What Are Cataracts?

Home | Expertise | Cataracts | What Are Cataracts?

Cataracts occur when the eye’s natural lens loses clarity, leading to progressive visual changes. This page explains how cataracts develop, how they affect light transmission and visual quality, and how to recognise early signs before vision is significantly impaired.

This information is intended to support understanding and does not replace a professional examination.

View VideoA brief overview of what cataracts are and how they are treated.

Cataracts are one of the most common causes of gradual vision change, particularly as we age. Despite how common they are, many people are unsure what cataracts actually are, how they develop, and how they affect vision over time.

A cataract is not a growth or a film over the eye — it is a change within the eye itself. Specifically, it occurs when the natural lens becomes cloudy, reducing the clarity of vision and altering how light is processed.

What happens in the eye

The eye functions in many ways like a highly refined optical system, similar to a camera — but far more complex.

Light enters the eye through the cornea (the clear front surface) and passes through the pupil, where the amount of incoming light is controlled by the iris. From there, light reaches the natural lens, which plays a critical role in focusing that light precisely onto the retina at the back of the eye.

The retina then converts this light into electrical signals, which are transmitted via the optic nerve to the brain, where images are interpreted.

In a healthy eye

The lens is clear and transparent, allowing light to pass through without obstruction
The lens remains flexible, enabling accurate focusing at different distances
Light is precisely focused onto the retina, producing sharp, detailed images
Visual signals are transmitted clearly, resulting in crisp, high-contrast vision

With a cataract

Over time, structural changes occur within the lens:

The normally clear lens becomes clouded due to protein changes
Light passing through the lens is scattered instead of precisely focused
The amount of light reaching the retina is reduced and irregular
Image quality deteriorates, leading to blurred, hazy, or distorted vision

How this affects what you actually see

Rather than simply “blurred vision,” patients often notice more specific changes:

A loss of contrast (objects appear less defined or “flat”)
Increased glare and halos, especially around lights at night
Difficulty seeing in bright conditions due to light scatter
Colours appearing faded, dull, or yellowed
A general sense that vision is not as clear or sharp as it used to be

View Video

How Cataracts develop

Cataracts do not develop suddenly. They form gradually over time as a result of structural and biochemical changes within the natural lens of the eye.

The lens is made up primarily of water and specialised proteins arranged in a highly organised structure. This precise arrangement allows the lens to remain clear and to focus light accurately onto the retina.

What changes over time?

As part of the natural ageing process — and sometimes due to other factors — these lens proteins begin to change:

The proteins can break down and clump together
The orderly structure of the lens becomes disrupted
The lens gradually loses its transparency and flexibility

This leads to the development of small cloudy areas within the lens, which may initially be too subtle to notice.

Why vision changes gradually

In the early stages, these changes affect only a small portion of the lens. The rest of the lens can still transmit light effectively, so vision may remain relatively good.

As the cataract progresses:

Clouding becomes more widespread
Light passing through the lens becomes increasingly scattered
The lens may become denser and less flexible
Visual clarity steadily declines

Because this process is typically slow, many patients adapt to the changes without realising how much their vision has altered.

Types of Cataracts

Cataracts are not all the same. They can develop in different parts of the lens, and the location of the change directly influences how vision is affected and how symptoms are experienced.

Understanding the type of cataract helps explain why some people struggle with glare, others with reading, and others with general blurring of vision.

Nuclear Cataracts (Central Lens)

Nuclear cataracts develop in the central part of the lens (the nucleus) and are the most common type associated with ageing.

What happens:

The central lens gradually becomes denser and yellowed
The lens may harden over time
Light transmission becomes less efficient

How vision is affected:

Gradual decline in distance vision
Colours may appear yellowed or less vibrant
In some cases, temporary improvement in near vision (“second sight”)

Clinical insight:

This type often progresses slowly and may go unnoticed initially, as patients adapt to the changes over time.

