

RELAXATION THEORY OF HELMHOLTZ

? He considered that lens was elastic and in normal state is

stretched and flattened by the tension of suspensory ligament.

--- Content provided by FirstRanker.com ---

? During accommodation: Ciliary muscle contracts causing lens

zonules to slacken, lens assumes more spherical form increasing
thickness and decreasing diameter, forward protrusion at centre

--- Content provided by FirstRanker.com ---

and relative flattening at periphery.

8

--- Content provided by FirstRanker.com ---

9

NEAR REFLEX

? It has 2 components :

--- Content provided by FirstRanker.com ---

? Convergence reflex comprising convergence of visual

axes of eyes and associated constriction of pupil.

? Accommodation reflex includes increased

--- Content provided by FirstRanker.com ---

accommodation and associated constriction of pupil.

? The near reflex comprises :

--- Content provided by FirstRanker.com ---

Accommodation , convergence and miosis of pupils.

10

--- Content provided by FirstRanker.com ---

ACCOMODATION REFLEX

? Af erent impulses-from

the retina to the

--- Content provided by FirstRanker.com ---

parastriate cortex

? Internuncial fibres relay

--- Content provided by FirstRanker.com ---

impulses from parastriate

cortex to Edinger

westphal nucleus of both

--- Content provided by FirstRanker.com ---

sides

? Ef erent fibres ?from

--- Content provided by FirstRanker.com ---

Edinger westphal

nucleus the ef erent

impulses travel along the

--- Content provided by FirstRanker.com ---

3rd nerve and reach the

sphincter pupil ae and

--- Content provided by FirstRanker.com ---

ciliary muscle

11

Physical and physiological accommodation

--- Content provided by FirstRanker.com ---

Two factors in accommodation

q Ability of lens to alter its shape

--- Content provided by FirstRanker.com ---

q Power of ciliary muscle

1.Physical accommodation- Expression of the actual physical
deformation of lens, measured in dioptres.
2. Physiological accommodation- Contractile power of the ciliary

--- Content provided by FirstRanker.com ---

muscle required to raise the refractive power of lens , measured in
myodioptres.

12
qThe far point of distinct vision is the position of an object

--- Content provided by FirstRanker.com ---

such that its image falls on the retina in the relaxed eye, i.e.

in the absence of accommodation. The far point of

--- Content provided by FirstRanker.com ---

emmetropic eye is at infinity.

qThe near point of distinct vision is the nearest point at

which an object can be clearly seen when maximum

--- Content provided by FirstRanker.com ---

accommodation is used.

13

--- Content provided by FirstRanker.com ---

qThe range of accommodation is the distance between far point

and near point.

qThe amplitude of accommodation is the difference in dioptric

--- Content provided by FirstRanker.com ---

power between the eye at rest and fully accommodated eye.

14
? The amplitude of accommodation is given by the

--- Content provided by FirstRanker.com ---

formula

? A = P - R
? where A is amplitude of accommodation in dioptres

--- Content provided by FirstRanker.com ---

? P is dioptric value of near point distance
? R is dioptric value of far point distance.

15

--- Content provided by FirstRanker.com ---

? Applying this formula to the case of an emmetropic eye with a

near point of 10 cm,

? P = 10 D ( the reciprocal of 0.10 m )

--- Content provided by FirstRanker.com ---

? R = 0 ( the reciprocal of infinity is zero)

? A = 10 D

--- Content provided by FirstRanker.com ---

16
? Far point and near point of the eye vary with the static

refraction of the eye

--- Content provided by FirstRanker.com ---

? In a hypermetrope eye far point is virtual and lies behind

the eye

? In a myopic eye far point is real and lies in front of the

--- Content provided by FirstRanker.com ---

eye.

17

--- Content provided by FirstRanker.com ---

In an emmetropic eye
? Far point is at infinity
? Near point varies with age
? About 7 cm at age of 10 years
? About 25 cm at age of 40 years

--- Content provided by FirstRanker.com ---

? 33 cm at age of 45 years

18
ANOMALIES OF ACCOMMODATION

--- Content provided by FirstRanker.com ---

DIMINISHED

INCREASED

ACCOMMODATION

--- Content provided by FirstRanker.com ---

ACCOMMODATION

1. PHYSIOLOGICAL

--- Content provided by FirstRanker.com ---

1. EXCESSIVE

(PRESBYOPIA )

ACCOMMODATION

--- Content provided by FirstRanker.com ---

2. PHARMACOLOGICAL

(Cycloplegia)

--- Content provided by FirstRanker.com ---

2. SPASM OF

3. PATHOLOGICAL

ACCOMMODATION

--- Content provided by FirstRanker.com ---

? Insuf iciency of accommodation
? Il sustained accommodation
? Paralysis of accommodation

--- Content provided by FirstRanker.com ---

19

PRESBYOPIA

? Presbyopia is not an error of refraction but a condition of

--- Content provided by FirstRanker.com ---

physiological insufficiency of accommodation due to

reduced amplitude of accommodation, leading to a

--- Content provided by FirstRanker.com ---

progressive fall in near vision.

