#8 re,strabismus & amblyopia (2)
TRANSCRIPT
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.