Strabismus

Refractive errors

Amblyopia

Strabismus

= Squint

- Misalignment of the eyes (fovea of one eye fixates at the target & and fovea of the other eye is off the target)

- affects~5% of the population

Anatomy of extra ocular muscles

-Six extra-ocular muscles in each eye(responsible for eye movements)

- Four rectus (straight) :- Superior rectus

- Inferior rectus

- Medial rectus

- Lateral rectus

- Two oblique:- - Superior Oblique

- Inferior Oblique

Cont…

Rectus muscles:- - Origin:-common annular tendon of Zinn,

around the optic foramen.

- Insertion:-sclera,various distances from

the limbus

- Blood Supply:- muscular branches of the

ophthalmic artery

Cont…

Innervation : - IIICN = - Medial Rectus

- Inferior rectus

- Superior rectus

- Inferior oblique

-IV CN = Superior oblique

-VI CN = Lateral Rectus

Actions of the rectus muscles

LR = abduction

MR = adduction

SR = elevation, intorsion and adduction

IR = depression, extorsion and adduction

Oblique Muscles

Inferior oblique:-

- origin:-inner end of the inferior orbital rim

- insertion:- outer part of the sclera behind

the equator, around the macula

- Action :- Extortion, elevation and abduction

Cont…

Superior Oblique

Origin:- upper and inner margin of optic

foramen

Insertion:-posterior to equator-supero-temporal

quadrant

( after passing through TROCHLEA)

Action :- intorsion, depression and abduction

Strabismus

- Strabismus = a Latin word for squint

- Squint= eyes are looking in different direction

- Many possible causes for a squint to develop=>a cause should be looked for

- For a squint to develop, Binocular reflexes should fail.

Binocular Reflexes

Involve Sensory and Motor parts

Sensory:- takes two images produced by the two eyes and joins them together in the brain.

Motor:-the two eyes always move together, so that they are always pointing in the same direction

The binocular reflexes are much weaker in children, and there fore squints usually start in early childhood

Cont…

Disorders of vision affect Sensory part of the reflex

-no stimulus from the diseased eye to

remain pointing in the same direction

as the healthy eye, so the diseased eye

develops a squint

e.g -corneal scar

-cataract

-retina/optic nerve lesion

Cont…

Disorders of the eye movements affect the motor part of the reflex

- Extra ocular muscles

-Congenital abnormalities

-Fractures of the orbital walls

-Dysthyriod eye diseases

-Diseases of the EOM(e.g.myopathy)

- Cranial Nerves

-Paralysis

Strabismus Cont…

Phoria:- a latent deviation where there is

an underlying tendency for the

eyes to drift apart

- held in alignment by motor fusion

Intermittent tropia:-

-a latent deviation becomes manifest

when fusion brakes at times

Tropia:-strabismus is manifest

Bruckner test=Red reflex test =Illumination test

Part of routine pediatric ophthalmology examination

Uses direct ophthalmoscope

In a dim room the observer views through the ophthalmoscope from a distance of ~ 1 meter.

Assesses the RED REFLEXES in both eyes SIMULTANEOUSLY- should appear BRIGHT and EQUAL in both eyes

Problems which can be identified by Brückner-test:

1. Squint

2. Anisometropia

3. Opacities within the optical media ( cornea,lens,vitreous)

4. Changes of the fundus (Coloboma, RBL)

Bruckner test cont…

Brighter reflex :-Strabismus

Dimmer reflex :- Ametropia

-Media opacity

N.B.: Strabismic angles as small as 1° are detectable!

Strabismus cont…

Esotropia:- inward deviation

Exotropia:- outward deviation

Hypertropia:- upward deviation

Hypotropia:- downward deviation

Esotropia

Inward turning of the eye

The most common form of childhood strabismus

Usually associated with hyperopia

Types:-congenital

-Acquired:-Accommodative

-Nonaccommodative

-Incomitant e.g VI nerve palsy

Management of Esotropia

Convex (+) glasses

Accommodative esotropia

Surgery

- Congenital Esotropia

- Acquired nonaccommodative esotropia

- Paralytic esotrpia

Parasympathomimetics

Exotropia

Outward deviation of the eye

Types:-

- Congenital

- Acquired - nonparalytic

- paralytic e.g III nerve palsy

Management of Exotropia

Nonsurgical

Corrective glasses espe. Myopia

Overminusing!

Surgical

Vertical Strabismus

Hypertropia, hypotropia

Types:-

-Comitant:-

usually accompanies horizontal

strabismus

-Incomitant - muscle restriction

- paralytic e.g IV nerve palsy

Management of Vertical strabismus

Surgery!

