Intraocular pressure (IOP) measurements in keratoconic patients: Do variations in IOP respect variations in corneal thickness and corneal curvature?

PURPOSE: To explore the relationship between intraocular pressure (IOP) measurements and topographical variations in corneal curvature and corneal thickness in a cohort of keratoconic patients presenting to a newly-established regional Keratoconic diagnostic and monitoring clinic in Northern Ireland.

METHODS

IOP was recorded, using a hand held ICARE tonometer, at central, nasal and temporal locations on keratoconic corneae of 27 consecutive patients attending clinic. Pachymetry and sagittal keratometry were recorded in matched locations using the Pentacam Topographer. Eyes with history of corneal surgery or anterior surface pathology were excluded.

RESULTS

The median (interquartile range) central keratometry, pachymetry (CCT) and IOP measurements for 49 eyes were 44.1D (42.2D-48.1D); 495 μm (460 μm-526 μm); 10 mmHg (8 mmHg-13 mmHg) respectively. Temporal and nasal keratometry, pachymetry, and IOP values, recorded on midline, were temporal 41.9D (40.7D-42.8D); 621 μm (579 μm-650 μm); 14 mmHg (11 mmHg-16 mmHg); nasal 40.8D (39.5D-42.5D); 641 μm (599 μm-698 μm); 13 mmHg (12 mmHg-17 mmHg). A moderate correlation was shown between reduction in CCT and increase in mean central keratometry (Spearman's Coefficient (ρ) -0.72 P = 0.00). A moderate correlation was found between reduction in CCT and reduction in IOP, as recorded centrally (ρ = 0.37 P = 0.01). Mid-peripheral values demonstrated similar trends in the relationship between keratometry and IOP (nasal ρ = -0.47 P = 0.00; temporal ρ = -0.38 P = 0.00) and pachymetry and IOP (nasal ρ = 0.29 P = 0.05; temporal ρ = 0.33 p = 0.02).

CONCLUSION

In this pilot study, a positive correlation exists between pachymetry, keratometry and IOP. Topographically variations in intraocular pressure mimic changes in keratometry and pachymetry.