Diseases of the Lens

Diseases of the Lens

CATARACT

Congenital and developmental cataracts

1. Cataracta centralis pulverulenta (embryonic nuclear cataract)
• Bilateral small rounded opacity with powdery appearance lying in the centre (embryonic nucleus)
• Hereditary with dominant genetic trait.

2. Lamellar (Zonular) cataract
• Commonest type, accounting for 50 percent cases.
• Usually bilateral, opacity involves a zone of foetal nucleus around the embryonic nucleus with peripheral riders.
• May be genetic or due to vitamin-D deficiency or maternal rubella between 7 and 8 weeks of gestation.

3. Sutural cataract
• Usually static, bilateral, punctate opacities scattered around the Y-shaped sutures, of different patterns, (floriform, coralliform, spear shaped and anterior axial embryonic cataract).

4. Anterior polar cataract
• Occurs due to delayed formation of anterior chamber or following corneal perforation.
• Morphological types are: thickened white plaque, anterior pyramidal cataract and reduplicated cataract or double cataract (the burned opacity is called ‘Imprint’).

5. Posterior polar cataract
• Occurs due to persistence of posterior vascular capsule of the lens.

6. Coronary cataract
• Occurs at puberty and thus involves the adolescent nucleus or deeper cortex.
• Characterised by club-shaped radiating opacities involving the periphery (so vision usually unaffected).

7. Blue-dot cataract (Cataracta-punctata cerulea)
• Stationary, rounded, bluish, punctate opacities involving adult nucleus or deep cortex. Develops in second decade of life. Does not involve vision.

8. Total cataract
• It may be hereditary’ or associated with rubella, either unilateral or bilateral.

9. Congenital membranous cataract occurs due to partial or total absorption of lens matter.

Management

• Surgical treatment within a few weeks of birth. Visual prognosis is very poor in unilateral advanced cataract because of dense stimulus deprivation amblyopia.
• Correction of paediatric aphakia above two years- with posterior chamber intraocular lens implantation, and below two years with extended wear contact lens, or spectacles in bilateral cases.

Diseases of the LensAcquired cataracts

I. Senile cataract

• It is the most common form of cataract.
• Senile cataract is an age change. Factors affecting its onset and maturation include: heredity, exposure to ultraviolet radiations from sunlight, diet, and dehydrational crisis in childhood.
• The main biochemical features of cortical senile cataract are decreased levels of total proteins, amino acids and potassium associated with increased concentration of sodium and marked hydration of the lens. While nuclear cataract is; accompanied by a significant increase in water insoluble proteins which give brown colour to nucleus.
• In a fully-developed cataract, glutathione, ascorbic acid and riboflavin are deficient or absent. These are- the principle agencies mediating the autooxidative system of the lens.
• Cuneiform cataract accounts for 70 percent cases, Cupuliform cataract for 5 percent cases and Nuclear cataract for 25 percent cases of senile cataract.

II. Metabolic cataracts

1. Diabetic cataract: The true diabetic cataract is characterised by ‘snow-flake opacities’, usually occurring in young adults. Accumulation of ‘Sorbitol’ due to aldose reductase pathway is primarily responsible for development of true diabetic cataract.
2. Galactosaemic cataract (oil droplet cataract) is associated with inborn error of galactose metabolism due to deficiency of galactose-1- phosphate uridy 1-transferase (GPUT). A related disorder occurs due to deficiency of galactokinase causing lamellar cataract. Accumulation of ‘dulcitol’ is primarily responsible for development of galactosaemic cataract. Development of cataract may be .prevented by early diagnosis and elimination of milk from the diet.
3. Hypocalcaemic cataract may be associated with parathyroid tetany.
4. Sunflower cataract may be associated with inborn error of copper metabolism (Wilson’s disease).
5. Cataract may be seen in Lowe’s (oculo-cerebral- renal) syndrome; an inborn error of aminoacid metabolism. Other ocular features are microphakia, posterior lentiglobus and glaucoma.

III. Complicated cataract

• It may occur secondary to uveitis, retinitis pigmentosa, myopic chorio-retinal degeneration and long standing retinal detachment.
• Posterior subcapsular cataract is typically characterised by polychromatic lustre and bread crumb appearance.

IV. Toxic cataracts

1. Corticosteroid induced cataract: Posterior subcapsular opacities may be associated with the use of topical as well as systemic steroids.
2. Miotics induced cataract: Anterior subcapsular granular cataract may be associated with the use of long acting miotics such as echothiophate and demecarium bromide.
3. Other causes of toxic cataracts are chlorpromazine, amiodarone, gold (used for treatment of rheumatoid arthritis, and busulphan (used for treatment of chronic myeloid leukaemia)

V. Radiational cataract

1. Infra-red (heat) cataract. It typically occurs as discoid posterior subcapsular opacities in workers of glass industry, hence the name ‘glass-blower’s cataract’.
2 Irradiation cataract: It may follow exposure to X-rays, gamma-rays or neutron.
3. Ultraviolet radiation has been linked with senile cataract.
• Most common type of radiational cataract is posterior subcapsular cataract (PSC)

VI. Electric cataract
It may occur following passage of powerful electric current through the body. Punctate subcapsular
opacities which mature rapidly.

