King Saud University College of Science Department of Biochemistry Disclaimer lThe texts, tables,...

King Saud University

College of Science

Department of BiochemistryDisclaimer

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Chapter 20Ocular Fluid

Professor A. S. Alhomida

Chapter 20Ocular Fluid

Professor A. S. Alhomida

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Anatomy of the Eye

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Anatomy of the Eye

Cornea• Protection

• Focusing

Aqueous Humor• Shape

• Nutrition

Iris• Light control• Focusing

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Lens• Focusing• Accommodation

Vitreous Humor• Shape

Retina• Rods: black and white, night vision• Cones: color, day vision• Fovea: sharpest vision (concentration of cones)

Anatomy of the Eye, Cont’d

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Optic Nerve• Nerve signals to brain• Optic Disk: blind spot

Eye Muscles• Eye movement• Convergence


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Sclera• Outer walls, hard, like a light-tight box

Pupil• Camera aperture

Eyelid• Lens cover


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Tear Production System

1. The eye's tears are composed of three layers: • Outermost oily layer is produced by the meibomian

glands which line the edge of the eyelids• Watery portion of the tear film is produced by the

lacrimal gland • The mucous layer comes from microscopic goblet cells in

the conjunctiva

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Tear Production System

2. Since the surface of the cornea is exposed during walking hours, there is constant evaporation of fluid on it is surface, resulting in concentration of tear

3. Then tear becomes hyertonic (25 mosmol) that inducing rapidly the flow of tear to be istotonic

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4. Diffusible nitrogous material and eletrolytes are present in tear in concentration similar to these of plasma

5. Function of protein is to lower the surface tension, permit wetting of the epithelial surfaces

6. Lysozyme is to protect the cornea from the infection

Tear Production System, Cont’d

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Meibomian Gland

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Lacrimal Gland

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Conjunctiva

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1. Constant Tears • They formed in the accessory lacrimal glands are

continuously produced to lubricate the eye at all times. These tears contain natural antibiotics to fight infection

2. Reflex Tears • They are only produced in response to irritation, injury, or

emotion to help rinse the surface of the eye. These tears are generated in the large lacrimal gland.

3. Between Constant and Reflex Tears• To a satisfactory blink reflex, helps ensure that the eyes

will be comfortable, well lubricated and well protected

Types of Tears

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Tear Composition

Tear ProteinsTear Proteins1. Lysozyme 300 omolar (4.6 mg/mL)

2. Lipocalin 74-85 molar (1.5 mg/mL)

3. Lactoferrin 24 molar (2 mg/mL)

4. Lipophilin 3 molar (45-100 g/mL)

5. IgA (5.9 g/mL)

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Tear Composition, Cont’d

Functions of Tear ProteinsFunctions of Tear Proteins• Lysozyme

• Antibacterial action by cleaving cell wall constituents

• Lipocalin• Scavenges lipids from the cornea surface, role in

tear film stability, antifungal activity by binding to fungal siderophores, endonuclease activity

• Lactoferrin• Antimicrobial action by competing for iron with

microbes

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Tear Composition

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Aqueous Humor

1. Clear liquid lies between the cornea and the lens

2. Produced by capillaries of ciliary bodies, exits via Canal of Schlemm, replaced every 90 min

3. Its rate formation is 2-3 L/min

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Aqueous Humor, Cont’d

4. Its secretion begins with active transport of Na+ into the spaces between the epithelial cells

5. Na+ pulls Cl- and HCO3- along with them to

maintain the electrical neutrality

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6. These ions together cause osmosis of the water from the supplying tissue into the same epithelial intracellular spaces, and resulting solution washes from the spaces onto the surfaces of the ciliary processes

7. Several nutrients are transported across the epithelial by active and passive transport

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8. Creates pressure, maintains shape, nutrients and wastes

9. Has the benefit of being fairly homogenous and, as a result, the optical properties are easily measured

10. The space that it inhabits is called the anterior chamber

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Eye Compartments

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Aqueous Humor Composition

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Aqueous Humor Composition, Cont’d

