is enveloped by an elastic capsule, which is thinnest at the nodal point posteriorly.
Anteriorly, the capsule is lined by a single layer of cubical epithelium which gives rise to new lens fibers at the equatores.
The lens mass consists of:
1) Peripheral cortex
The lens grows by proliferation of the peripheral cells ,. The cortex consists of the youngest cell and the nucleus of the oldest cells, The old cells, however cannot be cast off but undergo changes leading to lental sclerosis
Any opacity of the lens or its capsule whether developmental or acquired is called cataract.
To find out cataract:
distant direct ophthalmoscopy , when the patient's pupil is dilated. The examiner sits 22 to 25 cm in front of the patient and reflects light into his pupil. Normally a red glow is seen. In cases of cataract a black opacity is seen against a red background.
Many systemic conditions can cause cataract , but vast majority of them are very rare; the following are more common:
Intra uterine infection(TORCH) as rubella (German measles) : In the mother, particularly if the infection is contracted in the 2nd or 3rd month of pregnancy. Other congenital anomalies seen in rubella syndrome are microphthalmos, microcephaly, mental retardation …
2) Mother might complain of 'white opacity' in child's eye.
3) Squint or Nystagmus.
Lamellar or zonular cataract : is the commonest form of developmental cataract , accounts 40% of all developmental cataracts. The opacity is usually sharply demarcated and the area of lens within and around the opaque zone is clear. On dilating the pupil - a central disc shaped opacity surrounded by clear cortex is seen. Sometimes linear opacities like the spokes of a wheel riders may radiate towards the periphery from the opaque area. It is usually bilateral.
2) Blue dot cataract : multiple small opaque dots scattered all over the lens, appearing as tiny blue dots by oblique illumination with slit lamp, they are known as blue dot cataract.
3) Coronary cataract : club shaped opacities are arranged in the form of a crown in the peripheral part of the cortex.
4) Anterior capsular or polar cataract : It develops as a result of delayed formation of the anterior chamber during the development of lens. A white plaque is formed in the anterior lens capsule in the pupillary area. Sometimes this opacity may project into the anterior chamber in the form of a pyramid - anterior pyramidal cataract
More commonly anterior capsular cataract is acquired and follows contact of the lens capsule with the cornea, usually after the perforation of the corneal ulcer
5) Posterior capsular cataract: This is due to persistence of the posterior part of the vascular sheath of the lens.
6) Sutural cataract : tiny opaque dots crowded in the Y sutures of the lens are seen.
7 ) Coralliform cataract : there are opacities arranged in the central area of the lens in the form of a coral.
8) Floriform cataract : The opacities are arranged like the petals of a flower in the central part of the lens.
9 ) Total cataract : The whole lens is opaque.
10) Membranous cataract: Results from spontaneous absorption of lens matter.
Surgery: Cataract extraction for visually significant cataract
Bilateral cases: 1 week apart
Non visually significant cases : careful observation, possible pupillary dilation:
I. Medical Treatment
1) Prescription of glasses if necessary
2) Mydriasis : This is particularly useful in cases where there is a central dense opacity with a relatively clear periphery.
a) 10% phenylephrine 3 or 4 times a day. With this accommodation is retained.
b) 1% atropine or 1% tropicamide drops in younger children.
3) Magnifying lens can be used for near vision.
II Optical iridectomy : To avoid the constant photophobia due to mydriasis an optical iridectomy may be performed.
III. Surgery on lens : should not be performed if the vision is 6/12 or even 6/18. This vision with retained accommodation is to be preferred to probably improved vision after operation without accommodation.
Diabetes mellitus : In diabetic subjects senile cataract tends to develop at an earlier age.
