Eye

Eye Disorders

Anatomy of the Eye

  • Sclera
      - White layer of the eye
      - Contains the transparent cornea, allowing light to enter the eye

  • Three Chambers:
      - Choroid
      - Anterior Chamber
      - Retina
      - Posterior Chamber

  • Vitreous
      - Contains vitreous humor

  • Fovea

  • Ciliary Body

  • Aqueous Humor
      - Present in anterior chamber

  • Pupil

  • Lens

  • Iris
      - Colored part of the eye

  • Cornea

  • Optic Nerve

  • Central Retinal Artery

Three Layers of the Eye

  1. Sclera
       - The white protective outer layer of the eye
       - Contains the cornea, the transparent part allowing light entry

  2. Choroid
       - Contains blood supply and the iris
       - Pupil: Opening in the center of the iris, light enters through the pupil and is transmitted to the retina and optic nerve
       - Mydriasis: Pupil dilation
       - Miosis: Pupil constriction

  3. Retina
       - Contains photoreceptors; the lens focuses images on the retina
       - Fundoscopic exam allows for visualization of retina

Eye Anatomy & Function: Key Terms & Concepts

  • Lens
      - Suspended by zonule fibers attached to the ciliary body (muscle)
      - Changes shape based on ciliary muscle actions

  • Accommodation
      - The lens changes shape to form a sharp image on the retina

  • Macula and Fovea
      - Responsible for sharp central vision

Muscles & External Structures of the Eye

  • Four Rectus Muscles and Two Oblique Muscles
      - Attached to the eyeball

  • Six Cardinal Fields of Gaze

  • Conjunctiva
      - Palpebral: Pink membrane lining the eyelid
      - Bulbar: Colorless covering except on the cornea

  • Meibomian Glands
      - Located at the rim of the eyelids, secrete oily substance

  • Lacrimal Glands
      - Secrete tears

Basic Function of the Eyes

  • Light rays pass through the
      - Cornea
      - Anterior Chamber
      - Pupil
      - Lens
      - Posterior Chamber to the retina

  • The pupil dilates and constricts to allow light entry

  • Nerve impulses travel from the retina via the optic nerve to the brain

  • Clinical Note: Only place in the body where active vessels are visible; conditions like arteriosclerosis, hypertension, and diabetes can damage optic nerve and retina.

  • Papilledema: Increased intracranial pressure causing swelling of the optic disc with irregular borders.

  • Autonomic Nervous System Control:
      - Sympathetic Nervous System (SNS): Blocks drainage of aqueous fluid in the canal of Schlemm.
      - Parasympathetic Nervous System (PNS): Opens the canal of Schlemm to drain aqueous fluid.

  • Photoreceptor Cells
      - Comprise cones and rods allowing color vision, focus on images, and carry impulses to the optic disc

  • Nerve fibers from the optic disc form the optic nerve, which sends impulses to the optic tracts, optic radiations, and visual cortex of the brain

  • Nerve Fiber Pathways:
      - Nasal portion of fibers travels to the contralateral side of the brain,
      - Temporal portion travels to the ipsilateral side of the brain.

Ciliary Muscle Actions

  • (a) Ciliary Muscle Relaxed
      - Zonule taut
      - Lens flattened for distant objects

  • (b) Ciliary Muscle Contracted
      - Zonule relaxed
      - Lens rounded for close objects

Diagnostic Tests

  • Amsler Grid: Tests for macular problems.

  • Tonometry: Measures intraocular pressure.

  • Perimetry Testing: Evaluates the field of vision.

  • Slit-Lamp Examination: Examines the eye with high magnification.

  • Ishihara Color Chart: Tests color differentiation.

  • Ultrasonography: Identifies lesions in the globe or orbit.

  • Fluorescein Dye: Inserted into eye; Wood’s lamp used to detect corneal abrasion.

  • Snellen Chart: Measures visual acuity.

Types of Vision Impairment

  • Refractive Errors: Impairment due to shortened or elongated eyeball.
      - Myopia: Nearsightedness (distant vision is blurred).
      - Hyperopia: Farsightedness (near vision is blurred).
      - Presbyopia: Age-related vision decline.
      - Astigmatism: Irregular curvature of the cornea.
      - Amblyopia: Lazy eye.
      - Strabismus: Crossed eyes.
      - Color Blindness.
      - Blindness: Vision cannot be improved to better than 20/200; regular vision is at 20/20 or less than 20 degrees of visual field remaining.

Conjunctivitis

  • Inflammation of bulbar conjunctiva (covers sclera) and palpebral conjunctiva (lines eyelids).
      - Sometimes referred to as “pink eye.”

  • Causes:
      - Herpes-zoster may cause both conjunctivitis and keratitis.
      - Bacterial forms lead to mucopurulent exudate.
      - Viral forms exhibit watery discharge.
      - Caused by airborne antigens and may occur in individuals with asthma or eczema.

  • Symptoms:
      - Inflammation of the palpebral conjunctiva results in cobblestone appearance.
      - Tearing, redness, and itching of the eyes.

Infection & Inflammation of the Eye

  • Blepharitis: Inflammation of the eyelid (granulated eyelids) presenting with dry, gritty sensation in the eye and photophobia.

