The Eyes - How we see

-



The Eye is one of our 5 sense organs. The main function of the eye is to detect the visual stimuli and to convey the gathered information to the brain via the Optic Nerve. The average human eye can see around 100 different shades of colour and has a resolution that equals 576 gigapixels.




Parts of The Eye

  • Orbits: The two eyes are located in deep sockets or orbits. Each eye contains an eyeball and can be rotated with the help of six muscles.

  • Eyelids: The upper and the lower movable eyelids protect the outer surface of the eyeball and can shut out light. Each eyelid carries eyelashes which prevent entry of particles into the eyeball.

  • Tear glands (lacrimal glands): They are located at the upper sideward portion of the orbit. Six to twelve ducts of the gland pour the secretion over the front surface. The tears lubricate the eye and clear out dust particles. The enzyme Lysozyme kills germs.

  • Conjunctiva: It is a thin membrane covering the entire front part of the eye . It is continuous with the inner lining of the eyelids. It helps in protection of eyes.


Q. Name a disease of the conjunctiva and state why it occurs?

Ans- Conjunctivitis, also known as pinkeye, is an inflammatory disease of the conjunctiva.  Viruses are the most common cause of conjunctivitis. Bacteria such as Staphylococcus Aureus, allergens and foreign objects in the eye can also cause pink eye.



Structure of the Eye


The eyeball sits within the orbit, surrounded 

by the adipose tissue. It is enveloped in a thin fascial sheath called the Tenon’s capsule.


The wall of eyeball has 3 layers-


  • Sclera (Fibrous)

  • Choroid (Vascular pigmented layer, Uvea)

  • Retina (Nervous Layer)



Sclera


  • The sclera is an opaque, white, outer layer that surrounds the posterior five-sixths of the eyeball.

  • The function of the sclera is to protect the inner contents of the eye from the mechanical trauma

  • The cornea comprises the anterior one-sixth of the fibrous layer of the eyeball. It is a circular transparent layer that covers the pupil, iris and anterior chamber of the eye. The cornea is noticeably more convex to the outside than the sclera.

  • The main function of the cornea is to participate in the refraction of light. In fact, the cornea is the most important refractory structure of the eye as it has the highest refractive power (dioptric power equals 58 diopters).The cornea also has a protective role, protecting the eye's delicate components from foreign particles.



Vascular pigmented layer (Uvea)


It consists of three layers from posterior to anterior, these are the choroid, ciliary body and iris.


  • The choroid layer has many blood vessels accounting for 90% of blood flow in the eye.

  • Its function is to accommodate blood flow and prevent the blood rays from reflecting and scattering inside the eye with help of the dark black pigment Melanin.

  • The choroid expands to form the ciliary body which forms a ring around the iris.

  • The ciliary processes produce the aqueous humour and enables accommodation of the eye.

  • The iris is a contractile, heavily pigmented, circular diaphragm which has a circular opening in the centre, the pupil.

  • The iris contains two smooth muscles that enable its contractile property. These are the sphincter pupillae muscle and dilator pupillae muscle.

  • The function of the iris is to control the size of the pupil through the actions of the sphincter and dilator pupillae muscles. 

  • The dilation of the pupil is called mydriasis. It occurs when there is low light due to dilator pupillae muscle contraction.

  • The contraction of the pupil is called miosis. It occurs when there is high light intensity due to sphincter pupillae muscle contraction.




Nervous layer (retina)

The retina is the innermost layer of the eyeball that extends from the site of exit of the optic nerve to the posterior margin of the ciliary body. It is a site where the image of the environment is converted to the neural impulses that are transmitted to the brain via optic nerve to determine the image.


The photoreceptor layer of retina consists of 2 sense organs- Cones and Rods.


Cones- The cones are the conical cells that are specialised for high-intensity light, enabling the colour vision. They consist the pigment Rhodopsin or visual purple.

They are concentrated all throughout retina.


