Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

myopic eye requires very little accommodation. In contrast to this, the hypermetropic eye requires more accommodation hence the pupil is smaller in hypermetropia and larger in myopia.

The size of pupil is equal and shape symmetrical in two eyes in 80% of persons. Only in remaining, the size of the pupil differs in two eyes. This is called anisocoria. Anisocoria is said to be simple or essential when the size of any of the pupil does not change due to change in illumination. If the size of the pupil changes with illumination it means a pathological phenomenon. In such cases it must be decided, which pupil, the larger or the smaller is pathological.2 For example, in Horner’s syndrome the degree of anisocoria is most marked in dim illumination.4 However in case of unilateral visual defect size of the pupil does not change irrespective of opacity in media, or pathology of retina or optic nerve.

The size of the pupil depends on a delicate balance between the potency of constrictor and dilator muscles. Constrictor muscle has an enhanced tone than dilator more so in childhood and irritation of parasympathetic as seen in iridocyclitis. The pupil of a child is more resistant to mydriatic than that of an adult. A light coloured eye has a larger pupil that dilated better than a dark coloured iris.

The neural control of constrictor pupillae

The constrictor of the pupil is called the sphincter pupillae.5 It is ectodermal in origin and is placed in a circular fashion round the pupil. It is supplied by third cranial nerve via its parasympathetic system. The fibres start in the Edinger-Westphal nucleus and pass in the third nerve up to orbit where the third nerve divides into two branches. The lower branch supplies the inferior oblique. After leaving the inferior oblique, the nerve enters the ciliary ganglion as its motor root. From the ciliary ganglion start the post ganglionic fibres that pass along the short ciliary nerve and enter the sclera around the optic nerve.

Once the post ganglionic fibres enter the sclera, they pass in the supra choroidal space and terminate in the iris and ciliary body. Ninety percent of the fibres go to the ciliary body and only three percent to the iris, remaining supply the blood vessels.6 The neuro transmitters released at neuro muscular junction is acetylcholine.

Neural control of dilator pupillae

The dilator pupillae is also ectodermal in origin, it is arranged in radial fashion away from the pupillary margin. In comparison to constrictor it is a poorer muscle. The dilator muscle is differentiated later than sphincter and continues to develop even after birth. This may be the cause of smaller pupil in neonates. The dilator pupillae is supplied by cervical sympathetic. The post ganglion fibres from superior cervical ganglion accompany the internal carotid artery and then pass along the first division of the trigeminal nerve and emerge from the cavernous sinus with nasociliary nerve and long ciliary nerve to the iris. The neuro transmitter released at neuro muscular junction is nor epinephrine.

The pupil is kinetic indicator of functional state of iris, optic nerve, third cranial nerve and ocular sympathetic system.

The size of the pupil keeps on fluctuating with change in intensity of illumination, accommodation, convergence and integrity of parasympathetic and sympathetic path. Part of the parasympathetic path is common with visual path.

The two neural paths involved in pupillary reaction are

1.Light reflex

2.Near reflex

(a) Accommodation (b) Convergence (c) Miosis

The pupillary light reflex is a four-neurone arc with an afferent and an efferent component. The former spreads from retina to Edinger Weshphal nucleus and latter from

Edinger Westphal nucleus to the iris.

The first neuron extends from rods and cones to pretectal nucleus in the mid brain. The fibres from the temporal half go straight into the optic tract without decussation. The fibres from nasal retina decussate at the chiasma in the same manner as visual pathway. The crossed and uncrossed fibres travel in the optic tract up to its posterior third where they leave the visual path and turn to pretectal nucleus.

The second neuron connects pretectal nucleus on each side to the Edinger Westphal nuclei. The neurones that join the pretectal nucleus to the Edinger Westphal nucleus are called inter nuncial neurons. A decussation take place in the mid brain before entering the Edinger Westphal nucleus. This decussation explains consensual light reflex in the other eye when light is shown in one eye. In normal eye, the consensual light reflex is equal and symmetrical to direct reaction.

