Phacoemulsification conditions resulting in thermal wound injury.

PURPOSE: To determine and model the relationships between phacoemulsification conditions and viscoelastic agents that result in thermal wound injury. SETTING: Animal laboratory, Irvine, California, USA. METHODS: Mechanical and animal models, various wound sizes, phacoemulsification tips, and dispersive and cohesive viscoelastic agents were evaluated. Settings for phaco power, vacuum, and irrigation levels were controlled within a surgically relevant range. In the mechanical and animal models, incision temperature was assessed as a function of phacoemulsification parameters and time. In the animal model, wound damage was evaluated at the time of surgery. RESULTS: Induced time delays from the onset of phaco power to the onset of irrigation flow caused a thermal rise at the incision site. In these experiments, lack of irrigation and aspiration resulted in the greatest thermal rise and caused wound damage. Both the cohesive and dispersive viscoelastic agents were associated with a delay in the start of irrigation and aspiration, which resulted in similar maximum temperatures. Mathematical models were developed to estimate the maximum incision temperature from the phacoemulsification power, the duration (seconds) of occlusion, the tip gauge and type, and other phacoemulsification parameters. The models predict that under comparable conditions, occlusion with a viscoelastic agent will result in higher incision temperatures than occlusion with a balanced salt solution. CONCLUSION: Under comparable phacoemulsification conditions, both the cohesive and dispersive viscoelastic agents were associated with elevated temperatures that would be preventable by ensuring irrigation and aspiration flow before the onset of phacoemulsification power.

Is there a difference in incision healing based on location?

PURPOSE: To determine whether there is a difference in the healing process between incisions that begin in avascular region and those that begin in vascular region. SETTING: Wills Eye Hospital, Philadelphia, Pennsylvania, and Kresge Eye Institute, Detroit, Michigan USA. METHODS/MATERIALS: Feline evaluations were conducted at two sites (one evaluation at each site). Eyes in both evaluations were grouped by incision location: avascular (clear corneal) incisions or vascular (limbal) incisions. A series of postoperative examinations were conducted in each group of both evaluations that included slitlamp examination, measurements of external pressure and incision stability, and histological analysis. RESULTS: All limbal incisions were stable 7 days after surgery. Histological analyses in both evaluations showed a difference in tissue response between clear corneal and limbal incisions; the limbal incisions had an early fibroblastic response and the clear corneal, a delayed response. CONCLUSION: The predominant factors in incision healing and stability were incision geometry, architecture, and location. Endothelial pump action was effective in removing fluid but was not effective in incision stability. Histological analyses confirmed that starting incisions in the vascular region (limbus) resulted in a fibroblastic response that enhanced incision stability and allowed rapid incision healing within 7 days postoperatively compared with the 60 days healing time required for incisions started in the avascular region (cornea).

Relative stability of clear corneal incisions in a cadaver eye model.

Three different clear corneal square incisions--beveled (or paracentesis), stepped, and hinged--were studied in a cadaver eye model to determine whether a critical width existed for each incision type at which resistance to external pressure changed substantially, given identical tunnel length (1.75 mm to 2.00 mm) for each incision. As a comparison, the beveled (paracentesis) incision was also performed as a clear corneal incision at the anterior limbus, making it a limbal beveled incision. One surgeon performed all procedures. Incision width ranged from 2.5 mm to 5.0 mm in 0.5 mm increments. External pressure as high as 525 psi was applied to all eyes at two ranges of intraocular pressure (10 mm Hg to 15 mm Hg and 20 mm Hg to 25 mm Hg) to determine the relative ability of each incision type to resist leakage. The hinged incision performed better than the stepped and corneal beveled incisions. When the beveled (paracentesis) incision was made as a clear corneal limbal beveled incision at the anterior limbus, the limbal structures provided additional support in resisting externally applied pressure. When the clear corneal beveled technique is used, incision width should be 3.0 mm or less. When clear corneal stepped or hinged techniques are used, incision width should be 3.5 mm or less.(ABSTRACT TRUNCATED AT 250 WORDS)