? This usually begins between 40 years and 45 years of age.

20

--- Content provided by FirstRanker.com ---

? After the age of 40 years ,the NPA recedes beyond the

normal reading distance.

? This condition of falling near vision due to age related

--- Content provided by FirstRanker.com ---

decrease in the amplitude of accommodation or increase in
punctum proximum is presbyopia.

21

--- Content provided by FirstRanker.com ---

Causes of presbyopia

qAge related changes in lens which include

--- Content provided by FirstRanker.com ---

? Decrease in elasticity of lens capsule

? Progressive increase in size and hardness (sclerosis) of

lens substance.

--- Content provided by FirstRanker.com ---

qAge related decline in ciliary muscle power.

22
Causes of premature presbyopia include

--- Content provided by FirstRanker.com ---

? Uncorrected hypermetropia

? Premature sclerosis of crystalline lens

--- Content provided by FirstRanker.com ---

? General debility causing presenile weakness of ciliary

muscle

? Chronic simple glaucoma

--- Content provided by FirstRanker.com ---

23

Symptoms

--- Content provided by FirstRanker.com ---

? Difficulty in near vision : patients start complaining of

inadequacy of vision for small print and finer objects at usual

reading distance. Such problems start occurring in evening,

--- Content provided by FirstRanker.com ---

and in dim light.

? Asthenopic symptoms due to fatigue of ciliary muscle

--- Content provided by FirstRanker.com ---

? Intermittent diplopia at near may develop.

24
Treatment

--- Content provided by FirstRanker.com ---

Optical correction of presbyopia
Done by supplementing accommodation with convex
lens of appropriate power.
The difference between distance correction and
strength needed for near vision is called the add.

--- Content provided by FirstRanker.com ---

25

PRESBYOPIC ADD

--- Content provided by FirstRanker.com ---

? If patient is presbyopic, calculate the likely reading addition

and add this to the distance lenses in the trial frame. In
practice the reading addition is estimated from patient's age.

--- Content provided by FirstRanker.com ---

AGE RANGE

READING ADDITION

45-50 YEARS

--- Content provided by FirstRanker.com ---

+1.00 D

50-55 YEARS

--- Content provided by FirstRanker.com ---

+1.50 D

55-60 YEARS

+2.00D

--- Content provided by FirstRanker.com ---

OVER 6O YEARS

+2.50 D

--- Content provided by FirstRanker.com ---

26
MODES OF PRESCRIBING PRESBYOPIC ADD

o SPECTACLES
o CONTACT LENSES FOR PRESBYOPIA

--- Content provided by FirstRanker.com ---

2.SURGICAL TREATMENT OF PRESBYOPIA

o Refractive surgeries

--- Content provided by FirstRanker.com ---

27

Insufficiency of accommodation

Accommodative power is significantly and persistently

--- Content provided by FirstRanker.com ---

below normal physiological limits for patient's age
? Causes

?Premature sclerosis of lens

--- Content provided by FirstRanker.com ---

?Weakness of ciliary muscle due to systemic causes

such as diabetes mellitus.

28

--- Content provided by FirstRanker.com ---

Insufficiency of accommodation

Clinical features :

--- Content provided by FirstRanker.com ---

Treatment :

Headache

--- Content provided by FirstRanker.com ---

1.Treatment of systemic

Fatigue

cause

--- Content provided by FirstRanker.com ---

Blurring of vision for near

2.Near vision spectacles

--- Content provided by FirstRanker.com ---

work

3.Accomodation exercises

Intermittent diplopia

--- Content provided by FirstRanker.com ---

29

Paralysis of accommodation

--- Content provided by FirstRanker.com ---

? Paralysis of accommodation ,also known as

cycloplegia, refers to complete absence of
accommodation.

--- Content provided by FirstRanker.com ---

30
Causes

? Drug induced
? Internal ophthalmoplegia

--- Content provided by FirstRanker.com ---

? Paralysis of accommodation as a component of 3rd

nerve palsy.

