Cataracts vs Glaucoma: Differences, Symptoms, Causes and Treatment Explained

“Cataracts” and “glaucoma” are two eye conditions that many people have heard of. Because the names are often mentioned together, however, it is easy to wonder, “What is the difference?” or even, “Can a cataract eventually turn into glaucoma?”

In fact, these are different conditions that affect different parts of the eye, cause different changes in vision and are treated in different ways. A cataract occurs when the lens inside the eye becomes cloudy. Glaucoma, on the other hand, damages the optic nerve, which carries visual information from the eye to the brain, and can cause changes in the visual field.

Cataracts commonly cause overall blurring, haziness or increased sensitivity to glare. Glaucoma can be much harder to notice in its early stages, and visual field loss may progress without the person being aware of it. This difference in how the two conditions are noticed is an important point to understand.

In this article, we explain the differences between cataracts and glaucoma, including their causes and risk factors, symptoms, examinations and treatments, as well as intraocular lenses and normal-tension glaucoma.

What Is the Difference Between Cataracts and Glaucoma?

First, let us look at the main differences between cataracts and glaucoma.

It can be helpful to think of the eye as a camera. The lens, which becomes cloudy in cataracts, works rather like the lens of a camera. If a clear camera lens becomes cloudy, light can no longer pass through it properly and the image becomes hazy or blurred.

The optic nerve, which is affected in glaucoma, is an important pathway that carries visual information from the eye to the brain. You can think of it somewhat like a communication cable carrying the information captured by the eye to the brain. When this pathway is damaged, parts of the visual field may become difficult to see.

Another important point is that a cataract does not simply progress into glaucoma. They are separate eye conditions. A person may have only cataracts, only glaucoma, or both conditions at the same time.

What Is a Cataract? When the Eye’s “Lens” Becomes Cloudy

A cataract is a condition in which the lens inside the eye becomes cloudy, reducing visual function. The lens is normally almost transparent. It bends incoming light and helps focus it onto the retina at the back of the eye.

When the lens becomes cloudy, light may no longer pass through it clearly and may be scattered inside the eye. As a result, vision can appear misty or blurred, and bright light may become more uncomfortable or glaring.

The most common factor associated with cataracts is ageing. According to the Japanese Ophthalmological Society, cataracts are seen in approximately 70% of people in their 60s, around 90% of those in their 70s, and in most people in their 80s.

However, cataracts are not exclusively a condition of older age. Diabetes, eye injuries, certain medicines and radiation exposure can also be associated with cataracts, and some people are born with clouding of the lens, known as congenital cataract. The Japanese Ophthalmological Society also identifies factors such as smoking and ultraviolet exposure as being associated with cataract progression.

Cataracts cannot be explained by a single change in the proteins of the lens. As we age, various changes occur in the proteins and other components of the lens, gradually reducing its transparency.

What Does a Cataract Look Like? Causes, Symptoms and Tests

Cataracts usually progress gradually. In the early stages, a person may notice very little, but as the clouding of the lens increases, vision may begin to feel noticeably less clear.

Common changes include hazy or blurred vision, increased glare and seeing double or multiple images. Colours may appear less vivid, night vision may become more difficult, and headlights or streetlights may seem brighter or more dazzling than before.

For example, daytime vision may seem reasonably comfortable while oncoming headlights become much more dazzling when driving at night. Some people also notice that bright outdoor conditions make vision more difficult, or that printed text appears increasingly blurred.

However, these symptoms are not unique to cataracts. Glaucoma and conditions affecting the retina or cornea can also cause changes in vision. If changes persist, it is important not to assume that they are simply due to ageing or presbyopia.

How Are Cataracts Examined?

An eye examination generally includes a visual acuity test as well as a slit-lamp examination, which allows the eye doctor to examine clouding of the lens under magnification. The pupil may also be dilated when necessary to check the retina, optic nerve and other structures at the back of the eye.

This is important because even when a cataract is present, it may not be the only reason for reduced vision. If the retina or optic nerve is also affected by another condition, replacing the cloudy lens with a clear intraocular lens may not improve vision as much as expected.

Cataract Treatment | Surgery and Intraocular Lenses

Being diagnosed with a cataract does not mean that everyone needs surgery straight away. If the cataract is mild and is not significantly affecting daily life, it may be monitored while changes such as glasses adjustments are considered. Surgery may be discussed when activities such as reading, driving, working or doing household tasks become increasingly difficult.

According to the Japanese Ophthalmological Society, medicines including eye drops and oral treatments may be used with the aim of slowing cataract progression, but medication cannot restore an already-cloudy lens to its original transparent state. Surgery is therefore the main treatment when improved vision is required.

