congenital cataract

Anatomy of Lens and Congenital Cataract

Copy of power point presentation of lecture taken by Dr Sanjay Shrivastava, Prof of

Ophthalmology, Gandhi Medical College, Bhopal (M.P.) India, for Junior final year

MBBS students in November 2006

LENS

Anatomy

7th November 2006 dr sanjay shrivastava 3

Lens

• It is a highly organized transparent asymmetrical oblate spheroid structure that has evolved to alter the refractive index of the light entering in the eye. It does not posses nerve, blood vessels or connective tissue.

• Biconvex shape results from the anterior surface being less convex then posterior surface.


Anatomical Considerations

• Biconvex Lens• Diameter varies from 8.8 to 9.2 mm.• Lens grow in size continuously throughout

life. Its weight is about 65 mgm at the birth and up to 258 mgm by 80 years of age.

• Antero-posterior thickness changes with accommodation. Thickness is 4.75 – 5 mm (un-accommodated) in adults.

• Circumference is known as equator


Lens

• Lens is suspended in eye by Zonules which are inserted on anterior surface and equatorial lens capsule and attached to ciliary body. Zonular fibres are series of fibrillin rich fibre.


Lens - Anatomy

• Histologically lens consists of three major components:1. Capsule – is a thick collagenese basement membrane which is transparent, elastic acellular envelop, thick at anterior pre-equatorial region (21 micron m), thinnest at the posterior pole (4 micron m). Anterior pole is approximately 14 micron m thick. It contains the epithelial cells and fibres as a structural unit and allows a passage of small molecules both into and out of lens


Lens - Anatomy

2. Lens Epithelium – It is a single layer of cells lining the anterior capsule and extends to the equatorial lens bow.

Zone of epithelial cells:a. Central – cells do not actively

divide, they divide under pathological conditions only.

b. Pre-equatorial germinal zone : cells rarely divide.


Lens - Anatomy

c. Germinal zone: consists of the stem cell population. The newly formed cells from germinal zone are forced into transitional zone where they elongate and differentiate to form mass of the lens. The lens epithelium secretes the lens capsule and also regulate the transport of metabolite, nutrients and electrolytes to the lens fibres.


Lens - Anatomy

3. Lens substance: It constitute the main mass of the lens. It is divided into-

a. Nucleus

b. Cortex

Nucleus: consists of

(i) Embryonic nucleus (it contains primary lens fibres that are formed in lens vesicle)


Lens - Anatomy

(ii) Fetal nucleus: it contains embryonic nucleus and all fibres added to the lens before birth

(iii) Infantile nucleus: it contains embryonic , fetal nucleus together with all the fibres added up to the age of 4 years.

(iv) Adult nucleus: composed of all fibres added before sexual maturation. The nucleus consists of densely compacted lens fibres and has a higher refractive index than cortex.


Anatomy of Lens

CapsuleCortex

3

4

5

6

3 – Adult Nu 4 - Infantile Nu5 – Fetal Nu

6 – Embryonic Nu.


Lens Cortex

• It is located peripherally and is composed of secondary fibres formed continuously after sexual maturation. It is further divided into: – Deep cortex– Intermediate cortex– Superficial cortex


Lens Cortex

• The region between embryonic and fetal nuclear core and soft cortex i.e. infantile and adult nucleus is sometimes referred to as epinucleus. The region between deep cortex and adult nucleus is sometimes referred to as Perinuclear region.

• Lens fibres are held together by interlocking of lateral plasma membranes of adjacent fibres to form ball-and-socket and tongue-and-groove joints.


Lens - Sutures

• Are found both at anterior and posterior poles. They are formed by overlap of ends of secondary fibres in each growth shell. Each growth shell of secondary fibres formed before birth (fetal nucleus) has as anterior suture shaped as an erect Y and a posterior suture shaped as an inverted Y.


Lens - Crystalline

Lens fibres contain high concentrations of crystalline.

Crystalline represent the major protein of the lens (constitute 90% of total protein content of lens). Crystalline has the following constituents:

Alpha

Beta and,

Gamma


Lens - Functions

• The lens serves two major functions:

– Focusing of visible light rays on the fovea – Preventing damaging ultra-violet radiation

from reaching the retina


Lens – Physiology

• Lens function and transparency is dependant on the supply of appropriate nutrient to its various structures. Metabolic needs of adult lens are met by the aqueous and vitreous.

