Anatomy And Physiology Of Glaucoma Notes

Applied Physiology

1. Glaucoma:

• Glaucoma is a group of diseases characterized by increased intraocular pressure which causes damage of the optic nerve resulting in blindness.
• In glaucoma, the drainage of aqueous humor through trabeculae is blocked resulting in increased intraocular pressure. When the intraocular pressure rises above 60 mm Hg the optic nerve fibers at the optic disk are compressed. Initially, it decreases the visual field (loss of peripheral vision) which eventually leads to total blindness.
• However, with early treatment, often the eyes may be protected against serious vision loss. Untreated glaucoma leads to permanent damage of the optic nerve and results in blindness. In old age, glaucoma occurs due to the obstruction of trabeculae by fibrous structures.

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Types of Glaucoma:

Elevation of intraocular pressure causing glaucoma can occur at any stage of life. Congenital glaucoma develops in babies born with increased intraocular pressure. Glaucoma due to increased ocular pressure after birth is called infantile glaucoma. When it occurs in childhood it is known as juvenile glaucoma. Generally, glaucoma is divided into two types:

1. Primary open-angle glaucoma
2. Primary angle closure glaucoma

1. Primary open-angle glaucoma (POAG):

• POAG is the most common type of glaucoma and it accounts for about 80% of all cases of glaucoma. The term open-angle refers to a drainage system which is responsible for draining the aqueous humor from the eye.
• Actually, in POAG there is no visible obstruction in the drainage system. Still, the intraocular pressure increases causing damage to the optic nerve. The exact cause of POAG is not known yet.
• It is suggested that a microscopic (minute) blockage in the drainage system beyond the limbus may obstruct the flow of aqueous humor. It causes a gradual increase in intraocular pressure.

2. Primary angle-closure glaucoma (PACG):

• PACG is characterized by visible obstruction of the drainage system for aqueous humor. The iris is pushed against the cornea preventing the drainage of aqueous humor. The intraocular pressure rises over a period of a few hours.
• Causes of Glaucoma: The major cause of glaucoma is the blockage in the drainage system of aqueous humor in trabeculae resulting in increased intraocular pressure. Glaucoma also develops secondary to other disorders which affect the eyes. Common causes of secondary glaucoma are diabetes, inflammation or injury to the eye, and excess use of drugs such as corticosteroids.

Symptoms of Glaucoma:

• Primary open-angle glaucoma is a silent chronic disease without any early symptoms. Symptoms that develop in later stages include heaviness around the eyeball, headache, and rapid reduction in visual acuity and visual field.
• Early symptoms of angle closure glaucoma are severe pain in the eye or eyebrow, headache, nausea, blurred vision, and rainbow halo (colored rings) around bulb light. Immediate care should be taken if two or more of these symptoms appear together.

Treatment for Glaucoma: Treatment does not cure the disease but can prevent further damage of the optic nerve. The treatment is aimed at lowering intraocular pressure. It is achieved by using eye drops or medicines alone or in combination with laser treatment. If intraocular pressure cannot be controlled by these methods, surgery is required.

2. Cataract:

• A cataract is an opacity or cloudiness in the natural lens of the eye. It is the major cause of blindness worldwide. When the lens becomes cloudy, light rays cannot pass through it easily, and vision is blurred. A cataract develops in old age after 55-60 years.
• The lens is situated within the sealed capsule. The old cells die and accumulate within the capsule. Over the years, the accumulation of cells is associated with accumulation of fluid and denaturation of the proteins in the lens fibers causing cloudiness of the lens and blurred image.

Causes of Cataract: In addition to age, cataract also develops due to many causes:

• Eye injuries
• Previous eye surgery
• Diseases such as diabetes, Wilson’s disease, and hypocalcemia
• Long-term use of drugs such as steroids, diuretics, and tranquilizers
• Long-term unprotected exposure to sunlight
• Alcoholism
• Family history
• A diet containing a large quantity of salt.

Symptoms Of Cataract: Common symptoms of cataract are:

• Glare
• Painless blurred vision
• Poor night vision
• Diplopia in the affected eye
• Need for a bright light while reading
• Fading of colors.

Treatment for Cataracts: Surgery is the only treatment for cataracts. During surgery, the cloudy lens is removed from the eye through a surgical incision. The natural lens is replaced with a permanent, clear and plastic intraocular lens (IOL) implant. Different procedures were followed to remove the cloudy lens. The common methods are:

1. Extract and sugar extraction: This is rather an old technique. A 12 mm incision is made in the eye under an operating microscope to remove the lens as a whole. The posterior capsule of the lens is left in place to hold the IOL implant. Multiple sutures are required to seal the eye after surgery. The sutures must be perfect; otherwise, astigmatism may develop.

2. Phacoemulsification:

• This is the current technique. Phacoemulsification (phaco) is the procedure in which ultrasonic vibrations are used to break the cataract into smaller fragments. It is done through a small (3 mm) incision. An ultrasound (or laser) probe is used to break the lens material without damaging the capsule. The lens fragments are aspira¬ted out of the eye.
• A foldable intraocular lens (IOL) is then introduced through the incision. Once inside the eye, the lens unfolds to take position inside the capsule. No sutures are needed, as the incision is self-sealing.