Managing Positive Vitreous Pressure in Penetrating Keratoplasty: Techniques and Challenges

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Article initiated by:

Christine Wang MS, MD

All contributors:

Christine Wang MS, MD, Colleen Halfpenny, M.D., Christine Wang MS, MD, Ravi Patel MD MBA

Assigned editor:

Ravi Patel MD MBA

Review:

Assigned status Up to Date

 by Ravi Patel MD MBA on July 28, 2024.

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Contributing Editors:	add

Background

Positive vitreous pressure (PVP) is an uncommon but serious complication that can arise during penetrating keratoplasty (PKP), posing a risk to vision, particularly when accompanied by choroidal hemorrhage. Limited information is available regarding the occurrence of PVP during PKP, but studies find an incidence rate of 3.6% to as high as 40–50%. Given the potential sight loss, it is crucial to identify surgical approaches that minimize intraoperative complications while ensuring the preservation of the donor corneal tissue.

Pathophysiology of PVP

Positive vitreous pressure (PVP) can occur during penetrating keratoplasty (PKP) and intraocular anterior segment procedures due to acute hypotony resulting from open-sky surgery. The condition involves a gradual increase in vitreous cavity pressure relative to volume reduction that can be caused by external compression or intraoperative swelling. This concurrent aqueous loss and hypotony creates a pressure gradient between the vitreous cavity and the anterior chamber, resulting in displaced vitreous content.

This condition manifests as the anterior chamber exhibiting a resistant shallowing with the lens-iris diaphragm displaced forward. And it can be marked by recurring instances of iris prolapse and, in severe cases, the occurrence of zonular rupture alongside the possibility of vitreous or lens prolapse.

Prolonged and acute hypotony during PKP can increase transmural pressure, resulting in vessel rupture and the potential development of sight-threatening suprachoroidal hemorrhage.

Risk Factors of PVP

• Patient risk factors:
  • Increased systemic venous pressure due to
    • Positioning of the head below the heart
      • Congestive heart failure
      • Pulmonary edema
      • Obstructive sleep apnea
      • Chronic obstructive pulmonary disease
      • Valsalva maneuver
      • Severe obesity
      • Poorly positioned bull-necked patients with elevated venous pressure in the head
      • Rare cases of arteriovenous fistula
    • Younger age
      • Infants may have less rigidity and increased elasticity of the cornea and sclera, contributing to iris-lens diaphragm movement
    • Other risk factors:
      • Blood dyscrasias or coagulation defects
      • Diabetes mellitus
      • History of liver disease
      • Preoperative use of digoxin
      • Anxiety, which has been associated with higher PVP risk

• Ocular risk factors:
  • Ocular disorders:
    • Iris pathology
    • Presence of zonular instability
    • Shallow anterior chamber
    • Acute angle-closure glaucoma
  • Additional risks in patients with pseudophakia:
    • Ruptured capsule or IOL location outside the bag
    • Presence of an IOL or iris prolapse in pseudophakic or aphakic eyes is strongly correlated with a 100% incidence of PVP
  • Eye conditions:
    • Poor rigidity (i.e. keratoconus)
    • High myopia, High axial length of the eye leading to decreased orbital volume and increased pressure on globe
    • Buphthalmos
    • Short axial length
    • large crystalline lens
  • Orbital-related risk factors:
    • External compression during surgery (example: Lid speculum pressure on the eye)
    • Strong blink reflex
    • Anatomically small orbit or orbital deformity
    • Increased orbital tissue pressure from increased volume or fluid, such as retrobulbar or intraorbital hemorrhage
    • Orbital congestion from inflammation or edema (e.g., thyroid-related ophthalmopathy, orbital inflammatory syndromes)
    • Orbital tumors
    • Increased orbital fat in patients with marked obesity
  • Other risk factors:
    • History of infectious keratitis, ocular inflammation, or glaucoma (mechanism remains unknown)

• anesthesia risk factors
  • peribulbar anesthesia> general anesthesia
  • general anesthesia
  • positive end-expiratory pressure (PEEP) during general anesthesia
• surgeon risk factors
  • operating with the open-sky technique
  • length of time globe is open

Prevention

Mitigating risk factors of positive posterior pressure is critical to prevent this complication. In many cases, avoidance of sudden changes in intraocular pressure can be helpful. Avoid over-pressurization of the anterior chamber prior to entry during trephination. Some experts believe the utilization of a well placed Flieringa Ring or even two Flieringa Rings can be helpful in reducing transmural pressure gradient. Attempting to secure the new corneal button efficiently and avoiding prolonged open sky period can be helpful. Ultimately even with risk mitigation, positive vitreous pressure is likely to be encountered during some cases of penetrating keratoplasty and it is important to learn the tools for management.

Management

• Graft-over-host Technique
• Modified Graft-Over-Host Technique
• Mattress Sutures and Needle Techniques
• Vitrectomy or Vitreous aspiration