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Aqueous Humor Composition, Cont’d

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Aqueous Humor Outflow

1. Aqueous humor is produced by the ciliary body epithelium in the posterior chamber and flows into the anterior chamber

2. The aqueous exits the eye either through• Conventional pathway from trabecular meshwork into

Schlemm’s canal and aqueous veins or

3. Unconventional pathway• From ciliary muscle and other downstream tissues

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Aqueous Humor Outflow

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1. Gelatinous clear liquid lies between the lens and the retina

2. Maintains shape of eye

3. Substances can diffuse slowly

Vitreous Humor, Cont’d

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4. The space that it fills is called the vitreous body or posterior segment

5. Liquefaction of vitreous humor• One of the most common contributing factors

for retinal detachment with ageing

Vitreous Humor, Cont’d

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Vitreous Humor

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Composition of Vitreous Humor

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Composition of Vitreous Humor, Cont’d

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Retina Structure

1. Light Sensitive Layer• Made of photo-receptors: rods (120 millions) and cones

(7 millions) which absorb the light

2. Plexiform Layer• Nerve cells that process the signals generated by rods

and cones and relay them to the optical nerve

3. Choroid• Carries mayor blood vessels to nourish the retina and

absorb the light so that it will not be reflected back (dark pupil)

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Photoreceptors

1. The transduction (conversion) of light into nerve signals that the brain can understand takes placed in specialized cells in the retina called photoreceptors

2. Each photoreceptor has four parts: • Outer segment

• Inner segment

• Cell body

• Synaptic ending

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Photoreceptors, Cont’d

3. The outer segment consists of a stack of discs embedded in the cell membrane

4. The photoreceptor's light-sensitive pigments are located on these discs

5. It is the shape of the outer segment that distinguishes the two main types of photoreceptors: • Rods have a long, cylindrical, outer segment with many discs• Cones have a short, tapering outer segment with relatively few discs

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6. Because they have more discs, rods are over 1 000 times more light-sensitive than cones

7. That is why, at night and in other low-light conditions, your sense of vision comes from the rods alone. And conversely, in broad daylight, your cones are more active

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8. Retina has dual capabilities: • It can work in dim light, thanks to the rods• It can work in bright light, thanks to the cones

9. One of the other differences between the two types of photoreceptors is that only the cones are sensitive to colors

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Some of Eye Diseases

1. Dry Eye Syndrome

2. Glaucoma

3. Cataract

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Dry Eye Syndrome

1. It is one of the most common problems treated by eye physicians

2. It is usually caused by a problem with the quality of the tear film that lubricates the eyes

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Causes of Dry Eye Syndrome1. Normal Aging Process

• As we grow older, our bodies produce less oil – 60% less at age 65 then at age 18. This is more pronounced in women, who tend to have drier skin then men

2. Contact Lens Wearers • Because the contacts absorb the tear film, causing proteins

to form on the surface of the lens

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Causes of Dry Eye Syndrome3. Certain Diseases

• Thyroid conditions, and vitamin A deficiency• Diseases such as Parkinson’s and Sjogren’s

4. Other Factors• Such as hot, dry or windy climates, high altitudes, air-

conditioning, cigarette smoke and reading or working on a computer

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Symptoms of Dry Eye Syndrome

1. Itching

2. Burning

3. Irritation

4. Redness

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Symptoms of Dry Eye Syndrome, Cont’d

5. Blurred vision that improves with blinking

6. Excessive tearing

7. Increased discomfort after periods of reading, watching TV, or working on a computer

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Treatment of Dry Eye Syndrome

1. Eye Drops• Eye drops and artificial tears often offer relief for the

symptoms of Dry Eye Syndrome. The artificial lubricants come in different thicknesses and are recommended by your eye doctor based on the severity of symptoms and findings

2. Punctal Plugs• Through canalicular occlusion (the medical term that

describes the closure of your tear drainage ducts) there’s a simple, non-surgical procedure to provide long-term relief of Dry Eye Syndrome and congestion of the nose, throat and sinus that often accompanies it

