A Pilot Study of a Smartphone-Based Tonometer

Abstract

Purpose : A number of hardware attachments have been developed to allow a smartphone to perform various parts of the eye exam. However, a simple, smartphone-based method for assessing IOP has yet to be developed. We built a smartphone-based tonometer and compared its measurements against other common tonometers in a pilot study.

Methods : The smartphone tonometer uses fixed force applanation and in conjunction with a machine-learning computer algorithm, is able to calculate the IOP. Patients were laid supine, eyes were anesthestized with topical Fluress® and IOPs were measured with the smartphone-based tonometer, Goldmann applanation tonometry (GAT), ICare®, pneumotonometry (upright and supine positions) and Tono-Pen® (upright and supine positions) and the results were compared.

Results : 29 eyes of 15 patients were measured (Figure 1). The mean difference (in mmHg) for IOP measurements of the smartphone tonometer versus other devices was +6.1 for GAT, +4.5 for ICare, +2.4 for upright pneumotonometry, +5.5 for upright Tono-Pen, -2.4 for supine pneumotonometry and +6.4 for supine Tono-Pen. The 95% limits of agreement (LoA) for the smartphone tonometer versus other devices was 0.6 to 11.7 for GAT, -2.0 to 11.0 for ICare, -2.5 to 7.3 for upright pneumotonometry, -0.2 to 11.2 for upright Tono-Pen, -8.2 to 3.5 for supine pneumotonometry and 1.8 to 11.1 for supine Tono-Pen. Overall, the smartphone tonometer results correlated best with upright pneumotonometry (R²=0.59) (Figure 2). A study comparing GAT in the supine versus upright position found a mean increase of 4.1 mmHg in the supine position. If the GAT measurements in this study are “positionally adjusted” by adding 4.1 mmHg to the upright GAT measurements, then the mean difference between the smartphone tonometer and position adjusted GAT is +2.0 mmHg with a 95% LoA of -3.5 to 7.6 mmHg. Furthermore, once adjusted, 52% of the smartphone tonometer IOPs were within 2 mmHg of GAT and 90% were within 5 mmHg.

Conclusions : Preliminary measurements using a prototype smartphone-based tonometer are encouraging and are comparable to current clinical devices, especially after accounting for supine positioning.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Figure 1. IOP Measurements For Each Study Eye Using Various Tonometers

 

Figure 2. Correlation Between Smartphone-based Tonometry and Pneumotonometry