The third neuron spreads from Edinger Westphal nucleus to ciliary ganglion. The para sympathetic fibres change their relative position in third nerve during its course. Between the, mid brain and the cavernous sinus, the pupillo motor fibres are superficial in the nerve and are liable for a compressive lesion. Fortunately these lesion are less common in children. In the cavernous sinus and beyond, the pupillo motor fibres become central hence are not affected by mass lesion even when the third nerve is paralysed. In the orbit, the pupillomotor fibres reach the ciliary ganglion via nerve to inferior oblique.

The fourth neuron leaves the ciliary ganglion and accompanies the short ciliary nerve to reach the sphincter pupillae.

The whole of the pupillary light reflex is subcortical.

NEAR REFLEX

This is not a true reflex. It is better called near synkinesis of accommodation, convergence and miosis.7

In contrast to pupillary light reflex where Edinger Westphal nucleus acts as nucleus for pupillary light reflex, there is no definite nucleus for near reflex. These probably are supra nuclear areas one each in frontal and occipital lobe that mediate the reflex. The various components of the synkinesis can be modified either by optical device i.e. lens/prism or therapeutically. The accommodation can be relaxed by plus lenses while it can be enhanced by minus lenses. The convergence can be neutralised by base out prism and enhanced by base in prism. The miosis is overcome by mydriatic. Cycloplegic will abolish both accommodation and miosis in normal eye. The reflex can be initiated either by accommodation

or convergence. Vision is not needed for near reflex. It can be elicited in blind eyes if the patient is made aware of a near object like his own index finger and asked to look at it when kept near the eye. There is no condition where light reflex is present but near reflex is absent.2,4,7

The near reflex path is also parasympathetic in nature. The near reflex starts in visual cells of retina. It follows the same path as light reflex up to the posterior third of the optic tract where the pupillary light reflex fibres leave the tract to join the pretectal nucleus. The near reflex fibres continue with visual fibres along the optic radiation to the occipital cortex area17,18. Here the visual fibres terminate. The near reflex fibres continue to the frontal occulomotor centre where they become part of a mass reflex that is mediated through cortico-tectal tract to the occulomotor nuclei.

The efferent path starts from the Edinger Westphal nucleus and follows the third nerve like pupillary light reflex.

Convergence reflex can not be separated from other two synkinesises i.e. accommodation and miosis. Convergence enhances both accommodation and miosis. Miosis due to bright light does not influence accommodation or convergence. However accommodation strengthens convergence and increases miosis.

The reflex arc for convergence starts from medial rectus and follows the third nerve up to third nerve nucleus complex. The Perlia’s nucleus is supposed to control the convergence. The efferent path extends from the Perlia’s nucleus to the ciliary ganglion and its post ganglionic fibres.

Other pupillary reflexes

The other pupillary reflexes are not associated with either light or near reflex. They are

•Orbicularis reflex

•Vestibular and cochlear reflex

•Trigeminal reflex

•Vagotonic reflex

•Psychosensory reflex.

The orbicularis reflex is constriction of pupil on the side of forceful contraction of orbicularis against resistance. It is present in about 80% of persons. The exact path of the mechanism is not known.

The vestibular and cochlear reflex have little value in ophthalmic evaluation. They represent caloric, acoustic and rotational sensation from vestibular and cochlear area in the mid brain.

The trigeminal reflex - On touching the cornea, there is momentary mydriasis followed by miosis. The exact path of the reflex is not known. It is presumed that the afferent trigeminal fibres also stimulate the third nerve via mid brain.

The vagotonic reflex consists of mild dilatation of pupil on inspiration and slight constriction on expiration.

2. Directly acting on iris musculature

These are prostaglandines and histamine. They do not have any therapeutic use.

3. Centrally acting

These are central depressents that reduce supra nuclear inhibition on third nerve i.e. morphine and barbiturates.

Mydriatics and Cycloplegics

Mydriatics are the drugs that dilate the pupil. They are not cycloplegics. They can be locally acting or centrally acting.

Cycloplegics are the drugs that paralyse ciliary body and abolish accommodation. They are mydriatics as well. They can be locally acting or centrally acting.

Mydriatics and cycloplegics can be put into two broad groups i.e.

1.Cholinergic antagonists—Cycloplegic cum mydriatic.

2.Adrenergic—Agonist—Mydriatic.

1.Cholinergic antagonist—These are also known as parasympatholytic drugs. They are

A.Block cholinergic receptors (Atropine, home atropine, cyclopentolate, tropicamide, scopolamine and eucatropine. The last two are no more used in clinical practice.

