Glaucoma

 Glaucoma

Glaucoma is group of disorders characterized by;

1. Abnormally high intra-ocular pressure (IOP); IOP more than normal above 25mmHg.

2. Optic nerve dystrophy

3. Peripheral visual field loss

Pathophysiology

Intraocular pressure is function of production of liquid aqueous humor by ciliary processes of eye and its drainage through trabecular meshwork.

Aqueous humour is produced by ciliary body and flows into posterior chamber behind iris.

Exist by flowing between iris and lens around pupil edge and into anterior chamber.

Trabecular meshwork filters the aqueous humor into schlemm's canal.

Where fluid picked up by episcleral vessel and into systemic circulation.

Primary open angle glaucoma caused by degenerative changes in trabecular meshwork that inhibit outflow of aqueous humor causing increased IOP and damage to optic nerve.

Close angle glaucoma which block the outflow of aqueous humor from posterior chamber.

Classification of Glaucoma

1. Congenital glaucoma

2. Acquired glaucoma

1. Congenital glaucoma 

Defect in angle of anterior chamber obstruct outflow of aqueous humor, causing damage to optic nerve.

a. True congenital glaucoma

 IOP raised during intrauterine life.

b. Infantile glaucoma

c. Juvenile glaucoma

2. Acquired glaucoma

a. Primary open angle glaucoma (POAG) 

Primary open angle glaucoma/ glucoma simplex/ chronic open angle glaucoma.

Result from overproduction or obstruction of outflow of aqueous humor through trabecular meshwork or schlemm's canal, causing increased IOP and damage to optic nerve.

Primary open-angle glaucoma occurs when drainage channels are open, but fluid do not drain properly. 

b. Primary angle closure glaucoma/ narrow angle glaucoma/ pupil block glaucoma/ acute congestive glaucoma 

Obstruction cause narrow angle between bulging anterior iris and posterior corneal where drainage angle of eye is located.

Thickened iris/ Bulging iris; bulging iris press on trabecular network closing angle.

b. Secondary glaucoma

Secondary glaucoma result of another disease problem such as;

Uveitis (inflammation in middle layer of eye; uvea).

Intraocular hemorrhage 

Clinical Manifestations

1. Pain and redness in eye

2. Increase IOP 40-70 mmHg

3. Vision become blurred

4. Optic disk hyperemia (increase blood flow)

5. Halos (seen around light)

6. Headache

7. Nausea/vomiting

8. Cornea cloudy

9. Decreased visual acuity

10. Photophobia

11. Peripheral vision loss

Diagnostic Evaluation

1. Tonometry

To measure Intra-ocular pressure (IOP).

2. Ophthalmoscopy

To identify open angle glaucoma and close angle glaucoma.

3. Gonioscopy

Determine angle of eye's anterior chamber.

4. Perimetry or visual field test

To detect loss of peripheral vision.

5. Slit lamp examination

Eye's anterior structure; iris, cornea, lens.

6. Fundus photography

Monitor optic disk for 

Fundus photography captures the images of the retina, optic nerve head (blind spot/ optic disc) macula, retinal blood vessels, choroid, and the vitreous.

Medical Management 

1. Beta adrenergic blockers

To decrease aqueous humor production.

Timolol

Betaxolol

2. Cholinergic

To reduce IOP by facilitating outflow of aqueous humor.

Pilocarpine

Carbacol

3. Carbonic anhydrase inhibitors

Decrease formation and secretion of aqueous humor.

Dorzolamide

Methazolamide 

Acetazolamide 

4. Adrenergic agonists

Epinephrine; to reduce IOP by improving aqueous humor outflow.

5.  Prostaglandin analogs

Reduce IOP by increasing uveoscleral outflow.

Latanoprost

6. Osmotic agent

Intravenous mannitol (20%) or oral glycerine (50%) to reduce IOP by creating osmotic pressure gradient between blood and intraocular fluid.

Surgical Management

1. Argon laser Trabeculoplasty

To treat open angle glaucoma.

Thermal argon laser burns applied to inner surface of trabecular meshwork to open intra-trabecular spaces and widen canal of schlemm's.

Increase the outflow of aqueous humour and decrease IOP.

2. Laser Iridotomy

Opening is made by laser beam in iris to eliminate pupillary block. It relieves pressure and presence of vision by promoting outflow of aqueous humor.

3. Cyclocryotherapy

Application of freezing probe to sclera over ciliary body, destroy some ciliary processes, result in reduction of amount of aqueous humor produced.

4. Cyclodialysis

Small incision in scera, spatula type instrument is passed into anterior chamber, creating opening in angle.

5. Filtering procedures

Create opening or fistula in trabecular meshwork to drain aqueous humor from anterior chamber to subconjunctival space into bleb, by passing usual drainage structure allow aqueous humor to flow.

6. Trabeculotomy

Incision made into sclera, section of sclera remove to produce opening for aqueous humor outflow under conjunctiva, creating filtering bleb.

7. Sclerectomy

Incision made in sclera.

8. Drainage implants and shunts

Drainage implants and shunts are open tubes implanted in anterior chamber through sclerectomy to shunt aqueous humor in conjunctival space.