Poor Tonometry Reproducibility for Patients With Keratoconus Who Wear Scleral Lenses

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While reliable measurements were readily obtained by each device, their precision on individual patients was poor.

Handheld tonometers and pneumotonometers show poor reproducibility in measuring scleral intraocular pressure (IOP) in patients with keratoconus who wear scleral lenses, according to research published in Clinical Optometry.

Researchers analyzed 40 eyes of 20 patients with keratoconus, all utilizing a prosthetic replacement of the ocular surface ecosystem device (PD), or scleral lens. Participants were divided into 2 groups of 10 members. IOP was measured via handheld tonometry in group 1, and by means of pneumatonometry in group 2. Measurements were obtained through a point on the superotemporal sclera, approximately 1 mm posterior to the edge of the PD. Once investigators obtained 3 reliable measurements of 1 eye, the process was repeated on the other eye.

The mean standard deviation for reliable IOP measurements was ±2.92 mm Hg in the handheld tonometry group and ±1.98 mm Hg in the pneumatonometry group. No statistically significant difference was noted between the 2 groups (P =.07). Mean IOP ranges for the handheld and pneumatonometry groups were 5.5±3.80 mm Hg and 3.71±1.12 mm Hg, respectively, with no statistically significant difference (P =.06).

“The data presented in this report suggest that neither handheld tonometry nor pneumatonometry provide adequate precision/reproducibility to be an instrument of choice when collecting scleral IOP data for a subject while wearing a PD or scleral lens,” according to the researchers. “Although 3 measurements that the device considered ‘reliable’ were readily obtained in an average of 3.45 and 3.2 attempts in the handheld tonometer and pneumatonometry cohorts, respectively, the precision of these measurements on an individual participant was poor,” according to the report.

Study limitations include a single center design, small sample size, and strict inclusion criteria allowing only patients with keratoconus to participate.


Ganjei AY, Shlager GCL, Brocks D. Scleral tonometry precision during scleral lens wear: a pilot study. Clin Optom. 2021;13:341-350. doi:10.2147/OPTO.S339411