How the eye works

how an eye works

The eye is one of the most impressive organs in the body and the feat of human sight is something that shaped our evolution as a species.

  1. Find out how your amazingly intricate eye works – and what commonly goes wrong.
  2. Discover the causes of common disorders and what it’s like to have them.
  3. Get the facts about how to prevent, treat and recover from common vision problems.

Welcome to the ultimate guide to sight and common sight problems.


In the eyeball, there are multiple parts that make sight possible. Here we take a look at some of the main structures within the eye that enable sight.


Main Eye StructuresDescription
Ciliary BodyThe ciliary body is an extension of the iris and produces the fluid in the eye called aqueous humor. It’s also the part of the eye that includes the ciliary muscle, which controls the shape of the lens.
Aqueous HumorThe liquid that sits in a chamber behind the cornea.
CorneaActs as a window at the front of the eye.
PupilThe pupil sits in the middle of the Iris which controls the amount of light that enters the eye.
IrisThe coloured part of the eye.
LensA clear disc-like structure that helps to focus light on the retina.
Ciliary MuscleThe ciliary muscle controls the shape of the lens, so that we can see elements that are near and far away.
ScleraThe sclera is the white part of the eye and protects everything inside
ChoroidThe choroid is a layer of the eye that lies between the retina and the sclera. It is made up of layers of blood vessels that nourish the back of the eye.
RetinaThe retina is a light-sensitive part inside the inner layer of the eye. Its job is to turn light into signals about images that the brain can understand.
Optic NerveThe optic nerve delivers messages from the retina to the brain.
Vitrous HumorThe vitreous humor is the clear gel that fills the space between the lens and the retina


Now that you’re familiar with the major parts of the eye, find out how they come together to perform the miracle of sight. 

Vision occurs when the brain interprets light that is reflected from an object. 

The light enters the cornea through the pupil. The pupil is comprised of two types of muscular fibers. When exposed to light, the circular fibers contract and the radial fibers relax. When there is less light, the radial fibers contract and the circular relax.

The cornea (the transparent part in front of your pupil) causes the light rays to refract. This causes the image to partially focus. The light rays continue through the lens, which focuses the rays even more by changing shape.

This change is actually carried out by the ciliary muscle. With faraway objects, the ring of ciliary muscle relaxes causing ligaments to pull on the lens. This movement causes the lens to become thinner and flatter. With nearby objects the ciliary muscle contracts. The ligaments stop pulling and the lens returns to its natural shape.

The light rays cross the inside of the eye and reach the retina or inner lining of the eye that converts light into nerve impulses. The retina contains two types of cells. Rods handle vision in low light. They see only in black and white. Cones handle colour vision and detail.

The retina produces an inverted image of the object that is sent to the brain by the optic nerve. The brain processes the information and constructs an image of the object, and vision is the term for the process of seeing this object.


There’s a lot to learn when it comes to the eye. Here are a few interesting facts about your eyes and eyesight.

Did you know:

  • 70 percent of the body’s sensory receptors are located in the eyes
  • Your eyes contain around 107 million light sensitive cells
  • Humans can see more shades of green than any other colour.
  • The world’s most common eye colour is brown.
  • Your eyes contain 7 million cones which help you see colour and detail and 100 million cells called rods which help you to see better in the dark.
  • The average blink lasts for about 1/10th of a second.
  • Eyes heal quickly. With proper care, it only takes about 48 hours for the eye to repair a corneal scratch.
  • You blink about 12 times every minute.
  • Each of your eyes has a small blind spot in the back of the retina where the optic nerve attaches. You don’t notice the hole in your vision because your eyes work together to fill in each other’s blind spot.
  • 80% of vision problems worldwide are avoidable or even curable.


With such a complex structure, the eye can experience a number of problems and disorders that affect your ability to see.

Causes for these disorders range from ageing to infection to damage to the eye’s structure or nerves.

Below are the top 10 most common eye disorders, along with information about their causes and treatment.


Causes: Damage to the retina’s macula, which is responsible for the central, high-resolution, colour vision that is possible in good light.

Symptoms: Blurred vision, or lack of vision, in the centre of the visual field.

Treatment: There are several treatment types: Anti-VEGF (Anti–vascular endothelial growth factor) medication injected into the eye, laser coagulation and photodynamic therapy.


Causes: Typically caused by bacterial infection.

Symptoms: Chronic inflammation of the eyelid, usually at the base of the eyelashes.This results in scales and debris which can irritate and cause an itching or burning sensation of the eye.

