Corneal hysteresis in post-radial keratotomy primary open-angle glaucoma

Corneal hysteresis (CH) is a corneal biomechanical property measured by the ocular response analyzer (ORA). It is associated with primary open-angle glaucoma development, progression, and severity as well as intraocular pressure (IOP) measurement. Decreases in CH and changes in IOP measurements have been described for laser-assisted refractive surgery; however, patients with prior radial keratotomy (RK) have not been examined. We have performed a cohort study examining CH and intraocular pressure measurements (Goldmann applanation and ORA values including Goldmann-correlated and cornea-compensated IOP [adjusted for corneal hysteresis]) in RK patients and myopic controls with POAG.

Eighty POAG patients (28 RK and 52 myopic controls) were recruited. Central corneal thickness (CCT), prostaglandin analogue (PGA) use, perimetric stage, and history of cataract and glaucoma filtration surgery were assessed through chart review. Participants underwent testing with the ORA (yielding measures of CH, cornea-compensated [IOPcc], Goldmann-correlated IOP [IOPgc], and corneal resistance factor [CRF]), Goldmann applanation, A-scan for axial length (AL), and corneal topography. Slit lamp exam was performed to assess for number of incisions in RK patients.

Adjusting for AL and CCT, CH was significantly lower in the RK group with an estimated difference of 0.8585 mmHg (p = 0.0112). Cornea-compensated intraocular pressure was significantly higher in the RK group after controlling for Goldmann applanation, AL, and CCT (2.35 mmHg difference, p < 0.001). Corneal resistance factor and IOPgc were not significantly different. A correlational analysis did not reveal a significant correlation between numbers of RK incisions and CH.

We report significant differences, with lower CH and higher IOPcc, when comparing eyes with glaucoma and either a history of RK or myopia. These findings may aid in establishing normative decreases in CH with RK and POAG and indicate a possible under-estimation of pressure in RK patients.