What Are The Parts Of My Eye? (Excerpt from Dr. MacKay's forthcoming book " The Eye of A Surgeon")

What is my:

1. CORNEA?

Your CORNEA is the transparent, curved window in the front of your eye. All of the light that enters your eye comes through your cornea. Your cornea has three layers: the EPITHELIUM, the part that is exposed to the air; the ENDOTHELIUM, the innermost layer; and the STROMA, the layer in the middle.
Like every part of your body, your cornea needs nourishment, but it must be free of blood vessels in order to maintain its clarity, so, in place of blood, the epithelium is nourished by your tears, and the stroma and endothelium by your AQUEOUS HUMOR, the clear liquid that fills the front compartment of your eye..
Your cornea provides roughly 70% of the focusing power of the eye, the rest being provided by your LENS

2. LENS?

Your lens is a transparent structure the size and shape of an M & M candy. It is suspended by thin strands, called ZONULES, from a structure called the CILIARY MUSCLE, which runs around your eye immediately behind your IRIS.
Your lens has an inner, tougher center, called the NUCLEUS; a softer outer layer, called the CORTEX; and a skin, called the CAPSULE. When you want to focus up close, your ciliary muscle contracts, and your lens gets fatter; when this muscle relaxes, your lens gets thinner, and your eye focuses at distance.
Your lens grows all through your life, adding one layer each year.
As your lens gets larger, it gets stiffer, and harder to focus. By the time your are in your forties you will no longer be able to change the focus of your lens, so you will need magnifying glasses to read.
A cloudy lens is called a CATARACT.

3. IRIS?

Your IRIS is the part of your eye that gives it color. It is a muscle that has the shape of a lifesaver. Your iris acts like a window shade, opening and closing automatically to change the size of your PUPIL, the black opening in its center. This regulates the amount of light that is admitted into your eye.
The color of your iris-brown, blue, or green-is determined by the amount and distribution of a pigment, MELANIN. Brown eyes have more melanin than blue eyes, so they are less sensitive to bright light.

4. SCLERA?

Your SCLERA is the tough white outer covering of your eye.

5. CONJUNCTIVA?

Your conjunctiva is a flexible, clear mucous membrane that covers the inside of your lids, and the outside of your sclera. Hair-thin arteries and veins run through it. If these blood vessels become inflamed, you have CONJUNCTIVITIS.
Your conjunctiva keeps your eye moist. It is studded with GOBLET CELLS, which produce mucous, an important part of your tears.

6. TEAR FILM?

Tears protect, clean and lubricate your eye. All normal tears have three layers: an outer layer of OIL, which prevents your tears from evaporating; an inner layer of MUCOUS, which keeps your tears attached to your eye; and a middle watery layer, which is complex and fascinating. This middle tear layer is similar to your blood, but without cells. It contains most of the substances found in blood, including salts, sugar, hormones, and antibodies that protect against invading organisms. It is especially high in Vitamin C.
Most of your middle tear layer is produced by your LACRIMAL GLANDS, bean-sized glands which lie just above each upper eyelid. The oil in your tears is made by little bottle-shaped glands, called MEIBOMIANGLANDS, which are found along the margins of all four eye lids..

7. AQUEOUS?

AQUEOUS circulates steadily through the ANTERIOR CHAMBER of your eye, night and day, bringing oxygen and sugar to your cornea and lens, and washing away wastes. This clear fluid is produced by your CILIARY BODY, which runs around the eye just behind the iris, near the ciliary muscle.
Aqueous drains out of your eye through the TRABECULAR MESHWORK, into SCHLEMM’S CANAL and then into the veins around your eye.
Normally, inflow equals outflow, so the pressure inside your eye is maintained between 8 and 22 millimeters of mercury. However, if your eye has a drain that is not working properly, the pressure inside your eye will rise. This high pressure will eventually damage your OPTIC NERVE, and you will start to go blind. This is “GLAUCOMA”.

