Cataracts: Types, symptoms and treatments

Cataract is the clouding of the eye’s natural lens. It is the most common cause of vision loss in people over age 40 and is also the principal cause of blindness in the world. Types of cataracts include:

  • A subcapsular cataract occurs at the back of the lens. People with diabetes or those taking high doses of steroid medications have a greater risk of developing a subcapsular cataract.
  • A nuclear cataract forms deep in the central zone (nucleus) of the lens. Nuclear cataracts usually are associated with ageing.
  • A cortical cataract is characterised by white, wedge-like opacities that start in the periphery of the lens and work their way to the centre in a spoke-like fashion. This type of cataract occurs in the lens cortex, which is the part of the lens that surrounds the central nucleus.
Cataract symptoms and signs

At first, a cataract has little effect on your vision. You may notice that your vision is blurred a little, like looking through a cloudy piece of glass or viewing an impressionist painting.

Hazy, blurred vision may mean you have a cataract.

A cataract may make light from the sun or a lamp seem too bright or glaring. Or you may notice when you drive at night that the oncoming headlights cause more glare than before. Colours may not appear as bright as they once did.

The type of cataract you have will affect exactly which symptoms you experience and how soon they will occur. When a nuclear cataract first develops, it can bring about a temporary improvement in your near vision, called “second sight.”

Unfortunately, the improved vision is short-lived and will disappear as the cataract worsens. On the other hand, a subcapsular cataract may not produce any symptoms until it’s well-developed.

If you think you have a cataract, see an optician for an exam to find out for sure.

What causes cataracts?

The lens inside the eye works much like a camera lens, focusing light onto the retina for clear vision. It also adjusts the eye’s focus, letting us see things clearly both up close and far away.

The lens is mostly made of water and protein. The protein is arranged in a precise way that keeps the lens clear and lets light pass through it.

But as we age, some of the protein may clump together and start to cloud a small area of the lens. This is a cataract, and over time, it may grow larger and cloud more of the lens, making it harder to see.

No one knows for sure why the eye’s lens changes as we age, forming cataracts. But researchers worldwide have identified factors that may cause cataracts or are associated with cataract development.

Besides advancing age, cataract risk factors include:

  • Ultraviolet radiation
  • Diabetes
  • Hypertension
  • Obesity
  • Smoking
  • Prolonged use of corticosteroid medications
  • Statin medicines used to reduce cholesterol
  • Previous eye injury or inflammation
  • Previous eye surgery
  • Hormone replacement therapy
  • Significant alcohol consumption
  • High myopia (short sightedness)
  • Family history

One theory of cataract formation is that many cataracts are caused by oxidative changes in the human lens. This is supported by nutrition studies that show fruits and vegetables high in antioxidants may help prevent certain types of cataracts.

Cataract prevention

Though there is significant controversy about whether cataracts can be prevented, a number of studies suggest certain nutrients and nutritional supplements may reduce your risk of cataracts.

One 10-year study of female health professionals found that higher dietary intakes of vitamin E and the carotenoids lutein and zeaxanthin from food and supplements were associated with significantly decreased risks of cataract.

Good food sources of vitamin E include sunflower seeds, almonds and spinach. Good sources of lutein and zeaxanthin include spinach, kale and other green, leafy vegetables.

Other studies have shown antioxidant vitamins such as vitamin C and foods containing omega-3 fatty acids may reduce cataract risk.

Another step you can take to reduce your risk of cataracts is to wear sunglasses that block 100 percent of the sun’s UV rays when you are outdoors.

Cataract treatment

When symptoms begin to appear, you may be able to improve your vision for a while using new glasses, strong bifocals, magnification, appropriate lighting or other visual aids.

Think about surgery when your cataracts have progressed enough to seriously impair your vision and affect your daily life.

Many people consider poor vision an inevitable fact of ageing, but cataract surgery is a simple, relatively painless procedure to regain vision.

During surgery, the surgeon will remove your clouded lens and in most cases replace it with a clear, plastic intraocular lens (IOL).

New IOLs are being developed to make the surgery less complicated for surgeons and the lenses more helpful to patients. Presbyopia-correcting IOLs potentially help you see at all distances, not just one. Another new type of IOL blocks both ultraviolet radiation and high-energy visible blue light, which research indicates may damage the retina.

Eyewear after cataract surgery

In most cases, unless you choose presbyopia-correcting IOLs, you will still need reading glasses after cataract surgery. You may also need progressive lenses to correct mild residual refractive errors as well as presbyopia.

For the best vision and comfort possible with glasses prescribed after cataract surgery, ask your optician to explain the benefits of anti-reflective coating and photochromic lenses.

