Corneal Biomechanical Property Measurement with an IOP Loading Method in Keratoconic Patients

PURPOSE: To study the biomechanical properties of the corneas of both eyes in patients with evident keratoconus manifestation in one eye. METHODS: Our study consisted of nine patients with keratoconus and 25 volunteers in the control group. Both eyes of all participants were measured twice with a Pentacam Scheimpflug system: first with the standard Scheimpflug system and subsequently with the original version of the same technique in combination with a new device that can generate experimental artificial intraocular pressure (IOP) elevation. Diagnoses of keratoconus or non-keratoconus were made using the Pentacam Scheimpflug system software (StatSoft, Inc., Tulsa, OK). RESULTS: The artificially elevated IOP caused bulging of the anterior corneal surface in both eyes of keratoconic patients and a small flattening of the cornea in the eyes of the control group. Corneal ectasia, expressed in terms of diopters, during IOP loading in both keratoconic and nominally unaffected eyes was 4.12 D and 1.37 D, respectively. The changes were statistically significant (p < 0.05). Our dynamic study revealed a distinct weakness of the corneal tissue and an inability of keratoconic and contralateral eyes to resist IOP elevation. CONCLUSION: The IOP loading method permits evaluation of the biomechanical properties of the cornea across its entire surface. All nine contralateral unaffected eyes in patients with a diagnosis of unilateral keratoconus presented weak biomechanical properties and in fact should be considered as forme fruste keratoconus.