Cataract - Causes, types, Pathogenesis and treatment

What is Cataract?

The word ‘cataract’ dates from the Middle Ages and has been derived from the Greek word ‘katarraktes’  which means ‘waterfall’. This term was coined  assuming that an ‘abnormal humour’ developed  and flowed in front of the lens to decrease the vision.

As of today, the term cataract refers to development of any opacity in the lens or its capsule. Cataract, thus  may occur, either due to formation of opaque lens  fibres (congenital and developmental cataracts) or  due to degenerative process leading to opacification of the normally formed transparent lens fibres (acquired cataract). 

Clinically, the term cataract refers to an opacification of sufficient severity to impair the vision  (Dorland’s Illustrated Medical Dictionary, W.B. Saunders, Philadelphia).

In simple words Cataract is the opacity in the lens and it's capsule.

Pathogenesis of Cataract:

It is basically different in nuclear and cortical senile cataracts. 

1. Cortical senile cataract:

 Its main biochemical features are decreased levels in the crystalline lens of  total proteins, amino acids and potassium associated  with increased concentration of sodium and marked hydration of the lens, followed by coagulation of lens  proteins. The probable course of events leading to  senile opacification of cortex.

2. Nuclear senile cataract:

 In this the usual degenerative changes are intensification of the age-related nuclear sclerosis associated with dehydration and compaction of the nucleus resulting  in a hard cataract. It is accompanied by a significant increase in water insoluble proteins. However, the  total protein content and distribution of cations remain normal. There may or may not be associated  deposition of pigment urochrome and/or melanin derived from amino acids in the lens.

Classification:

A. Etiological classification

I. Congenital and developmental cataract

II. Acquired cataract

1. Senile cataract

2. Traumatic cataract (see page 429)

3. Complicated cataract

4. Metabolic cataract

5. Electric cataract

6. Radiational cataract

7. Toxic cataract e.g.,

i. Corticosteroid-induced cataract

ii. Miotics-induced cataract

iii. Copper (in chalcosis) and iron (in siderosis)

induced cataract

8. Dermatogenic cataract

9. Cataract associated with osseous diseases

10. Cataract with miscellaneous syndromes e.g.,

i. Dystrophica myotonica

ii. Down’s syndrome

iii.Lowe’s syndrome

iv. Treacher-Collin’s syndrome.

Morphological classification:

1. Capsular cataract. It involves the capsule and may be,

i. Anterior capsular cataract

ii. Posterior capsular cataract

2. Subcapsular cataract. It involves the superficial most part of the cortex (just below the capsule) and includes: 

i. Anterior subcapsular cataract

ii. Posterior subcapsular cataract

3. Cortical cataract. It involves the major part of the cortex. 

4. Supranuclear cataract. It involves only the deeper parts of cortex (just outside the nucleus). 

5. Nuclear cataract. It involves the nucleus of the crystalline lens.

6. Polar cataract. It involves the capsule and superficial part of the cortex in the polar region  only and may be: 

i. Anterior polar cataract

ii. Posterior polar cataract

Management of Cataract:

Treatment of cataract essentially consists of its surgical removal. However, certain nonsurgical  measures may be of help, in peculiar circumstances, till surgery is taken up. 

A. Non - surgical measures:

1. Treatment of cause of cataract.In acquired cataracts, thorough search should be made to find out the  cause of cataract. Treatment of the causative disease,  many a time, may stop progression and sometimes in  

early stages may cause even regression of cataractous changes and thus defer the surgical treatment. Some  common examples include: 

• Adequate control of diabetes mellitus, when discovered. 

• Removal of cataractogenic drugs such as corticosteroids, phenothiazenes and strong  miotics, may delay or prevent cataractogenesis. 

• Removal of irradiation (infrared or X-rays) may also delay or prevent cataract formation.  

• Early and adequate treatment of ocular diseases like uveitis may prevent occurrence of complicated  cataract. 

2. Measures to delay progression include:

• Topical preparations containing iodide salts of calcium and potassium are being prescribed in  abundance in early stages of cataract (especially  in senile cataract) in a bid to delay its progression. 

• However, till date no conclusive results about their role are available. 

• Role of vitamin E and aspirin in delaying the process of cataractogenesis is also mentioned. 

3.Measures to improve vision in the presence of incipient and immature cataract may be of great solace to the  patient. These include: 

• Prescription of glasses refractive status, which often changes with considerable rapidity in patients with cataract, should be corrected at frequent intervals. 

•  Arrangement of illumination. Patients with peripheral opacities (pupillary area still free), may  be instructed to use brilliant illumination. 

•  Conversely, in the presence of central opacities, a dull light placed beside and slightly behind the  patient’s head will give the best result. 

•  Use of dark goggles in patients with central opacities is of great value and comfort when worn outdoors. 

•  Mydriatics. Patients with a small axial cataract, frequently may benefit from papillary dilatation.  

This allows the clear paraxial lens to participate in light transmission, image formation and focussing.  

Mydriatics such as 5% phenylephrine or 1% tropicamide; 1 drop b.i.d. in the affected eye may  clarify vision.

B. Surgical management:

I. Intracapsular cataract extraction (ICCE)

In this technique, the entire cataractous lens along with the intact capsule is removed. Therefore, weak  and degenerated zonules are a pre-requisite for this  method. 

Indications. ICCE has stood the test of time and had been widely employed for about 100 years over  the world (1880-1980). Now (for the last 35 years)  it has been almost entirely replaced by planned  extracapsular techniques. 

At present the only indication ofICCE is markedly subluxated and dislocated lens.

II. Extracapsular cataract extraction techniques 

In these techniques, major portion of anterior capsule with epithelium, nucleus and cortex are  removed; leaving behind the intact posterior capsule. 

Indications: Presently, extracapsular cataract extraction techniques are the surgery of choice for  almost all types of adulthood as well as childhood  cataracts unless contraindicated. Contraindications: The only absolute contraindication  for ECCE is markedly subluxated or dislocated lens. 

Advantages of ECCE techniques over ICCE include:

1. ECCE is a universal operation and can be performed at all ages, except when zonules are  not intact; whereas ICCE cannot be performed  below 40 years of age. 

2. Posterior chamber IOL can be implanted after ECCE, while it cannot be implanted after ICCE. 

3. Postoperative vitreous related problems (such as herniation in anterior chamber, pupillary block  and vitreous touch syndrome) associated with  ICCE are not seen after ECCE. 

4. Incidence of postoperative complications such as endophthalmitis, cystoid macular oedema and  retinal detachment are much less after ECCE as  compared to that after ICCE. 

5. Postoperative astigmatism is less with ECCE techniques, as the incision is smaller. 

6. Prognosis for subsequent glaucoma filtering or corneal transplantation (if required) is much  improved with ECCE. 

7. Incidence of secondary rubeosis in diabetics is reduced after ECCE. 

Different techniques of extracapsular cataract extraction 

The surgical techniques of ECCE presently in vogue are:

• Conventional extracapsular cataract extraction (ECCE), 

• Manual small incision cataract surgery (SICS),

• Phacoemulsification.