View VideoDetails the progression of the nuclear cataract, the most common type of cataract, showing a gradual hardening of the nucleus, expanding to other layers of the lens, potentially causing severe vision loss which can only be restored through surgery.

Cortical Cataracts (Outer Lens)

Cortical cataracts begin in the outer edges of the lens (the cortex) and extend inward in a spoke-like pattern.

What happens:

White, wedge-shaped opacities develop
These changes disrupt how light enters from the periphery

How vision is affected:

Increased glare and light sensitivity
Difficulty with night driving
Halos around lights
Fluctuating vision depending on lighting conditions

Clinical insight:

Symptoms are often more noticeable in bright or low-light environments due to light scatter.

View VideoDetails progression of cortical sclerosis cataracts, starting as a small spoke-like opacity which grows around the edge of the lens, potentially causing severe vision loss which can only be restored through surgery.

Posterior Subcapsular Cataracts (Back of Lens)

These cataracts form at the back surface of the lens, just in front of the posterior capsule.

What happens:

A small but dense opacity develops centrally at the back of the lens
Even a small cataract in this location can significantly affect vision

How vision is affected:

Difficulty with reading or near tasks
Reduced vision in bright light
Glare and halos
Often progresses more quickly than other types

Clinical insight:

This type tends to cause symptoms earlier and more noticeably, even when the cataract is relatively small.

View VideoA posterior subcapsular cataract is a small opacity at the back of the lens, which can have significant symptoms early on and can develop rapidly. We appreciate Dr. Sandy Feldman for lending his expertise on this piece.

What Cataracts Are Not

Cataracts are often misunderstood. Many patients have heard descriptions that are not medically accurate, which can lead to confusion about symptoms, progression, and treatment.

Understanding what cataracts are not is just as important as understanding what they are.

Cataracts are not a film or layer growing over the eye

A common misconception is that cataracts form as a “film” on the surface of the eye.

In reality, cataracts develop inside the eye, within the natural lens.
The front surface of the eye (the cornea) remains clear.

This is why cataracts cannot be wiped away or treated with surface-based drops.

Cataracts are not a separate growth or foreign object

Cataracts are not something new that appears in the eye.

They are a change in the existing lens structure, where the normally clear lens becomes cloudy over time.

Nothing is “added” — the lens itself is altered.

Cataracts are not caused by overusing your eyes

Reading, screen use, or focusing for long periods does not cause cataracts.

Cataracts are primarily related to:

Ageing
Metabolic changes
Environmental and medical factors

Eye strain may cause temporary discomfort, but it does not lead to cataract formation.

Cataracts cannot be reversed with medication or eye drops

There are currently no proven medications or eye drops that can reverse or remove cataracts.

Glasses may improve vision temporarily in early stages
But they do not stop or reverse the underlying process

Definitive treatment involves surgical removal of the cloudy lens.

Cataracts are not always the cause of blurred vision

Not all vision changes are due to cataracts.

Other conditions can produce similar symptoms, including:

Retinal diseases
Glaucoma
Diabetic eye disease
Corneal conditions

This is why a proper eye examination is essential before assuming cataracts are the cause.

Cataracts do not always require immediate surgery

Another common misconception is that cataracts must be removed as soon as they are diagnosed.

In reality, treatment depends on:

The level of visual impact
How symptoms affect daily life

Many cataracts are monitored until they begin to interfere with function.

Cataracts do not “spread” from one eye to the other

Each eye develops cataracts independently.

One eye may be more affected than the other
Progression can occur at different rates

Your Next Step

Cataracts develop gradually, but their impact on vision can become significant over time. Understanding how they form and how they affect visual clarity is key to recognising when something has changed.

Because symptoms are often subtle at first, changes may go unnoticed until daily activities are affected. A comprehensive eye assessment ensures an accurate diagnosis and helps determine the most appropriate next step — whether that is monitoring or treatment.

What Are Cataracts?