Scleral Tonometry Precision During Scleral Lens Wear: A Pilot Study

Purpose: To evaluate the reproducibility, and therefore the utility, of using traditional tonometry devices for measuring intraocular pressure (IOP), while a prosthetic replacement of the ocular surface ecosystem device (PD) or scleral lens is applied to the eye.

Patients and methods: Twenty subjects (40 eyes) with keratoconus were enrolled. With PD applied, the first 10 consecutive patients had IOP measured multiple times with a handheld tonometer (Tono-Pen AVIA, Reichert, Depew, NY) on the superotemporal sclera 1 mm posterior to the PD edge. This identical procedure was repeated for the next 10 consecutive patients with a pneumatonometer (Model 30, Reichert, Depew, NY). Once three reliable measurements, as defined by the study protocol, were obtained for an eye, the procedure was repeated with the same tonometer device on the fellow eye.

Results: The mean standard deviation for reliable IOP measurements was ±2.92 mmHg, median (IQR) of 2.62 (1.68 to 3.53) mmHg in the handheld tonometer group and ±1.98 mmHg in the pneumatonometer group. There was no statistically significant difference between the groups (p = 0.07). The mean IOP range for the reliable IOP measurements was 5.5 ± 3.80 mmHg, median (IQR) of 5 (3 to 7) mmHg for the handheld tonometer group and 3.71 ±1.12 mmHg in the pneumatonometer group. There was no statistically significant difference between the groups (p = 0.06).

Conclusion: Handheld tonometry and pneumatonometry have poor reproducibility when used to measure scleral IOP in keratoconus patients, while a PD is applied to the eye. An alternative research model and methodology should be investigated and confirmed to have precision prior to proceeding with further analysis of any relationship between scleral lens wear and IOP.