18.3 Acute Ophthalmologic Emergencies

Acute Painless Monocular Vision Loss: CRAO, CRVO & Retinal Detachment

Acute, painless monocular visual loss is a terrifying symptom that demands urgent bedside evaluation. The primary clinical priority is distinguishing between an acute vascular occlusion (arterial vs venous) and a mechanical retinal detachment.

Comparison of Acute Painless Visual Loss Etiologies

Central Retinal Artery Occlusion as a Stroke Equivalent

CRAO represents an acute ischemic stroke of the central nervous system. Modern guidelines from the American Heart Association / American Stroke Association (AHA/ASA) mandate immediate Stroke Code activation for patients presenting within the acute therapeutic window. Diagnostic workup must include:

1. Brain MRI with diffusion-weighted imaging (DWI; identifies silent concurrent cerebral cortical infarctions in ~25%);
2. Carotid duplex ultrasonography or CTA head/neck to evaluate ipsilateral carotid stenosis requiring urgent carotid endarterectomy;
3. Echocardiography (transthoracic or transesophageal) and cardiac telemetry to detect cardioembolic sources (atrial fibrillation, patent foramen ovale, left ventricular mural thrombus);
4. Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) in patients aged ≥50 years to exclude arteritic CRAO secondary to Giant Cell Arteritis (GCA). If GCA is suspected, administer immediate high-dose IV methylprednisolone (1 g daily for 3 days) without waiting for temporal artery biopsy, to prevent irreversible bilateral blindness.

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Acute Angle-Closure Glaucoma: Pathophysiology & Emergency Therapy

Acute Angle-Closure Glaucoma (AACG) is an ophthalmic emergency caused by sudden mechanical blockage of aqueous humor drainage through the trabecular meshwork into the canal of Schlemm, precipitating a dangerous spike in intraocular pressure (IOP) from normal levels (10–21 mm Hg) to 40–80 mm Hg.

Mechanism & Precipitating Triggers

• Pupillary Block: In anatomically predisposed eyes with shallow anterior chambers (hyperopia/farsightedness, advanced cataracts, elderly, Asian and Inuit descent), contact between the posterior iris and the anterior lens blocks flow of aqueous humor from the posterior chamber into the anterior chamber.
• Iris Root Crowding: As aqueous fluid builds behind the iris, pressure bows the peripheral iris forward (iris bombé) against the trabecular meshwork, sealing the iridocorneal angle.
• Precipitating Factors: Mid-dilation of the pupil maximizes iris-lens contact and bunches the peripheral iris into the angle:
  • Low-ambient light environments (e.g., walking into a dark movie theater or dim evening room);
  • Pharmacological agents with anticholinergic properties (atropine, scopolamine, ipratropium, oxybutynin, diphenhydramine, tricyclic antidepressants);
  • Sympathomimetic agents (pseudoephedrine, phenylephrine, ephedrine);
  • Sulfa-based medications causing choroidal effusion (topiramate).

Clinical Presentation & Cardinal Examination Findings

• Symptoms: Severe, excruciating, boring unilateral ocular and periorbital pain; radiating ipsilateral frontal headache; blurred vision and rainbow-colored halos around lights (caused by corneal epithelial edema scattering light); severe nausea, profuse vomiting, and abdominal pain (frequently mistaken for acute gastroenteritis, migraine, or an acute surgical abdomen).
• Physical Examination Findings:
  1. Ciliary Flush: Violaceous, deep injection surrounding the limbus (circumcorneal injection);
  2. Corneal Edema: Diffusely hazy, cloudy, "steamy" cornea with complete loss of normal corneal luster;
  3. Pupillary Abnormality: Fixed, mid-dilated (4 to 6 mm), vertically oval pupil that is unreactive to direct light and accommodation;
  4. Shallow Anterior Chamber: Slit-lamp exam shows slit-like space between cornea and iris; oblique penlight illumination casts a prominent nasal iris shadow;
  5. Induration: Digital palpation through closed eyelids reveals a rock-hard globe compared to the normal contralateral eye;
  6. Tonometry Confirmation: Intraocular pressure dramatically elevated (typically >40–70 mm Hg; normal 10–21 mm Hg).

Stepwise Medical Pharmacotherapy Regimen

Emergency treatment aims to rapidly lower intraocular pressure, clear corneal edema, and break the pupillary block:

