Biomechanically-Corrected Measurements Accurately Determine IOP in Keratoconus

Biomechanically-corrected intraocular pressure (bIOP) may be best suited for measuring intraocular pressure (IOP) in patients with keratoconus (KC), according to research published in Cornea. Unlike Goldmann applanation tonometry (GAT) or other noncontact pneumotonometry devices, bIOP does not have a significant correlation with thinnest corneal thickness, according to the report. 

Researchers retrospectively analyzed data from 246 patients (mean age, 36.5 years; 68.3% men) with KC. The team determined KC severity using the topographic keratoconus classification system and ABCD KC classifications obtained from corneal tomography. Participants underwent IOP measurements using GAT, and 2 noncontact pneumotonometry devices, including a newer bIOP-measuring device that considered corneal thickness, patient age, and biomechanical response when correcting IOP measurements.

Mean IOP values for the GAT and older and newer bIOP devices were 12.65, 10.98, and 14.37 mm Hg, respectively. Participants’ IOP was strongly associated with thinnest corneal thickness measurements for GAT and the older pneumotonometry device (P ≤.003 for both), but not for the newer bIOP device (P =.813). Significant differences were noted in IOP measured in early and late stage KC with all devices except for the newer bIOP device, according to the report. 

“The measurement results from GAT in patients with KC should be interpreted with care and always in view of corneal thickness,” according to the researchers “As a rule of thumb, we suggest to add at least 2 mm Hg to the measured GAT value, regardless of the KC stage.”

Study limitations include a retrospective nature.