What Happens During Cataract Surgery?

During cataract surgery, the cloudy natural lens is removed and replaced with an artificial intraocular lens (IOL). In a commonly used procedure, the contents of the lens are broken into small pieces and removed through a small incision. Part of the capsule that surrounded the natural lens is retained, and the artificial lens is placed inside it.

Cataract surgery is widely performed, but it is still surgery and therefore carries possible complications such as infection, inflammation, retinal detachment and changes in intraocular pressure. It is therefore important not to assume that surgery will always restore vision completely. The expected benefits and possible risks depend on the condition of the eye and whether other eye diseases are present.

There Are Different Types of Intraocular Lenses

Several types of intraocular lenses are available for cataract surgery. The Japanese Ophthalmological Society lists options including monofocal, multifocal and toric intraocular lenses.

The lens with the most features is not automatically the best choice for everyone. The most suitable option depends on factors such as which distances are most important in everyday life, whether you drive, whether you frequently do detailed close work, how important night vision is to you, and whether other eye conditions are present.

Some people experience renewed cloudiness months or years after cataract surgery. This is known as posterior capsule opacification, sometimes called a “secondary cataract”, but it does not mean that the original cataract has returned. The artificial lens itself does not become cataractous. Instead, part of the remaining lens capsule becomes cloudy. When necessary, this can be treated with a YAG laser procedure.

So far, we have seen that cataracts mainly affect the lens of the eye and that surgery may be considered depending on how much the condition affects everyday life.

What about the similarly named condition glaucoma?

What Is Glaucoma? It Is Not Simply “High Eye Pressure”

Glaucoma is a condition in which the optic nerve and retinal ganglion cells are damaged, causing characteristic changes in the visual field. Cataracts affect the lens that allows light to pass through the eye, whereas glaucoma affects the nerve pathway carrying visual information from the eye to the brain. As a result, rather than causing uniform cloudiness across the whole field of vision, glaucoma can cause small areas of reduced vision that gradually expand.

An especially important point is that glaucoma is not simply a condition in which eye pressure is high. Intraocular pressure (IOP) is the pressure inside the eye and is maintained by the balance between the production and drainage of a fluid called aqueous humour. The Japanese Ophthalmological Society describes approximately 10–20 mmHg as the general normal range, but the level of pressure an individual optic nerve can tolerate varies from person to person.

For this reason, normal-tension glaucoma can occur even when intraocular pressure is within the generally accepted normal range. Conversely, some people have elevated intraocular pressure without detectable optic nerve damage or visual field loss. This is known as ocular hypertension.

The Tajimi Study: Around 1 in 20 People Aged 40 and Over

One of the best-known epidemiological studies of glaucoma in Japan is the Tajimi Study, conducted in Tajimi City, Gifu Prefecture, from 2000 to 2001. It found that approximately 5% of people aged 40 and over — around 1 in 20 — had glaucoma. Prevalence increased with age, from approximately 2.2% among people in their 40s to 6.3% among those in their 60s and around 10.5% among those in their 70s.

Another notable finding concerned normal-tension glaucoma. In the Tajimi Study, the prevalence of normal-tension glaucoma among people aged 40 and over was 3.6%. Given that overall glaucoma prevalence was around 5%, this demonstrates that glaucoma occurring within the generally accepted normal range of intraocular pressure is relatively common in Japan.

In other words, a normal eye-pressure measurement does not necessarily rule out glaucoma. Examination of the optic nerve and visual field is also important.

Why Is Glaucoma Difficult to Notice? Types, Symptoms and Tests

One of the reasons glaucoma requires particular attention is that there are often few or no noticeable symptoms in the early stages. In many forms of glaucoma, vision does not suddenly disappear across the entire visual field. Instead, a small area may gradually become harder to see and expand slowly over a period of years. Central vision can remain relatively well preserved for some time, which can make a person feel that they are still seeing normally.

Glaucoma can broadly be considered in terms of open-angle glaucoma and angle-closure glaucoma. The “angle” refers to the area near the drainage pathway through which aqueous humour leaves the eye.

Sudden Severe Eye Pain, Vision Loss and Nausea Require Urgent Medical Attention

Many forms of glaucoma progress slowly, but an important exception is an acute angle-closure glaucoma attack. If the drainage pathway suddenly becomes blocked, intraocular pressure can rise rapidly and cause severe eye pain, sudden loss or blurring of vision, redness, headache, nausea and vomiting.

Open-angle glaucoma, by contrast, often progresses without dramatic symptoms, making it difficult to detect early on symptoms alone.

