Our Eyes and Eyesight
Our Eyes and Eyesight

Our eyes are one of the most complex organs of our body. They rely on three different layers and more than two million components to make our eyesight possible.

The first layer - and also the outermost layer - contains the cornea and the sclera. The sclera is a thin, fibrous yet tough structure that acts as a shield, protecting your eye's more fragile components within. Together with the cornea, the transparent front surface of the eye, it protects your eyes from bacteria, dirt and other harmful particles.

The second (middle) layer is comprised of the blood vessels providing oxygen and nutrients to those tiny muscles that move the lens.

The third and innermost layer is called the retina, a superfine structure with millions of light-sensitive cells, receptors, and neurons. These cells connect with the nerves passing the light signals to the brain.

WHAT MAKES US SEE
125 Mio
Receptors and Neurons
48 Hours
Self-Repair Time
for a minor scratch
5 Mio
Blinks per Year
ANATOMY OF AN EYE

Photoreceptors are part of the retina and are classified into tapered cone cells and blunt-ended rod cells. The tapered cone cells are responding to bright light while the rod cells are extremely light sensitive and respond well to dim light. Protein-based photopigments that are contained in the receptors absorb different colors as different light waves which is the foundation for our eyes to see. The diameter of a human eye is about 25mm or about one inch. Our tears keep the cornea moist and a watery, aqueous lubricant on the inside keeps the lens moist on all sides.

Cornea

The cornea is the outermost membrane made of five different layers that protect your eyes from bacteria, infections, and dirt. About half an inch in diameter, it covers the front of the eye including the pupil. Without any blood vessels, it receives nutrients through the tears which get replenished with every blink. The cornea plays an important role in our ability to see. As it is clear, light can pass through the cornea and gets focused through the pupil onto the lens.

Sclera

The 'White' of the eye is called sclera. The majority of the eyeball's surface is covered by the sclera containing mainly collagen and tough yet elastic fibers. It keeps our eyball in shape and protects our eye from serious damage such as rupture or external trauma caused by pressure. It is covered by a thin membrane responsible for keeping the eyeball lubricated and smooth.

Iris

Our iris plays a crucial role in controlling the amount of light getting through our pupils and reaching the retina. Have you ever noticed how small your pupils are in bright light versus at dark? By adjusting the diameter and size of the pupil, the right amount of light reaches the back of our eyes. And the small fibres that make up the color of our eyes are tiny smooth muscle fibres that make the iris also an excellent unique and personal identifier.

Pupil

Simply put, the pupil is a hole right in the center of the iris. Light waves can enter our eyes and hit the retina only by getting through the pupil and the lens. And why is it black? The light rays entering the eye through the pupil are either absorbed by the retina and the tissues inside or simply diffused via reflections within the eye hence most of the light cannot exit through the small pupil.

Lens

No visually sharp objects without the eye lens: Whether an object is close or far, tiny muscles that are connected to the lens, control the lens to be more or less flat. As a result, an object is projected to the retina with the right focal point.

Choroid

The choroid is a vascular layer between the retina and the sclera. As thick as 0.2 mm at the rear end of the eyeball, it supports the transport of oxygen-rich blood through tiny blood vessels to the neighboring retina.

Retina and Macula

The retina is a light-sensitive layer at the back of the eyeball. It contains more than 125 million receptor cells that trigger nerve signals to the brain. The retina covers about two-thirds of the inside back of the eyeball. The rod cells and cone-shaped cells covering the retina react to light waves of various length (= colors) and trigger nerve impulses. These are passed to the optic disc (optical nerve head) and further on to the brain where they get further processed into an image.
Part of the retina is the oval-shaped macula. While it is just about five millimeter wide, it is key to our central vision. As such, this area contains a higher number of photoreceptor cells enabling us to see the fine details and colors. The other area of the retina is supporting our peripheral vision.