• Small, non-dissolvable silicone plugs are inserted in the tear drainage ducts

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Treatment of Dry Eye Syndrome, Cont’d

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Treatment of Dry Eye Syndrome, Cont’d

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Glaucoma Glaucoma ((Sneak Thief of Sight)

1. It is a leading cause of blindness in the world, especially for older people. But loss of sight from glaucoma is preventable with early diagnosis and treatment

2. It is a disease of the optic nerve that carries the images we see to the brain

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Glaucoma, Cont’d Glaucoma, Cont’d

3. Many people know that glaucoma has something to do with pressure inside the eye. The higher the pressure inside the eye, the greater the chance of damage to the optic nerve.

4. Glaucoma can damage nerve fibers, causing blind spots to develop

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5. Gradual loss of peripheral vision is the main sign of glaucoma

6. Often people don’t notice these blind areas until much optic nerve damage has already occurred


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7. If the entire nerve is destroyed, blindness results

8. Early detection and treatment by the eye doctor are the keys to preventing optic nerve damage and blindness from glaucoma


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Glaucoma, Cont’d Glaucoma, Cont’d The optic nerve is the

nerve that takes all of the visual information from the retina to the brain

It can sometimes become swollen in diabetics

The cause of this optic neuropathy is unclear but it may also be due to insufficient blood supply

This is an uncommon problem in diabetics

Healthy optic nerve

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Risk Factors for GlaucomaRisk Factors for Glaucoma

1. Age• In a major study, less than 1% of people age 60 to 64 had

chronic open-angle glaucoma• Among people 10 years older, the prevalence more than

doubled to 1.3%, and among those 80 to 84, it more than doubled again to 3%

2. Family History• Like so many diseases, glaucoma tends to run in

families; different genes, however, are involved in different families

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Risk Factors for Glaucoma, Cont’dRisk Factors for Glaucoma, Cont’d

3. Ethnic Background• Chronic glaucoma is four times more common in

African-Americans than in whites• It also develops earlier: African-American risk starts to

increase after age 45, white risk at age 60• Among whites, groups at higher risk include people with

Scandinavian, Irish and Russian backgrounds

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4. Certain Medical Disorders• Diabetes, extreme nearsightedness and previous eye

surgery are risk factors for chronic open-angle glaucoma• A condition that requires the use of oral or inhaled

steroids, particularly high doses for prolonged periods, that can increase your risk as well

• People who suffering from hypothyroidism, leukemia and arthritis

Risk Factors for Glaucoma, Cont’dRisk Factors for Glaucoma, Cont’d

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Type of Glaucoma

1. Primary Open-angle Glaucoma• It affects about 4 out of 5 adult glaucoma patients• The damage to the optic nerve happens so slowly

and gradually that the affected person is usually not aware of any loss of peripheral vision

• Since there are no symptoms or pain, early detection and treatment is the best way to prevent loss of vision

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Primary Open-angle Glaucoma

(A) Normal

(B) Abnormal

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The angle between the iris and the cornea is normal, but the drainage holes get

clogged from the inside aqueous outflow by these pathways is diminished

Clogged Drainage holes

Normal Drainage Picture

The Trabecular meshwork – is the eye’s drain

The Ciliary Body – is the eye’s “faucet” or “tap” where fluid is made

When this drainage of the fluid gets blocked, excess pressure is formed leading to Glaucoma

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2. Acute Closed-angle Glaucoma • It occurs when there is a sudden blockage of the

drainage channels in the eye• As a result, eye pressure builds up rapidly causing

blurred vision, severe pain, rainbow halos around lights, sometimes even nausea and vomiting

• It is an emergency situation, since the rapid, large increase in intraocular pressure can cause permanent damage to the optic nerve in only one day

Types of Glaucoma, Cont’d

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Acute Closed-angle Glaucoma

Iris is abnormally positioned so as to block aqueous outflow through the anterior chamber (iridocorneal) angle

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Blocked Drainage holes

The angle between iris and the cornea narrows or closes. If fluid can’t flow easily through the opening in the pupil, the iris pushes forward and blocks the drainage holes

