Lens-Related Glaucoma

Kanski's Clinical Ophthalmology: A Systematic Approach, 10th Edition (pp. 393-394)

1. Phacolytic glaucoma
2. Phacomorphic glaucoma
3. Pupillary block from disruption of lens position

1. Phacolytic Glaucoma

Pathogenesis

Important distinction: Phacolytic glaucoma must NOT be confused with phacogenic (phacoanaphylactic) uveitis, which is an autoimmune granulomatous reaction to exposed lens proteins occurring when the capsule is compromised (not intact).

Diagnosis

• Symptoms: Pain; poor vision due to cataract
• Slit lamp findings:
  • Corneal oedema
  • Hypermature cataract with a deep anterior chamber
  • Large floating white particles in the AC (lens protein + protein-containing macrophages)
  • Dense milky aqueous if particles are very abundant
  • Pseudohypopyon may form (Fig. 11.48C and D)
• Gonioscopy: Open angle with lens-derived material and inflammatory cells, most prominent inferiorly

Fig. 11.48C - Dense milky aqueous and pseudohypopyon in phacolytic glaucoma

Treatment

1. Medical IOP control first (to reduce inflammation and corneal oedema)
2. Wash out proteinaceous material from the AC
3. Cataract extraction (definitive treatment)
   • Note: The zonule is likely more fragile than usual - handle with care during surgery

2. Phacomorphic Glaucoma

Pathogenesis

• Equatorial age-related lens growth slackens the suspensory ligament → lens moves anteriorly
• Anteroposterior growth increases iridolenticular contact
• This potentiates pupillary block and iris bombé

Diagnosis

• Presentation similar to acute primary angle-closure glaucoma (PACG): shallow AC and mid-dilated pupil
• A dense white (intumescent) cataract is evident

Fig. 11.49 - Intumescent cataract, shallow AC, dilated pupil, and corneal oedema in phacomorphic glaucoma

• Fellow eye: More likely in eyes with shorter axial length and shallower AC; the fellow eye may paradoxically show a deep AC and open angle
• Anterior segment OCT or US biomicroscopy may be useful

Treatment

1. Medical treatment initially similar to acute PACG
   • Miotics are OMITTED - they increase iris-lens apposition and shift the lens anteriorly
   • Dilatation may be helpful but should be used with caution
   • Systemic hyperosmotic agents may be required more commonly than in PACG
2. Laser iridotomy - may be worthwhile but often not possible (corneal oedema or lens-cornea proximity) or ineffective
3. Laser iridoplasty - useful temporizing measure
4. Cataract extraction - definitive treatment, ideally after IOP is normalized and the eye is quiet
   • Surgery is difficult and carries a higher risk of complications
5. Consider a similar prophylactic procedure for the fellow eye

3. Pupillary Block from Disruption of Lens Position

Causes

• Blunt ocular trauma (even relatively trivial)
• Congenitally small lens (microspherophakia), e.g., Weill-Marchesani syndrome

Pathogenesis

• Dislocation may be into the AC
• Zonules may be stretched, or only partial disruption with the intact part acting as a hinge
• The lens may remain fully or partially in the posterior chamber
• Vitreous herniation may be contributory

Diagnosis

• A lens fully or partially dislocated into the anterior chamber is usually evident on slit lamp
• Acute pupillary block causes sudden severe IOP elevation with visual impairment
• Ultrasound biomicroscopy is often diagnostic

Fig. 11.50 - Traumatic dislocation of a normal-sized lens into the anterior chamber

Treatment

1. IOP reduction with osmotic agents (reduce vitreous volume) - urgent
2. Initial repositioning attempt: Patient adopts supine posture with pupil dilated → attempt to reposition lens in posterior chamber → miotic can then be used with caution
3. Bilateral laser iridotomy may provide extended control in some cases
4. Definitive treatment: Surgical lens extraction
   • An anterior chamber IOL, iris-fixated IOL, or sclera-fixated IOL will be necessary

Summary Comparison Table

Treatment of Snakebite

Overview

STEP 1: First Aid / Pre-Hospital

DO these:

• Remove jewelry and tight clothing from the affected extremity (anticipate swelling)
• Immobilize and splint the limb in a functional position (reduces discomfort; may slow venom spread)
• Limit exertion - especially walking for lower extremity bites
• Transport to a specialized centre with snakebite experience as soon as possible
• Do NOT wash the bite wound if in Australia/PNG - a venom identification swab kit may be used

