Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

Treatment is directed towards glaucoma. Initially medical treatment is tried if it fails. Trabeculectomy is the best surgical choice. The trabeculectomy hole may be blocked by ICE cells. Next alternative is Molteno valve.

B. Mesodermal dysgenesis (Anterior chamber cleavage syndrome)

Mesodermal dysgenesis consists of :

1.Posterior embryotoxon

2.Axenfeld anomaly

3.Riegers anomaly

4.Peters anomaly

1.Posterior embryotoxon—18, 19. This is the mildest form of mesodermal dysgenesis.20 This anomaly is present in all forms of mesodermal dysgenesis. Ten to thirty percent of normal eyes show posterior embryotoxon without any other symptom21 except cosmetic blemish. The Schwalbe’s line is prominent and shifted centrally. It is formed by splitting of Descemets membrane into two leaves that contains collagenous tissue that is nearer to trabecular meshwork than cornea. The thickened Schwalbe’s line projects in the AC as a ridge all around 1 mm inside the limbus or it may be fragmented. Its appearance is similar to arcus juvenilis that develops at the end of the Bownan’s membrane, rest of the cornea, iris, angle and trabecular mesh work are normal. The condition does not require any treatment.

2.Axenfeld’s anomaly. This condition may be considered to be more advanced form of posterior embryotoxon. In this condition strands of peripheral iris tissue are attached to the thickened Schwalbe’s line. Glaucoma need not be present in all cases because angle remains unaffected in most of the eyes. The iris and pupil are also normal. Glaucoma when present is difficult to manage. The condition is bilateral without any predilection for sex. The condition becomes obvious in childhood due to prominent posterior embryotoxon. Glaucoma is not met with in childhood. It is a feature of late adolescence or adulthood.

3.Riegers anomaly22, 23. Riegers anomaly represents gross anomaly of the structures that arise from mesoderm. It involves cornea, iris and trabeculum in various combinations. The corneal change is represented by posterior embryotoxon. Iris shows hypoplasia of stroma with full or partial thickness holes that may be present as deformity of the pupil in the form of corectopia, dyscoria, pseudocoria or slit like pupil. There may be positive transillumination of the iris. The peripheral iris is attached to the thickened Schwalbe’s line as slender or broad adhensions. These adhesion may be in patches or may encircle the whole of the angle. The trabecular meshwork itself is normal. The iridocorneal adhesion is the cause of glaucoma that is seen in half of the cases. Rise of intraocular tension may go unnoticed unless looked for specifically. Severe rise of tension in infancy causes typical buphthalmos. Other less common findings are23A. Persistent hyaloid vasculature, partial or total absence of choroidal and retinal pigment epithelium, dysplasia of retina. The lens is not primarily involved, lenticular changes are secondary to glaucoma.

Skeletal changes are sometimes seen in Riegers anomaly limited to face and teeth. There is hypoplasia of maxilla, hypodontia and micro-dontia.

The ocular features are bilateral but not symmetrical. Common inheritance is autosomal, sporadic cases are also known.

Once glaucoma develops the aim is to keep the tension low medically if that fails surgical intervention may be required.

4. Peter’s anomaly—24, 25, 26. This condition is rarest among all mesodermal dysgenesises. The most striking feature is a central corneal defect. It is a bilateral condition, present at birth, seen equally among boys and girls, has autosomal recessive inheritance. It can be divided into following groups :

(a) Type I—associated with posterior embryotoxon. It has combined picture ofAxenfelds and Riegers anomaly with central corneal defect in the form of central facet at the level of Descemets membrane. The endothelium is absent in the facet. The iris is attached to the cornea all around the defect, leading to stromal opacity. The anterior chamber is slit like in between the central adhesion and peripheral iridocorneal synechea. The lens is in place.

(b) Type II—No evidence of Axenfeld or Riegers anomaly. Only feature is central iridocorneal adhesion as in type one.

(c) Type III—The findings are similar to type II. The anterior lens capsule is adhered to central corneal defect. The anterior chamber is shallow. The lens soon becomes opaque. Glaucoma is seen in fifty percent of cases. Other anomalies include microphthalmos, cornea plana, sclerocornea, vitreo retinal defects.