• There is continuous transport of ions into and out of the lens.


Lens - Physiology

• Lens function is dependent on the metabolism of glucose to produce energy , protein synthesis and a complex antioxidant system. Glutathione is found in high concentration in lens and helps protect its structure from oxidative damage.


Lens - Physiology

• The transparency is dependent on highly organized structure of lens, dense packing of crystalline

• By act of accommodation it changes focusing power. Accommodation occurs by increasing the curvature of anterior surface thereby changing refractive index of lens.

• Light transmission and elasticity of lens decreases with age.


Age changes in the Lens

• The lens exhibit age related changes in the structure, light transmission , metabolic capacity and enzyme activity.

• Overall light transmission decreases with age, lens becomes less elastic, reducing its ability to accommodate which leads to presbyopia.

• Metabolic activity is decreased , reduction in antioxidant system with age makes lens prone to oxidative damage.

• Changes in the crystalline are characterized by aggregation, degradation and increased insolubility.


Cataract


Cataract

• Any opacity in the lens or its capsule, whether developmental or acquired is called cataract.

• Developmental opacities are usually partial and stationary, whereas acquired opacities are progressive. They progress until the entire lens is involved, but exceptions are well known in both types.


Risk Factors for Cataract

• Senility• Sunlight (specially UV –A and UV-B component)• Severe Diarrhoeal dehydration• Vitamin A,C, E deficiency• Diabetes• Smoking• Corticosteroids• Genetic


Classification of Cataract

1. Developmental

2. Age related (senile)

3. Cataract associated with ocular diseases

4. Cataract associated with systemic diseases (pre-senile)

5. Traumatic Cataract

6. Drug induced cataract


Developmental Cataract

• When cataract is present at birth it is called congenital.

• Types

1. Punctate: most common manifestation, in its minute form it is of universal occurrence. Multiple small opaque spots are seen scattered all over the lens. Types:

a. Blue dot – appearing as tiny blue dots in oblique illumination.


Punctate Cataract

b. Sutural – when opaque spots are crowded in the Y sutures

c. Central Pulverulent Cataract – Autosomal dominant inherited, non-progressive, central spheroidal or biconvex opacity consisting of fine white powdery dots within embryonic or fetal nucleus.


Developmental Cataract.. Types

2. Zonular Cataract: accounts for approximately 50% of all visually significant congenital cataracts.

Etiology – May have a genetic origin with a strong hereditary tendency of autosomal dominant type. They may have an environmental origin, due to malnutrition at late intra-uterine or early infantile life and Vitamin D deficiency. Patient may have Rickets and defective enamel of permanent teeth.


Zonular Cataract

• Zone around embryonic nucleus, usually area of fetal nucleus is affected and opacified. Its extent depends on the duration of the inhibiting factor. Sharply demarked opacity, area within and around opacity is clear; with linear opacities resembling spokes of a wheel (riders) running towards equator.

• Such cataracts are usually bilateral formed just before or shortly after birth, may be sufficient in diameter to fill the pupillary area and vision is affected.


Developmental Cataract- types

3. Fusiform Cataract – Spindle shaped, axial or coralliform. There is antero-posterior spindle shaped opacity sometimes with offshoots giving an appearance of coral.

Discoid Cataract is disc shaped opacity in posterior cortex behind nucleus.


Developmental Cataract - Types

4. Nuclear Cataract: Due to inhibition at an early stage, the central nucleus (embryonic nucleus) remains opaque.A progressive type of nuclear cataract is observed in child when mother suffers from rubella (German measles) during 2nd or 3rd month of pregnancy.Nucleus is necrotic, the whole lens becomes opaque, with accompanying retinitis (salt and pepper retinopathy) at the posterior pole.


Nuclear Cataract

• Other congenital deformities like, congenital heart disease (PDA), microphthalmos, micrencephaly, mental retardation deafness and dental anomalies may be associated.

• If the lens matter remains in eye during surgery, it is followed by a chronic inflammatory endophthalmitis.


Nuclear Cataract

• Prevention of rubella by administration of MMR vaccine or rubella vaccine to pre-pubertal girls or women planning to start family may be considered to prevent this condition.

• Medical termination of pregnancy may be considered if evidence of rubella infection is confirmed during 2nd or 3rd month of pregnancy to prevent birth of a child with multiple congenital anomalies.



