Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

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57.Faunfelders F.T. : Kaposi sarcoma in Current ocular therapy. fifth edition, edited by Fraunfelder F.T. Roy F.H. and Randall J., p. 241, W.B. Saunders Company Philadelphia 2000.

57A. Spitzberg D.H. : Pars planitis in Current ocular therapy. Edition fifth, edited by Fraunfelder F.T., Roy F.H., p. 517-519, W.B. Saunders Company, Philadelphia, 2000.

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57E. Deborah Pavan Langstone : Uveal tract in Manual of ocular diagnosis and therapy. Third edition, p. 191-196, Lippincott.

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(2) Secondary lens fibres are derived from the equatorial part of the lens epithelium2. The secondary lens fibers keep multiplying through out the life. The older fibers are pushed towards centre and are converted in to the nucleus. The central fibers are the oldest and peripheral are most recent.

1.The peripheral soft fibers are called Cortex while relatively hard fibers are called Nucleus. There is no histological demarcation between the cortex and the nucleus. It may be said, nucleus of present day is the cortex of yesterday5.

2.The nucleus of the lens. The nucleus of the lens is not a separate entity; it is mere condensation of centrally pushed lens fiber. The oldest fiber are deepest, the number of fiber keep on increasing throughout the life without much gain in size of the lens. According to period of development the nucleus has been assigned various names.

They are

(a) Embryonic (b) Foetal

(c) Infantile

(d) Adult.

(a) The embryonic nucleus is the innermost and earliest to come into existence it is formed by primary lens fibre, initially there is a circular empty space surrounded by single layer of cuboidal cells. The posterior cells elongate to obliterate the space, as the posterior cells elongate the lumen becomes crescent shaped and becomes completely-extinct.

(b) The foetal nucleus develops from the secondary lens fibber over the embryonic nucleus. The size of the embryonic and foetal nuclei do not change, in life they are pin point in size.

(c) The infantile and adult nuclei are formed after birth. The infantile nucleus is completed before puberty, the adult nucleus develops there after. Size of adult nucleus keeps on increasing without much change in overall dimension of the lens. The lens fiber that are not converted into nucleus are known as cortex. So child has more cortex and small nucleus while a person in sixth decade has larger nucleus and scanty cortex. The nucleus not only enlarges in size it gets sclerosed as the person ages.

The secondary fiber are not long enough to span the lens pole to pole, they do not meet at a point. The fiber in the same level meet in a peculiar fashion forming a Y shaped figure called.

Lens suture. There are two sutures the anterior one is an erect Y while the posterior one is inverted Y. The sutures start forming in the first two months and seen in foetal life. The advantage of these sutures are that they give an elliptical shape and better optical property to the lens.

(d) The zonules are entirely different from the lens, developmentally and functionally, their only purpose is to keep the lens in the papillary area and help change its curvature during accommodation. The zonules are infact tertiary vitreous. They extend from the apices of the ciliary process to the capsule. There are three groups of zonule. The anterior, middle and posterior attaching to anterior, middle and posterior part of equator respectively.

The anterior zonule extends for a few millimetres on the anterior lens capsule. The posterior zonule may extent from oraseratta to equator of the lens.

The tunica vasculosa lentis. The postnatal lens is avascular and gets its nutrition solely form aqueous. In first half of the gestation the lens gets nutrition from a rich framework of vessels that envelop the lens all round and is called tunica vasculosa lentis. Developmentally, it has two parts; the anterior vasculosa lentis and posterior vasculosa lentis. The anterior is a part of pupillary membrane while the posterior is formed by the terminal branches of hyaloid artery which is part of ophthalmic artery and enters the eye through the foetal fissure, it covers the developing posterior capsule and the equator. The tunica vasculosa lentis starts regressing even before the whole of the lens has formed. By fifth month it is fully atrophied.

DEVELOPMENT OF THE LENS

The lens is ectodermal in origin. Its presence becomes evident at 4mm stage7, when the optic vesicle comes in contact with the surface ectoderm. This contact between two surfaces triggers thickening in the surface ectoderm called the lensplate, at the same time another important change takes place in the optic vesicle that starts inveginating to form the opticcup a two layered structure from which the retina develops. The cells of lens plate elongate and increase in number and the single layered structure instead of spreading laterally bows inside forming a pitcher like structure, the mouth of which gradually narrows and by 8mm stage it closes completely and separates from the surface ectoderm. The surface ectoderm closes to form the subsequent corneal epithelium. The closed single layered structure separated from the surface ectoderm is called lens vesicle that starts moving away from the surface ectoderm towards the optic cup in the space between the two will later develop cornea proper, iris and AC.