C. Trabeculo dysgenesis27, 28, 29. In this condition the developmental anomaly lies in the trabecular meshwork, rest of the angle, anterior chamber and iris are developmentally normal. It is present at birth, more common in boys, it is familial, more than one sibling may be effected. The inheritance is heterogeneous but may be autosomal recessive. The exact mechanism of the anomaly is not well understood. There are two schools of thought, the first believes that there is an anatomical mal-developmental. The other postulates that there is arrest of maturation. There is an incomplete cleavage of uveal periphery from the corneoscleral wall. The meridional fibres are inserted either in the trabecular meshwork or in Schwalbe’s line.

Gonioscopically the angle is wide but the trabecular meshwork is not clearly visible due to a thin membrane like structure on the surface of the trabeculum. This is eponymed as Barkan’s membrane. Many authors have doubt about its presence. As the trabecular meshwork is plastered with mesodermal tissue, the aqueous fails to reach the canal of Schlemm resulting into rise of intra ocular tension that causes primary infentile glaucoma or buphthalmos with its consequences.

Comparison between iridocorneal dysgenesis and mesodermal dysgenesis.

Aqueous humour

A.This is a crystal clear fluid that fills both the anterior and posterior chamber. The exact time it starts forming is not establishing but must be before birth because the aqueous drainage system is ready to function before birth6.

B.The functions of aqueous humour are to :

1.Give and maintain an optimal intraocular pressure compatible with vision.

2.Provide nutrition to avascular structures of the eye i.e. the cornea and lens.

3.Remove waste products of metabolism.

4.Act as an important optical medium.

C. The composition of aqueous humour :

The aqueous humour differs greatly from plasma from which it seems to be derived by the way of its low, protein, sodium, bicarbonate and glucose. The ascorbate content is very high, chlorides and lactic acid have higher concentration.

The aqueous humour is acidic, and slightly hypertonic. The albumin globulin, ratio is same as in plasma. The human aqueous contains only IgG and not IgA and IgM.

There is hardly any change in the composition of aqueous in anterior and posterior chamber. The composition of aqueous in phakic and aphakic eyes are the same proving thereby that lens does not participate in formation of aqueous. The refractive index of aqueous is 1.33710 which is less than both the cornea and lens.

D. Formation of aqueous humour. The aqueous humour is derived from the plasma in the capillary network of the ciliary process. There are three theories of production of aqueous in the ciliary processes.

1.Diffusion

2.Ultra filtration

3.Secretion

The plasma passes through three tissue layer that allow fluid with specific quality to pass through it. They are : The wall of the capillary, the stroma of the ciliary process and the

ciliary epithelium. None of the above process fulfil all the conditions to be fit into one process. It seems all the processes take part in different proportion. The most important out of the three is secretion.

E.Rate of formation of aqueous humour. The rate of aqueous production is called in flow of aqueous. It is measured in micro litres per minute (ml/min). It is not uniform throughout the day and night. It shows a diurnal variation. The normal range in adults is

2.8to 4.3 ml/mt The production is least in the night12. The inflow increases following drinking of large volume of water and is decreased by ingestion of many locally and systemic acting drugs.

F.Rate of outflow. To maintain intraocular pressure within normal range, there should be an equilibrium between inflow and outflow of aqueous. The aqueous is produced in the ciliary processes that passes successively through posterior chamber, pupil and anterior chamber where the aqueous circulates between the cornea and the iris by convection current. The aqueous leaves the anterior chamber via trabecular meshwork, canal of Schlemm and is finally picked up by episcleral vessels. This mode of outflow that is about 85% of total outflow is called conventional outflow, rest is drained by what is known as unconventional outflow. The unconventional path comprises of uveoscleral and uveovertex pathway. Presence of uevoscleral channel is well etablished. There is no unanimity regarding presence of uveo vertex path.