Optic Nerve Head

With an average diameter of about 1.8mm, the optic nerve head (also called optic disc) is the area at the back of the inner wall of the eyeball where the retina connects with the nerves carrying the image data to the brain. As this area of the retina is not covered with photosensitive cells, it also creates a blind spot. You can easily test your blind spot, by writing a plus and minus sign on a piece of paper, approximately 5 inches apart. Cover one eye and slowly move the paper towards your eyes until one of the signs disappears. You have found your blind spot. And yes - we all have one!
EYE CONDITIONS AND TREATMENT OPTIONS
Our eyes are extremely complex - in fact, the eye is the second most complex organ only surpassed by the brain. So it's no surprise that with such complexity there are many eye conditions caused by many factors: age, medical history, family history, lifestyle, gender, and even ethnicity.

Refractive Errors

Blurry vision caused by unfocused projection through the cornea and lens to the retina.

Refractive Errors

The most common conditions are near- and farsightedness, astigmatism and presbyopia. In most cases they can be corrected using:
  • Glasses have been around for centuries and are still a very popular choice to correct bad eye sight.
  • Contact lenses are getting increasingly popular, especially since the arrival of daily silicone hydrogel lenses.
  • Refractive surgery using laser technology

Glaucoma

Occurs when the intraocular pressure increase caused by an increase of the jellylike substance inside the eyeball.

Glaucoma

Blurry vision that is caused by an increased interior eye pressure, damaging the optic nerve system.
  • Did you know, that glaucoma is the second leading cause of blindness?
  • Health conditions, medical history, age, ethnicity and family history are important glaucoma risk contributors.
Treatment options include prescribed eye drops or pills, and surgery. Surgery depends on the type of glaucoma and may involve pressure-causing tissue removal or a laser procedure called 'laser peripheral iridotomy'.

Cataract

Often found amongst the elderly population, this condition stems from a cloudy lens and typically results in a vision with halos.

Cataract

A cataract develops over a long time and is caused by proteins building up within the lens. And with a cloudy lens, clear images cannot get through to the retina where they get processed and send to the brain. More than 50% of the US population will have a cataract by the age of 80. Treatment options include:
  • Surgery: The protein clumps can be broken up and removed by using ultrasound waves - a procedure also known as phacoemulsification.
  • A healthy diet, active lifestyle, normal weight and protecting your eyes from UVB rays can keep a cataract in check.

Macular Degeneration

Blurry vision caused by damaged cells in the macular area of the retina. Most commonly found in people of age 60 and older.

Macular Degeneration

The most common form is dry macular degeneration (MD) caused by tiny yellow particles (called drusen) building up under the macula. As with other eye conditions, a healthy lifestyle is important for preventing MD and age-related MD.

Unfortunately, there is currently no cure but vision therapy is an option to manage and cope with vision loss. Another option is surgery by implanting a magnifier lens.

Amblyopia

Have you ever heard the term 'lazy eye'? This condition is most commonly found in children of age 6 and younger.

Amblyopia

This vision disorder affects primarily children in early childhood development. Often affecting one eye only, it can be caused by several interfering conditions: Irregular shape of the cornea, a cloudy lens, improper eye alignment.
Often combined with dedicated eye exercises, treatment options focus on training the lazy eye and include:
  • Eye patch to cover the good eye
  • Atropine eye drops to blur the good eye
  • Glasses

Diabetic Retinopathy

Caused by diabetes, the tiny blood vessels can no longer nourish your retina. This can cause blindness and - at an earlier stage - dark spots.

Diabetic Retinopathy

This condition affects around 80% of diabetics with a 20 year or longer diabetic history. It is the result of damage to the small blood vessels that are very vulnerable to poor blood sugar levels. The reduced retinal blood flow damages cells and neurons resulting in blurry vision first and black spots later. Early treatments have a high chance of success limiting vision loss. Treatment options include:
  • Laser surgery (photocoagulation)
  • Special medications
  • Vitrectomy surgery
FURTHER READING