Anatomy of the Eye

Eye Anatomy and Structure

• The chapter covers basic structure and function (anatomy and physiology) of the eye.
• Eyes have muscles to control movement.
• There are three pairs of muscles that control the eyes:
  • Superior and inferior rectus muscles.
  • Medial and lateral rectus muscles.
  • Superior and inferior oblique muscles.

Lacrimal Apparatus

• It manufactures and drains tears to keep the eye moist and clear debris.
• Tears are composed of:
  • Salt.
  • Mucus.
  • Bactericidal enzymes (lysozymes).
• Blinking helps to expel tears and remove debris.
• Tears empty into the nasal lacrimal ducts and drain into the nasal cavity.
• Conjunctiva location: Inner surface of the eyelids and outer surface of the eyeball.

Internal Structures of the Eye

• Three layers:
  • Outermost: Fibrous tunic.
    • Sclera: Thick, white, opaque structure of collagen fibers, known as the white of the eye. It gives the eye shape. (individual eye shapes vary).
    • Cornea: Anterior portion of the sclera, highly sensitive tissue innervated by cranial nerve number five (trigeminal nerve).
  • Aqueous humor: Watery fluid in front of the lens and in the anterior chamber.
    • Curvature is more pronounced in youth and flattens with age.
    • The junction of the sclera and cornea is called the canal of Schlemm.
• Retina contains rods and cones.
  • Cones are divided into three types, sensitive to red, green, and blue colors.
  • Yellow vision might indicate a problem.
  • Posterior chamber is filled with vitreous humor.
    • Vitreous humor is a transparent, jelly-like substance that also gives shape to the eye.

Physiology of Vision

• Four basic processes for image formation:
  • Refraction: Eye's ability to bend light rays to fall on the retina.
  • Accommodation: Eye's ability to focus on objects at various distances.
  • Constriction: Adjustment of pupil size to regulate light entering eye.
  • Convergence: Medial movement of both eyes allowing light rays from an object hitting the same point on both retinas.
  • Eye assessment valuable; can indicate a stroke, where one pupil is reactive, and the other is blown out and non-reactive.

Nursing Considerations for Eye Complications

• Symptoms include:
  • Eye pain.
  • Sensitivity to light (photophobia).
  • Double vision (diplopia).
  • Headaches.
  • Involuntary rhythmic eye movements (nystagmus).
  • Allergies and medication side effects may cause eye issues.
  • Wearing glasses or contact lenses affects eye care.

Laboratory and Diagnostic Exams

• Goals:
  • Evaluate visual acuity, visual fields, refraction, peripheral vision, and overall eye health.
  • Additional tests assess specific disorders and diseases.

Visual Acuity Test

• Most common test involves placing a patient 20 feet from a Snellen chart.
  • 20/20 vision: Patient can read at 20 feet what a normal eye can read at 20 feet.
  • 20/40 vision: Patient can read at 40 feet what a normal eye can read at 20 feet.

Automated Perimetry Test

• Patient stares at a computer screen and presses a button when they see a flashing light.

Amsler Grid

• Assesses disturbances in central vision and evaluates macula health.
• Used to detect macular degeneration.

Slit Lamp Examination

• Uses magnification to view eyelid, sclera, iris, conjunctiva, and cornea.
• Evaluates intraocular pressure (IOP) via tonometry to detect glaucoma.

Mydriatics (Dilating Drops)

• Evaluate internal surfaces of the eye.
• Cause photosensitivity for hours after the exam; protective eyewear needed.
• Help diagnose cataracts and corneal injuries.

Fluorescent Angiography

• Invasive procedure involving dye injection.
• Requires signed consent and allergy assessment (iodine, shellfish, latex).
• Post-test, urine may be dark or orange for a few days.
• Tests for retinal detachment, retinopathy, tumors, and macular degeneration.

Tonometry

• Puff of air to measure how light reflects off the eye.

Goldman Tonometry

• More invasive; numbs the eye before measuring IOP.

Eye Conditions

• Hyperopia: Farsightedness.
• Myopia: Nearsightedness.
• Strabismus: Crossed eyes.
• Astigmatism: Irregular curvature of the cornea or lens.
• Esotropia: A form of strabismus where one or both eyes turn inward.
• Exotropia: A form of strabismus where one or both eyes turn outward.

Blindness and Near Blindness

• Total blindness: No light perception and no usable vision.
• Legal blindness: Maximum visual acuity of 20/200 with corrective eyewear or visual field sight capacity reduced to 20 degrees (normal is 180 degrees).
• Congenital blindness: Present from birth due to defects.
• Acquired blindness: Results from disorders like diabetic retinopathy, glaucoma, retinal degeneration, infections, tumors, or trauma.

