vision

Chapter 19: Disorders of Visual Function

Glaucoma

  • Definition:

    • An optic nerve disorder characterized by optic disk cupping and visual loss.

    • It is no longer considered merely an eye pressure problem.

    • Leading Cause:

    • #1 cause of irreversible blindness worldwide.

  • Causes:

    • An increase in pressure due to an imbalance between aqueous humor production and outflow.

    • Increased ocular pressure greater than 21 mmHg (normal pressure is 10-21 mmHg).

    • The most common cause of increased pressure is inadequate aqueous outflow from the anterior chamber.

Classifications of Glaucoma

  • Angle-Closure (Narrow-Angle) vs. Open-Angle (Wide-Angle):

    • Based on the location of the blockage and the circulation and resorption characteristics of the aqueous humor.

  • Congenital vs. Acquired Conditions:

    • Congenital: Present from birth.

    • Acquired: Develops later in life due to various factors.

  • Primary vs. Secondary Disorder:

    • Primary: The cause is unknown.

    • Secondary: Results from another cause such as infections affecting the eye, tumors, or trauma to the eye.

Wide-Angle (Open-Angle) Glaucoma

  • Description:

    • Most common type of glaucoma.

  • Risk Factors:

    • Age: Individuals 40 years old and older.

    • Ethnicity: Higher prevalence in African Americans.

    • Family History: A familial predisposition exists.

Narrow-Angle Glaucoma

  • Characteristics:

    • The condition worsens with pupil dilatation.

  • At-Risk Populations:

    • Individuals of Asian or Eskimo descent due to structural characteristics of the eye.

  • Symptoms:

    • Eye pain, headache, and blurry vision.

Congenital Glaucoma Symptoms

  • Signs:

    • Excessive tearing and photophobia (sensitivity to light).

    • Affected infants are fussy, have poor eating habits, and rub their eyes frequently.

    • The eye may take on a grayish-white appearance.

    • Enlargement of the optic globe is noted.

Glaucoma and Visual Impairment

  • Impact:

    • Temporary or permanent vision loss can occur due to damage to the retina and optic nerve as well as corneal edema and opacification.

  • Treatment:

    • Medications aimed at reducing intraocular pressure or surgical interventions may be necessary.

Disorders of Refraction

  • Hyperopia (Farsightedness):

    • Condition where the anterior-posterior dimension of the eyeball is too short, resulting in images being focused behind the retina.

  • Myopia (Nearsightedness):

    • Condition where the anterior-posterior dimension of the eyeball is too long, resulting in the focus point for distant objects falling in front of the retina.

Cataract

  • Description:

    • The lens becomes cloudy, interfering with light transmission to the retina.

    • It is the most common cause of age-related visual loss globally.

  • Causes:

    • Multifactorial origins include aging, genetic predispositions, environmental and metabolic factors, medications, and trauma.

    • Specific factors influencing cataract development:

    • Diabetes, long-term exposure to sunlight, heavy smoking, congenital lens defects, trauma, or disease processes.

  • Treatment:

    • No effective medical treatment. Surgical intervention is necessary to correct vision loss associated with cataracts.

    • Intraocular lens implantation is the standard surgical treatment.

Papilledema

  • Anatomy Description:

    • Involves the entrance and exit of the central artery and vein of the retina through the back of the eye.

  • Causes:

    • Conditions leading to persistent increased intracranial pressure such as cerebral tumors, subdural hematomas, hydrocephalus, and malignant hypertension.

  • Effects:

    • Results in optic nerve destruction, leading to permanent blindness.

    • It is often a later symptom of a more severe underlying condition.

Diabetic Retinopathy

  • Characteristics:

    • Features engorgement of retinal veins, thickening of the endothelial basement membrane, and formation of capillary microaneurysms.

  • Symptoms:

    • Typically asymptomatic until advanced, with potential macular edema, tendency to bleed easily, and potential retinal detachment.

  • Treatment:

    • Prevention through the control of diabetes mellitus (DM) is critical along with laser surgery to manage bleeding events.

Retinal Detachment

  • Description:

    • A serious emergency characterized by the separation of the retina from the back of the eye.

    • Quick treatment is essential to save vision.

  • Causes:

  • Symptoms:

    • Notable changes in vision.

  • Risk Factors:

    • High-grade myopia, glaucoma, family history, diabetes mellitus (DM), tumors.

  • Treatment:

    • Immediate intervention is necessary; treatment includes laser surgery.

Macular Degeneration

  • Description:

    • Degenerative changes in the macula primarily leading to a loss of central vision.

  • Forms:

    • Age-Related Macular Degeneration:

    • Dry Form: Involves shrinkage of the macula.

    • Wet Form: Exudative.

  • Risk Factors:

    • Age, gender (female), ethnicity (white), smoking, genetic factors.

  • Symptoms:

    • Central vision loss, difficulty discerning colors, challenges seeing distances.

  • Treatment:

    • Laser treatments, steroid injections, and growth factor injections can be employed.

Retinoblastoma

  • Description:

    • Childhood cancer of the eye associated with a genetic defect on Chromosome 13.

  • Demographics:

    • Typically occurs in children under 2 years of age, with high mortality if untreated.

  • Symptoms:

    • Notable “cat eye” reflex often observed in family photos or during wellness checks with healthcare providers.

  • Treatment:

    • Options include chemotherapy and eye removal (enucleation) with the primary goal of saving the child's life.