True diabetic cataract occurs in young people due to osmotic influences. A large number of fluid vacuoles appear under the anterior & posterior parts of the capsule, producing a diffuse opacity which at this stage is reversible. Thereafter a cloud of opacities resembling snow flakes appear all over the cortex. The entire lens becomes completely opaque very soon.
a) Concussion or blunt injury: It is due partly to the mechanical effects of the injury on the lens fibres and the entrance of the aqueous into the lens due to damage of the capsule (impairment of semipermeability or actual tear).
b) Perforating injury
Types of traumatic cataract:
1) Punctate opacities in the cortex
2) Rosette - shaped cataract: It is usually seen in the posterior cortex, sometimes in the anterior. The star shaped cortical sutures are delineated and from them radiate feathery lines of opacities. It may remain stationary or it may progress until the entire lens becomes opaque.
3) Total cataract: It develops when the lens capsule is severely damaged. The whole of the lens becomes opaque.
Causes of traumatic cataract Penetration Concussion ‘ Vossius’ ring from imprinting of iris pigment Flower-shaped
Definition : This results from a disturbance of the nutrition of the lens & action of toxins. It accompanies or follows other diseases of the eye which may be inflammatory, degenerative, neoplastic etc
Even in the early stages vision is usually much impaired owing to the position of the opacity at the nodal point.
The opacification usually commences in the center of the posterior part of lens (posterior cortical cataract). This part of the lens being most actively metabolic is most vulnerable to disturbance of nutrition. In addition the ant. capsule has sub-capsular epithelium to prevent entry of toxins. With the slit lamp the opacity is seen to have irregular borders extending diffusely towards the equator and the nucleus bread crumb appearance) and a characteristic rainbow display of colours often replaces the normal achromatic sheen polychromatic luster) progress:
1) Such a cataract may remain stationary indefinitely, in other cases it spreads to involve the whole cortex.
Lens extraction is to be done under the cover of systemic steroids when the eye has been free from active inflammation for 6 months to 1 year.
1) Intracapsular cat. extraction (ICCE) : This was the definite-indication earlier on the grounds that retained lens matter following extracapsular extraction induces recurrent iridocyclitis and thick after cataract.
2) Extracapsular cat. extraction (ECCE) : Modern ECCE surgery has been perfected to such a degree that the results in cases of uveitis compare with that of ICCE. The intact posterior capsule guards against vitreous loss and provides a support for introduction of a posterior chamber IOL. There is also a lesser chance of developing cystoid macular oedema in the presence of an intact posterior capsule.
Extracapsular cataract extraction 1. Anterior capsulotomy 2. Completion of incision 3. Expression of nucleus 4. Cortical cleanup 6. Polishing of posterior capsule, if appropriate 5. Care not to aspirate posterior capsule accidentally
8. Grasping of IOL and coating with viscoelastic substance Extracapsular cataract extraction ( cont. ) 7. Injection of viscoelastic substance 9. Insertion of inferior haptic and optic 11. Placement of haptics into capsular bag 10. Insertion of superior haptic 12. Dialling of IOL into horizontal position and not into ciliary sulcus
Phacoemulsification 1. Capsulorrhexis 2. Hydrodissection 3. Sculpting of nucleus 4. Cracking of nucleus 5. Emulsification of each quadrant 6. Cortical cleanup and insertion of IOL
Posterior capsular opacification (after cataract or secondary cataract)
Posterior capsular opacification (PCO) refers to the opacification of the lens remnants along the posterior capsule occurring after ECCE, phacoemulsification & lensectomy
In these operations the posterior and part of the anterior is left behind. In many cases these remnants are fine, forming a thin membrane, which does not affect vision. However in other cases the membrane may be thick causing decrease in vision.
If the after cataract is thin, vision is not affected. However, when it is thick vision is diminished even with intraocular lenses, spectacle correction or contact lenses.
Preoperatively the pupil should be well dilated with mydriatics.
1. Laser capsulotomy is done using Neodymium YAG (1 YAG) laser. The laser energy is used to create an opening in the after cataract. This avoids the problems associated with intraocular surgery such as infection and can be done as an outpatient procedure
2. pars plana membranectomy is done using VTSC (Vitreo infusion suction cutter)
3. Needling or discission : This is done with Ziegler's knife needle or Bowman's needle. A rent is made in the after cataract in the pupillary area.
4. Capsuloiridectomy is done in cases where the after cataract is associated with an updrawn pupil.