The facility of outflow is measured by a non invasive method called tonography. The outflow of facility is expressed in ml/min/mm.Hg. The outflow canbe increased by applying pressure over the globe and by topical drugs. The normal value is about 0.20 ml/mt/mm Hg.

Intraocular pressure :

A.Normal intraocular pressure ranges between 15-20 mm of Hg. It is hardly influenced by age or sex. It shows a physiological variation of 2 to 3 mm between the highest and lowest pressure during the days and is called diurnal variation. In most of the eyes the tension is maximum in the morning however some persons may show an evening rise. A biphasic rise is also possible.

B.Measurement of intraocular pressure - Intraocular pressure is the lateral pressure exerted by intraocular contents on the outer coats of the eye i.e. the cornea and the sclera. There are two clinical methods of clinical methods of measuring it.

1.Indentation tonometer

2.Applanation tonometer

The applanation tonometer is more accurate than indentation as it is not influenced by scleral rigidity. The advantages of indentation tonometer are that it is very cheap, easy to handle and gives fairly accurate reading. Out of all applanation tonometers most widely used tonometer is Goldmann’s tonometer. The other is Draeger tonometer. The applanation tonometer can be mounted on a slit lamp or may be handheld (Perkins).

Other used applanation tonometers are :

A.The pneuno tonometer

B.The air puff non contact tonometer.

Gonioscopic anatomy of angle of anterior chamber. The angle of anterior chamber has been called the cockpit of glaucoma. It is not visible in normal eye with oblique illumination. To see it, special optical devices called gonioscopes are employed. The gonioscopic anatomy of the anterior chamber has following visible landmarks from peripheral iris to peripheral cornea.

A.Ciliary body. This is the part of the ciliary body visible from the insertion of the iris to the ciliary body to the insertion of the ciliary body in the scleral spur. The width of ciliary body is wider in myopia and narrower in hypermetropia. The colour is grey to dark brown.

B.Scleral spur. This is the part of the sclera to which the ciliary body is inserted. This represents the posterior sharp edge of the scleral sulcus. The ciliary body is attached little behind the posterior attachment of trabecular meshwork. On gonioscope, it looks as a prominent white line in front of ciliary band and behind the trabecular meshwork.

C.The trabecular meshwork. The trabecular meshwork is porous structure that stretches across the angle of anterior chamber, bridging it between the scleral spur and

Schwalbe’s line. It has two distinct parts, a non-functioning anterior part and a functioning posterior part.

The angle of anterior chamber is examined for presence of pigment, new vessels, exfoliations, synechia and foreign body. Common causes of increased pigmentation are - acute and chronic glaucoma, uveitis, trauma.

D.Schwalbe’s line. This is the termination of Descemets membrane and represents the anterior limit of the trabecular meshwork. It looks like a translucent circular band. In case of posterior embryotoxon, it is very prominent and shifted anteriorly.

E.The Schlemm’s canal. This is not visible in all eyes. When visible it looks like a darker line in the lower trabeculum. If the episcleral pressure is higher than intraocular pressure blood may be seen in Schlemm’s canal. However blood can also be seen in hypotony with normal episcleral pressure.

F.The angle recess is the term used to denote dipping of iris in the ciliary body as it inserts in the ciliary body.

Gonioscopy. Gonioscopy is a non invasive clinical method of visualising the angle of the anterior chamber.

The rays arising from the angle of anterior chamber do not leave the eye. They are reflected back hence are not visible because the rays arising from angle pass through aqueous and cornea into air which has refractive index less than the former two. The critical angle of the rays is more than 46° hence they are reflected back. This difficulty is overcome by eliminating air corneal interface and allowing the rays to pass a contact lens making the angle visible. The device is called gonioscope.

There are two types of gonioscopes

1.Direct gonioscope

2.Indirect gonioscope

The direct gonio-lens has an anterior curvature that does not allow the critical angle to be reached hence the rays are refracted at goniolens air interface. In case of indirect

gonioscope, it has a contact lens and either a reflecting mirror or a prism. The reflecting angle is almost 90° to the lens air interface hence can be picked up by slit lamp or an operating microscope. A large number of gonioscopes in both the categories are available, each with specific design and purpose.