Rods- The rods are cylindrical cells adapted for absorbing the dim light, being responsible for producing the images in the grayscale. They consist of the pigment Iodopsin. Found only in yellow spot.




YELLOW SPOT - The macula lutea is an area at the center of the posterior retinal layer. It is a site of the brightest and most coloured vision as it contains the highest amount of cone cells.


BLIND SPOT- The blind spot is where the optic nerve and blood vessels leave the eyeball.There are no photoreceptors here therefore mo vision.

( Go to this page to check your blind spot- https://www.webmd.com/eye-health/eye-blind-spot#1)




COMMON EYE DISORDERS



  • Myopia- Nearsightedness (myopia) is a common vision condition in which you can see objects near to you clearly, but objects farther away are blurry. 

  • Hypermetropia- Farsightedness (Hypermetropia) is a vision condition where you can see objects far away clearly but objects near are blurry.



Image
Differences between Myopia
and Hypermetropia


We can conclude that the eye is a very special irreplaceable organ which we must protect. Eating fruits and vegetables containing Vitamin B1 are necessary to keep the eye healthy. Blue lenses and UV blockers help to protect the eyes from harmful rays and keep it safe.



-Subhaditya ghosh, team edixite





Bibliography-

Comments

Post a Comment

Popular posts from this blog

Myocardial Infarction - An agonizing malady

-
Image
C ommonly known as heart attack; Myocardial Infarction is one of the predominant Cardiovascular diseases (CVDs).CVDs are often defined as physical conditions, concerned with the heart or blood vessels . They are the primary cause of deaths all across the world; causing nearly 30% of the world’s total deaths out of which 85% are only due to Myocardial Infarction (MI) and Cerebrovascular Accident (CA) commonly known as Stroke . Heart Attack is the most common  cause of death in the world followed by Stroke So, What triggers a Heart attack? A heart attack is chiefly caused due to the blockage of coronary arteries. As the coronary arteries provide oxygenated blood to the Cardiac muscles, there is a cut-off in the supply of Oxygen which leads to Atherosclerosis or  Coronary Artery Disease (CAD) which ultimately leads to a heart attack. Such a condition arises when there is a plaque build-up in the arteries due to congestion of fatty deposits such as Cholesterol . Attacks can...
Read more

Black Fungus - A hurdle to the Indian Spectrum of hope

-
Image
  A lso known as Mucormycosis , Black Fungus is a condition caused by fungal contamination. The term Mucormycosis is widely apted to specify infections caused by molds belonging to the group Mucormycetes. Mucromycosis - Microscopic view This disease, though often considered pernicious, is rare throughout the world. In the recent times, a spike in the number of cases has been observed in India, out of which most of the patients are affected in their Post-Covid period .   What is the relation between Covid-19 and  Black Fungus? Under o rdinary circumstances, our body has the capability to combat such fungal infections. However, Due to Covid-19, our immunity is severely affected thus, making us vulnerable to other ailments as well. Medical professionals have stated many factors for the rise of this disease in India, particularly in Post-Covid Patients. One of them being the use of Steroid Drugs in the treatment of Covid-19, which suppress our body’s ability to ta...
Read more

Artificial Intelligence- A huge leap in the world of technology

-
Image
      Introduction to Artificial Intelligence:-   Human civilization has come a long way, from creating fire with the help of stones to LED; from invention of wheels to Cars, Aeroplanes and Autonomous Vehicles. Curiosity and Necessity are the leading factors of our improvement over the years.  In the late 1900's  scientists realised the need of automation in a better way along with the urge to describe human intelligence or consciousness. AI - A huge leap in the world of technology A brief history of AI:- The beginnings of modern AI can be traced to classical philosophers' attempts to describe human thinking as a symbolic system. But the field of AI wasn't formally founded until 1956, at a conference at Dartmouth College, in Hanover, New Hampshire, where the term "artificial intelligence" was introduced. Ancient Greeks and Chinese people had myths about artificial robots and intelligence. However building an AI wasn't that easy practically. It too...
Read more