B . Drugs that block parasympathetic nerve ending i.e. Botulium toxin.

2. Adrenergic agonist - These are also known as sympathomimetic drugs. They are

(a) Directly stimulating alpha receptors—Epinephrine, phenyle-pherine, nor adrenaline. The last has no therapeutic use.

(b) Drugs that release nor adrenaline from nerve ending - Ephidrine and hydroxyamphetamine. They do not have much therapeutic use. Hydroxyamphetamine (Paredrine 1%) is used to diagnose level of lesion in Horner’s syndrome.

Cocaine is a sympathomimetic drug that blocks the re uptake of nor adrenaline at nerve ending is a good mydriatic and local anaesthetic, is no more in use. It has synergistic action with parasympatholitic drugs. It is exclusively used to diagnose Horner’s syndrome. Cocaine 4% will dilate normal pupil but not Horner’s pupil.

Abnormal pupillary reaction11

Abnormality of pupillary reaction can be abnormality of light reflex or abnormality of near reflex. Or there may be a dissociation of light near reflex.

The abnormalities can be in:- Afferent path of third nerve Efferent path of third nerve Oculosympathetic chain

The anomalies are either neurological or pharmacological.

Afferent pupillary defect are -

1.Total afferent pupillary defect.

2.Relative afferent pupillary defect.

3.Wernicke’s hemianopic pupil.

4.Argyll Robertson pupil

The characteristics of afferent pupillary defects are

1.The lesion may be anywhere from retinal visual cells to the pretectal nucleus.

2.There is decreased amplitude of contraction to light stimulus.

3.The latency in reaction to light stimulus is increased.

4.The pupil dilates on prolonged exposure to light.

5.Both the direct and consensual reflexes are involved.

6.The afferent pupillary light reflex can be present in blind eye if the cause of blindness is retro chiasmal.

While testing pupillary light reflex, it should be ensured that the accommodation is at rest. The room is dimly lit and the source of light is small, sharp and bright.

Total afferent pupillary defect (TAPD)

This is also known as amaurotic pupil.11 The lesion causing the defect is unilateral either as an extensive damage to the retina or complete loss of conduction in the optic nerve anywhere from disc to the chiasma. There is no perception of light in the affected eye. Both the pupil are of same size. In case of bilateral blindness due to pre geniculate lesion, the pupil tend to be larger than normal. When light is thrown in the pupil of the blind eye neither pupil react i.e. there is absent direct pupillary reaction in the affected eye and absent indirect reaction on the contra lateral side. When normal eye is stimulated by light, both the pupil react. Any amount of opacity in media is not capable of producing total afferent pupillary defect.

Relative afferent pupillary defect (RAPD)

This happens when the affected eye has some vision. The cause of which is located in anterior visual path i.e. extensive retinal lesion or lesion in optic nerve. There is asymmetric conduction defect. If both eyes have diminished vision, the eye with poorer vision develops relative afferent defect. The difference between the conduction in two eyes can be estimated with use of neutral density filter. The condition is also called Marcus Gunn pupil and is demonstrated by swinging flash light test. Swinging flash light test consists of following steps :11,12

1.Vision in both eyes is noted with and without correction separately.

2.The room is semi-darkened.

3.The patient is asked to fix at a distant object.

4.Size of the pupil is noted in diffused light.

5.Direct and indirect light reflex are noted.

6.The eye with—less vision, larger pupil and sluggish direct light reaction in the eye effected.

7.Throw bright well-focussed light in one eye and note the reaction.

8.Quickly shift the light to the other eye and note the reaction.

9.Repeat above steps by moving the light from one eye to the other and note the reaction.

Interpretation

1.In normal eye both the pupil constrict equally and symmetrically i.e. isocoria.

2.In presence of RAPD, the affected pupil shows reduced amplitude of miosis and enhanced dilatation.

The swinging flash light test is positive when only afferent pre-chiasmal conduction defect is present and efferent arc is intact.

A modified and less sensitive test is

1.Occlude the normal eye for sometime, observe the affected eye. The pupil of unexposed but affected eye will be larger than before the normal eye was occluded.

