Eye: Glaucoma

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GLAUCOMA
Glaucoma is a group of ocular conditions characterized by increased IOP, optic nerve atrophy & peripheral visual field loss.
The optic nerve damage is related to the increased IOP caused by congestion of aqueous humor in the eye.

Aqueous Humor & Intraocular Pressure
Aqueous humor flows between the iris and the lens, nourishing the cornea and lens.
Most (90%) of the fluid then flows out of the anterior chamber, draining through the spongy trabecular meshwork into the canal of Schlemm and the episcleral veins.
About 10% of the aqueous fluid drains out through the ciliary body into the suprachoroidal space and then drains into the venous circulation of the ciliary body, choroid, and sclera.
Unimpeded outflow of aqueous fluid depends on an intact drainage system and an open angle (about 45 degrees) between the iris and the cornea.  
A narrower angle places the iris closer to the trabecular meshwork, diminishing the  angle.
The amount of aqueous humor produced tends to decrease with age, in systemic diseases such as diabetes, and in ocular inflammatory conditions.
IOP is determined by the rate of aqueous production, the resistance encountered by the aqueous humor as it flows out of the passages, and the venous pressure of the episcleral veins that drain into the anterior ciliary vein.
When aqueous fluid production and drainage are in balance, the IOP is between 10 and 21 mm Hg.
When aqueous fluid is inhibited from flowing out, pressure builds up within the eye.  
Fluctuations in IOP occur with time of day, exertion, diet, and medications. It tends to increase with blinking, tight lid squeezing, and upward gazing.
Systemic conditions such as hypertension and intraocular conditions such as uveitis and retinal detachment have been associated with elevated IOP.
Exposure to cold weather, alcohol, a fat-free diet, heroin, and marijuana have been found to lower IOP.
Etiology:
Degenarative changer in trabecular meshwork

Risk factors for Glaucoma
  • Family history of glaucoma
  • African American race
  • Older age
  • Diabetes
  • Cardiovascular disease
  • Migraine syndromes
  • Nearsightedness (myopia)
  • Eye trauma
  • Prolonged use of topical or systemic corticosteroids


Pathophysiology
There are two accepted theories regarding how increased IOP damages the optic nerve in glaucoma.
 The direct mechanical theory suggests that high IOP damages the retinal layer as it passes through the optic nerve head.
The indirect ischemic theory suggests that high IOP compresses the microcirculation in the optic nerve head, resulting in cell injury and death.
Some glaucomas appear as exclusively mechanical, and some are exclusively types. Typically, most cases are a combination of both.

Stages
Initiating events: precipitating factors include illness, emotional stress, congenital narrow angles, long-term use of corticosteroids, and mydriatics
Structural alterations in the aqueous outflow system: tissue and cellular changes caused by factors that affect aqueous humor dynamics lead to structural alterations   

Functional alterations: conditions such as increased IOP or impaired blood functional changes
Optic nerve damage: atrophy of the optic nerve is characterized by loss of nerve fibres and blood supply.
Visual loss: progressive loss of vision is characterized by visual field defects.


Classification of glaucoma
  1. Open-Angle Glaucoma
Usually bilateral, but one eye may be more severely affected than the other.
In open-angle glaucoma, the anterior chamber angle is open and appears normal.
  1. Chronic open-angle glaucoma (COAG)-Optic nerve damage, visual field defects, IOP
>21 mm Hg. May have fluctuating IOPs. Usually no symptoms but possible ocular pain, headache, and halos.
  1. Normal tension glaucoma-IOP < 21 mm Hg. Optic nerve damage, visual field defects.
  2. Ocular hypertension- Elevated IOP. Possible ocular pain or headache.
  3. Angle-Closure (Pupillmy Block) Glaucomas
Obstruction in aqueous humor outflow due to the complete or partial closure of the angle from the forward shift of the peripheral iris to the trabecula. The obstruction results in an increased IOP.
  1. Acute angle-closure glaucoma (AACG)- Rapidly progressive visual impairment, periocular pain, conjunctival hyperaemia, and congestion.
Pain may be associated with nausea, vomiting, bradycardia, and profuse sweating.
Reduced central visual acuity, severely elevated IOP, corneal edema.
Pupil is vertically oval, fixed in a semi-dilated position, and unreactive to light and accommodation.
  1. Subacute angle-closure glaucoma- Transient blurring of vision, halos around lights; temporal headaches and/or ocular pain; pupil may be semi-dilated.
  2. Chronic angle-closure glaucoma- Progression of glaucomatous cupping and significant visual field loss;
IOP may be normal or elevated; ocular pain and headache.

Clinical Manifestations
  • Glaucoma is often called the silent thief of sight because most patients are unaware that they have the disease until they have experienced visual changes and vision loss.
  • Blurred vision
  • “halos' around lights
  • Difficulty in focusing
  • Difficulty in adjusting eyes in low lighting
  • Loss of peripheral vision
  • Aching or discomfort around the eyes
  • Headache

Diagnostic Findings
Medical history to investigate the history of predisposing factors
Tonometry to measure the IOP
Ophthalmoscopy to inspect the optic nerve
Gonioscopy to examine the filtration angle of the anterior chamber
Perimetry to assess the visual fields

Medical management
Prevention-of optic nerve damage
To maintain an IOP within a range unlikely to cause further damage.
 
PHARMACOLOGIC THERAPY
Systemic and topical ocular medications that lower IOP

SURGICAL MANAGEMENT
Laser trabeculoplasty for glaucoma, laser burns are applied to the inner surface of the trabecular meshwork to open the intratrabecular spaces and widen the canal of Schlemm, thereby promoting outflow of aqueous humor and decreasing IOP
Laser iridotomy for pupillary block glaucoma, an opening is made in the iris to eliminate the pupillary block. Laser iridotomy is contraindicated in patients with corneal edema, which interferes with laser targeting and strength.
Filtering procedures for chronic glaucoma are used to create an opening or fistula in the trabecular meshwork to drain aqueous humor from the anterior chamber to the sub-conjunctival space into a bleb, thereby bypassing the usual drainage structures.
Trabeculectomy is the standard filtering technique used to remove part of the trabecular meshwork.
Drainage implants or shunts are open tubes implanted in the anterior chamber to shunt aqueous humor  to an attached plate in the conjunctival space. A fibrous capsule develops around the episcleral plate and filters the aqueous humor, thereby regulating the outflow and controlling IOP.  

COMPLICATIONS
  • Hemorrhage
  • An extremely low (hypotony) or elevated IOP,
  • Uveitis
  • Cataracts
  • Bleb failure
  • Bleb leak
  • Endophthalmitis

Nursing diagnosis
  • Risk for injury related to visual acuity deficits
  • Self-care deficits related to visual acuity deficits
  • Acute pain related to pathophysiologic process and surgical correction
  • Noncompliance related to the inconvenience and side effects of glaucoma medications


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notes.nursium.com: Eye: Glaucoma
Eye: Glaucoma
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