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Glaucoma Symptoms

1. Primary Open-angle Glaucoma• No symptoms at first

2. Acute Closed-angle Glaucoma• Include severe pain, nausea, vomiting, blurred vision,

and seeing a rainbow halo around lights

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Tunnel vision

Red eye, pain in the eye,

Halo around lights

Blurred vision

Vision loss

SYMPTOMS

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Glaucoma Treatment

1. Drug Therapy• Glaucoma medications lower intraocular pressure by

helping fluid leave the eye or by reducing the amount of fluid produced in the eye

• Prostaglandin analogs -lockers: Timoptic, Betoptic, Betagan, Carteolol,

Optipranolol -agonists

• Carbonic anhydrase inhibitors

• Cholinergic agents

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Glaucoma Treatment, Cont’d

2. Operative Surgery• When operative surgery is needed to control

glaucoma, and creating a new drainage channel for the aqueous fluid to leave the eye

• Surgery is recommended only if the ophthalmologist feels that it is safer to operate than to allow optic nerve damage to continue

3. Laser Surgery • It creates a hole in the iris (iridotomy) to improve the

flow of aqueous fluid to the drain

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Eye drops Pills

Laser surgery Eye operations

Or Combination method

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Medical Treatment Drugs increase

conventional outflow


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Medical Treatment Drugs reduce

production of fluid in the eye


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Laser

Surgical Treatment Making a tiny

opening in the iris with a laser allows fluid to drain freely

Glaucoma Treatment, Cont’dGlaucoma Treatment, Cont’d

Opening Iris

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How often should I get my eye examined?

If you have no risk factors for glaucoma*

If you have risk factor for glaucoma*

Under 45 years old: Every 4 years Every 2 years

45 years and older: Every 2 years Every year

If you are diagnosed with glaucoma, your doctor will set a treatment cycle based upon your medical needs.

* Risk factors for glaucoma:

Family history, myopia (nearsightedness), previous eye injury, low blood pressure, African descent, diabetes, long exposure to cortisone

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Cataract

1. The crystalline lens of the eye focuses light rays so that images are clear and distinct when they strike the retina in the back of the eye

2. When the lens opacifies (gets cloudy), usually due to aging, light rays become obstructed and vision becomes dim and hazy

3. When this occurs, it is called a cataract4. Heredity, disease, injury, sun exposure, and

medications can also play a role in the development of cataracts

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Cataract, Cont’d

Normal lens

Lens clouded and discolored by cataract

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Cataract Symptoms

1. Dimming and blurring of vision

2. Halos around lights at night3. Increased glare, especially at

night

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Cataract Symptoms

4. Double vision in single eye5. Fading or yellowing of colors6. Frequent changes or cleaning

of glasses

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Types of Cataracts

1. Nuclear Cataract• It is most commonly seen as it forms. This cataract forms in the

nucleus, the center of the lens, and is due to natural aging changes

2. Cortical Cataract• It forms in the lens cortex, gradually extends its spokes from the

outside of the lens to the center. Many diabetics develop cortical cataracts

3. Subcapsular Cataract• It begins at the back of the lens. People with diabetes, high

farsightedness, retinitis pigmentosa or those taking high doses of steroids may develop a subcapsular cataract

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Risk Factors In Adults

1. Exposure to sunlight (UV light)2. Smoking3. Diabetes4. Trauma (blunt or penetrating)5. Family history of cataracts

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Risk Factors In Adults

6. Corticosteroid therapy7. Radiation exposure8. Electrical injury 9. Myotonic dystrophy10. Free radicals

• Diet high in antioxidants, such as beta-carotene (vitamin A), selenium and vitamins C and E, may forestall cataract development

11. Uveitis- Ocular inflammation

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Cataract Treatment

1. Clear corneal cataract surgery

2. Micro incision (3 mm or <) is made into the perimeter of the cornea on the side of the eye which is closest to the temple

3. Two things happen during cataract surgery

• The clouded lens is removed, and

• A clear artificial lens is implanted

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THE ENDTHE END

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