DO NOT do these (historical treatments to AVOID):

• No incision and suction - not recommended since 1980; only tiny amounts of venom extracted and risk of injury to vessels/tendons/nerves
• No ice or cryotherapy - associated with a high rate of amputation
• No tourniquets or ligation
• No massage of the wound
• No electrical current (some have tried outboard motor generators - ineffective and dangerous)

Pressure bandage / constrictor band is species-specific:

• Elapid bites (neurotoxic - e.g., Australia, coral snakes): Apply pressure bandage between wound and heart at ~55 mmHg - shown to reduce systemic toxicity
• Crotalid bites (US pit vipers): Constrictor band concentrates venom locally → increased necrosis - DO NOT use

STEP 2: Emergency Department Assessment

History and Identification

• Do not risk a second bite to catch the snake; do not handle dead snakes (reflexive bites possible)
• Contact regional poison control for identification, expected toxicity, and antivenom location
• Document time of bite, species if known, first aid given

Clinical Assessment

• Pain, edema, erythema at bite site
• Distance between fang marks correlates with snake size
• Mark the advancing border of edema with a pen every 30 minutes

• Muscle twitching, perioral paresthesias, metallic taste
• Crotalid: hypovolemia, coagulopathy, hemolysis
• Elapid: confusion, muscle spasm, nausea/vomiting, blurred vision, speech difficulty, respiratory failure

Investigations

• CBC, coagulation profile (PT, aPTT, fibrinogen), blood type and crossmatch
• Metabolic panel, renal function
• Repeat labs every 4 hours or after each antivenom course

STEP 3: Antivenom - The Definitive Treatment

Indications for Antivenom

• Any evidence of local envenomation
• Worsening significant thrombocytopenia (<100,000/μL) or hypofibrinogenemia (<100 mg/dL)
• Progressive edema despite initial treatment
• Systemic envenomation signs

Crotalid (Pit Viper) Antivenom

• FabAV (Crotalidae Polyvalent Immune Fab, Ovine) or equivalent
• Goal: establish initial control = cessation of progression of all components - local effects, systemic effects, and coagulopathy
• Additional doses if condition worsens
• FabAV is also effective for copperhead envenomation where progression occurs
• Measure limb circumference at multiple sites above and below bite every 30 minutes as guide

Elapid (Coral Snake) Antivenom

• Neurotoxicity onset: immediate (15-30 min for mamba/Australian brown snake) or delayed (2-5 hours for coral snakes)
• No longer any antivenom available for North American coral snakes - local zoos and other countries may help for exotic species
• Neurotoxic symptoms: confusion, muscle spasm, respiratory failure, cranial nerve palsies

Antivenom Reactions

• Incidence of acute reactions to modern antivenoms is low
• If allergic reaction occurs: stop infusion immediately, administer H1 and H2 antihistamines, have epinephrine ready for anaphylaxis

STEP 4: Supportive Care

• Fluid resuscitation with isotonic fluids for hypovolemia; vasopressors for refractory hypotension
• Blood component replacement (only if active bleeding AND after antivenom has been given - antivenom is the best treatment for hematologic abnormalities)
• Wound care: clean wound, tetanus prophylaxis
• Pain management

STEP 5: Compartment Syndrome Management

Key principle: The most effective treatment for snakebite-associated compartment syndrome is neutralizing the venom with antivenom - not fasciotomy. Antivenom reduces compartment pressure. Prophylactic fasciotomy has no role. Fasciotomy may actually increase severity of local tissue loss.

STEP 6: Surgical Considerations (Crotalid)

• Wound debridement may be required for necrotic tissue
• Fasciotomy only when compartment pressures do not respond to antivenom and mannitol
• Post-fasciotomy: consider negative-pressure wound therapy
• Do NOT do elective early debridement of tissue that may be salvageable with antivenom

Summary Algorithm

Snakebite
   ↓
First Aid: Remove jewelry, immobilize, limit exertion
   ↓
Transport to ER → Identify snake type, call poison control
   ↓
Assess: Local + systemic signs, serial labs
   ↓
Dry bite (no signs)?     Yes → Observe 8-12h, discharge if no progression
        ↓ No
Antivenom (species-specific) → critical care setting
   ↓
Monitor progression (mark edema, serial labs every 4h)
   ↓
Compartment syndrome?  → Mannitol + more antivenom → Fasciotomy if unresponsive
   ↓
Supportive: Fluids, vasopressors, blood products if needed