Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

2.Amblyopia is obligatory i.e. suppression is present when the eye squints and continues during forced fixation28.

3.The condition goes unnoticed because the child is unaware of less vision in one eye and the parents do not notice because there are no external signs.

4.The eyes have fairly good binocular function.

5.The steriopsis is good.

6.Chances of eccentric fixation is minimal or absent.

7.The blurred image in the amblyopic eye acts as hindrance to binocular vision.

8.Only rough correlation exists between degree of anisometropia and depth of amblyopia.

9.It is possible to have amblyopia in both eyes.

10.The condition has better chance of improvement following treatment.

Diagnosis. Diagnosis of amblyopia in squint is easy. All squinting eyes should be examined for possibility of amblyopia. Strabismic children have 15 times more chances of developing amblyopia than non strabismic children. Squint is responsible for one third case of amblyopia.

The diagnosis depends on :

1.Recording of vision.

2.Crowding phenomenon.

3.Unchanged or improved vision with neutral density filter.

Treatment :

1.Management of amblyopia is rewarding

(i) If diagnosed early,

(ii) If treatment is initiated early,

(iii) If treatment is continued for sufficient time and maintained for sufficient time after vision has improved and come to equal level in both eyes.

All above factors depends upon compliance of the patient and co-operation of parents and teachers.

Management begins with—Refraction under cycloplegia followed by prescription of best possible power in both eyes which gives the child a comfortable vision according to standard protocol of prescription of glasses for children with special attention to astigmatism. Any opacity in the media should be removed, so should be any physical obstruction like ptosis, tumours of lid.

This is followed by occlusion of sound eye to begin with. Occlusion is a time honoured method of treatment for amblyopia in children.

Occlusion therapy should take into consideration following parameters :

1.When to start occlusion.

2.Gap between two visits.

3.Type of occluder to be used.

4.How long should occlusion be continued.

5.Should the better eye be occluded and how long.

Occlusion should be started as soon as amblyopia has been confirmed. Occlusion after six years of age do not have much impact on amblyopia though it has been observed to give fairly good result up to age of fifteen.23

The occlusion should be complete and constant to begin with.

There are various types of occluders. The best is a skin patch attached to the forehead and check by an adhesive tape. This occludes the eye fully. The child has no chance to peep over the patch which is always possible with spectacle occluders i.e. Doyne’s occluder or ground glass occluders. These are not favoured because the child has tendency to peep over the occluders. In a co-operative child an opaque contact lens may give equally good result like a patch especially if the child is already using contact lens.

1.Minimum amount of occlusion required per day is not known.

2.Constant occlusion for a period calculated as per age of the child gives good results.

3.75% waking hours occlusion also gives fairly good result and has the advantage of not being amblyogenic to the better eye.

4.Occlusion for less than 50% waking hours are not likely to be of much help.

Calculation of duration of occlusion. The commonly used formula is one week for each year of age in between the visits. Younger the child better is the result of the treatment. Occlusion of better eye is called conventional occlusion that is effective irrespective of fixation pattern of fixing eye. Occlusion of amblyopic eye is called inverse occlusion.

A rough estimate of occlusion as per age of the child is as follows26

As far as possible occlusion should be full time i.e. during all waking hours. Part time occlusion means that the eye is occluded only for a few hours. During rest of the time both the eyes are open which goes against the principle of total occlusion.

Occlusion therapy may be accompanied by enhanced near vision work like tracing picture, joining dots, hand video games.

Follow up. The child should be followed up at the frequency of 1 week per year of age, i.e. a child aged one should be examined every week while a child of three years is examined after three weeks of occlusion.

What to look for on follow up visits :

1.On every visit child’s vision in both eyes must be recorded separately with correction when needed on the same Snellen’s chart in the same setting always.

2.The fixation pattern of the amblyopic eye should be noted on every visit.

How long should occlusion be continued ?

Occlusion is continued till :

1.Vision in amblyopic eye is as good as in normal eye.

2.Fixation becomes alternating.

3.There is no improvement of vision following occlusion for three months.