Childhood Glaucoma

Roughly two percent of population above forty years suffer from some type of glaucoma or other, mostly chronic symptomsless primary open angle glaucoma. The incidence rises with age and by eighty years the percentage reaches an alarming figure of five percent. Fortunately, awareness of adut prevalence of glaucoma is quite high nowadays and more and more persons are benefited by early detection and proper treatment. Childhood glaucoma differs from adult glaucoma in many ways.30 Most of the cases are symptomatic hence seek medical advice early unless it is unilateral and mild. Loss of vision is fast and gross. If the condition is not treated, permanent visual damage is inevitable. Prevalence of childhood glaucoma is far less than adult glaucoma hence chances of missing it are more.

Classification of glaucoma in children. There is no unanimity regarding classification of glaucoma. There are many ways to classify them. Some of them are :

A.According to age of onset

1.Those manifesting within first two years of age.

2.Those developing after two years but before puberty.

3.Developing in early childhood.

B.According to involvement of ocular structures -

1.Those due to developmental anomalies in the eyes. (a) Anomaly in the angle only.

(b) Multiple anomalies of anterior segment including angle.

2.Secondary to causes not related to developmental anomalies of the eye. The group A is designated as congenital or developmental glaucoma.

The group B consists of conditions that constitute a heterogeneous group of glaucoma called secondary glaucoma, both the groups can have wide or narrow angle.

C.The most widely accepted classification that fulfils almost all criterions is one given by Duke Elder in 196430,31.

This divides congenital glaucoma’s into :

1.Developmental buphthalmos (a) Simple buphthalmos

(b) Associated buphthalmos

2.Secondary congenital buphthalmos

All the eyes under three years of age that have raised intraocular tension will go into buphthalmos irrespective of cause.

Simple buphthalmos

General consideration—35, 36. The term buphthalmos is not a specific clinical entity. It embraces many diverse conditions. The only common feature among them is enlargement of the globe secondary to raised intraocular tension. The eye ball is enlarged and looks more or less like a bovine eye, to be specific eye of an Ox. Buphthalmos is seen not only in congenital glaucoma but in all conditions that cause rise of intraocular tension under three years of age.

The cornea stops enlarging after three years of age so enlargement of the globe is either arrested or minimal by three years.

The term buphthalmos will be used in the text to denote primary developmental glaucoma as a general practice rather than its accuracy.

Primary buphthalmos is relatively uncommon disorder. It is inherited as autosomal recessive trait. It may be present in the siblings. Some of the older members of the family may have early onset of chronic simple glaucoma. In sixty percent cases it is bilateral which need not be symmetrical. Due to some ill understood causes it is more common in boys. The ratio between boys to girls is 3:2. The disease may either be present at birth as true congenital glaucoma, or may manifest in first year as infantile glaucoma. On rare instances the disease may have still late presentation. These are the cases where instead of complete shutdown of flow of aqueous, the flow is slower than normal and rise of tension late and slow.

In true congenital glaucoma rise of intraocular tension and its consequences are present in intrauterine life. The disorder is caused due to trabecular dysgenesis of angle of anterior chamber32, 33, rest of the eye does not suffer from any other congenital anomaly, the child does not have any other extra ocular or systemic congenital anomaly.

The eye in primary buphthalmos :

1.Enlargement of cornea. The most spectacular changes are seen in cornea, which is enlarged in all directions. At birth the diameter of the normal cornea is 10.5 mm to

11.0mm, by one year it varies between 11.5 mm and 12.0 mm, at two years it should not exceed 12 mm and enlargement virtually comes to stand still. Corneal diameter more than 13 mm at any age and more than 12 mm at 1 year should be seen with suspicion and investigated for buphthalmos.34 In advanced cases of buphthalmos diameter as high as 18 mm have been reported. The size of the cornea depends on range of intraocular tension and duration of raised intraocular tension. Very high tension cause enlargement quickly. Relatively low tension takes more time to reach the same dimension.