There is difference in development of cell forming the anterior and posterior walls of the lens vesicle, the anterior cells remain cuboidal while the posterior cells elongate forward to obliterate the space of the lens vesicle resulting into a solid globular structure calledembryonic lens nucleus. The lens capsule that is a true basement membrane starts forming and by 13mm stage, the capsule envelops the growing lens fully.

After formation of embryonic nucleus, formation of new lens fibber is shifted to the equatorial region . These fibber are called secondary lens fiber. As the fibers are formed the nuclei of elongated cells disappear this is one of the causes for clarity of the lens.The fibber meeting at the centre of the core form the anterior and posterior Y sutures.

As more and more fibers are formed at the equator, the earlier fiber are pushed centrally and compressed to form various nuclei : the foetal , infantile and adult nucleus.

PHYSIOLOGY OF THE LENS8,9,10

Lens is avascular, depends upon aqueous for its nutrition. It has both anaerobic and aerobic metabolism. The lens contains 65% water and 35% protein, the highest concentration of protein in any tissue. Ninety percent of protein is water soluble, they are devided into three types alpha , beta and gamma crystalline and remaining portion is insoluble albunoid. The

concentration of insoluble protein increases with age. In cataract almost all the protein is converted into insoluble albunoid. The lens protein is organ specific and not species specific i.e. a body sensitised to lens protein will behave adversely later if exposed to lens protein of any species. This has an important bearing in lens induced uveities and endophthalmitis phacoanaphylactica.

The lens has a good concentration of ascorbic acid which is synthesised by the lens and ciliary epithelium. It also contains glutathion both in oxidised and reduced form. The amount of ascorbic acid and glutathion decrease with age and cataract formation. The transparency of the lens depends greatly on its metabolism and physiochemical status of protein.

CONGENITAL ANOMALIES OF THE LENS

Congenital anomalies of the lens are common but all need not be treated as many are asymptomatic.

Anomalies that involve embryonic and foetal nuclei are true congenital and others are called developmental defects.

Some of the congenital anomalies are obvious at birth, others are detected late due to associated diminished vision, squint and nystagmus.

A.The congenital anomalies may be :

1.Limited to Lens

2.Associated with other anomalies of the eye

3.Associated with systemic disorders

4.Combination of all above

B.Congenital anomalies can be :

1.Loss of transparency

2.Change in shape of the lens

3.Change in position

4.Various combination of above three.

B. Congenital anomalies can be

1. Congenital loss of transparency. Loss of transparency complete or partial is clinically known as congenital or developmental cataract. They are in the form of opacities. The opacities that involve embryonal and foetal nuclei are called congenital while rest excluding traumatic are developmental. Many a times it is difficult to differentiate between the two. The congenital opacities are generally central, dens and may be large enough to cover the entire papillary area and, are generally soft. Congenital and developmental cataracts are often bilateral but can be unilateral. The cataracts in childhood are frequently stationary because the cataractogenic factor effects a particular zone of developing lens, the lens fibers laid before or after the stoppage of cataractogenesies remain clear, 25% to 30% of cataracts are hereditary how ever some time they may be sporadic.

Etiology

Etiology of congenital and developmental cataracts are not well understood it can be: (i) Idiopathic in 40 % to 50 % of cases. These are generally sporadic11.

(ii) Heredity one third of all congenital and developmental cataracts are hereditary.12,13,14,15 due to genetically determined chromosomal anomaly.

(iii) Maternal

●Maternal infection during pregnancy commonest virus resulting in cataract is Rubella, others are cytomegalo inclusion virus, rubeola, mumps influenza. Toxoplasmosis is yet another cause of congenital anomaly if acquired during late months of pregnancy maternal syphilis can also cause congenital cataract.13

●Maternal malnutrition specially fat soluble vitamins.

●Drugs : many of the drugs if taken during first trimester result in foetal cataract i.e. thalidomide, steroids.

●Maternal radiation during pregnancy.

●Endocrine disturbance.12

(iv) Foetal

●Birth Trauma

●Placental haemorrhage leading to poor oxygen supply to foetus.

●Metabolic disorders

(i) Foetal

(ii) Infantile

●Various syndromes

●Prematurity

●Persistence of anterior hyloid system

●Intra ocular tumours.

CLASSIFICATION OF CONGENITAL AND DEVELOPMENTAL CATARACT

It is difficult to have a uniform, universally accepted classification. A broad classification16 is dividing these cataracts into the broad categories as :—

A.Capsulo lenticular (Capsulo cortical)

B.Lenticular

Congenital cataract can be either nuclear or cortical. It is not uncommon for both to exist in the same eye. It is frequent for nuclear cataract to become total cataract.

A.The capsulo lenticular cataracts are—

1.Anterior polar and anterior capsular cataract.

2.Posterior capsular—Mittendorf dot. posterior lenticonous.

3.Posterior polar cataract.