4.Once vision has been equalised or the child has developed alternating. Full time occlusion can be stopped and the dominant eye is occluded for part of the waking hours. This part time occlusion is continued up to age of eight years after which chances of improvement are less. Visual improvement is generally better in straight eye amblyopia than amblyopia with squint. Anisometropic amblyopia may require occlusion in addition to correction of refraction. Amblyopia is known to recur following completion of occlusion. So all children with amblyopia should be examined frequently and as soon as there is recurrence, occlusion is started as was done on the first occasion.

Occlusion of sound eye is contra indicated in amblyopia with eccentric fixation.

CAM vision stimulator. The normal eye is occluded for 7 minutes. The child uses the amblyopic eye to draw patterns on the transparent cover placed over the stimulator that has slow rotation, high contrast grating with sharp edges. The child may be exposed to the stimulator 10 to 20 times at a stretch. This method is not superior to conventional occlusion.

Complication of occlusion. Occlusion is a safe, simple and sound method for treatment of amblyopia provided it is done properly in selected children for sufficiently long time. The co-operation of the child and parent are some of the prerequisites.30

They are :

1.Occlusion amblyopia in better eye.

2.Development of new strabismus.

3.Worsening of pre-existing strabismus

4.Intractable diplopia

5.DVD

6.Allergic reaction to occluder

7.Infection may develop in occluded eye.

Pharmacological defocusing (Penalisation). This may be considered as a modified type of occlusion without actually covering the eye. This uses cycloplegic drug and spectacle in various combination to change the accommodation. The vision is blurred in better eye and forcing the amblyopic eye to see. The best results are obtained in amblyopia of moderate depth in moderate hypermetropia. The amblyopic eye is given full correction. The better eye is denied spectacle correction. One drop of one percent atropine is instilled in the better eye once a day. Follow up and duration is similar to that of occlusion. It is recommended if the child does not tolerate occlusion or peeks over the occlusion. It takes more time for improvement than occlusion.

Surgery. Squint surgery is performed after amblyopia has been treated. However ptosis, haemangioma of lid, cataract are operated before starting occlusion.

Medical treatment. Levodopa has been tried in small groups of amblyopic children with improvement of vision in both amblyopic and non amblyopic eye without any side effect.

REFERENCES

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2.Marmor M.F. ; Clinical physiology of the retina in Principles and practice of ophthalmology. Vol. II. p-868–887, Edited by Peyman G.A., Sanders D.R., Goldberg M.F. First Indian edition. Jay Pee Brothers, New Delhi, 1987.

3.Brain R.W. ; Visual fibres and visual fields in Diseases of nervous system. Sixth edition. p-49–58, Oxford Medical Publication, London, 1962.

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5.Shaffer D.B. ; Fundus albipunctatus in Text Book of ophthalmology. Edited by Scheie H.G. and Albert D.M. Ninth edition. p-307, W.B. Saunders Company, Philadelphia, 1977.

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7.Majji A.B. ; Sharma Y.R., Rajashekhar Y.L. and Nath R. Colour vision and colour blindness in Modern ophthalmology. Vol. II. Second edition. p-1032–1036, Edited by Dutta L.C. Jay Pee Brothers, New Delhi, 2000.

8.Speath G.L., Auerbach V.H. ; Cone vision in Pediatric ophthalmology. Vol. II, second edition. p-1061–1064, Edited by Harley R.D. WB Saunders Company, Philadelphia, 1983.

9.Seal S.K. ; Symptomatic disturbance of visual function in G.N. Seal’s Text Book of Ophthalmology. Fifth edition. p-352–353, Current Book International, Kolkata, 2002.

10.Boger W.P., Peterson R.A. ; Pediatric ophthalmology in Manual of ocular diagnosis and therapy. Third edition. p-262–263, Edited by Deborah Pavan Langston. Lippincot Williams and Wilkins, Philadelphia, 1991.

11.Duke Elder S. ; Colour sense in System of Ophthalmology. Vol. VII. p-380–383, Henry Kimpton, London, 1962.