Glaucoma Cannot Be Diagnosed by an Eye-Pressure Test Alone

Glaucoma examinations do not rely solely on intraocular pressure. Eye doctors assess the optic nerve and retina as well as the person’s visual field, using several types of tests together.

OCT is particularly useful for examining structures such as the retinal nerve fibre layer in detail and, together with visual field testing, plays an important role in diagnosing and monitoring glaucoma.

Glaucoma Treatment | Eye Drops, Laser and Surgery

Cataract surgery can aim to improve vision by replacing a cloudy lens with an artificial intraocular lens. With glaucoma, however, visual field that has already been lost cannot currently be restored by treatment. The main goal of glaucoma treatment is therefore to lower intraocular pressure and slow further optic nerve damage, helping preserve remaining visual function for as long as possible.

The Japanese Ophthalmological Society explains that lowering intraocular pressure is the treatment with clearly established effectiveness for glaucoma. This also applies to normal-tension glaucoma. Even if the original pressure is within the general normal range, reducing it below the person’s untreated level may help slow progression.

Treatment Can Include Eye Drops, Laser and Surgery

Glaucoma treatment broadly includes medication, laser treatment and surgery. The most appropriate approach depends on the type of glaucoma, intraocular pressure, the degree and rate of visual field loss, age and other eye conditions.

Eye drops are a common treatment. Different medicines lower intraocular pressure by reducing the production of aqueous humour or helping it drain more effectively. If one medicine is not sufficient, eye drops with different mechanisms may be combined.

Laser treatment may include selective laser trabeculoplasty (SLT) for open-angle glaucoma, which aims to improve the drainage of aqueous humour. In some people with angle-closure glaucoma, laser peripheral iridotomy may be used to create a small opening in the iris.

If adequate pressure reduction cannot be achieved with eye drops or laser treatment, or if visual field damage continues to progress, surgery may be considered. In addition to procedures such as trabeculectomy, MIGS (minimally invasive glaucoma surgery) procedures are now available in some situations, with treatment selected according to the individual patient’s condition.

Glaucoma often requires long-term treatment and monitoring. Even when intraocular pressure has been reduced, visual field tests and OCT findings may be followed over time and treatment targets adjusted when necessary.

Can Cataracts and Glaucoma Occur Together? When to See an Eye Doctor

Cataracts and glaucoma are separate conditions, but the same person can have both. Because both become more common with age, glaucoma may be discovered during a cataract examination, or cataracts may progress in someone already being monitored for glaucoma.

The two conditions can also be related when treatment is being considered. In angle-closure glaucoma, removing the natural lens and replacing it with a thinner artificial intraocular lens can widen the drainage angle and may help lower intraocular pressure. For this reason, cataract or lens surgery may be considered as a treatment option in some patients.

This does not mean that a cataract has “turned into” glaucoma. Rather, the size and position of the natural lens can influence how narrow the drainage angle inside the eye is.

When Should You See an Eye Doctor?

Glaucoma may already have progressed by the time noticeable symptoms develop. Waiting until vision becomes obviously difficult is therefore not always enough for early detection. If a health examination identifies abnormalities involving intraocular pressure or the optic nerve, it is important to have a detailed eye examination even if you feel that your vision is normal.

What to Know About Diet and Supplements

When researching cataracts and glaucoma, you may come across a great deal of information about diet, nutrients and eye health. However, there is currently no basis for saying that a particular food or supplement alone can prevent cataracts or glaucoma, or stop glaucoma from progressing.

For glaucoma in particular, current treatment centres on lowering intraocular pressure and slowing optic nerve damage. A balanced diet and general health management remain important for overall health, but they are not substitutes for diagnosis or medical treatment.

Ageing itself cannot be avoided as a factor in cataract development, but ultraviolet exposure and smoking are among the recognised associated factors. When spending time outdoors in strong sunlight, measures such as a hat and sunglasses with appropriate UV protection may help reduce UV exposure. People with conditions such as diabetes should also receive appropriate medical care.

Summary | Cataracts and Glaucoma Are Very Different Conditions

Cataracts and glaucoma may often be mentioned together, but they are very different eye conditions.

A cataract is clouding of the natural lens, which can cause hazy or blurred vision, glare and other visual changes. Cataracts become increasingly common with age, and when they significantly interfere with daily activities, surgery to replace the cloudy lens with an artificial intraocular lens is the main treatment.

Glaucoma, by contrast, damages the optic nerve. It can occur even when intraocular pressure falls within the generally accepted normal range, and it may progress for a long time without obvious symptoms. Because visual field already lost to glaucoma cannot currently be restored, detecting the condition and lowering intraocular pressure to slow further progression are important.