B.The lenticular cataracts are—

1.Zonular

(a) Lamellar

(b) Total Cataract

(c) Cataracta central pulverulenta. (d) Membrenous

2.Sutural

3.Axial

According to shape the catracts can be :—

1.Disciform

2.Coraliform

3.Coronary

4.Others—Corkscrew cataract, spear shaped cataract, Christmas tree cataract, blue dot cataract.

A.The Capsulo lenticular cataracts

1. Anterior Polar and Anterior Capsular Cataract. Sometimes these are described separately but as their clinical presentation, pathogenesis and management are similar they are being discussed in one group.

Anterior polar cataracts are common but not detected unless specifically looked for under magnification, are generally bilateral and do not block the pupil due to their size that may be pin point to 1 to 2 mm in diameter. They are generally small slightly raised plaque, may project in anterior chamber as a triangular growth with base on the centre of the anterior capsule and called pyramidal cataract they are of two type:

(a) Developmental due to delayed separation of anterior lens capsule from the surface ectoderm.

(b) Acquired. This occures frequently in badly managed ophthalmia neonatorum resulting in central perforation, loss of A.C., prolonged contact between anterior lens capsule and cornea. These are generally bilateral and associated with nystagmus. Sometimes there may be localised opacification of anterior lens capsule resulting into true anterior capsular cataract. More frequent are reduplication or imprint cataract where a second opacity develops little below the anterior polar cataract with a clear zone in between, the size of the reduplication cataract is either same as the base of the pyramidal cataract or larger. Sometimes there may be a third imprint still posteriorly. Occasionally the two opacities may be joined by a strand of opacity traversing the clear zone in between. The anterior polar cataract may be associated with persistent pupillary membrane or central corneal opacity. The opacities are stationary and do not cause much visual disturbance, hence do not need any treatment.

2. Posterior polar and posterior capsular cataracts. Posterior polar and posterior capsular opacities are as common as their anterior counterpart. There are two forms of posterior polar cataracts, one commonly known as Mittendorf dot. This is formed due to incomplete absorption of anterior part of the hyaloid artery that supplies nutrition to the lens during

first three months of gestation. Some times a small stalk of vessel may remain attached to the lens. This condition is stationary and cause visual disturbance due to its proximity to the nodal point of the eye, how ever it is generally discovered and diagnosed during routine retinoscopy or direct ophthalmoscopy. It does not require any treatment. The other progressive form causes great visual loss as the opacity increase in size after birth by developing opacities in the posterior cortex either as a sheet of opacity or radiating opacities from a central opacity. The condition is not known to involve the nucleus16. If the opacity is dense enough it causes diminished vision, and amblyopia it should be operated by any standard microsurgical procedure.

CATARACTS INVOLVING THE NUCLEUS AND DEEPER LAYERS OF CORTEX

Most of these cataracts are developmental and have been put under category of lenticular developmental cataract2,16.

The commonest in the group is lamellar or perinuclear also refereed as zonular cataract.

1. Lamellar cataract is commonest congenital cataract, it amount for about 50% of all developmental cataracts. It is generally bilateral, symmetrical and stationary, boys are more effected than girls, it may be prenatal or postnatal. There is a rough measurement to find out whether it is prenatal or postnatal which says that if the opacity is smaller than diameter of lens of new born i.e. 5.75 mm it is most probably prenatal otherwise post natal. Actual size varies according to on set of cataractogenesis and level of lens fibres involved. It most commonly develops in foetal and infantile nuclei in lamellar formation, the lamellae may be single or multiple. The opacity inside and out side the affected nucleus are clear. The opacity may be fully opaque or may be translucent. On the surface of the opacity many ridges are visible on oblique illumination. These ridges radiate from the centre and vary in number they may be limited at the periphery of the cataract or may project in the clear cortex with club or spine shaped projections called riders.

Most of the lamellar cataracts are hereditary, transmitted as autosomal dominant trait may be present in parents or in siblings. The sporadic cataracts are generally due to derangement of calcium metabolism in the mother with vitamin “D” deficiency during growth of the lens, the opacity develops in a layer that corresponds with maximum level of noxious substance. The fibres laid before and after this cataractogenesis are clear.

On examination the opacity may cover whole of the pupillary area, on dilatation a clear zone of the cortex is visible both on retinoscopy and ophthalmoscopy.

Treatment depends up on size and density of the cataract. Translucent lenses with good vision need no treatment, some may benefit with dilatation of the pupil. Otherwise the treatment is removal of opacity by standard microsurgical method preferably with P.C.I.O.L.

2. Congenital nuclear cataract. This type may be confined to the embryonic nucleus due to changes at 3 months gestation. These are dens, powdery hence called pulverulent cataract which are generally bilateral, non progressive with out much visual loss.