Medicine – Cataracts

A cataract is an opacity or clouding of the normally transparent crystalline lens of the eye. The loss of lens transparency interferes with the passage and focusing of light onto the retina, producing progressive, painless impairment of vision.

Cataracts may be congenital or acquired. Ageing is by far the most common cause, but cataracts can also occur because of genetic disorders, congenital infections, ultraviolet exposure, medications, ocular inflammation, metabolic disease, and several systemic disorders.

1. Clinical Features of Cataract

The typical presentation is gradual, painless deterioration of vision.

Patients may complain of blurred or cloudy vision, glare from bright lights, difficulty driving at night, reduced contrast sensitivity, altered colour perception, or frequent changes in their spectacle prescription.

Some patients describe halos around lights, particularly at night.

2. Red Reflex

As the lens becomes increasingly opaque, the normal red reflex may become reduced or absent.

With advanced cataract, the pupil itself may appear grey or white because the opaque lens is visible behind it.

This is particularly important in children because a white pupil or abnormal red reflex requires urgent assessment to distinguish cataract from other serious causes of leukocoria, especially retinoblastoma.

3. Congenital Cataracts

Congenital cataracts are present at birth or develop during early infancy.

They may affect one or both eyes and can result from genetic abnormalities, congenital infections, metabolic disorders, or developmental abnormalities.

Congenital cataracts are especially important because a dense cataract can prevent normal visual development and cause deprivation amblyopia.

Early detection and treatment are therefore essential.

4. Autosomal Dominant Inheritance

Inherited congenital cataracts frequently show an autosomal dominant inheritance pattern, although autosomal recessive and X-linked forms also exist.

A positive family history of childhood cataracts may therefore provide an important diagnostic clue.

The exact appearance and severity of inherited cataracts vary according to the underlying genetic abnormality.

5. Maternal Rubella Infection

Congenital rubella syndrome is a classic cause of congenital cataracts.

Maternal rubella infection, particularly during early pregnancy, can interfere with fetal eye development.

The classic congenital rubella pattern includes:

Cataracts + sensorineural deafness + congenital heart disease.

Cardiac abnormalities classically include patent ductus arteriosus and pulmonary artery stenosis.

6. CMV and Toxoplasmosis

Congenital cytomegalovirus (CMV) and congenital toxoplasmosis can produce important ocular disease.

However, cataract is much more classically associated with congenital rubella.

Congenital toxoplasmosis is particularly associated with chorioretinitis, while congenital CMV commonly causes chorioretinitis and neurological abnormalities.

Therefore, although these infections can be considered in congenital ocular disease, remember:

Rubella → classic congenital cataract association.

7. Down Syndrome

Children and adults with Down syndrome have an increased risk of several ocular abnormalities, including cataracts.

Cataracts may develop at a younger age than in the general population.

Other associated ocular problems include refractive errors, strabismus and keratoconus.

8. Age-Related Cataract

Age-related cataract, historically called senile cataract, is the most common form of cataract.

With increasing age, lens proteins undergo progressive structural and biochemical changes that reduce lens transparency.

The process is usually gradual and bilateral, although the severity may differ between the two eyes.

The modern term age-related cataract is preferred to “senile cataract.”

9. Types of Age-Related Cataract

Age-related cataracts can be classified according to the part of the lens predominantly affected.

Important patterns include:

Nuclear sclerotic cataract.

Cortical cataract.

Posterior subcapsular cataract.

Different patterns can coexist in the same patient.

10. Ultraviolet Light

Long-term exposure to ultraviolet radiation, particularly UV-B, is associated with an increased risk of cataract formation.

Chronic UV exposure contributes to oxidative and structural damage within the lens.

Appropriate UV-protective eyewear may therefore help reduce cumulative ocular ultraviolet exposure.

11. Corticosteroids

Long-term corticosteroid therapy is an important drug-related cause of cataract.

The classic pattern is a posterior subcapsular cataract.

The risk generally increases with greater cumulative steroid exposure, although susceptibility varies between individuals.

Steroids may also increase intraocular pressure and contribute to glaucoma in susceptible patients.

12. Other Drugs

Although corticosteroids are the classic examination association, several other medications can occasionally contribute to lens abnormalities.

A medication history should therefore form part of the assessment of unusually early or rapidly developing cataracts.

13. Uveitis

Chronic or recurrent uveitis can cause secondary cataract formation because persistent intraocular inflammation damages the lens environment.

The risk may be further increased because patients with significant uveitis often require prolonged corticosteroid treatment.