Treatment: Routine eyelid hygiene, such as a warm compress, eyelid massage, and eyelid scrubs. Some ophthalmologists and optometrists may prescribe a low-dose antibiotic.


Causes: Cataracts can be brought on in myriad ways – age, blunt trauma and skin diseases are commonly seen causes, as are smoking, alcohol abuse, even radiation exposure.

Symptoms: Your vision may be impacted in several ways, including faded colours , blurry vision, trouble with bright lights, trouble seeing at night, and halos appearing around brighter light sources.

Treatment: Cataract surgery, sometimes also referred to as lens replacement surgery.


Causes: One of the most important risk factors in glaucoma is increased pressure within the eye, known as ocular hypertension. Other elements, such as dietary habits, genetics and ethnicity, are sometimes also factors.

Symptoms: Loss of peripheral vision at first, sometimes followed by loss of central vision and potentially blindness if left untreated.

Treatment: Laser surgery, traditional surgery and medication are all options for treatment of glaucoma.


Causes: Amblyopia has three main causes:

  • Strabismic; caused by misaligned eyes
  • Refractive; due to refractive error in one or both eyes
  • Deprivational; brought on by deprivation of vision in early life from vision obstructing disorders.

Symptoms: Often not noticed until later in life, symptoms include poor pattern recognition, abnormalities in spatial vision, and reduction in visual acuity and contrast sensitivity.

Treatment: Usually treated by wearing spectacles to correct the vision deficit in the affected eye, it’s also sometimes treated by topical application of the good eye in order to force use of the amblyopic eye.


Causes: Retina separates from the layer of blood vessels beneath it.

Symptoms: Retinal detachment, or Retinal tears result in an increased number of ‘floaters’, flashes of light, and worsening of the outer section of the visual field.

Treatment: Treatment is often urgently needed for this condition, and is possible through a number of techniques: laser photocoagulation, scleral buckle surgery and pneumatic retinopexy.


Causes: Brought on by the damage that diabetes mellitus causes to the blood vessels in the tissue at the back of the eye (retina).

Symptoms: Early symptoms include floaters, blurriness and dark areas of vision. Blindness can sometimes occur.

Treatment: Mild cases can be treated through the careful management of diabetes, while more severe, advanced cases require surgery or laser surgery.


Causes: Chronic lack of sufficient lubrication and moisture on the surface of the eye

Symptoms: The main symptom of course is dryness of the eyes, but this can lead to constant eye irritation and significant inflammation and sometimes even eye scarring.

Treatment: Often, the routine application of artificial tears to the eye is sufficient treatment. In more severe cases, an ophthalmologist may recommend other eye medications to help your body to create and secrete more tears.


myopia (nearsightedness), which is when far-away objects look blurry.

hyperopia (farsightedness), which is when close-up objects look blurry.

astigmatism, which can result in blurry vision because the cornea is not perfectly shaped to direct light into the eye.

presbyopia, which is farsightedness caused by the loss of elasticity of the eye’s lens due to ageing.


Taking care of your eyes is the best way to prolong your eye health and maintain your sight. 

Below are a few ways you can take better care of your eyes. 

Take your contacts out before you shower, swim, or otherwise get water on your face. Not doing so could end up damaging your contact lenses and, more importantly, your eyes. Bacterial buildup behind the contact lens has, in extreme cases, led to parasitic infections. 

Wear safety glasses when you do any home improvement projects—even with simple stuff.

See an eye doctor at least every two years, or more frequently if you have high blood pressure, high cholesterol, or diabetes. Many eye conditions are contingent on having other conditions, so make sure you pay close attention to your ocular health if you have diabetes, high cholesterol or high blood pressure. 

Wear your sunglasses – yes, even when it’s cloudy or cold! It may seem counterintuitive, but the right colour of sunglass lens can in fact improve your vision. They not only combat glare but also reduce UV light rays, which can damage the eyes in the long term and impact vision. 

Take regular breaks from the computer. Your mum might have told you that your eyes would turn square from too much telly. She wasn’t wrong about long-time screen exposure being damaging, although it’s not square eyes you need to worry about. Prolonged screen time can lead to eye dryness, irritation , eye fatigue, blurred vision, and in extreme cases, myopia.

Quit smoking. While the impact of smoking on lung disease has been known for some time, recent research shows that smoking increases the risk of age-related macular degeneration, cataracts , glaucoma and diabetic retinopathy. Also, you don’t look cool.




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