Human eyes

Table of Contents

Eyes are the human’s sense organ for vision. 

Your eyes are the primary sensory organ that detects light, which transmits visual information to your brain with the ability to distinguish between colour and depth. Therefore, more than 75% of the information you receive comes from your eyes.

Despite their small size, your eyes are very complex organs. In general, your eyes are about 1 inch wide, 1 inch deep, and 0.9 inches tall. Your eyes, as a sense of sight, have a 200-degree viewing angle and can see 10 million colours and shades.

Anatomy of The Eye and Its Functions

The eye has the shape of a round ball, with a slight bulge at the front. The eye is divided into two sections – the inner and the outer parts. Below are more details about the anatomy of human’s most important sense: 

Tear Film

This is the eye’s first layer. It is clearly visible and has a moist texture. Its function is to keep the eyes smooth and clear. 


The cornea is the outer, transparent structure located at the front of the eye. It covers the iris, pupil, and anterior chamber. It has a perfectly round shape. The cornea has no blood vessels and is highly sensitive to pain. However, the cornea serves as a protective window that focuses and controls the entry of light into the eye. 


The conjunctiva is the eye’s thin layer that produces fluid to keep the cornea moist. The conjunctiva functions as a mucous membrane, which covers the surface of the eye and the insides of the eyelids.


The sclera or the white of the eye, is the opaque, fibrous layer of the eye that contains collagen and elastic fiber.


The iris is a pigmented tissue with two muscles that control the constriction and dilation of the pupil. The iris is the colored part of the eye and it functions to control the amount of light that enters the eye.


The pupil is the hole in the middle of the iris, located behind the retina. The light that enters through the pupil will be transmitted through the eye lens, which then will be absorbed in the retina.

Anterior chamber

The anterior chamber is the fluid-filled space between the iris and the inner surface of the cornea, which consists of the endothelium. The endothelium is a thin layer of cells lining blood vessels.

Eye lens

Eye lens is located behind the pupil. It serves to focus light on the retina. This is a fibrous tissue that can change shapes to increase or decrease the size of the lens, allowing the eye to focus on an object.


The retina is a light-sensitive tissue that captures light energy and sends that energy to the brain as nerve impulses. It is located in the back of the eye

Optic nerve

The optic nerve is a network of nerve cells that receives impulses from the layer of nerve fibers on the retina. It functions to transfer nerve impulses to the brain.

Symptoms of Eye Disorders

If you experience the following symptoms of eye problems, you are advised to speak with an ophthalmologist about your condition. 

Symptoms that may indicate eye problems include: 

Eye Strain 

Do you often look at a computer screen for hours? Or spend all day reading a book? These are some examples of situations that can strain your eyes since you use your eyes too often to work. As with any other parts of the body, your eyes also need to rest. When you experience eye strain, you should take a break and let your eyes rest. Call your doctor if it does not get better within a few days.

Red Eyes

When you look in the mirror, you may notice your eyes turn red. This can occur because the surface of the eye is covered with blood vessels that become swollen due to irritation or infection. Other causes of red eyes may include tired eyes, lack of sleep, or allergies. It is a different case if you have an eye injury–you should talk to your doctor. 

Night Vision Problems 

If you have trouble seeing in darkness, you may have something called night blindness. It may lead to nearsightedness, cataracts, or  vitamin A deficiency.

Poor Color Vision

Colour blindness is a term used for someone who cannot see certain colours. Are you having trouble distinguishing colours or unable to see certain colours? This can happen if certain cells in the eye do not work correctly. You will have to run a series of tests to identify your condition accurately.  

Eye Coordination Difficulties

Poor eye coordination is usually referred to as a squint (crossed eyes). This can occur when the position of the eyes is misaligned and points in different directions. This condition is caused by poor eye muscle control. 

Types of Eye Disorders

Below are some of the most common types of eye disorders, such as: 


Cataracts are when the eye lens becomes cloudy, which causes light not to enter properly. There are several types of cataracts and the most severe condition of cataract is complete blurred vision. 

Macular Degeneration

The macula is a small, round area, located behind the retina – 3.5 mm from the disc’s temporal and 0.5 mm from the disc’s interior. Macular degeneration is an eye disease that mostly affects the elderly. The disease damages the eye’s macula which is located in the centre of the retina. This condition may lead to vision loss. 


Glaucoma is an eye disease that gradually results in vision loss by causing damage to the optic nerve that sends visual images to the brain. You may not realize that you have a glaucoma disorder, as it will only be detected if your optive never becomes severely damaged.

Retinal Diseases

Retinal diseases are usually hereditary or genetic eye disorders. It occurs when the cones in the retina deteriorate, resulting in impaired vision or vision loss.


Presbyopia is an eye disease that occurs gradually with symptoms of losing the ability to focus and see objects within near distance.

Methods of Eye Examinations

The following are several eye tests that your ophthalmologist may perform, including:


In tonometry, your ophthalmologist will measure the pressure required to flatten your cornea in a specific area. This type of eye exam helps your doctor diagnose and trace any indications of glaucoma. Your doctor may apply numbing eye drops in your eye when air pressure is applied using an instrument called a tonometer.

Corneal Topography

Computerized corneal topography tests can show problems on the surface of your eye, such as inflammation and other conditions. This test is usually performed before surgery, corneal transplant, or contact lens insertion.

Retinal Tomography

Tomography is a diagnostic technique that provides information about structure and anatomy of organs. Retinal tomography is performed to obtain detailed retinal images of all layers. This test is usually performed to check macular degeneration.

Visual Acuity Test

This eye exam checks how well your eye can see from both near and far distance. Your ophthalmologist will ask you to read some letters or writings. If you are unable to read clearly, special eye tests may be performed. 

Specialist Doctors for Eye Disorders

Eye examinations are not only recommended for people with visual impairments, but also people with healthy vision. Eye specialist doctors are known as ophthalmologists, optometrist, or optician.

Tips for Healthy Eyes 

You should pay attention to your eye health. Your eyes are the most important organs of sense. You perceive most information through your sight on a daily basis. You are recommended to implement the following tips to maintain your eye health, such as:

 Eat Healthy Foods

The first step you can take to maintain your eye health is by eating healthy foods, such as omega-3 fatty acids, lutein, vitamin C, and vitamin E. These types of foods can help prevent age-related vision problems. Some of the best foods for eye health may include:

  • Egg
  • Orange
  • Oyster
  • Green vegetables
  • Salmon and tuna
  • Legumes

Quit Smoking

Smoking habits make you more susceptible to eye conditions such as cataracts, optic nerve damage, and macular degeneration. Try to reduce your cigarette intake, slowly but surely. Quit smoking for healthier eyes. 

Wear Sunglasses

Frequent exposure to UV rays puts you at risk of cataracts and macular degeneration. Wearing sunglasses can help protect your eyes from being exposed to UV rays

Limit Your Screen Time

Looking at your computer screen for too long can cause eye strain, dryness, difficulty focusing, and even headaches. Take frequent breaks to let your eyes rest. There are also several ways that you can do to relieve your computer eye strain, such as:

  • Sit in a comfortable work chair.
  • Rest your eyes for 20 minutes.
  • Position the screen at eye level.
  • Avoid glare from windows and lamps.
  • Blink frequently to prevent you from dry eyes.

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