2.Stretching of the cornea. Stretching of the cornea in all meridians cause thinning of the cornea that alters the curvature of the cornea, initially the corneal curvature is increased. The enhanced corneal curvature is not uniform. There is a relative flattening in the centre of cornea. As the cornea stretches, the Descemets membrane gives away giving rise to striated opacities that assume various forms. They start as fine branched striae in the central part, the rupture in the centre looks like a horizontal line while ruptures on the periphery are concentric with limbus. The peripheral ruptures are more common in lower part of the cornea. There may be more than one rupture in the same cornea. The lines produced by rupture of Descemets membrane in primary buphthalmos are known as Haab’s striations.

They may be present in other forms of congenital or developmental glaucoma as well. The lines become opaque and more prominent with time. The Haab’s striations must be differentiated from rupture in Descemet’s membrane due to birth trauma, specially following forceps delivery. Such ruptures are vertical. The Haab’s striations may become whirl like sometimes. The ruptured Descemets membrane allows aqueous to permeate into the stroma and cause clouding of corneal epithelium, lacrimation and photophobia.

3. The stretching, clouding, development of opacity in the cornea, relative flattening in the centre of the cornea lead to irregular astigmatism.

The stretching is not limited to the cornea, whole of the globe undergoes stretching and enlargement, due to high intraocular pressure in an immature eye.

4. Stretching of sclera :

1.The stretching of sclera is not uniform in all directions. It is most pronounced in anterior posterior diameter followed by horizontal diameter. The vertical diameter is least effected.

2.Due to unequal stretching of the globe instead of becoming an enlarged sphere it becomes more or less like an egg.

3.Over all enlargement of globe specially in anterio posterior axis gives an appearance of pseudo proptosis.

4.The other effect of enlargement of outer coat of the eye is obliteration of the corneoscleral sulcus that brings about significant change in the surgical anatomy of the limbus resulting in accidental placing of sclerotomy too posterior during surgery5.

5.Stretching is most marked in pre-equatorial area than posterior sclera. In long standing cases there may be formation of equatorial or ciliary staphyloma.

5. Anterior uvea. Stretched sclera causes an increase in limbal diameter in all meridians. The ciliary body that is attached to the scleral spur, is shifted peripherally resulting in stretching of the zonules and the iris. The stretched iris becomes thin and the pupil becomes larger than normal. Other cause of large pupil in buphthalmos of course is optic nerve change and tension related iridoplegia in late stages.

As the sclera moves more peripherally, the suspensory ligament becomes tight and flatten the lens. A strained suspensory ligament may give way, resulting in subluxation or dislocation of the lens.

6.Anterior chamber. The effect of increased corneal curvature, thinning of iris, and flattening of lens is deepening of anterior chamber. A clear deep anterior chamber with large cloudy cornea in a child should be investigated for primary buphthalmos.

7.Lens. Flattening of lens and sometimes subluxation of lens leads to tremulousness of lens. After sometimes the clear lens or lens with variable degree of opacity may dislocate, commonest direction of dislocation is posteriorly, however large pupil can predispose anterior dislocation.

8.The vitreous, choroids and retina do not show any significant change.

9.Optic disc. The changes in optic nerve in primary buphthalmos are prominent. The changes are mostly due to stretching of the sclera and backwards shifting of lamina cribrosa.

The optic nerve changes are reversible. If the intraocular tension is brought low and kept low, the optic nerve changes shift towards normal. However after three years when anterior segment enlargement stops, the optic nerve changes become accentuated and progress.

10.Intraocular tension. Intraocular tension is generally above 40 mm Hg., when the child presents for the first time. It may be as high as 80 mm Hg.

11.Error of refraction. Due to increased axial length, the eyes are moderately myopic. This myopia is partially neutralised due to flattening of central cornea, flattening of lens and posterior shift of lens. Myopia is invariably associated with irregular astigmatism.

12.Vision. Vision in an eye with primary buphthalmos is always subnormal, due to :

1. Corneal opacity, 2. Error of refraction, 3. Lenticular changes, 4. Changes in optic nerve head, 5. Amblyopia, 6. Nystagmus.

