Cataract is the clouding of the natural lens in the eye. It is most commonly due to ageing but can also be caused by trauma to the eye or illnesses such as diabetes. It occurs when there is a disruption to the fine arrangement of the lens protein as we age. When the lens gets cloudy, it reduces the amount of light entering the eye, hence causing a decrease in vision.
The natural lens consists of different layers:
- Capsule (the outer-most layer of the lens; a ‘bag’ that holds the entire lens)
- Cortex (the middle layer of the lens that surrounds the lens nucleus)
- Nucleus (the centre of the lens)
In this article, we will share on cortical cataract, which occurs at the lens cortex.
Cortical cataract starts out as little liquid bubbles (called vacuoles) in the lens cortex. Over time, they progress into wedge-shaped or radial spoke-like pattern in the outer edge (periphery) of the lens.
Common symptoms of cortical cataract are:
- Night-time glare when looking at light sources
- Reduced contrast sensitivity
- Reduced visual acuity
In the early stages of cortical cataract, the first symptom experienced is usually glare when looking at light sources at night. This occurs as the pupil dilates in dark environment, hence more light enters the eye. When the light hits the cataract in the lens outer edges, light scatters as a result.
Reduced contrast sensitivity
When told by your optometrist you have 6/6 or 20/20 visual acuity (how sharp your vision is), yet your vision is not as good as it used to be? This may be attributed to what is known as reduced contrast sensitivity. Contrast sensitivity is the ability to identify subtle differences in colours and shades, such as distinguishing an object from its background. Objects with low contrast is generally harder to see. Hence, people with poor contrast sensitivity may have good visual acuity, but still have trouble seeing well. In the early stages of cortical cataract, contrast sensitivity is reduced but the visual acuity can remain satisfactory.
Reduced visual acuity
As the cortical cataract progresses further from the lens periphery to the centre, the clouding will further reduce vision, whether is it distance or near vision. Generally, vision gets hazier as the clouding of the lens thickens. This is when people start to get frustrated when they can no longer see well with any form of visual aids (glasses, contact lenses).
Other common age-related cataracts, such as nuclear sclerosis (cataract at the lens nucleus), can cause a yellowish tint in the vision, due to the way the clouding progresses. People with nuclear sclerosis may complain of colour vision changes; whereas this is not common in people with cortical cataract. Cortical cataract can remain unchanged for a prolong period of time or it can progress rapidly.
The only effective treatment of cortical cataract is through cataract surgery. There are 2 main types of modern-day cataract surgery – micro-incision phacoemulsification and laser-assisted cataract surgery.