Clinical Manifestations

• Double vision, blurred vision, pain, floaters or flashes of light, sensitivity, burning, tearing, loss of peripheral vision, halos around lights.
• Emotions: Anxiety, disorientation, helplessness.

Medical Management

• Corrective eyewear for partial sight.
• Assistive devices (canes, dogs).
• Magnifying systems and specialized computer setups.
• Surgical correction or corneal transplants to improve eyesight.

Nursing Interventions

• Prioritize safety due to fall risk.
• Foster independence, encourage self-care.
• Provide information about support services and agencies for the visually impaired.

Refractory Errors

• Astigmatism, strabismus, myopia, hyperopia.

Medical Management

• Glasses/contacts, surgical procedures.

Surgical Management

• Refractive surgery (reshaping corneal curvature).
• Myopia commonly corrected by laser surgery.
• Usual age for correction is 20-60 years.
• Procedures: Radial keratotomy (RK), photorefractive keratectomy (PRK), LASIK, LTK, CK.

Nursing Interventions and Patient Teaching

• Eye patch post-surgery.
• Assist with ambulation.
• Manage photosensitivity and blurred vision.
• Stress importance of follow-up exams (day after surgery, one week, then monthly for six months).
• Stop wearing contact lenses 1-2 weeks before surgery.
• Rest first day post-op.
• Report persistent pain after the first day.
• Educate about complications (dry eyes, pain, photophobia, burning, itching, infection).
• Visual acuity may not immediately be 20/20.
• May experience glare/halos and need glasses for night driving.

Eyeglasses Nursing Interventions and patient teaching

• Eyeglasses should fit properly on the bridge of the nose to eliminate slippage and an uneven level on each ends.
• The hospitalized patient wearing corrective eyewear requires daily assistance in cleaning and maintaining that eyewear.
• Encourage patient to see their optometrist or ophthalmologist every year.

Contact Lenses

• Keep your hands clean; don't be digging in your butt and then putting your contacts in and, you know, that kind of stuff. Also, contact lens wearers should follow the contact lens care, you know, your do's and don'ts.

Inflammatory and Infectious Disorders of the Eye

Conjunctivitis (Pink Eye)

• Most common eye disorder; inflammation of the conjunctiva.
• Causes: bacterial, viral, environmental factors (pollen), allergies.
• Usually starts in one eye, spreads to the other(s).
• Bacterial causes: pneumococcal, staph, strep, gonococcal, chlamydial organisms, Haemophilus influenzae.
• Eye is a breeding ground due to moisture, warmth, and vascularization.
• Trachoma: Highly contagious form caused by chlamydia (rare in the US, major cause of blindness in Asia/Mediterranean).
• Viral causes: respiratory infections, adenovirus, herpes simplex one virus (highly contagious).
• Symptoms: erythema(redness) in conjunctiva, swelling, crusting from discharge.
• Lack of treatment can lead to blindness.
• Patients complain of excessive tearing, itching, burning; discharge on eyelids.

Nursing Interventions and Patient Teaching

• Clean lids/lashes with normal saline and warm compresses (2-4 times/day).
• Eye irrigations with normal saline or lactated Ringer's solution.
• Topical antibiotic or steroid medication prescribed.
• Eye pads contraindicated; promote bacterial growth.
• Avoid sharing items.
• Throw away eye makeup.
• Use individual washcloths/towels.
• Practice hand hygiene.
• Avoid noxious fumes/smoke.
• Do not wear contact lenses.
• Needs to be treated to avoid ophthalmitis.
• Blepharus, Calazan, Cordolin - Review disorders of the eye

Keratitis (Inflammation of the Cornea)

• Due to bacterial or viral influences (syphilis, herpes simplex virus), fungal infections (candida), nervous disorders.

• Can be superficial or invade deeper membranes.

• Symptoms: Acute pain, ulcers, scarring of corneal surface.

• Bacterial causes: Pseudomonas, staph, strep, Haemophilus organisms.

• Viral cause: Herpes simplex virus.

• Common in immunocompromised patients (cancer, HIV/AIDS, steroid use).

• Severe eye pain is the most common symptom.

• diagnostic tests includes the slit lamp examination

Medical Management

• Topical/systemic antibiotics.
• Corneal debridement followed by topical therapy (2-3 weeks) for viral keratitis.
• Corticosteroids are contraindicated for this patient because they contribute to longer longer course, possible deeper ulceration of the cornea, and systemic complications.
• Antiviral medications, analgesics for pain/inflammation.
• Pressure dressings to relax eye muscles.
• Warm/cold compresses (2-4 times/day).
• Epithelial debridement.
• Surgical management: corneal transplant (keratoplasty).

Nursing Implications

• Emphasize safety and hand hygiene.
• Avoid rubbing eyes.
• Notify provider of discharge changes or increased pain.