12.Boger W.P. and Peterson R.A. ; Achromatopsia in Manual of ocular diagnosis and therapy. Third edition. p-273–274, Edited by Deborah Pavan Langston. Lippincot Williams and Wilkins, Philadelphia, 1991.

13.Kanski J.J. ; Neurophthalmology in Clinical ophthalmology. Second edition. p-441, Butterworth, London, 1989.

14.Martyn Lois J. ; Colour vision disorder in Pediatric ophthalmology. Vol. II. Second edition. p-781, Edited by Harley R.D. WB Saunders Company, Philadelphia, 1983.

15.Keys M.P. ; Dyslexia in Current ocular therapy. Fifth edition. p-213–214, Edited by Fraunfelder F.T., Roy F.H. W.B. Saunders Company, Philadelphia, 2000.

16.Roy H.F. ; Visual agnosia in Ocular differential diagnosis. Third edition. p-453, Jay Pee Brothers, New Delhi, 1984.

17.Shirley H. Wray. ; The visual fields in Manual of ocular diagnosis and therapy. Third edition. p-329, Edited by Deborah Pavan Langston. Lippincot. Williams and Eilkins, Philadelphia, 1991.

18.Rosenberg M.A. ; Topographic diagnosis of field defect in Principles and practice of ophthalmology. Vol. III. First Indian edition. p-1936–1943, Edited by Peyman G.A., Sanders D.R. and Goldberg M.F. Jay Pee Brothers, New Delhi, 1987.

19.Norma Graber. Matching field defect to pathology in Visual field examination. First Indian edition. p-18-33, Jay Pee Brothers, New Delhi, 1989.

20.Bajandas F.J., Kline L.B. ; Visual field in Neurophthalmology review manual. Third edition. p-1–42, Jay Pee Brothers, New Delhi, 1989.

21.Rabinowicz M. ; Amblyopia in Pediatric ophthalmology. Vol. I, edition second. p-293–341, Edited by Harley R.D. WB Saunders Company, Philadelphia, 1983.

22.Eggers H.M. ; Amblyopia in Text Book of Ophthalmology. First edition. p-13.1– 13.16, Edited by Podos S.M. and Yanoff M. Gower Medical Publication, London, 1993.

23.Rohatgi J.N. ; Amblyopia in Modern ophthalmology. Vol. II. Second edition. p-875- 878, Edited by Dutta L.C. Jay Pee Brothers, New Delhi, 2000.

24.Sharma P. ; Amblyopia in Strabismus simplified. First edition. p-41–49, Modern Publishers, New Delhi, 1999.

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28.Boger W.P. and Peterson R.A. ; Pediatric ophthalmology in Manual of ocular diagnosis and therapy. Third edition. p-307, Edited by Deborah Pavan Langston. Lippincot. Williams and Wilkins, philadelphia, 1991.

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The ocular movements can be divided into four broad groups3—The saccades, the smooth pursuit movements, the vergence and vestibulo ocular movements.

The saccades are rapid conjugate eye movements, they are voluntary movement due to quick burst of activity. They jump from one fixation to a new object of regard.4 They are present at birth.3

The smooth pursuits are involuntary movements that follow a slow moving object. They are also conjugate movements.

The vergence5—When the eye movements are disjugate (disjunctive), the movements are called vergence. The eyes move in opposite direction to allow both fovea to maintain fixation at the same time even when the object moves near or farther away, the former is called convergence and the other is called divergence. The advantage of this bifoveal fixation is binocular single vision and stereopsis.4

The vestibulo ocular movements3

These movements are related to maintaining eye position when there is an altered head position or body posture.

The ability of the human eyes to move in various directions is immense, the human eyes can have almost 180° of binocular field. The eyes can be moved 50° in each direction from the primary position.

Various position of the eye (Gaze)

1.Primary position. When the eyes fix an object at 20 feet straight ahead with the head straight.

2.Secondary position consists of right gaze, left gaze, straight up and straight down gaze.

3.Tertiary position. There are four oblique position of the eye.