8. VITREOUS?

The VITREOUS is the transparent jelly that fills the POSTERIOR CHAMBER of your eye. The vitreous is firm and clear when you are young. As you get older, it gets less firm, and more watery. It eventually collapses on itself, like a tent folding, or a balloon that has lost its air. Because this process detaches the vitreous from the RETINA, it is called a VITREOUS DETACHMENT. After your vitreous detaches you will notice strands called FLOATERS.

9. RETINA?

Your RETINA is an extension of your brain. It is a light-sensitive nerve tissue that lines the inside of your eye, like the film inside a camera. It has 12 layers.
When light is focused by the cornea and lens onto your retina, millions of tiny PHOTORECEPTORS give off electrical signals. These signals feed into 1.2 million OPTIC NERVE fibers. The optic nerve acts as a cable, carrying this information up to the VISUAL CORTEX, which is in the OCCIPITAL LOBE, in the back of your brain.
Most human blindness is caused by diseases of the retina: in infants, amblyopia, or lazy eye; in adults, diabetic retinopathy; in the elderly, macular degeneration.

10. RODS AND CONES?

Photoreceptors come in two different types, 120 million RODS, and 6 ½ million CONES.
Your rods, mainly located in the periphery of your retina, are super sensitive. They operate only when the light is dim. They can only detect large forms and shapes, in black, white, and shades of gray.
Cones, located mainly in the center of the retina, operate in bright light. The ones in your MACULA enable your eye to see details. There are three different types of cones: red, green, and blue. This allows you to have color vision.

11. RETINAL PIGMENT EPITHELIUM?

The retina sits on top of a layer of darkly pigmented cells called the RETINAL PIGMENT EPITHELIUM, or RPE. The RPE is packed with melanin, which absorbs scattered and reflected light. The RPE acts as a nurse for the retina, trimming off the aging tops of the photoreceptors every day, and bringing the retina the chemicals it needs for vision.

12. MACULA?

The MACULA is a tiny area right in the center of your retina. Although it is only the size of the head of a pin, it is responsible for all of your detailed sight. 90% of the signals that go to your occipital lobe come from your macula.
If your macula is damaged, you will no longer be able to read, or drive, or recognize faces. You will, in fact, be legally blind, although you will still retain your peripheral vision.
The little indentation in the very center of your macula is called your FOVEA. The fovea provides your most detailed sight. There are no blood vessels, and no rods, in the fovea.

13. THE BLOOD SUPPLY OF YOUR RETINA?

The inner third of your retina is nourished by your CENTRAL RETINAL ARTERY (CRA) and CENTRALRETINAL VEIN (CRV). These enter and leave your eye at the OPTIC DISK, the place where the optic nerve originates. They fork, like the branches of a tree, as they run out to the periphery of the retina.
The outer two thirds of your retina is nourished by your CHOROID, a thick layer of blood vessels sandwiched between your RPE and your sclera.
The retina and the conjunctiva are the only parts of your body where your doctor can see your blood vessels. When a doctor looks at these blood vessels, he gets a lot of information about the health of your body.

14. THE EYE MUSCLE SYSTEM?

There are six tiny muscles connected to each of your eyes. They are the size of thick rubber bands. They pull the eye up and down, left and right, and clockwise and counterclockwise.
These muscles are commanded and coordinated by three nerves, located in the brain stem.

EYE DANGER SIGNS

If you experience any of the following eye symptoms, you should call your doctors office immediately. 

Eye Danger Symptoms

·       Flashing lights/floating black spots, veils or curtains. These can be symptoms of a retinal tear or a retinal detachment, which needs immediate attention.

·       Pain/ extreme redness /deceased vision/ light sensitivity. These may have several causes, including infections of the cornea, corneal abrasions, inflammation in the eye and acute glaucoma

·       Distorted vision/wavy lines. These can be caused by retina problems, including “wet” macular degeneration.

·       In a child under 6 years of age, one eye suddenly turning out, in or up. After an eye turns, it may become “lazy” and will lose vision.

