The Significance of Intraocular Pressure Alterations from Common Therapeutic Interventions: Preliminary Study with Clinical Implications

Objective: Human intraocular pressure (IOP) is normally controlled within narrow limits to maintain ocular form and firmness while allowing abundant retinal perfusion. Dangerous IOP elevation can occur when this equilibrium is challenged by common therapeutic manoeuvres which acutely increase intraocular volume or acutely decrease eye wall volume, such as intravitreal injection or scleral buckling. The purpose of this study is to confirm the relationship between acute intraocular volume changes and IOP elevation in an experimental model, review the pertinent literature, and discuss the ocular tolerance for acute IOP elevation as well as how to avoid related complications. Methods: A porcine eye model was used to demonstrate the relationship between the volume of normal saline or air injected into the vitreous and resulting IOP increase. Incremental injections of normal saline or air were performed and IOP measured. Results: Both normal saline and air injections of only 0.2 ml resulted in a dramatic increase of IOP. Injection of 0.3 ml or greater increased IOP to levels which potentially compromise retinal perfusion. Similar volumes of scleral buckling cause equivalent pressure elevations. Conclusion: Dangerously elevated IOP caused by acute ocular volume changes associated with therapeutic intraocular injection or with scleral buckling may compromise retinal perfusion and may necessitate medical or surgical therapeutic manoeuvres. The safe interval for complete central retinal artery occlusion is probably only about 15 minutes rather than 90 minutes as commonly expressed in the literature.