Management of Strabismus

In children:-

1. Find the cause

2. Correct refractive errors with spectacles

3. Treat Amblyopia

4. Straighten the eyes with surgery

In adults:-

- If the squint started in childhood= cosmetic surgery

- If the squint is recent

- look for a cause

-wait 6 mons.before considering surgery

Refractive Errors

Refractive states of the eye

Measured looking in the distance(usually 6mts) so that the ciliary muscle is relaxed (that is not accommodated)

Emmetropia

A normal condition

Parallel rays of light from infinity come to a focus on the retina(fovea)

=> no error of refraction/visual acuity is normal

Ametropia

Abnormal condition/absence of emmetropia

Parallel rays of light from infinity do not come to a focus on the retina (fovea)

=>error of refraction

* Myopia or short/Near-sightedness

* Hyperopia or long/Far-sightedness

* Astigmatism

** Presbyopia

Anisometropia

Unequal refractive power of the eyes

e.g :-

1. one eye emmetropic, the other one myopic

2. OD;- 0, OS:- -3.0 D

3. OD:- +1.5 D, OS:- +3.5 D

Pinhole test

Any patient with defective visual acuity should be tested again with a pinhole

If visual acuity improves with pin hole=> refractive error

If no improvement=>the loss of vision is from eye disease

Ametropia cont…

Axial ametropia:-

- the eye ball is either unusually long

(Myopia)or short(Hyperopia)

Refractive ametropia:-

-The length of the eye is normal

- Excessive power in myopia, inadequate

in hyperopia

e.g of extreme refractive hyperopia=Aphakia

Myopia=Short-sightedness

Short-sightedness

A condition where the light rays from a distance object are focused in front of the retina.

There fore the image at the retina is blurred and the vision is poor for distance objects, but good

for near objects.

The greater the degree of myopia, the closer the patient has to hold things to see them clearly without any spectacles

Treatment of myopia

Concave(-) spherical glasses

Contact lenses(concave)

Laser surgery

Hyperopia/Hypermetropia =long-sightedness

An error of refraction in which parallel rays of light from infinity come to a focus behind the retina, so they are blurred at the retina.

Visual acuity is decreased except for young people who can use their accommodation to focus on the retina.

With age the power of accommodation decreases.

Symptoms of Hyperopia

Blurring of near vision

Not much compliant regarding distance vision, as distance vision does not need accommodation that much.

Headache due to constant strain on accommodation

Treatment

Convex (+)spherical glasses

Convex contact lenses

Laser surgery

Astigmatism

The eye has a different focus in different planes

An error of refraction in which the parallel rays of light from infinity cannot converge to a point focus due to unequal refraction in different meridians of the optical focus of the eye.

Causes of astigmatism

a. Unequal curvature of the cornea or lens in different meridians, so that the refractive surfaces are not spherical.

b. Decentering of the lens due to slight shifting in position or tilting of the lens as occurs in subluxation.

Symptoms of astigmatism

Diminished visual acuity

Headache due to exertion of accommodation to rectify the defect particularly in hypermetropic astigmatism

Treatment

Cylindrical lenses

-spectacles

-contact lenses

Laser surgery

Presbyopia

Usually becomes age beyond 40 years

Part of the natural ageing process in the lens

With age lens becomes harder=>loss of elasticity of the lens=>loss of accommodative response

The eye can still see distant objects clearly, but cannot focus on near objects.

Symptoms of Presbyopia

Blurring of vision while reading books/carry out near- vision tasks.

Vision improves if the object is held further away from the eye.

Those doing close work feel the symptoms earlier.

Treatment of presbyopia

Convex spherical lenses, which is added on glasses if any for distant vision.

Amblyopia

=>Poor vision caused by abnormal visual experience early in life. (i.e. in the immature visual system)

Visual development…

Continues until 7/8 years

Latent period in first 6/52 of life

Followed by critical or sensitive period

Affected by disease/visual deprivation in sensitive period

Cont…

Amblyopia=a greek term

amblyos=dull/blunt, Opia=vision

Occurs in 2-4% of the general population

The most common cause of decreased vision in childhood(birth-7/8 yrs.)

Definition of amblyopia

A unilateral/bilateral reduction of best corrected visual acuity that can’t be attributed to the effect of any structural abnormality of the eye or posterior visual pathway.

If best corrected vision in one eye is at least two lines worse in the snellen chart than the other eye or a vision of 6/12 or worse in both eyes

Pathophysiology

i. Abnormal binocular interaction

ii. Retinal image blur

iii. Both

Three “D”s i. Deviated i.e strabismus

ii. Defocused i.e anisometropia, ametropia

iii. Deprived e.g. cataract,corneal opacity,etc

Management

One of the most time consuming tasks in pediatric ophthalmology ,but if successful it is one of the most rewarding!

Cont…

Basic Strategies:-

1. Provide a clear retinal image

2. Correct ocular dominance

Cont…

1. Occlusion:-

-”gold standard” - priciple:- cover the sound eye to force

the poor seeing eye to see better

2. Penalization(optical/pharmacologic):-

Blurring of the sound eye to force

fixation with the amblyopic eye.