4.The cardinal position. They are six in numbers brought about by one muscle and its yoke muscle.

Agonist and antagonist muscles

These are descriptive terms used to denote the action of an extra ocular muscle. An agonist is the prime mover for a required direction.

An antagonist of the same eye acts directly against the agonist.

If right lateral rectus is agonist for right lateral gaze, the medial rectus is its direct antagonist in the same eye.

Synergist muscle

A muscle in the same eye that enhances the action of a particular muscle to achieve a particular action is called synergist. In fact both of them are synergist to each other. For example superior rectus is synergist to inferior oblique for elevation. It is synergist to superior oblique for intortion. Adduction is enhanced for medial and inferior rectus.

Yoke muscles. These are pairs of muscles one from each eye that work together in binocular movement in one direction (version).

Duction is movement of one eye i.e. abduction moving laterally, adduction moving medially.

Sursum duction (elevation)7.8 is upward movement either in primary position or when the eye is either adducted or abducted. Deorsum duction is downward movement (depression or infraduction). This can be in primary position or secondary position of adduction or abduction. Similarly there can be in cycloduction when the twelve O’clock meridian dips nasally or excycloduction when twelve O’clock meridian dips temporally.

Versions. These are binocular movements in the same direction i.e. conjugate movement. Versions are noted in three diagnostic directions. Right sided binocular movements are called dextroversion, levo version denotes left binocular movements, dextro elevation and dextro depressions represent right and up, left and down movement respectively.

Sursum version means moving both eyes up. Deorsum version is moving both eyes down. The binocular torsional movements are Dextro cycloversion when the right eye extorts and left eye intorts at the same time. Levo cyclo version similarly denotes right intorsion and left extorsion.

Advantage of testing version is that paresis that may be missed on uniocular movement can be diagnosed on binocular testing.

Vergences

Binocular movements in opposite directions are called vergences.

They are—Convergence, when both eyes move inwards and divergence when both eyes move outwardly.

Laws governing ocular movements

They are Hering’s law of equal innervation and Sherrington’s law of reciprocal innervation.

Hering’s law of equal innervation means that the synergists of one eye gets equal and simultaenous innervation for any movement, e.g. amount of innervation of the right medial rectus is exactly the same as that of left lateral rectus and inhibitory responses to the right lateral rectus is exactly the same as that of left medial rectus.

Sherrington’s law states that increased action of an extra ocular muscle associated with diminished contraction of its antagonist for example during convergence there is increased contraction of both medial recti with reduced contractibility of both lateral recti.

Neural control of ocular movements

Binocular movements of the eye consists of a delicate control of many systems and not confined to motor nerve supply to the muscles only. They consist of two independent groups of movement i.e. version and vergence7, both are binocular movements. The versions are conjugate movements while vergence are disjugate movements. Depending on input, the ocular movements can be classified into fast eye movement, slow eye movement and vergence eye movement.

The fast eye movements :

1.Saccade

2.Quick phase of nystagmus.

The fast eye movements bring the object of interest on the fovea.

The slow eye movements :

Smooth pursuit Optokinetic Vestibular Vergence

The slow eye movements hold the image of the object of interest on the macula.

In vergence the eyes move in opposite direction i.e. converge or diverge so that images of single object are placed on both foveae.8

The fast eye movements (saccade) are brought about by fronto mesencephalic path ways and superior colliculus. The quick phases of nystagmus is brought about by para median reticular formation in mid brain and pons.

The slow eye movements (smooth pursuits) are brought about by parieto-occipial temporal pathway.