·       In a child, a white pupil

Do You Have Dry Eye Syndrome?

If your eyes burn and sting, if you have a foreign body sensation (like grit), if your eyes are sensitive to light, or if your vision is intermittently blurred, you could have dry eye syndrome.

To diagnosis dry eye, your ophthalmologist will examine your eyes with a slit lamp using a special stain. He or she may also use a filter paper test called a "Schirmer test".

Dry eyes are common in the elderly. Dry eyes can result either from a decrease in tear production or from a change in the amount of fluid in tears, which makes the tears excessively salty. Women are affected more often than men. Dry eyes get worse when the air humidity is low, for example, in winter, and in the summer, with air conditioning.

Dry eyes can be caused by some medications, such as antidepressants, antihistamines, decongestants, acne medication, beta blockers (which are used for rapid pulse and high blood pressure) and diuretics, Chemotherapy and radiation can also cause dry eye and so can certain diseases like arthritis, high or low thyroid and acne rosacea. Dry eye often develops in patients who have had Lasik surgery or cosmetic lid surgery.

The treatment for dry eye syndrome depends on the severity. For mild dry eye, your doctor will recommend an artificial tear, such as Refresh or Tears Naturalle, for you to use several times a day.

For moderate dry eye, when you must use drops more than four times a day, you should switch to preservative free tears (eg. Refresh PF), and use them every few hours. You should also add a lubricating ointment or gel (eg. Genteal gel) at night. A humidifier in your bedroom at night is essential, especially in the winter.

For severe dry eye, your doctor may suggest a mild anti-inflammatory drop, such as FML or Acular. Punctal occlusion (silicon inserts placed in the tear drain) can also be considered.

NB: Patients with dry eyes should not have Lasik or cosmetic lid surgery, or wear soft contact lenses.

Parents Beware: That Laser Pointer Could Blind Your Chid

Laser pointers are not toys! The number of eye injuries in children from lasers is rising because too many parents are unaware that a hand-held laser pointer can cause a laser burn injury to their child’s macula if the child looks directly into the beam, especially if it is a high-power laser bought over the internet.
This burn can cause legal blindness and the inability to read or recognize faces.

Laser pointers cannot be sold in the US unless their energy output is 5 milliwatts or lower, but lasers purchased abroad can have energy outputs of up to 1,000 milliwatts. These lasers are extremely dangerous to eyes, and it is illegal to own them. Pointing any laser at an aircraft is a serious federal crime that is punishable by fines and in some cases imprisonment.


Always follow these rules:

• Do not buy a laser pointer that emits more than 5 milliwatts
• Never shine a laser pointer at a human eye
• Do not buy a laser pointer for your child, or allow them to play with your pointer

Migraine and Their Consequences

A MIGRAINE HEADACHE is an intense, throbbing or boring pain in one part of the head that is usually accompanied by nausea or vomiting, sensitivity to light, sound or smell, and fatigue. Migraines usually last between four and seventy two hours.

About one third of migraine patients have so-called CLASSIC MIGRAINE, where their headache is preceded by an AURA, i.e. some type of sensory warning symptom, such as flickering or flashing lights similar to static on a television, often taking the shape of zig-zag lines in an arc like the crown of the Statue of Liberty ("fortification scotoma"), blind spots, or numbness or tingling in an arm or a leg.

    

Auras always come on GRADUALLY over five to fifteen minutes, last between five minutes to an hour, and then fade away SLOWLY.

    

Roughly one percent of patients have ACEPHALGIC OR SILENT MIGRAINES, i. e. they experience auras but they do not have any headache.

   

Recent studies have shown that people who suffer from CLASSIC MIGRAINE, i.e. migraine with an aura, are at increased risk for heart attacks and strokes. These people should reduce their risk by exercising, eating a healthy diet (low in saturated fats and refined sugars, and high in fruits and vegetables), maintaining a healthy weight, and not smoking. Women who have classic migraine should not take contraceptive pills or supplemental estrogen or progesterone.