Eye Anatomy and Function

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Eye Anatomy and Function:

The cornea, a clear window at the front of the eye, covers the iris and the pupil. A clear lens, located behind the pupil, acts like a camera lens by focusing light onto the retina at the back of the eye. The retina is a light-sensitive inner lining at the back of the eye.

Light passes through the front of the eye (cornea) to the lens. The cornea and the lens help to focus the light rays onto the back of the eye (retina). The cells in the retina absorb and convert the light to electrochemical impulses which are transferred along the optic nerve and then to the brain.

What are the five layers of the cornea?

• Epithelium
• Bowman's layer
• Stroma
• Descemet's membrane
• Endothelium 

What are 4 structures that protect the eye?

• Orbit -কক্ষপথ
• Eyelashes -চক্ষুর পাতার লোম
• Eyelids -চোখের পাতা
• Lacrimal glands

What are the 10 layers of retina?

• Inner limiting membrane
• Nerve fiber layer (NFL)
• Ganglion cell layer
• Inner plexiform layer
• Inner nuclear layer
• Middle limiting membrane
• Outer plexiform layer
• Outer nuclear layer
• External limiting membrane
• The layer of rods and cones

Eyeball:

• The eyeball is a bilateral and spherical organ, which houses the structures responsible for vision. It lies in a bony cavity within the facial skeleton – known as the bony orbit.
  
  
• Eye is the organ of sight. There is one pair of eyes in the human body. Eye located within orbit. Eye is a ball shaped organ. So in anatomy eye known as eye ball.

Sclera: 

• The sclera is the part of the eye commonly known as the “white.” It forms the supporting wall of the eyeball, and is continuous with the clear cornea.
• The sclera is covered by the conjunctiva, a clear mucus membrane that helps lubricate the eye. It is thickest in the area surrounding the optic nerve.
• The white of the eye; a protective fibrous layer that is the outer covering of the eyeball except for the part that is the cornea.
• এটা চোখের আচ্ছাদনকারী সাদা অংশ।

Iris:

• The colored part of the eye which helps regulate the amount of light entering the eye. When there is bright light, the iris closes the pupil to let in less light. And when there is low light, the iris opens up the pupil to let in more light. 

• Pigmented tissue lying behind cornea that (1) gives color to the eye, and (2) controls amount of light entering the eye by varying size of black pupillary opening; separates the anterior chamber from the posterior chamber.
• এটা চেখের রঙিন অংশ যা অনেকটা আংটির মত। এটা বিভিন্ন রঙের হয়। যেমন- বাদামি, সবুজ, নীল ইত্যাদি। আলোর তীব্রতার উপর নির্ভর করে আইরিশ সংকোচিত বা প্রসারিত হয়।

Pupil:

• The pupil appears as a black dot in the middle of the eye. This black area is actually a hole that takes in light so the eye can focus on the objects in front of it.
• Variable-sized, circular opening in center of iris; it appears as a black circle and it regulates the amount of light that enters the eye.
• এটা হল আইরিশের মাঝের খোলা অংশ যেখান দিয়ে আলো লেন্সে প্রবেশ করে।

Cornea:

• The slight bulge in the sclera at the front of the eye is a clear, thin, dome-shaped tissue called the cornea.  It lies directly in front of the iris and pupil, and it allows light to enter the eye.
  
  
  
• The cornea acts as the eye's outermost lens. It functions like a window that controls and focuses the entry of light into the eye.
• Transparent front segment of the eye that covers iris, pupil, and anterior chamber, and provides most of an eye’s optical power.
• এটা গম্ভুজ আকারের স্বচ্ছ পর্দা যা চোখের সামনের অংশ ঢেকে রাখে। এটি চোখে বহীরাবরকের সামনের দিকের ১/৬ অংশ স্থান জুড়ে অবস্থিত। এটা স্বচ্ছ, কারণ এতে কোন রক্তজালিকা নেই। চোখ প্রতিস্থাপন (eye transplant) বলতে আসলে কর্নিয়ার প্রতিস্থাপন বুঝায়।
  

Choroid:

