Purpose:
Published studies on stromal hydration (HYD) of clear corneal incisions (CCI) after cataract surgery have demonstrated that HYD persists beyond 1 day postoperatively and that CCI length, intraocular pressure (IOP), and the incidence of focal Descemet detachments all increase after stromal HYD. However, the impact of stromal HYD on central corneal topography has not been well defined. The purpose of this study is to determine the initial topographic changes induced by stromal HYD of CCIs and to serve as a pilot for a prospective clinical trial.
Methods:
IRB approval was obtained. 5 freshly (<12hrs) enucleated sheep eyes free of ocular pathology were studied. Eyes were placed vertically into a custom mount and IOP was modulated by adjusting a circular rubber grommet placed peripheral to the limbus until the desired range (10±3mmHg) was obtained. IOP was measured in triplicate by tonopen and averaged to obtain a pre-CCI IOP. The Orbscan II was used to construct curvature maps using a 3mm central anterior float best fit sphere from which central corneal curvature (CCC) and astigmatism (AST) were calculated. Topography was taken in triplicate and maps were averaged to obtain pre-CCI CCC and AST. A peripheral, mid-stromal self-sealing CCI was performed temporally using a 2.75mm metal slit blade under a surgical microscope. IOP was then adjusted by injecting BSS into the anterior chamber and burping the wound as necessary. Again, IOP and topography were taken in triplicate and averaged to obtain post-CCI IOP, CCC and AST. Finally, stromal HYD with balanced salt solution (BSS) was introduced into CCIs via a blunt-tipped cannula, using stromal clouding across the entire width of the CCI as an endpoint. Again IOP was adjusted by burping/injecting BSS as necessary and IOP and topography were taken in triplicate and averaged to obtain post-HYD IOP, CCC and AST. Statistical comparisons of IOP, CCC and AST between pre-CCI, post-CCI and post-HYD states were all performed using ANOVA (one factor, p<0.05).
Results:
IOP was unchanged between states (p=0.79). There was a statistically significant (p=0.004) steepening of CCC from pre-CCI (37.72±1.0D) to post-CCI (38.46±0.9D) to post-HYD (38.85±0.8D). AST was also statistically different (p=0.004) between each state showing a decrease from pre-CCI (2.5±0.5D @ 179±10o) to post-CCI (1.4±0.7D @ 165±33o), and an increase from post-CCI to post-HYD (5.2±0.3D @ 001±17o).
Conclusions:
Stromal HYD of peripheral CCIs causes an immediate increase in central corneal AST in enucleated sheep eyes. Prospective clinical studies are needed to determine the duration of topographical changes induced by stromal HYD.
Keywords: cornea: clinical science • topography • refractive error development