Therefore, cataract formation in uveitis may result from both:

Chronic inflammation + corticosteroid exposure.

14. High Myopia

High myopia is associated with an increased risk of developing cataracts and may lead to cataract formation at a younger age.

Highly myopic patients also have increased risks of other ocular complications, particularly retinal abnormalities.

15. Diabetes Mellitus

Diabetes mellitus is an important metabolic risk factor for cataract formation.

Chronic hyperglycaemia alters glucose metabolism within the lens, causing osmotic and oxidative changes that promote lens opacity.

Diabetic patients may therefore develop cataracts earlier and more rapidly than non-diabetic individuals.

16. Cushing Syndrome

Cushing syndrome can be associated with cataract formation, particularly in the context of prolonged glucocorticoid excess.

The relationship is especially relevant because exogenous corticosteroid therapy is itself a major cause of posterior subcapsular cataract.

17. Hypocalcaemia

Chronic hypocalcaemia can be associated with cataract formation.

This may occur in disorders such as hypoparathyroidism, where persistent low serum calcium contributes to abnormal lens metabolism.

Therefore:

Hypoparathyroidism → hypocalcaemia → cataracts is a useful clinical association.

18. Myotonic Dystrophy

Myotonic dystrophy has a strong association with cataracts.

The characteristic cataracts may have a distinctive multicoloured or “Christmas-tree” appearance on slit-lamp examination.

They can occur relatively early in life.

Other clues to myotonic dystrophy include myotonia, muscle weakness, frontal balding, cardiac conduction abnormalities, and endocrine manifestations.

19. Retinitis Pigmentosa

Retinitis pigmentosa is also associated with cataract formation.

The typical cataract associated with retinitis pigmentosa is a posterior subcapsular cataract.

Because RP itself progressively impairs retinal function, cataract formation can further reduce the patient’s remaining useful vision.

20. Diagnosis

Cataracts are diagnosed primarily by ophthalmological examination, particularly slit-lamp examination of the lens.

Visual acuity testing establishes the functional effect of the cataract.

The retina and optic nerve should also be assessed whenever possible because visual impairment may have more than one cause.

21. Treatment

The definitive treatment for a visually significant cataract is surgical removal of the opaque lens.

Modern cataract surgery commonly uses phacoemulsification, in which ultrasound energy fragments the cataractous lens so that it can be removed through a small incision.

An artificial intraocular lens (IOL) is then implanted to replace the focusing power of the natural lens.

22. When Is Surgery Required?

The presence of a cataract alone does not automatically require surgery.

Surgery is generally considered when the cataract causes sufficient visual impairment to interfere with daily activities, work, driving, reading, or quality of life, or when removal is necessary for another ophthalmological reason.

In children with dense congenital cataracts, treatment may need to occur urgently to allow normal visual development and prevent amblyopia.

23. Cataracts – Causes in Note Form

Congenital: inherited or developmental cataracts occurring at or shortly after birth.

Autosomal dominant: common inheritance pattern among familial congenital cataracts, although other inheritance patterns exist.

Congenital rubella: classic maternal infection associated with congenital cataracts.

CMV and toxoplasmosis: important congenital infections causing ocular disease, although cataract is much more classically associated with rubella.

Down syndrome: increased risk of cataract formation.

Ageing: the most common overall cause; modern terminology is age-related cataract.

Ultraviolet radiation: chronic exposure increases cataract risk.

Corticosteroids: classic drug association, particularly with posterior subcapsular cataracts.

Uveitis: chronic ocular inflammation can cause secondary cataracts; steroid treatment may contribute further.

High myopia: associated with increased and earlier cataract formation.

Diabetes mellitus: cataracts may develop earlier and progress more rapidly.

Cushing syndrome: glucocorticoid excess can contribute to cataract formation.

Hypocalcaemia: chronic hypocalcaemia, particularly from hypoparathyroidism, can cause cataracts.

Myotonic dystrophy: classically associated with Christmas-tree cataracts.

Retinitis pigmentosa: associated particularly with posterior subcapsular cataracts.

Key Clinical Pattern

Remember cataract as:

Progressive + painless + cloudy/blurred vision + glare + reduced red reflex.

Important examination associations are:

Congenital rubella → congenital cataracts.

Steroids → posterior subcapsular cataracts.

Diabetes → earlier cataract formation.

Uveitis → secondary cataracts.

Myotonic dystrophy → Christmas-tree cataracts.

Retinitis pigmentosa → posterior subcapsular cataracts.

And the definitive treatment for a visually significant cataract is:

Cataract extraction + intraocular lens implantation.