• The choroid lies between the retina and the sclera, which provides blood supply to the eye. Just like any other portion of the body, the blood supply gives nutrition to the various parts of the eye.
• The middle layer is the choroid. The front of the choroid is the colored part of the eye called the iris.
• The choroid is a thin, highly vascular membrane, of a dark brown or chocolate color.
• কোরয়েড রেটিনাতে রক্ত সরবরাহ করে এবং রেটিনা হতে আগত অতিরিক্ত আলো শোষণ করে নেয়। এর ভিতরে রয়েছে আইরিশ ও লেন্স। এটি একটি ঘন রন্জিত পদার্থের স্তর।

Eye lens:

• The lens sits directly behind the pupil. This is a clear layer that focuses the light the pupil takes in. It is held in place by the ciliary muscles, which allow the lens to change shape depending on the amount of light that hits it so it can be properly focused.
• Natural lens of eye; transparent intraocular tissue that helps bring rays of light to focus on the retina.
• রেটিনার উপর আলোক রশ্মি কেন্দ্রীভূত করে। এতে রক্ত সরবরাহ নেই। এর আকার সিলীয় পেশী দ্বারা নিয়ন্ত্রিত হয়।এটা আইরিশের মাংসপেশি দ্বারা সঙ্কুচিত ও প্রসারিত হতে পারে। এর ফলে আমরা সহজেই কাছের ও দূরের জিনিস দেখতে পাই। (উল্লেখ্য যে কাছের জিনিস দেখতে আমাদের চোখের লেন্স প্রসারিত হয় এবং দূরের জিনিস দেখতে আমাদের চোখের লেন্স সঙ্কুচিত হয়।)

Retina:

• The nerve layer lining the back of the eye. The retina senses light and creates electrical impulses that are sent through the optic nerve to the brain.
• Special cells called cones and rods are located in the retina. These cells are known as photoreceptors and help absorb light.
• Part of the eye that converts what we see into electrical impulses sent along the optic nerve for transmission back to the brain. Consists of many named layers that include rods and cones.
• এটা হল চোখের আলোক সংবেদী অংশ। এটা আলোকরশ্মিকে তড়িৎ সংকেতে (electrical signal) রূপান্তর করে দর্শন স্নায়ুর মাধ্যমে মস্তিষ্কে পাঠায়।
• রেটিনায় দুই ধরনের আলোকসংবেদী কোষ (photoreceptor) থাকে। এরা হল – রডকোষ (rod) এবং কোন্‌কোষ (cone)। রডকোষ আবছা/মৃদু আলোতে দেখতে সাহায্য করে, আর কোন্‌কোষ স্বভাবিক/উজ্জ্বল আলোতে দেখতে সাহায্য করে। কোন্‌কোষ থাকার জন্য আমরা বিভিন্ন রং চিনতে পারি এবং তাদের মধ্যে পার্থক্য করতে পারি। অর্থাৎ আমাদের রঙিন বস্তু দর্শনে কোন্‌কোষগুলো দায়ী।

Optic nerve:

• A bundle of more than a million nerve fibers carrying visual messages from the retina to the brain.
• The optic nerve is located in the back of the eye. It is also called the second cranial nerve .
• The job of the optic nerve is to transfer visual information from the retina to the vision centers of the brain via electrical impulses
• Largest sensory nerve of the eye; carries impulses for sight from retina to brain.
• এটা মানুষের দ্বিতীয় করোটিক স্নায়ু (cranial nerve)। এর মাধ্যমে চোখ থেকে আলোকসংবেদ মস্তিষ্কে পৌছায়।

Aqueous humor:

• The aqueous humor is a thin, transparent fluid similar to plasma. It’s made up of 99.9% water ­­– the other 0.1% consists of sugars, vitamins, proteins and other nutrients. This fluid nourishes the cornea and the lens, and gives the eye its shape. If the patient’s aqueous humor is not draining properly, they can develop glaucoma.
• এটা জলীয় পদার্থের মত তরল পদার্থ যা সিলিয়ারি বডি থেকে উৎপন্ন হয়। চোখের সামনের অংশ (লেন্স এবং কর্নিয়ার মধ্যবর্তী অংশ) এই তরলে পূর্ণ থাকে।
  

Vitreous humor:

• The vitreous humor is the gel located in the back of the eye which helps it hold its shape. This gel takes in nutrients from the ciliary body, aqueous humor and the retinal vessels so the eye can remain healthy.
• Transparent, colorless, gelatinous filling; in the rear two-thirds of the interior of the eyeball, between the lens and the retina.
• এটা জেলির মত পদার্থ যা চোখের বেশিরভাগ অংশ পূর্ণ করে রাখে (লেন্সের পিছন থেকে রেটিনা পর্যন্ত)।

Eye ball

Structure:

• The eyeball can be divided into the fibrous, vascular and inner layers. These layers have different structures and functions. We shall now look at these layers in further detail.