VII. Syndermatotic cataract

It is associated with skin disorders like atopic dermatitis, scleroderma and keratosis.

Management of cataract in adults

• Extracapsular cataract extraction (ECCE) with posterior chamber IOL is the treatment of choice.
• Incidence of post-operative complications such as endophthalmitis, cystoid macular oedema and retinal detachment is comparatively low with extracapsular cataract extraction (ECCE) as compared to intracapsular cataract extraction (ICCE).
• Phacoemulsification is an advanced technique of ECCE. The phaco needle vibrates longitudinally at an ultrasonic speed of 40,000 times per second.
• Manual small incision cataract surgery (SICS) is a low-cost alternative to phacoemulsification which offers the advantages of sutureless cataract surgery with the added advantages of having wider applicability and an easier learning curve. Intraocular lens implantation is the best method i for correction of aphakia.
• Anterior chamber IOLs: These lie entirely in front of the iris and are supported in the angle. These are not much popular due to comparatively higher incidence of bullous keratopathy. Commonly used IOL is Kelman multiflex lens.
• Iris supported lenses: These are fixed on the iris with the help of sutures, loops or claws. These are also not popular due to higher rate of complications.
• Posterior chamber lenses: These lie behind the iris and may be supported by ciliary sulcus or capsular bag. These are very popular and are available in modified C-loop and other designs.

Three types of PCIOLs available are:

• Rigid IOLs made of PMMA
• Foldable lOLs made of silicone, acrylic or hydrogel for implantation through a small (3.2 mm) incision.
• Rollable lOLs are ultrathin lenses for implantation through micro incision (1 mm) after phakonit technique.
• Primary IOL implantation refers to the use of IOL during surgery for cataract, while secondary IOL is implanted to correct aphakia in previously operated eye.
• Calculation of IOL power is done by SRK formula: P=A-2.5 L-0.9K; where P = IOL power in diopters, A = specific constant of IOL, L = axial length of eyeball in mm and K=average keratometric reading.

DISPLACEMENTS OF THE LENS

• On distant direct ophthalmoscopy edge of the clear subluxated lens is seen dark due to total internal reflection of the light.
• Anterior dislocation (in anterior chamber): Clear lens is seen as an oil drop in the aqueous.
• Posterior dislocation (in vitreous humor): lens may be floating in the vitreous (lens nutans) or fixed to the retina (lens fixata).
• Simple ectopia lentis: Displacement is bilaterally symmetrical and usually upwards. Autosomal dominant inheritance.
• Ectopia lentis et pupillae: Displacement of lens is associated with slit-shaped pupil. Other associations may be cataract, glaucoma and retinal detachment.
• Ectopia lentis with systemic anomalies include: Marfan’s syndrome: Lens is subluxated upward and temporally in both eyes.
• Homocystinuria: Lens is subluxated downward.
• Weil Marchesani syndrome: Characterised by spherophakia and anterior subluxation of lens.
• Ehlers-Danlos syndrome. Subluxated lens may be associated with blue sclera, keratoconus, angioid streakes.
• Consecutive or spontaneous displacements as seen in hypermature cataract, buphthalmos, high myopia, intraocular tumours, and chronic cyclitis.

CONGENITAL ANOMALIES

Coloboma of the lens: A notch usually seen in the inferior quadrant of the equator. Occurs due to defective development of the suspensory ligament in that part.
Anterior lenticonus: Cone-shaped anterior axial bulge. May occur in Alport’s syndrome.
Posterior lenticonus: Posterior axial bulge.
Micro-spherophakia: A small spherical lens may occur as an isolated finding or as a feature of Weil Marchessani’s or Marfan’s syndrome
Microphakia is a small lens which occur in Lowe’s syndrome.
Lentiglobus: Generalized hemi-spherical deformity.

SOME SALIENT POINTS

• The lens is incapable of becoming inflamed due to the capsule.
• The most common manifestation of developmental cataract is punctate cataract (blue dot cataract).
• Presenile cataract occurs in patients with atopic dermatitis (stellate opacities mostly posterior), dsytrophica myotonia (Christmas tree cataract), and GPUT and GK enzyme deficiency.
• Zonular or lamellar cataract is the commonest congenital cataract causing visual impairment (otherwise blue dot cataract is the commonest congenital cataract).
• Most common postoperative complication of extracapsular cataract extraction is posterior capsule thickening.
• The best method to decide about the immaturity and maturity of senile cataract is distant direct ophthalmoscopy.
• The visual loss in posterior polar cataract is much more than the anterior polar cataract, because the former is close to the nodal point of the eye.
• Cryoextraction is the safest method for intracapsular technique in intumescent cataract.
• Cupuliform or posterior cortical cataract seldom matures.