2.Occlude the affected eye in same fashion. The pupil of the non occluded normal eye will be smaller.

The causes of RAPD are

1.Optic neuritis

2.Optic atrophy

3.Retro bulbar neuritis

4.Traumatic optic neuropathy

5.Advancedglaucomatousopticatrophy

6.Advanced and extensive retinal disease

Pupillary reaction in mid chiasmal lesion

The nasal fibres of retina decussate at the middle of the chiasma, the temporal fibres pass without decussation. Hence in a mid chiasmal lesion, light directed from temporal field produce less pupillary constriction than light directed from nasal field. The causes are pituitary tumour, cranio pharyngioma, tubercular meningitis and trauma.

Pupillary reaction in anterior junctional lesion

Anterior chiasma syndrome is caused due to a lesion involving one optic nerve and half of chiasma on the same side. The pupil when seen in diffuse light are slightly dilated and large. The pupillary reaction is a combination of Marcus Gunn pupil in one eye and chiasmatic hemianopia pupillary reaction in the other eye. Importance of this type of pupillary reaction lies in the fact that it is seen in craniopharygioma and parasellar extension of pituitary tumour which are common in children.

Pupillary reaction in lesion of optic tract

Lesions of anterior optic tract cause Wernike’s hemianopic pupil. A lesion near the lateral geniculate body does not produce any pupillary change because the pupillary fibres leave the optic tract anterior to the junction of posterior 1/3 to anterior 2/3. Wernicke’s

hemianopic pupil requires special efforts to demonstrate its presence. It is done by throwing a bright narrow beam of light from the field of hemianopia that produces less constriction than light thrown from the side of normal field. A bright beam from slit lamp give best result. The lesion is associated with incongruous homonymous field defect. It is seen in trauma to temporal lobe, abscess in temporal lobe and Schilder’s disease.

A lesion near the end of the optic tract and pretectal area causes loss of light reflex with preserved accommodation. This is called light near dissociation.13

A classical example of light near dissociation is Argyll Robertson pupil due to neurosyphilis which is not seen in children but there are other causes of light near dissociation which are put collectively as pseudo Argyll Robertson pupil and are seen in children.

The exact site of lesion in classical Argyll Robertson pupil is not known. Commonly agreed lesion is pretectal. In Argyll Robertson pupil accommodation reflex is retained while light reflex is lost but vision is maintained.

Characteristics of Argyll Robertson are

1.It is a bilateral condition.

2.One eye is more involved than the other.

3.It is seen after third decade.

4.The pupil are miotic and irregular.

5.Pupillary light reflex is absent.

6.Pupil dilates poorly with atropine.

7.Accommodation reflex is present.

8.Vision is good.

9.Patches iris atrophy are present these may be mistaken as heterochromia.

10.Orbicularis reflex is often retained.

11.The cases are always associated with positive serological test for syphilis.

Sometimes unilateral Argyll Robertson pupil like reaction has been reported for which the lesion has to be small that blocks input to only one Edinger Westphal nucleus.

Inverse Argyll Robertson pupil is very rare where the pupillary light reflex is present with failure of pupil to near reflex is usually associated with failure to converge the eye. Most probable site of the lesion is Perlia’s nucleus in mid brain.

Pseudo Argyll Robertson pupil

In these condition, the pupil is generally normal in size or mildly dilated but light reflex is poor. There may be spasm of accommodation, diminished amplitude of accommodation. Other presenting signs may be lid retraction, ptosis, nuclear oculomotor palsy, convergence palsy, spasm of convergence, vertical gaze palsy and vertical nystagmus.12 Commonly seen in Parinaud’s syndrome, aqueductal stenosis and aberrant regeneration of third nerve.

The list of conditions that cause light near dissociation are

1.Pseudo Argyll Robertson pupil.

2.Parinauds syndrome.

3.Aqueductal stenosis.

4.Unilateral Argyll Robertson pupil.

5.Aberrant regeneration of third nerve.

6.Adie-Holmes pupil.

7.Juvenile diabetes.

Efferent pupillomotor defect

Size of the pupil and its reaction to light is a delicate balance between parasympathetic and sympathetic system. The parasympathetic system is little more effective than its sympathetic counterpart. As the efferent path of the pupillary reaction is parasympathetic in nature, slightest under action results in relatively greater loss of pupillary and ciliary reflex.