Fibrous Layer:

• The fibrous layer of the eye is the outermost layer. It consists of the sclera and cornea, which are continuous with each other. Their main functions are to provide shape to the eye and support the deeper structures.

The sclera comprises the majority of the fibrous layer (approximately 85%). It provides

attachment to the extraocular muscles – these muscles are responsible for the movement of the eye. It is visible as the white part of the eye.

The cornea is transparent and positioned centrally at the front of the eye. Light entering the eye is refracted by the cornea.

Vascular Layer: 

• 
• The vascular layer of the eye lies underneath the fibrous layer. It consists of the choroid, ciliary body and iris:
• Choroid – layer of connective tissue and blood vessels. It provides nourishment to the outer layers of the retina.
• Ciliary body – comprised of two parts – the ciliary muscle and ciliary processes. The ciliary muscle consists of a collection of smooth muscles fibres. These are attached to the lens of the eye by the ciliary processes. The ciliary body controls the shape of the lens, and contributes to the formation of aqueous humor

Other Structures in the Eyeball:

• Within the eyeball, there are structures that are not located in the three layers. These are the lens and the chambers of the eye.
• Lens--The lens of the eye is located anteriorly, between the vitreous humor and the pupil. The shape of the lens is altered by the ciliary body, altering its refractive power. In old age, the lens can become opaque – a condition known as a cataract.

Anterior and Posterior Chambers:

• There are two fluid filled areas in the eye – known as the anterior and posterior chambers. The anterior chamber is located between the cornea and the iris, and the posterior chamber between the iris and ciliary processes.
• The chambers are filled with aqueous humor – a clear plasma-like fluid that nourishes and protects the eye. The aqueous humor is produced constantly, and drains via the trabecular meshwork, an area of tissue at the base of the cornea, near the anterior chamber.
• If the drainage of aqueous humor is obstructed, a condition known as glaucoma can result.

Vasculature:

• The eyeball receives arterial blood primarily via the ophthalmic artery. This is a branch of the internal carotid artery, arising immediately distal to the cavernous sinus. The ophthalmic artery gives rise to many branches, which supply different components of the eye. The central artery of the retina is the most important branch – supplying the internal surface of the retina. Occlusion of this artery will quickly result in blindness.
• Venous drainage of the eyeball is carried out by the superior and inferior ophthalmic veins. These drain into the cavernous sinus, a dural venous sinus in close proximity to the eye.

Mechanism of vision:

• For people with normally functioning eyes, the following sequence takes place:
• Light rays enter the eye through the cornea at the front of the eye.
• The light passes through a watery fluid (aqueous humor), and enters the pupil to reach the lens.
• The lens can change in thickness to bend the light, which will focus it onto the retina at the back of the eye.
• On the way to the retina, the light passes through a thick, clear fluid called a vitreous humor. The vitreous humor fills the eyeball and helps maintain its round shape.
• The light then reaches the back of the eye and hits the retina. The retina translates the light into electrical impulses which are then carried to the brain by the optic nerve.
• Finally, the visual cortex (or centre) of the brain interprets these impulses as what we see.

Important parts of eye ball:

♣ Conjunctive- the mucous membrane lining the inner surfaces of the eyelids and anterior part of the sclera.
♣ Sclera- it is opaque and forms the posterior five sixths of eye ball. It is composed of dense fibrous tissue which maintains the shape of the eye ball.

♣ Cornea- is transparent. It replaces the sclera over the anterior one sixth of the eye ball.
♣ Iris- a circular, contractile disc in between the cornea and the lens of the eye and perforated by a circular pupil.

♣ Lens- the lens is a transparent structure which is placed between anterior and posterior segment of eye and play an important role in vision.

♣ Suspensory ligament- the ligaments inside the eye that hold the lens in tension.
♣ Anterior chamber- the part of the eye in front of the iris. It contains the aqueous humor.