  • Stye (Hordeolum): Bacterial infection near the eyelash root; appears externally; most commonly caused by S. aureus.

  • Chalazion: Blocked meibomian gland near the eyelid margin.

  • Keratitis: Inflammation of the cornea, often caused by herpes simplex virus (HSV); may progress from superficial to deeper damage.

  • Acanthamoeba Keratitis: Occurs if contact lenses are contaminated; can lead to corneal scarring, uveitis, scleritis, and cataracts.

Eye Infection & Inflammation

  • Common in autoimmune disorders; often associated with reduced tear production.

  • Keratoconjunctivitis Sicca (Dry Eye): Inflammation of the lacrimal sac, potentially occurring in newborns; presents as red, watery eyes with purulent exudate.

  • Dacryocystitis: Inflammation of the sclera, associated with severe pain possibly radiating to the eyebrow or temple, accompanied by photophobia and linked to autoimmune disorders.

  • Scleritis: Inflammation of the sclera related to autoimmune conditions.

Structural Disorders: Corneal Abrasion

  • Most common type of eye injury, typically heals within 24 hours.

  • Involves damage to the epithelial surface of the cornea; contact lens wearers are at greater risk.

  • Symptoms may include a sense of foreign body in the eye, gritty feeling, and photophobia.

  • Diagnosed via slit lamp examination which reveals corneal defects; fluorescein dye and Wood’s lamp contribute to diagnostics.

Glaucoma

  • Definition: Condition characterized by elevated intraocular pressure (IOP).
      - Known as the “silent thief of sight” due to gradual progression.
      - Increased pressure can damage the optic nerve, potentially leading to blindness.

  • Risk Factors:
      - Age over 40 years
      - Ethnicity
      - History of migraine headaches
      - Cardiovascular diseases
      - Diabetes

  • Types of Glaucoma:
      - Primary Open-Angle Glaucoma (POAG): Silent, slowly progresses; accounts for 90% of glaucoma cases.
      - Primary Angle-Closure Glaucoma (PACG): Sudden onset; requires emergency attention; involves a narrow angle between iris and cornea leading to blockage and sudden vision loss.

Glaucoma Pathophysiology

  • Pathophysiology of POAG:
      - Not completely understood; involves changes in the ciliary muscle, trabecular meshwork, and canal of Schlemm, preventing the drainage of aqueous fluid.
      - High IOP impacts the retina and optic nerve junction, leading to an enlarged optic cup.

  • Pathophysiology of PACG:
      - Higher risk in individuals with a narrow angle between the iris and cornea.
      - Certain medications (e.g., sympathomimetics, anticholinergics, antidepressants) may increase PACG risk.
      - Sudden IOP increase can result in rapid loss of peripheral vision.

Glaucoma: Clinical Presentation and Diagnosis

  • Patient History:
      - Age, lens usage, family history, medications (specifically anticholinergics).

  • Patient Complaints:
      - Eye pain, redness, halos around lights, vision loss.

  • Signs and Symptoms:
      - Rapid development in PACG and progressive in POAG.

  • Clinical Presentation:
      - Increased optic cup to optic disc ratio observed during fundoscopic exam.

Diabetic Retinopathy

  • High glucose levels from diabetes mellitus damage retinal vessels.

  • Two Forms of Diabetic Retinopathy:
      - Nonproliferative: Early stage of diabetes; fundoscopic exam shows tiny aneurysms, microinfarcts, and "cotton wool spots."
      - Proliferative: Later diabetes stage; increased vasoactive growth factors lead to new blood vessel growth in the retina.

  • Clinical Presentation:
      - Documentation of glucose control, medications, and prior ophthalmic exams is essential.
      - Initially asymptomatic, but as the condition progresses, symptoms may include blurred vision and poor night vision.

  • Diagnosis: Involves slit lamp examination and fundoscopic exam.

Cataracts

  • Result from excessive growth of the epithelial layer of the lens.

  • Types of Cataracts:
      - Senile Cataracts: Associated with aging, smoking, obesity, diabetes, UV exposure.
      - Congenital Cataracts: Develop in the fetus due to infections such as rubella, syphilis, cytomegalovirus (CMV).

  • Symptoms: Gradual vision loss, night-time halos, lens cloudiness.

  • Diagnosis: Tonometry, visual acuity testing, dilated eye exam, ultrasound, CT, or MRI.

  • Treatment: Cataract removal and replacement with an artificial lens.

Age-Related Macular Degeneration

  • The macula, an area of the retina, deteriorates, leading to a blind spot and a slow, painless vision loss.

  • Caused by a combination of genetic, environmental, and behavioral factors.

  • Types:
      - Dry (Nonexudative): 90% of cases; involves inability to remove cellular debris, leading to drusen deposits (yellow-white accumulations) in the macula.
      - Wet (Exudative): More severe, characterized by inadequate clearance of debris.

  • Diagnosis: Amsler grid used to measure central vision; detection of black spots.

Retinal Detachment

  • Occurs when the retina pulls away from the back of the eye.

  • Symptoms: Patients may report photopsia, “floaters” in the vision, and shadows in peripheral field.

  • Diagnosed through ophthalmoscopic examination.