31

--- Content provided by FirstRanker.com ---

DRUG

MAXIMUM

--- Content provided by FirstRanker.com ---

MAXIMUM

DURATION OF

DURATION OF

--- Content provided by FirstRanker.com ---

MYDRIASIS

CYCLOPLEGIA

--- Content provided by FirstRanker.com ---

MYDRIASIS

CYCLOPLEGIA

ATROPINE 1% TID 30-40 MIN

--- Content provided by FirstRanker.com ---

1 DAY

7-10 DAYS

--- Content provided by FirstRanker.com ---

2 WEEKS

CYCLOPENTOLAT 15 MIN

15-30 MIN

--- Content provided by FirstRanker.com ---

1 DAY

24 HRS

--- Content provided by FirstRanker.com ---

E 0.5%-1%

HOMATROPINE

30-60 MIN

--- Content provided by FirstRanker.com ---

30-60 MIN

1-2 DAYS

--- Content provided by FirstRanker.com ---

1-2 DAYS

2%

TROPICAMIDE

--- Content provided by FirstRanker.com ---

15-30 MIN

20-25 MIN

--- Content provided by FirstRanker.com ---

4-6 HRS

5-6 HRS

0.5%-1%

--- Content provided by FirstRanker.com ---

32
? Clinical features

? Treatment

--- Content provided by FirstRanker.com ---

? Blur ing of near vision

? Self recovery-drug induced

--- Content provided by FirstRanker.com ---

? Photophobia (due to mydriasis )

paralysis and in cases when

? Micropsia

--- Content provided by FirstRanker.com ---

systemic cause is treated.

? Abnormal receding of near point

--- Content provided by FirstRanker.com ---

? Dark glasses ? reduce glare

? Signs of 3rd nerve palsy

? Convex lenses ?for near vision

--- Content provided by FirstRanker.com ---

if paralysis is permanent.

33

--- Content provided by FirstRanker.com ---

Excessive accommodation

? A situation in which an individual exerts more than normal

required accommodation for performing a certain near work.

--- Content provided by FirstRanker.com ---

? Excessive near work is an important precipitating factor

especially when done in inadequate illumination.

--- Content provided by FirstRanker.com ---

34
Clinical features

? Varying degrees of blurred vision

--- Content provided by FirstRanker.com ---

? Symptoms of accommodative asthenopia

? Difficulty in performing near vision tasks

35

--- Content provided by FirstRanker.com ---

Treatment

1. Optical treatment : refractive error to be corrected
2. General treatment : Near work should be minimised and

--- Content provided by FirstRanker.com ---

when done should be in proper illumination.

3. The general health of the patient should be improved.

--- Content provided by FirstRanker.com ---

36
CONVERGENCE

37

--- Content provided by FirstRanker.com ---

? Definition: Convergence is a disconjugate movement in which

both eyes rotate inward so that lines of sight intersect in front
of eyes.

--- Content provided by FirstRanker.com ---

? Allows bifoveal single vision to be maintained at any fixation

distance.

? Convergence does not deteriorate with increasing age.

--- Content provided by FirstRanker.com ---

? The power of convergence can be increased by exercises.

38

--- Content provided by FirstRanker.com ---

Convergence reflex

? Af erent pathway ?the afferents from medial recti travel

centrally via the 3rd nerve to the mesencephalic nucleus of the

--- Content provided by FirstRanker.com ---

5th nerve, to a presumptive convergence centre in tectal or
pretectal region.

? Internuncial fibres : from the convergence centre go to the

--- Content provided by FirstRanker.com ---

Edinger Westphal nucleus .

39

? Ef erent pathway-

--- Content provided by FirstRanker.com ---

along the 3rd nerve.
From the 3rd nerve
ef erent fibres of
convergence reflex

--- Content provided by FirstRanker.com ---

relay in the accessory
ganglion, before
reaching sphincter
pupil ae.

--- Content provided by FirstRanker.com ---

40


? Angle of convergence

--- Content provided by FirstRanker.com ---

?It refers to the angle that is formed between primary

lines of sight during convergence

?Its size depends on

--- Content provided by FirstRanker.com ---

? the fixation distance

and
interpupillary distance ( IPD )

--- Content provided by FirstRanker.com ---

41

Metre angle

--- Content provided by FirstRanker.com ---

? One metre angle

convergence is
exerted by each eye
when the eyes are

--- Content provided by FirstRanker.com ---

directed to object at a
distance of 1 m of the
meridian line between
the two eyes.

--- Content provided by FirstRanker.com ---

42
? In an emmetropic eye, the number of dioptres of

accommodation required to see an object clearly is equal

--- Content provided by FirstRanker.com ---

to the number of metre angles through which each eye

must converge to see the object singly.

? Thus 1D of accommodation is associated with 1 ma of

--- Content provided by FirstRanker.com ---

convergence of each eye

43

--- Content provided by FirstRanker.com ---

qThe near point of convergence is the closest point at

which an object can be seen singly during bifoveal vision
when maximum convergence is exerted.

