What are the Types of Cataract?
Cataracts are considered the leading cause of reversible vision loss in Western society. In Australia, this makes cataract surgery one of the most commonly performed procedures, particularly because we have an ageing population.
What is a Cataract?
A cataract is any opacity of the crystalline lens inside the eye. At birth, a healthy lens is transparent, allowing the transmission of light to the retina where the process of vision begins. As we get older, this lens naturally begins to become cloudy. This makes age-related cataracts the most common out of all the types of cataract.
As the lens loses its transparency, it begins to cause vision problems. Depending on which of the types of cataract is involved, its location within the lens, and how advanced the cataract is, your vision problems can vary from a mild clouding of your vision to significant vision loss.
A cataract can only be treated with cataract surgery, which involves the extraction of the entire hazy lens from the eye. In Australia, patients rarely reach the stage where they experience complete vision loss from a cataract. This is due to the accessibility of cataract surgery, whether through the public system or with a private eye surgeon.
Types of Cataract
A cataract can be categorised in a number of different ways. One way is to identify a cataract by its underlying cause.
Age-related cataracts, as mentioned previously, are the most common out of all the types of cataract. These are also known as senile cataracts. Cataract surgery is typically able to restore vision back to pre-cataract levels. However, with age, we are also more at risk of other eye diseases that contribute to vision problems, such as age-related macular degeneration.
Traumatic cataracts occur after an injury. An injury can be a blunt, concussive blow to the eye, such as from a punch, or from a penetrating injury like a splinter going through the eye. Other types of trauma that may cause a traumatic cataract include radiation exposure, chemical burns, or electrocution. Sometimes cataract surgery may not be sufficient to restore vision loss in these cases if other parts of the eye have also been damaged, such as the cornea or the retina.
It is possible for a baby to be born with a cataract or develop one shortly after birth. These are known as congenital cataracts. A congenital cataract may be caused by an illness in the mother during pregnancy, such as measles or rubella, or due to certain medications taken during pregnancy.
If a congenital cataract is considered to be visually significant, cataract surgery is usually performed promptly in order to give the baby’s visual system the best chance of developing normally.
Certain metabolic diseases are associated with cataracts. Diabetes is perhaps the most well-known of these conditions. Changes to the water content of the crystalline lens due to elevated blood glucose levels are responsible for inducing a cataract. Other systemic metabolic conditions that may cause a cataract include galactosaemia, Wilson disease, or myotonic dystrophy.
Age-Related Cataracts
Age-related cataracts deserve a bit more attention due to their prevalent nature. There are in fact three types of age-related cataract. An eye can have just one type of cataract or even all three present at the same time.
● Nuclear sclerosis. Nuclear sclerosis appears as a brownish-yellowish haze in the centre of the crystalline lens, an area known as the nucleus. The more advanced nuclear sclerosis is the browner the colour of the cataract. Nuclear sclerosis will typically cause symptoms such as a hazy, foggy, or cloudy sensation to the vision. It can also cause a change to your colour perception, as the yellow-brown tinge of the lens filters out certain wavelengths of colour. Some patients also experience a myopic shift, which is when your vision becomes more short-sighted. This is due to the developing cataract altering the refractive index of the lens.
● Cortical cataracts. Cortical cataracts appear as grey or white spoke-like opacities radiating from the edges of the lens towards the centre if viewed from the front on. This type of cataract usually develops in the outer layers at the front of the lens, known as the anterior cortex. A cortical cataract will often be associated with glare sensitivity, as the incoming light is scattered by the cataract opacities. The development of an anterior cortical cataract may also cause a hyperopic shift, which is when the eye becomes more long-sighted.
● Posterior subcapsular cataract. This typically carries the most significant visual impact on the eye, due to its location in the lens. A posterior subcapsular cataract often forms in the centre at the back surface of the lens and looks like a white plaque. It can be responsible for a significant decrease in clarity of vision as well as a lot of glare sensitivity. Cataract surgery for age-related cataracts can typically be delayed until you feel your vision is no
longer good enough for your usual activities. Once your vision has deteriorated to this point, cataract surgery is a quick, uncomplicated procedure that can effectively return your clarity of vision. Your optometrist and eye specialist are the best people to discuss when your vision is ready for cataract surgery.
Note: Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second
opinion from an appropriately qualified health practitioner.
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