 

Source:

www.allaboutvision.com/en-gb/conditions/cataracts/


How Does the Eye Work?

The human eye is a wonder of engineering. It consists of many different parts that work together to provide visual information to the brain, which then translates it into information that is useful to the body.

Parts of the eye

1. The cornea

The first step in this complex process occurs when light passes through the clear slightly convex cornea at the very front of the eye. This is the transparent part of the eyeball.

A thick white sheath called the sclera surrounds the rest of the eyeball. The cornea refracts light slightly. The narrow, liquid-filled space behind the cornea is called the aqueous humor. This drains through spaces at the medial corner of the eye, and is constantly renewed.

2. The iris

The iris is a colored diaphragm of thin circular and longitudinal muscle fibers just behind the cornea. It has an aperture in the center. This can expand or contract to let in more or less light, respectively, depending on the light in the surroundings.

This opening is called the pupil. Light passing through the cornea and the pupil falls on the anterior surface of the lens. The aqueous humor keeps the iris from sticking to the lens behind and the cornea in front.

3. The lens

The lens is a clear crystalline globe which almost touches the posterior surface of the pupillary opening. The ciliary muscles are attached to the surface of the lens. The help the lens to change shape in order to focus.

As they contract, they cause the lens to become more round or long, so that the rays bend more or less, according to need. If the object focused on is far away, the lens needs to bend the light rays from it more sharply, to make them fall on the center of the retina, where vision is sharpest. For objects close-up, the lens becomes elongated so that light rays are bent less.

4. The posterior chamber

The refracted rays now pass through the jelly-like tissue that fills out the eyeball behind the lens. This part is called the posterior chamber. At the back, the eyeball is bounded by the choroid, a network of capillaries which nourishes all the structures of the eye.

In front of it lies the retinal pigment epithelium, a layer of melanin-rich cells which supplies special nutrition to the sensory layer of the eye. The retina is nourished and renewed by the pigment epithelial cells.

5. The retina

The retina is a multilayer membrane comprising a sensory photoreceptor array, a few layers of connecting neurons and an inner ganglion cell layer. The axons from the ganglion cells travel backward to pierce the retina and leave the eye through the optic nerve. There is a blind spot in the retina where the ganglion cells pass through.

Rods and cones

The photoreceptors in the eye consist of rod and cone cells. The rods are found mostly in the peripheral part of the retina and are responsible for perception of light and dark, including shades of gray. They are more numerous than cones, and are very sensitive to light.

The cone cells are responsible for visual acuity and color vision, and millions of them are closely assembled in the central part of the retina, also called the macula. At the fovea, which is the central point of the macula, only cones are present, and normal vision uses this point to achieve sharp vision at maximum resolution.

The pathway of vision
As the light rays fall on the photoreceptor cells, changes occur in the pigments they contain. This leads to bleaching of the pigments, and electrical impulses are generated. These are transmitted through a chain of neurons to the ganglion cells which carry the impulses to the visual cortex of the brain. There they are processed and the object is seen.

Each eye receives information from half of the visual field. Thus the middle parts of both fields overlap, and this leads to binocular vision. However, the difference in the peripheral parts of the left and right fields of vision lead to depth perception or three-dimensional vision. It helps in gauging distances accurately and estimating the depths and dimensions of objects.

Sources:

The Structure and Function of the Eyes, www.merckmanuals.com/…/structure-and-function-of-the-eyes
Healthy Eyes Facts, https://nei.nih.gov/health/healthyeyes
Eye and its Function, http://www.pages.drexel.edu/~dh329/bmes212/eyeFunction.html
Last Updated: Feb 26, 2019

Written by Dr. Liji Thomas


Optical Illusions

Optical Illusions can use color, light and patterns to create images that can be deceptive or misleading to our brains. The information gathered by the eye is processed by the brain, creating a perception that in reality, does not match the true image.

Here are a few of our favorites

The awkward dots

A simply brilliant image that plays real havoc with both your eyesight and your brain. This image was shared by Will Kerslake on Twitter with the caption “There are twelve black dots at the intersections in this image. Your brain won’t let you see them all at once.”

 

Confusing shadows

Another brilliant optical illusion created simply by the sun being at a specific place in the sky. This one seems to show oddities in the windows caused by their shadows which makes the building look like it belongs in Inception

 

The revolving snakes

This one is a simple trick of the eye. This is not an animated picture, it’s a static file that shows a mass of intertwined snakes. But if you stare at different sections you’ll see the snakes writhing and squirming

Source :

https://www.google.co.uk/amp/s/www.pocket-lint.com/apps/news/140473-best-internet-optical-illusions-you-won-t-believe-your-eyes.amphtml