♣ Posterior chamber- space between the iris and the lens.
♣ Aqueous humor- this is a clear fluid which fills the space between the corneas and lens.
♣ Ciliary muscle- a semitransparent, circular band of smooth muscle fibers attached to the choroid of the eye.
♣ Choroid- it is thin pigmented layer which separates the posterior part of sclera from retina.
♣ Vitreous body- It is a colorless jellylike transparent mass which fills the posterior segment of eyeball.

♣ Retina- it is the thin delicate inner layer of the eye ball. It continuum posteriorly with the optic nerve. There are two type of receptor cell in retina-(a) Rod cell: concerned with dim light vision. (b) Cone cell: concerned with bright, color vision.

♣ Optic disk- the intraocular portion of the optic nerve formed by fibers converging form the retina and appearing as a pink to white disk. It is insensitive to light Called also blind spot.
♣ Optic nerve- the cranial nerve responsible for vision. It attached to the posterior part of eye ball.

Surgery of Eye- চোখের সার্জারি:

Glaucoma:

Glaucoma is a common eye condition where the optic nerve, which connects the eye to the brain, becomes damaged. It's usually caused by fluid building up in the front part of the eye, which increases pressure inside the eye. Glaucoma can lead to loss of vision if it's not diagnosed and treated early.

Glaucoma হল চোখের একটি সাধারণ অবস্থা যেখানে চোখের সাথে মস্তিষ্কের সংযোগকারী অপটিক নার্ভ ক্ষতিগ্রস্ত হয়। এটি সাধারণত চোখের সামনের অংশে তরল জমা হওয়ার কারণে হয়, যা চোখের ভিতরে চাপ বাড়ায়। Glaucoma যদি রোগ নির্ণয় ও প্রাথমিকভাবে চিকিৎসা না করে তাহলে দৃষ্টিশক্তি হ্রাস পেতে পারে।

Causes of Glaucoma:

1. Family history of glaucoma

2. Underlying conditions like diabetes or high blood pressure

3. Regular use of certain medications, including steroids

4. Eye injury or trauma

5. Thin corneas (the clear layer in front of your pupils)

6. Being over age 60

Symptoms of Glaucoma:

1. Intense eye pain

2. Nausea and vomiting

3. A red eye

4. A headache

5. Tenderness around the eyes

6. Seeing rings around lights

7. Blurred vision

Tests for glaucoma:

♣  Glaucoma can usually be detected during a routine eye test at an opticians, often before it causes any noticeable symptoms.
♣  The tests are carried out in the opticians by an optometrist.
♣  You should have a routine eye test at least every 2 years.
♣  Several quick and painless tests can be carried out to check for glaucoma, including vision tests and measurements of the pressure inside your eye.

Glaucoma Prevention:

You can’t prevent glaucoma. But if you find it early, you can lower your risk of eye damage. These steps may help protect your vision:

1. Have regular eye exams. The sooner your doctor spots the signs of glaucoma, the sooner you can start treatment. All adults need to be checked for glaucoma every 3 to 5 years. If you’re over age 40 and have a family history of the disease, get a complete eye exam from an eye doctor every 1 to 2 years. If you have health problems like diabetes or are at risk of other eye diseases, you may need to go more often.

2. Learn your family history. Ask your relatives whether any of them have been diagnosed with glaucoma.

3. Follow your doctor’s instructions. If they find that you have high eye pressure, they might give you drops to prevent glaucoma.

4. Exercise. Do moderate activity like walking or jogging at least three times a week.
5. Protect your eyes. Use protective eyewear when playing sports or working on home improvement projects.

Homoeopathic Treatment: 

1. Phosphorus: For Glaucoma with optic nerve damage.

2. SILICEA: Glaucoma in people who are always cold, chilly and lack vital heat. 

3. Belladonna: For Glaucoma with acute symptoms.

4. SPIGELIA - Severe headache on the left side. 

5. COLOCYNTHIS: Colocynthis is considered a good remedy for glaucoma. 

6. Physostigma: For Glaucoma following Injury.

7. GELSEMIUM 200- Gelsemium is also a very effective remedy for glaucoma .

8.CONIUM MAC 200- Sensation of pressure in the eyes when reading , writing or doing any fine work