Corneal curvature stability with increased intraocular pressure

To examine the corneal shape and ocular refraction under conditions of increased intraocular pressure (IOP) and to consider the possible influences of direct digital forces, corneal thickness, limbal and scleral rigidity, and the duration and frequency of IOP loading on the results.

Forces applied digitally to the temporal sclera were used to obtain 15 optimized videokeratographic records for two subjects under different levels of IOP loading. Stability of refraction was also examined under the same conditions.

Relative to normal IOP, four levels of IOP increments were induced: 43% to 61% (from a normal 18.8 mm Hg to approximately 28.6 mm Hg), 119% to 153% (from a normal 12.2 mm Hg to approximately 28.8 mm Hg), 181% to 213% (from a normal 18.8 mm Hg to approximately 55.8 mm Hg), and 374% to 443% (from a normal 12.2mm Hg to approximately 62.1 mm Hg). Significant changes in response to IOP loading were few in number and of a minor degree. For example, the maximum simulated keratometry change was 0.20 diopters (D), and the maximum change in refractive error recorded was 0.625 D in cylinder.

Corneal shape and refraction were found to show only minor evidence of instability under conditions of IOP loading. The small number and minor degree of corneal changes recorded under IOP loading suggest that under these conditions of measurement, corneal stability may be the result of stress stiffening. However, mechanisms for corneal shape changes that depend on limbal and scleral rigidity may also contribute to corneal shape stability.