--- Content provided by FirstRanker.com ---

qThe far point of convergence refers to relative position of

eyes when they are completely at rest, usually at infinity.

44

--- Content provided by FirstRanker.com ---

qThe range of convergence is the distance between far

point and near point of convergence

--- Content provided by FirstRanker.com ---

qThe amplitude of convergence is the difference in

convergence power exerted to maintain the eye in a

--- Content provided by FirstRanker.com ---

position at rest and in a position of maximum convergence.

45

Measurement of amplitude of convergence

--- Content provided by FirstRanker.com ---

1. Prism bar

2. Synoptophore

--- Content provided by FirstRanker.com ---

46
Anomalies of convergence

1) Convergence insuf iciency
Inability to maintain adequate binocular

--- Content provided by FirstRanker.com ---

convergence for any length of time without
undue effort.

47

--- Content provided by FirstRanker.com ---

? Aetiology

A. Primary or idiopathic ?
Wide IPD, general debility, overwork.
B. Refractive errors- uncorrected high hypermetropia and myopia

--- Content provided by FirstRanker.com ---

C. Presbyopia
D. Muscular imbalances-
Exophoria, intermittent exotropia and vertical muscle
imbalances.

--- Content provided by FirstRanker.com ---

48
Clinical features

1. Symptoms of

--- Content provided by FirstRanker.com ---

2. Symptoms due to

muscular fatigue

failure to maintain

--- Content provided by FirstRanker.com ---

binocular vision

? Eyestrain
? Headache and eye

--- Content provided by FirstRanker.com ---

? Blurred near vision

ache

--- Content provided by FirstRanker.com ---

? Intermittent crossed

? Difficulty in changing

diplopia

--- Content provided by FirstRanker.com ---

the focus from distant

to near

--- Content provided by FirstRanker.com ---

? Itching, burning and

soreness of eyes

49

--- Content provided by FirstRanker.com ---

Diagnosis

1. Remote NPC ? if NPC > 10 cm, Convergence

--- Content provided by FirstRanker.com ---

insufficiency is said to exist.

2. Decreased fusional convergence for near-when measured

on synoptophore, if there is difficulty in attaining 30? of

--- Content provided by FirstRanker.com ---

convergence.

3. Exophoria

50

--- Content provided by FirstRanker.com ---

Treatment
1. Optical treatment- Myopes are given full correction and

hypermetropes undercorrection to stimulate their

--- Content provided by FirstRanker.com ---

accommodation and simultaneously convergence.

2. Orthoptic treatment- exercises to increase the near point

of convergence (NPC) and also to increase amplitude of

--- Content provided by FirstRanker.com ---

fusional convergence.

51

--- Content provided by FirstRanker.com ---

Treatment

3. Prism Therapy
Base in ( BI ) prisms reading glasses or bifocals with prism
in lower segment are useful.

--- Content provided by FirstRanker.com ---

4. Surgical treatment

? Last resort

? Medial rectus muscle resection may be performed.

--- Content provided by FirstRanker.com ---

52
Convergence paralysis

CAUSES

--- Content provided by FirstRanker.com ---

? Head injury
? Encephalitis
? Tabes dorsalis
? Narcolepsy

--- Content provided by FirstRanker.com ---

? Tumours

53

Convergence paralysis

--- Content provided by FirstRanker.com ---

? Clinical features

? Convergence is completely absent
? Exotropia and crossed diplopia occurs on attempted near vision

--- Content provided by FirstRanker.com ---

? Adduction is normal



54

--- Content provided by FirstRanker.com ---

Convergence paralysis

? TREATMENT

qBase In (BI) prisms

--- Content provided by FirstRanker.com ---

qPlus lenses with BI prisms

55

--- Content provided by FirstRanker.com ---

Summary

? Accommodation is the mechanism by which eye changes its

refractive power by altering the shape of the lens in order to

--- Content provided by FirstRanker.com ---

focus objects at variable distances.

? Convergence is a disconjugate movement in which both eyes

rotate inward so that the lines of sight intersect in front of eyes.

--- Content provided by FirstRanker.com ---

? Near reflex comprises : Accommodation , convergence and

miosis.

--- Content provided by FirstRanker.com ---

56
Question

? Which of the following is true regarding accommodation and

--- Content provided by FirstRanker.com ---

contact lenses?

? a. In a myopic patient, contact lenses decrease the

accommodative demand compared to spectacles.

--- Content provided by FirstRanker.com ---

? b. In a hyperopic patient, contact lenses increase the

accommodative demand compared to spectacles.

--- Content provided by FirstRanker.com ---

c. In a myopic patient, contact lenses increase
accommodative demand compared to spectacles.
? d. There is no difference noted in accommodation when

wearing contact lenses.

--- Content provided by FirstRanker.com ---

57