The efferent pupillomotor fibres may be involved anywhere between the third nerve nucleus and the eye. It is a peripheral lesion, generally unilateral. It may involve only the pupil but more common is internal ophthalmoplegia that is a combined paralysis of pupil and ciliary body. It is present in total third nerve palsy and in total ophthalmoplegia. However pupil is spared in diabetic third nerve. A third nerve lesion in cavernous sinus has normal sized pupil because it is also associated with involvement of oculosympathetic under action. The mydriasis of third nerve palsy in cavernous sinus is counteracted by miosis of sympathetic, resulting in normal sized pupil in cavernous sinus disease.

Before diagnosing efferent pupillary defect, it is essential to rule out

1.Congenital anomaly of pupil

2.Trauma to iris

3.Instillation of mydriatic and cycloplegic in the eye

Pharmacological mydriasis and cycloplegia is not counteracted by instillation of pilocarpine but a neurological mydriasis will respond to pilocarpine.

1.The causes in children may be in the mid brain i.e. Pineal tumour, encephalitis, brain abscess, trauma.

2.Oculomotor nerve

3.Ciliary ganglion—Adies pupil

4.Short ciliary nerve—Trauma.

In total oculomotor nerve palsy the eyeball is deviated down and out with ptosis and dilated pupil that does not react either to light or accommodation, convergence is also absent.

Hutchinson’s pupil

This is a common pupillary defect due to compression of third nerve due to an expanding subtentorial or subdural lesion. Commonly seen in head injury, there is always lowering of consciousness with raised intracranial pressure. The mechanism consists of raised intracranial pressure that compresses the third nerve either against the pteroclinoid ligament or dorsum sella causing progressive herniation of brain, resulting acute internal ophthalmoplegia, which is an ominous sign following head injury requiring early surgical intervention.

Classical Hutchinson’s pupil consists of

1.Initial homelateral miosis due to irritation of third nerve.

2.Followed by moderate dilatation of same pupil with sluggish light reflex and convergence.

3.Dilatation of pupil with loss of light and convergence

4.Signs of third nerve palsy.

5.Miosis of contra lateral pupil.

6.Bilateral dilated pupil.

Adie’s pupil (Tonic pupil)

This is an efferent disorder of pupil with light near dissociation. It is caused by denervation of post ganglionic constrictor fibres and ciliary muscle. Most probable cause is presumed to be viral in origin. In 80% cases, it is unilateral generally seen in women between 20-40 years. It can be seen less frequently in children. If the tonic pupil in a child is hypersensitive to methacholine, the child has familial dysautonomia i.e. Riley Day syndrome.

Characteristics of Adies pupil

1.The pupil is large and circular.

2.The pupil when examined in dim light after exposure to usual light is smaller.

3.Light reflex in affected pupil is either absent or very slow or is localised as vermiform movement of a sector of iris when seen on slit lamp.

4.Near reflex miosis is slow so is redilatation on distant vision.

5.Accommodation is low, amplitude of accommodation is less, relaxation of accommodation is poor resulting in to temporary blurred vision for distance following near work.

6.Consensual reflex is intact.

7.Vision is normal.

8.The pupil is hypersensitive to parasympathomimetic drops.

Normal pupil does not constrict following instillation of 0.125% of pilocarpine or 2% methacholine. In Adies pupil the pupil constricts to both the drugs in 30 minutes.

Horner’s pupil12,15,16

The pupillary anomaly is part of a syndrome which has following characteristics

1.It is mostly acquired but may be congenital or may be due to a birth trauma.

2.It is generally unilateral.

3.There is mild ptosis not more than 2 mm due to paralysis of Muller’s muscles. There is no change in superior rectus.

4.Upside down ptosis i.e. slight upward shift of lower lid margin due to weakness of inferior tarsal muscle.

5.Miosis due to unopposed action of sphincter pupillae.

6.Pupil is central, circular, reacts normally to light and accommodation.

7.Heterochromia is seen mostly in congenital cases.

8.Reduced sweating on the side on the lesion if the lesion is below the superior cervical ganglion.

9.The miosis is greater in dim light.

10.There is increased amplitude of accommodation.