The vestibular slow eye movements are brought about by labyrinthine-pontine-path-

way.8

Anatomy of extra ocular muscles The horizontal muscles

The medial rectus muscle

This is a straight muscle, the plane of the muscle coincides with the visual axis of the eye. It originates from the apex of the orbit from the medial side of circle of Zinn. It is 41 mm (actually 40.8 mm) in length. It passes forward between the medial wall of the orbit and the globe with in the horizontal meridian of the eyeball. The anterior 3.7 mm to 4.5 mm (mean 4 mm) is its tendon that is 10.3 mm wide. It inserts in the sclera in vertical linear fashion 5.5 mm away from the limbus. Its insertion is nearest to the limbus when compared to other extra ocular muscles insertion. It is innervated by lower division of third cranial nerve that pierces the muscle from its ocular surface. It gets its blood supply by two twigs of anterior ciliary artery. The venous drainage is through the corresponding veins of the same name that drains in the superior and inferior opthalmic vein. The sensory supply is through the trigeminal. It has only one action in horizontal plane that is adduction. Adduction is better in slightly lowered gaze, this helps in converging the eye to near work. Under action of this muscle causes exotropia. Its arc of action with the globe is 7 mm. Near the apex of the orbit, the dura of the optic nerve is closely related to the muscle.

The lateral rectus

The lateral rectus arises from the apex of the orbit mostly from the lateral part of the circle of Zinn and partly from spina lateralis recti which is a spike in the greater wing of the sphenoid. Its muscle plane coincides with the visual axis so it has only one horizontal action

i.e. abduction. Its average length is 41 mm. It passes between the lateral orbital wall and the globe. Its tendon is about 9 mm in length and 9.2 mm wide. It gets inserted in front of the equator 7 mm from the limbus in a vertical line. It is innervated by abducent nerve that pierces the muscle from the inner surface. It gets its blood supply from a single anterior ciliary artery, all other recti get their blood supply by two anterior ciliary arteries. The anterior ciliary arteries do not supply any of the obliques. Its venous supply is via the veins of the same name that drain in the ophthalmic vein. Its sensory supply is through trigeminal. The action of lateral rectus is best for distant fixation in slight up gaze.

The upper border of the lateral rectus almost reaches the lower border of the lacrimal gland along with lacrimal artery in the anterior part of the orbit. The tendon of the inferior oblique lies between the lateral rectus and the globe at its insertion.

The cyclo vertical muscles

These are two recti, the superior and inferior rectus and two obliques - the superior and the inferior obliques. The actions of the cyclo verticals are more in number and more complex in nature. They have all the three actions i.e. primary, secondary and tertiary in different gaze. Their long axes do not coincides with the visual axis in primary position. The two cyclovertical recti are adductors while the two obliques are abductors. The superior cyclo verticals, the S.R. and S.O. are intortors.

The two inferior cyclo verticals are extortors. The primary action of all the cyclo vertical muscles is best in abduction. The obliques have effective origin in front of the globe and insertion behind the equator. The recti originate from the apex of the orbit and are inserted anterior to the equator.

The cyclo vertical recti

The superior rectus (S.R.)

The superior rectus originates from the upper part of the circle of Zinn, lateral side of optic foramen and sheath of the optic nerve, it travels forward under the roof of the orbit. It’s average length is 42 mm. Its tendon is 5.5 mm in length and is 10.5 mm wide at the insertion, which is 7.7 to 7.8 mm away from the limbus. The tendon does not insert in a straight line but has a mild convexity forward. The superior rectus lies under the levator and above the superior oblique. Its insertion is farthest from the insertion of any other rectus.

In primary position, the long axis of the superior rectus form an angle of 23° with the visual axis. The axis of the muscle coincides with visual axis only when the eye is abducted 23°. At this position, if the superior rectus contracts, the eyeball will be elevated without any torsion. Elevation is the primary action of the superior rectus. Ability to elevate the globe increases with abduction and decreases in adduction. For intortion, the eyeball rotates to 67° medially, it is no more an elevator but is an intortor which is secondary action of superior rectus. Adduction is the tertiary action of the superior rectus. Thus superior rectus is an elevator, intortor and adductor of the globe. It is supplied by the upper division of the third nerve. It gets its blood supply by two anterior ciliary arteries. It has its corresponding venous drainage. Its sensory supply is through the trigeminal. One of its protective reflex action is Bell’s phenomenon. The superior rectus and inferior rectus work together as adductor but oppose each other as cyclo vertical muscles.