5. Coronary Cataract: It is a developmental cataract, similar to zonular cataract, occurring around puberty. Situated in deep layer of the cortex and the most superficial layers of adolescent nucleus. Appears as corona of club shaped opacities at periphery, hidden by iris. Axial area and periphery of lens remains clear. Vision is usually not affected. These opacities are non-progressive.



6. Anterior Capsular (polar) Cataract: may be due to delayed development of anterior chamber (congenital cataract) or due to contact of anterior lens capsule and posterior surface of cornea due to perforation of ulcer, as in case of ophthalmia neonatorum. Types – Anterior Polar, Pyramidal Cataract and Reduplication cataractUsually these opacities are non-progressive and rarely interfere with vision.


Developmental Cataract – Types

7. Posterior Capsular (Polar) Cataract: Is due to persistence of the posterior part of vascular sheath of the lens. In minimal degree it is common and usually is insignificant.

Sometimes in cases of persistent hyaloid artery, the lens is deeply invaded by fibrous tissue and a total cataract forms.


Etiology of Developmental Cataract

• Usually unknown• Maternal (and infantile) malnutrition• Maternal Viral (rubella) infection• Placental Haemorrhage causing deficient

oxygenation • Hypocalcaemia• Chromosomal abnormality (Down syndrome)• Metabolic disorders (galactosaemia)


Symptoms of Developmental Cataract

Informant – usually parents History of white spot in pupillary area Child is usually brought with history of

diminution of vision / does not recognize objects and parents

Unsteady eyes Deviation of eye Associated symptoms of systemic

disease, if present


Signs

• Diminished vision (at times it is difficult to establish in very young children)

• Lenticular opacity• Nystagmus• Deviation of eye, usually convergent

squint• There may be other ocular and systemic

abnormalities in cases of rubella nuclear cataract


Management of Developmental Cataract

I. Investigations:

1. Detailed history

2. Detailed clinical examination- visual status, intra-ocular tension, fundus examination, B scan ultrasonography to exclude posterior segment abnormality like growth/ retinoblastoma, A scan to determine axial length of the eye, retinoscopy, cover test to exclude squint.



3. Laboratory investigations:

A. Blood Test

Blood glucose, calcium and phosphorus

RBC transferase and Galactokinase levels

TORCH test

Hepatitis B virus



B. Urine analysis:

For reducing substance for galactosaemia

For amino acids (to exclude Lowe syndrome in suspected cases)



B. Treatment

1. Timing of surgery

a. Bilateral Dense cataract – by 6 weeks

b. Bilateral partial – if vision is not significantly affected, surgery may be delayed up to the age of 2 years or up to puberty



c. Uniocular dense cataract- urgent surgery with in days

d. Partial Uniocular cataract- if vision is not significantly affected, surgery may be delayed up to the age of 2 years or up to puberty



2. Treatment options – * No treatment if vision is not significantly

affected* Mydriatics- if opacity is central and vision

improves with mydriatics * In cases in Rubella Cataract operation

may be delayed till 1-2 years of age. But early surgery may be indicated if cataract is total, squint and nystagmus is developing.



* Uniocular cataract – if vision is affected then early surgery, preferably within first six weeks of birth with immediate fitting of contact lens.

* Fixation develops between 2-4 months of age, therefore any cataract interfering with vision should be dealt before this age, and the earliest possible time is preferred

* Medical/ Paediatric fitness for anaesthesia should be obtained.



3. Operative procedure

a. Aspiration and irrigation (ECCE)

b. Lensectomy (Pars plana or anterior route)

c. Aspiration and irrigation (ECCE) with primary posterior capsulotomy with partial anterior vitrectomy



4. Post-operative visual rehabilitation:

a. Posterior Chamber IOL (PMMA or acrylic polymer foldable lens) in patients who are more than two years in age, Uniocular cataract where contact lens fitting is not possible/ practical.

b. Contact lens – after surgery for uniocular cataract at very young age.



c. Aphakic Spect- In bilateral cataract operated cases below the age of two years. These cases are implanted posterior chamber IOL as secondary procedure at later age.

d. Occlusion therapy for treatment of amblyopia / prevention of amblyopia.


Post-operative complications

• Posterior capsular opacification

• Secondary membrane formation

• Proliferation of lens epithelium (Sommerring ring)

• Glaucoma

• Retinal detachment

congenital cataract

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