                   ACUTE ANGLE-CLOSURE GLAUCOMA COCKTAIL
                   
    ┌────────────────────────────────────────────────────────────────────────┐
    │ STEP 1: SUPPRESS AQUEOUS HUMOR PRODUCTION (Triple Topical Drops)       │
    │ • Timolol 0.5% (Beta-blocker): 1 drop                                  │
    │ • Apraclonidine 1% (Alpha-2 agonist): 1 drop                           │
    │ • Prednisolone acetate 1% (Topical steroid): 1 drop (reduces uveitis)  │
    └───────────────────────────────────┬────────────────────────────────────┘
                                        │
                                        ▼
    ┌────────────────────────────────────────────────────────────────────────┐
    │ STEP 2: SYSTEMIC CARBONIC ANHYDRASE INHIBITION                         │
    │ • Acetazolamide 500 mg IV bolus (or 500 mg PO if tolerated)            │
    │ • Blocks ciliary body carbonic anhydrase; halts aqueous synthesis      │
    │ • Avoid in documented severe sulfa allergy                             │
    └───────────────────────────────────┬────────────────────────────────────┘
                                        │
                                        ▼
    ┌────────────────────────────────────────────────────────────────────────┐
    │ STEP 3: SYSTEMIC OSMOTIC DEHYDRATION OF VITREOUS (If IOP >50 or N/V)   │
    │ • IV Mannitol 1.0 to 2.0 g/kg infused over 30-45 minutes               │
    │ • Creates osmotic gradient, pulling fluid from vitreous into blood     │
    └───────────────────────────────────┬────────────────────────────────────┘
                                        │
                                        ▼
    ┌────────────────────────────────────────────────────────────────────────┐
    │ STEP 4: MIOTIC AGENT (STRICT TIMING REQUIREMENT)                       │
    │ • Pilocarpine 1% to 2%: 1 drop every 15 minutes for 2 doses            │
    │ • CRITICAL EXAM RULE: Administer ONLY AFTER IOP drops <30 mm Hg        │
    │ • Reason: At IOP >40-50, iris sphincter is ischemic and paralyzed;     │
    │   premature pilocarpine is ineffective and worsens pupillary block     │
    └───────────────────────────────────┬────────────────────────────────────┘
                                        │
                                        ▼
    ┌────────────────────────────────────────────────────────────────────────┐
    │ STEP 5: DEFINITIVE SURGICAL / LASER CURE                               │
    │ • Bilateral Laser Peripheral Iridotomy (LPI)                           │
    │ • Mandatory: Prophylactic LPI of the contralateral (fellow) eye!       │
    │ • >50% of fellow eyes develop angle closure within 5 years untreated   │
    └────────────────────────────────────────────────────────────────────────┘

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Chemical Ocular Burns: Alkali vs Acid & Copious Irrigation

Chemical ocular injury is one of the few true ophthalmic emergencies where therapy must precede history taking, examination, or visual acuity measurement.

Alkali vs Acid: Pathophysiology

Emergency Copious Irrigation Protocol

1. DO NOT WAIT: Never delay irrigation to test visual acuity, obtain an in-depth medical history, or await ophthalmology consultation. Time to irrigation is the single greatest determinant of visual recovery.
2. Instill Topical Anesthetic: Instill 1 to 2 drops of proparacaine 0.5% or tetracaine 0.5% to overcome blepharospasm.
3. Initiate Irrigation: Connect a Morgan lens or standard intravenous tubing to Lactated Ringer's (preferred, physiological pH 6.0–7.5) or 0.9% Normal Saline. Irrigate continuously with 1 to 2 liters of fluid over 30 to 60 minutes.
4. Sweep Fornices: Evert upper and lower eyelids. Particulate chemical matter (especially lime, cement, mortar, or plaster) embeds in the conjunctival fornices and continually leaches chemical into tears. Mechanically sweep the fornices with a moistened cotton swab.
5. Document Neutral pH Endpoint: Stop irrigation; wait 5 to 10 minutes to allow tear film equilibration. Touch a universal pH litmus strip to the inferior conjunctival fornix. The target endpoint is a neutral pH of 7.0 to 7.2. Continue irrigation until neutrality is achieved. Re-check pH 30 minutes later to ensure no rebound shift from hidden chemical particles.

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Open Globe Injury & Penetrating Ocular Trauma

An open globe injury is a full-thickness disruption of the cornea, sclera, or both, resulting from blunt rupture or penetrating projectile trauma.

Cardinal Physical Examination Signs

• Positive Seidel Test: Apply concentrated moistened fluorescein dye directly over the suspected laceration under cobalt blue light. Escaping clear aqueous humor dilutes and washes away the dark orange fluorescein, appearing as a bright green river or waterfall flowing downward under the slit lamp.
• Peaked / Teardrop Pupil: The pupil is distorted and points directly toward the site of corneal or scleral rupture.
• Uveal Tissue Prolapse: Brownish, pigmented tissue (iris, ciliary body, or choroid) protruding through the wound defect.
• Shallow / Flat Anterior Chamber: Collapse of anterior chamber depth compared to the unaffected eye.
• Bullous 360-Degree Subconjunctival Hemorrhage: Frequently conceals an underlying posterior scleral rupture.

Strict "Do No Harm" Management Protocol

1. Absolute Contraindication to Pressure: DO NOT apply any pressure to the eye. Never palpate the globe, check for induration, or perform tonometry (measuring intraocular pressure can cause immediate, irreversible extrusion of intraocular contents and permanent blindness).
2. DO NOT Instill Eye Drops: Avoid topical antibiotics, cycloplegics, or ointments (ointments cause toxic chemical endophthalmitis if introduced inside the eye).
3. Place a Rigid Eye Shield (Fox Shield): Rest the metallic or plastic shield securely on the bony orbital margins (forehead and cheek). Never place an eye patch or gauze pad underneath the shield that can compress the globe.
4. Keep Patient Strictly NPO: Prepare for emergent operative microsurgical globe repair.
5. Prevent Valsalva / Spikes in IOP: Administer IV antiemetics (e.g., ondansetron 4 mg IV) immediately; nausea and vomiting cause massive venous spikes that extrude intraocular contents.
6. Systemic Antibiotic Prophylaxis: Administer broad-spectrum intravenous antibiotics (e.g., IV Vancomycin plus IV Ceftazidime or Ciprofloxacin) to prevent bacterial endophthalmitis. Update tetanus vaccination.
7. Immediate Ophthalmology Consultation: Direct transfer to the operating room for primary microsurgical closure.

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Preseptal (Periorbital) vs Orbital (Postseptal) Cellulitis

The orbital septum is a thin, fibrous connective tissue sheet extending from the orbital periosteum to the tarsal plates of the eyelids, functioning as an anatomical barrier separating the superficial eyelid tissues from the deep orbital cavity.

Clinical Differentiation