Main diagnostic features in primary buphthalmos :

A.The main diagnostic feature of primary buphthalmos lies in the angle of anterior chamber. The angle should be examined by a suitable gonioscope in every eye that has large, cloudy cornea with deep and clear anterior chamber.

B.The examiner should have a good knowledge of gonioscopic appearance of angle of anterior chamber in neonate and infants that differs from that of an adult angle.

C.The angle of a new born has following features :

1.The angle recess is very narrow.

2.The peripheral iris and blood vessels produce a scalloped appearance.

3.The trabecular sheets are translucent.37, 38

4.The anterior part of the ciliary body and its insertion in the scleral spur is seen clearly.

D.The gonioscopic examination in case of primary buphthalmos is done by direct gonioscope of Koeppe or its modification.

E.The advantages of direct gonioscopy are :

1.It can be done by placing the child on its back.

2.Both the eyes can be examined simultaneously by using two gonioscopes and the changes compared in two eyes.

3.360° of an angle is visible at a given time.

4.It can be done either by handheld microscope with suitable illumination or operating microscope.

5.An additional advantage of Koeppe’s gonioscopy is that direct ophthalmoscopy can be done over the gonioscope because it gives extra magnification.

Neonate need not be given general anaesthesia to do direct gonioscopy but a child above three months may not co-operate without sedation, may even require general anaesthesia.

If the cornea is hazy due to epithelial edema, the epithelium should be scrapped either mechanically by the blunt side of a cataract knife or chemically by rubbing the cornea with swab soaked in alcohol32,33. Instillation of 5% hyper tonic sodium chloride drop few times may also clear epithelial haze.

F.Gonioscopic findings34,35,36 :

1.Gonioscopic findings are not uniformly spread all over the angle, it need not be symmetrical in two eyes.

2.The other eye should also be examined even when it is apparently normal.

3.In primary buphthalmos, the anterior chamber is of normal depth before corneal stretching and enlargement ensue, with rise of tension and passage of time the anterior chamber deepens.

4.The angle is wide open.

5.On the inner surface of trabecular meshwork a translucent membrane called

Barkan’s membrane may be present.

6.There is no angle recess.34

7.The peripheral iris is inserted in the line of Schwalbe.

8.The scleral spur is not well visible.

G.Measurement of Intraocular tension—Intraocular tension is primary buphthalmos is always raised, it may vary between 40 mm to 80 mm Hg depending upon severity of trabecular block, duration and therapeutic measures undertaken. The tension is measured either by Schiotz’s tonometer, Perkin’s handheld applanation tonometer or tonopen. In children over three years tension should be recorded under general anaesthesia under a competent anaesthetist well versed in paediatric anaesthesia. Allowance should be made for general anaesthesia induced rise of tension. Some of the anaesthetic agents themselves alter intraocular tension. halothene and barbiturates lower tension, while ketamine elevates the tension.38,39,40 Tension recorded in a struggling child is not good enough. Digital recording of tension should always be avoided.

Diagnosis

A.Diagnosis of full blown case of primary buphthalmos is not difficult, provided there is enough awareness among the attending neonatologist, obstetrician and attending nurse.

B.Unless looked for carefully, chances of missing the condition in very high specially in bilateral cases with mild to moderate manifestation.

C.Unilateral cases draw early attention of the mother to relatively prominent eye. Besides prominent eye/eyes, other symptoms that point towards possibility of buphthalmos are: lacrimation, photophobia, blepharospasm, and large cloudy cornea. The child with buphthalmos has poor appetite and the child is withdrawn. The child with bilateral disease prefers to be in dark place, keeps both the eye closed and moves the face away from light. In unilateral cases the child keeps the effected eye closed. As the child grows, the symptoms become more pronounced. The child may open the eyes at night due to reduced intensity of light and then it is realised that the child has poor vision.

D.A positive history in siblings, in first cousins, require thorough examination of a new born. Similarly children and grand children of persons who had early onset of wide angle glaucoma should also be suspected to have primary buphthalmos and investigated.